Vol. 1, No. 2 – April 29, 2004

In this issue

	The roles of ground beetles in organic production systems
	The soybean aphid, biology as observed in the Midwest
	Managing weed seedbanks throughout the growing season
	Weed watch: weed species emergence is based on soil temperature
	Managing cover crops for improved water efficiency in organic vegetable systems
	General information on cover crops
	Meet our team of organic growers
	Reports from organic growers – April 28

Next issue posted May 13.

The roles of ground beetles in organic production systems

Jonathan G. Lundgren
Center for Ecological Entomology
Illinois Natural History Survey

Why are we interested in ground beetles?
Insects that feed on other insects and weed seeds are an important component of the agroecosystem for several reasons. Perhaps foremost is the role of insects in reducing pest densities and potentially leading to a reduced reliance on pesticides. Another reason is that predators and seed-feeders are good indicators of habitat quality; for example, poor quality sites tend to harbor less diversity in potential prey species, and this effect is magnified in populations and communities that feed on these prey. In general, it is advisable to conserve beneficial insects within your cropland whenever possible, and these conservation efforts are greatly influenced by what types of management strategies one chooses for a particular piece of land. Of the predatory and seed-feeding insects that are encountered within cropland, ground beetles (Coleoptera: Carabidae) are some of the most abundant and important in terms of their role in pest suppression and ability to serve as indicators of biodiversity.

Ground beetles have been appreciated for their importance to agriculture for more than a century- Stephen A. Forbes (1883) was one of the first to examine their gut contents to reveal their predatory nature, and to his surprise he determined that some groups of ground beetles also consumed large quantities of plant material, especially plant seeds. The role of ground beetles as predators of insect pests has been the focus of considerable research by biological control scientists (Brust et al. 1986, Kromp 1999), and certain species have been observed to feed on black cutworm, corn rootworm, corn earworm, and armyworms. Because they are generalist predators, they will accept a wide range of insects as prey, but the majority of species are most efficient as predators of other ground-dwelling insects. Within the last 20–30 years, scientists have also been exploring the importance of ground beetles as mortality factors for weed seed banks (Brust & House 1988, Cromar et al. 1999). Within agricultural habitats, insects are often the dominant granivores, and ground beetles invariably dominate the insect community that feeds on seeds. Seed removal rates by ground beetles have been estimated to be as high as 50 percent of seeds per day, but more often fall into the range of about 2 to 10 percent of surface seeds per day. Thus, ground beetles can be important sources of mortality for both insects and weeds.

The diversity of ground beetles, and their sensitivity to habitat qualities, are a double-edged sword; these qualities are critical aspects of their use as biological control agents, but also hamper research on them and make general recommendations concerning their conservation and application as pest control agents impractical to large regions. Communities of ground beetles in cropland typically consist of 30 or more species, but are typically dominated by around five species. These communities vary with region, crop, and field conditions; for example, in central Illinois Poecilus chalcites (Figure 1) represents 75 percent of the ground beetles at our research site, whereas Cyclotrachelus sodalis was the most abundant beetle in Michigan and P. chalcites represented only 1percent of ground beetles captured (Clark et al. 1997). Tillage, fertilizers, insecticides, plant communities, edge habitat, and soil characteristics all can influence the constituents of ground beetle communities (Kromp 1999). In fact, European researchers have identified certain species of ground beetles that are only prevalent in organic production systems!

How do ground beetles respond to organic transition strategies?
In Champaign, Illinois, I have been addressing the impacts of organic transition strategies on ground beetle communities, as a component of a multidisciplinary evaluation of the efficacy of different management strategies. Three strategies are being evaluated, beginning in 2003:

1) A low intensity strategy with minimal input (represented by an extensive ley system),

2) An intermediate intensity strategy that involves an organic cash grain (soybeans in 2003), and

3) A high intensity vegetable production strategy (tomatoes in 2003).

In order to understand the impacts of these different strategies on ground beetle assemblages, we conducted a season-long sampling regiment using pitfall traps (jars with a preservative in them that are embedded in the soil; ground beetles are readily collected in these traps). Actual density samples revealed that in our 4,800 m 2 experimental area, we had an estimated 133,328 predatory insects and spiders. Of this estimated number, we actually collected more than 8,000 ground beetles. As mentioned earlier, the dominant species was P. chalcites (nearly 75 percent of specimens), a species that is exclusively predatory. Of the remaining ground beetles, 78 percent of individuals are known to feed on seeds. Data is still being tabulated from our plots, but preliminary results show significant effects of the different management strategies on ground beetles. For example, we found that P. chalcites densities were significantly higher in the low intensity system, and that the intermediate intensity system was higher than the high intensity vegetable system (Figure 2).

So, ground beetle abundance is altered by different management strategies—what does this mean for pest control in the different strategies? We will begin to address this question in 2004 by examining predation rates and seed removal rates in the different treatments. As a result of this research, we hope to identify key interactions between weed species, insect pests, and the ground beetles that consume them. The long-term implications of these management strategies on biological control potential will be of interest as one component of organic farming that is affected by the transition process.

Brust, G. E., B. R. Stinner, and D. A. McCartney (1986) Predator activity and predation in corn agroecosystems. Environmental Entomology 93: 1437–1443.

Clark, M. S., S. H. Gage, and J. R. Spence (1997) Habitats and management associated with common ground beetles (Coleoptera: Carabidae) in a Michigan landscape. Environmental Entomology 26: 519–527.

Cromar, H. E., S. D. Murphy, and C. J. Swanton (1999) Influence of tillage and crop residue on postdispersal predation of weed seeds. Weed Science 47: 184–194.

Forbes, S.A. (1883) The food relations of the Carabidae and Coccinellidae. Bulletin of the Illinois State Laboratory for Natural History 1: 33–64.

Kromp, B. (1999) Carabid beetles in sustainable agriculture: a review on pest control efficacy, cultivation impacts and enhancement. Agriculture, Ecosystems, and Environment 74: 187–228.

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The soybean aphid, biology as observed in the Midwest

David Voegtlin
University of Illinois, Entomology

Many researchers in the Midwestern states have been studying the biology of the soybean aphid (scientific name: Aphisglycines Matsumura) since its arrival in North America. The following is a general compilation of the information that has been freely distributed at meetings or in publications to date.

The life cycle of the soybean aphid is relatively complicated. It spends the summer feeding on soybeans and spends the winter as eggs on a weedy shrub/small tree of European origin called buckthorn (scientific name: Rhamnuscathartica). After the eggs hatch in the spring, colonies of aphids develop on buckthorn and winged aphids are produced that fly off in search of soybeans. These winged aphids move throughout a soybean field depositing a few nymphs on several different plants. These nymphs mature and begin colonies that themselves begin to produce some winged offspring in subsequent generations. The winged aphids produced in the summer on soybeans leave the plant on which they developed and fly to other soybeans. The distance these summer migrants move depends on the speed of the wind and the length of time that they continue to fly. It may be as far as a few miles to more than 100 miles. In the fall there is a migration back to buckthorn by a winged form of the aphid that feeds on buckthorn and produces an egg laying form (oviparae). Males are formed on soybean in late fall and fly to find buckthorn and the oviparae. Mated oviparae deposit the overwintering eggs adjacent to buds.

Buckthorn is much more common north of Interstate 80, but it is not evenly distributed in this area. Sometimes buckthorn is found in urban areas south of I-80 and these isolated plants may serve as overwintering hosts of the soybean aphid. Based on the distribution of spring populations, successful overwintering is primarily limited to areas where buckthorn is abundant. In areas where the aphid is known to overwinter, populations have peaked in late July to early August. In areas south of where the overwintering host is common, such as Missouri, Southern Illinois, Southern Indiana , Southern Ohio, Kentucky and Tennessee, field populations begin with migrants from the north and peak later in the summer to early fall. The broad distribution of the aphid, from the Dakotas to the east coast over the past two summers, suggests that successful overwintering has occurred outside of the core area of Wisconsin, Minnesota, N. Iowa, N. Illinois, N. Indiana and Minnesota, where overwintering has been documented.

As with all aphids, soybean aphids are parthenogenetic. This means that throughout the summer there are only females that give birth to live females. The new born nymphs can mature and begin reproducing on their own in four to five days. Adults may live for two weeks or more and produce multiple nymphs each day. So a mother, daughter, and granddaughter may all be reproducing at the same time on the same plant. Combine this overlapping of generations with optimum temperatures of between 70 and 80 deg. F, and populations of the soybean aphid can double in two to three days.

While soybeans are in the vegetative stage, the soybean aphid colonies are found on the actively growing upper leaves and tip of the plant. In the early reproductive stages of soybean growth the aphids move, and during the remainder of the season they can be found on leaves throughout the plant and on the developing pods. Aphids persist on the plants into the fall when migration to buckthorn occurs. Early leaf drop and harvest appears to eliminate populations of the aphid.

There seems to be no clear visual indication that a soybean plant or field is infested. Fields of healthy looking soybeans with hundreds to thousands of aphids per plant cannot be distinguished visually from a field without aphids.

A more extensive discussion of the biology of the soybean aphid can be found at: http://www.bioone.org/bioone/?re quest=get-document&issn=0013-8746&volume=097&issue=02&page=0204

A search for Aphisglycines on the web brought up over 1,700 pages so there is plenty of information available.

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Managing weed seedbanks throughout the growing season

Adam S. Davis
MSU Crop and Soil Sciences

Many of the most important weeds in field crop production are annuals—they germinate, grow, produce seed and die, all within a single year. Why are annual weeds such a problem then? Couldn’t a single year of weed control wipe out the entire population and leave behind a clean field for future years? The old saying, “one year’s seeding, seven year’s weeding” holds the answer to these questions. Annual weeds don’t only spread throughout a field. They also disperse through time by producing dormant, long-lived seeds. Only a small number of the seeds produced in a given year will germinate the following year. The rest of the seeds remain dormant in the soil, ready to germinate at some point in the future when the conditions are right. This collection of different-aged seeds, with different probabilities of surviving and germinating in a given year, is referred to as a weed seedbank.

The weed seedbank is what makes weed management such an unpredictable, repetitive task. Managing the weed seedbank is often overlooked, but seedbank size can have an important effect on overall weed pressure. It’s especially important for organic growers to manage their weed seedbanks in order to keep mechanical and hand weeding operations manageable. Luckily, there are many opportunities to manage the weed seedbank throughout the growing season.

Scout your weed seedbank
A little effort in understanding your weed seedbank can give you valuable information about what weeds to expect in a given growing season, weed density, and when most weed germination will take place. To get a weed preview, you can germinate weeds indoors as you’re waiting to plant. For summer annual weeds, such as velvetleaf, foxtail, lambsquarters and pigweed, March-April is a good time to sample weed seedbanks in the North Central region. Using a soil probe or a garden trowel, take 20 samples to a 2” depth in a ‘W’ pattern from the field you’re interested in. Place the soil in a pie dish, put in a warm place (> 65 º F) and keep moist. Within one to two weeks, you should have an idea of what weeds will be emerging in your field as the soil warms.

Different weed species begin to germinate at different times in the growing season, depending upon how many growing degree days (GDD) have accumulated. [For a base temperature of 48 degrees F, if you have three days in a row with average temperatures of 45, 50 and 53 degrees, you would have 0 + 2 + 5 = 7 GDD accumulated in that time period.] Table 1 shows emergence patterns for some common weed species in North Central field crop production systems. Knowing the weed emergence sequence of common weeds in your fields can help you plan scouting and weed management operations.

Table 1. Weed emergence sequences (adapted from Iowa State Extension poster IPM64a)

Emergence groups arranged according to GDD (base temperature = 48 ° F) at 10% seedling emergence. For groups 1-4, different levels of shading refer to different durations of weed seedling emergence. White = 2-3 weeks, light gray = 3-7 weeks, dark gray = 8-10 weeks. Full color poster available through ISU extension: http://www.extension.iastate.edu/pubs/.

Reduce your weed seedbank
It’s no accident that most weed management tactics are directed at plants rather than seeds. Weed seeds are small, are protected by burial within the soil, and have tough seed coats. Even so, there are ways to reduce the size of your weed seedbank.

1) Stale seedbed. This time-honored tactic uses repeated tillage or cultivation to stimulate weed seeds to germinate. The technique is based on using germination cues (changes in light, moisture, temperature, oxygen due to tillage) to trick dormant seeds into germinating, after which they can be eliminated with a physical control method such as cultivation or flaming. Depending upon when the stale seedbed technique is applied, different weed species will be affected. Spring operations affect mainly summer annuals, whereas late-summer/fall operations affect mainly winter annuals. The type of tillage will also affect which seeds are stimulated to germinate. Chisel plowing mainly disturbs seeds at the surface. Moldboard plowing brings seeds up from deeper in the soil profile, and buries some of the surface seeds. If you know weed seeds have accumulated at a specific depth in your soils, you may be able to choose a tillage practice that targets those seeds.

2) Seed predation. A single good-sized common lambsquarters plant can produce several 100,000 seeds. Giant foxtail and other grass weeds can produce several 1,000 seeds per plant. Weed seedbanks rarely have more than a few hundred seeds per square foot. Where do all the weed seeds go? Just as humans rely upon grain crops as a major part of their diet, many other organisms eat seeds, including weed seeds. Organisms that eat seeds are called seed predators. Some of the most important seed predators in field crop systems are ground beetles, crickets, small rodents, birds, and earthworms (Figure 1).

Seed predators can eat a large percentage of newly produced weed seeds. Some predators eat weed seeds while they are still on the plant, whereas others eat the seeds after they have fallen to the ground. Over the course of a year, seed predators may eat over 80 percent of the weed seeds produced in a single growing season. To take advantage of this level of seed-feeding activity, however, weed seeds must be left on the soil surface for as long as possible after weed seed shed. For no-till farmers, or those who plow in spring, weed seeds will be left at the soil surface for much of the year. Those who plow in fall will have to weigh the benefit of fall tillage against the weed management benefits from predation.

The type of crop and non-crop plants you have on your farm can also affect the number of weed seeds eaten by seed predators. Use of switchgrass border areas may increase seed predation by ground beetles, while underseeding small grains to legumes can increase seed predation by crickets and mice. In general, increasing crop diversity on your farm can have a beneficial effect on seed predator organisms. See Michigan State University Extension Bulletins E2716 and E2749 (http://web2.msue. msu.edu/bulletins/subjectsearch.cfm) for more information on how to manage your farm to increase weed seed predation.

3) Weed suppressive soils . Microorganisms also help to reduce the size of weed seed banks. As weed seeds age, their seed coats become less resilient, and microbes, mainly fungi, may enter the seed and cause it to decay. Seed-feeding insects, such as weevils, can provide an entrance for soil microbes into even healthy seeds. Soil management may also affect the rate at which weed seeds decay. Incorporation of green manure residues into the soil in late fall can increase overwinter seed decay of some weed seeds. There is a growing interest among research scientists in this relatively new area of research.

Condition your seedbank to reduce weed emergence
For every farmer that uses the stale seedbed method, there is another who won’t go near a field with tillage equipment in the spring. In this approach, the farmer tries to avoid stimulating weed seeds to germinate. Primary tillage often takes place in the fall in this approach, after which soil disturbance by cultivation is avoided until absolutely necessary. For those who own a flame weeder, the flamer can be used to kill emerging seedlings while letting the dormant seeds deeper in the soil stay dormant. Many European growers find that tilling their soil at night in late fall can condition the weed seedbank to have less seedling emergence the following spring. Lightless tillage can reduce weed seedling emergence by as much as 50 percent compared to daytime tillage. Lightless tillage is effective only on small-seeded broadleaf weeds like common lambsquarters and pigweed species. Lightless tillage has little or no effect on annual grasses and large-seeded broadleaf weeds like cocklebur and velvetleaf.

Tillage can also be used to place weed seeds at different depths in the soil. As mentioned earlier, the chisel plow leaves many seeds near the soil surface, whereas the moldboard plow sends more seeds to deeper soil layers. No-till leaves all seeds on the soil surface. There are trade-offs for each tillage method. As seeds are placed deeper in the soil profile, they are less likely to germinate, but they are also less exposed to seed predators and weathering at the soil surface (Table 2). Flexible use of different tillage systems may allow a grower to cope with different weed situations. For example, if a giant foxtail infestation gets out of control one year and produces a lot of seed, a moldboard plow may be used to send the seed deep into the soil profile. In the following year, a shallower form of tillage should be used to avoid bringing up the buried seed, and give the foxtail seed time to decay at depth.

Prevent new weed seeds from entering the seedbank
The most critical part of weed seedbank management is preventing new seeds from entering the weed seedbank. Without careful attention to limiting weed seed return, all other weed management is a bit like “closing the barn door after the horses are out.” Each plant can produce many seeds, each of which can produce a new plant. If weed seed production is unchecked, the number of seeds in the soil seedbank can increase very quickly. When the seedbank is very large, you can be sure that many weed seedlings will come up in the following growing season, even if only a small percentage of the seedbank emerges. High densities of weed seedlings can reduce the effectiveness of cultivation and flaming, leading to expensive hand-weeding or unacceptable levels of crop yield loss. An ounce of prevention is worth a pound of cure in this case.

Having a healthy, competitive crop is probably an organic farmer’s best line of defense in preventing excessive weed seed return. A strong corn crop can make the difference between 60 weed seeds produced and 6,000 weed seeds produced per plant. Different crops also have different competitive abilities against various types of weeds. Corn is very competitive against erect grass and broadleaf weeds, but less so against creeping, low-lying weeds such as chickweed. Small grains are highly competitive against many weeds, but unless they are underseeded to a legume, can provide an entry point for warm-season weeds like common ragweed and redroot pigweed to grow and produce thousands of weed seeds once the grain is harvested. Soybean can be vulnerable to weeds in organic production systems. Narrow rows can help improve the competitiveness of soybean against many weeds. However it is difficult to cultivate rows that are narrower than 18”. Forages are very competitive against many weeds, and can provide an opportunity for weed seed decay and low weed seed return when used as part of a crop rotation.

Certain weed species are less likely to remain in the soil seedbank for long periods of time than others, due to differences in germination and decay rates (Table 3). For weed species, such as common lambsquarters or yellow foxtail, whose seeds can form a very persistent seedbank, it may be worth the extra cost of selective hand weeding. Effective hand-weeding of velvetleaf requires that the plant be removed from the field, since it can re-root from its stem. For particularly bad patches of weeds with long-lived seeds, it may be worthwhile to spot-plant the patch to a forage crop for a couple of years to prevent the weed patch from spreading, while giving some of the seeds a chance to decay.

The combine grain harvester is truly a technological triumph, allowing a relatively small number of people to farm large acreages. Itis also the most efficient weed seed spreading device ever developed. Before the advent of chemical herbicides, early combine models directed weed seeds separated from grain into a weed seed collection pan for later disposal. As combines and acreages got larger, and herbicides took over as the primary tool for weed control, this feature was eliminated from combines. Weed seeds are now blown out the back of the combine along with the chaff, taking localized weed problems and making them whole-field weed problems. In parts of the world where herbicide resistant weed species have become a major problem, such as Australia and Canada, weed seed collecting combines have re-appeared. A two-stage harvesting system for small grains is available through McLeod Harvest in Manitoba (http://www.mcleodharvest.com).

Other farmers, including some in the North Central Region of the U.S., have modified their own equipment to collect weed seeds (note, this is not possible with a rotary combine). One organic farmer in Michigan modified his 1974 Gleaner K series to collect weed seed by taking the weed screen in the re-clean elevator and moving it from the bottom to the top of the stack. From there, he routed the weed seed to a 15-gallon drum mounted on the outside of the combine. In 2003, he used the modified combine to prevent seed return from a severe velvetleaf infestation in soybean, and caught over 55 gallons of velvetleaf seed—15 million seeds—on 11 acres.

Table 3.Persistence of common North Central weed seeds in the soil seedbank

Data compiled from Burnside et al. (1996), Buhler and Hartzler (2001), Dawson and Bruns (1976), Lewis (1973), and Roberts and Feast (1972).

A final important method of prevention is sanitation. Avoid spreading weed problems from field to field by cleaning equipment in between operations on different fields. Don’t let weeds spread from field margins and fencerows. Vigorous plantings of native perennial plants, such as prairie seed mixtures, are relatively low-maintenance once established, and can help prevent the buildup of agricultural weed populations in areas bordering your fields. Keep a close watch under telephone lines, where resting birds can disperse seeds from berries such as nightshades. Consider the quality of your crop seed source: what percentage of weed seeds are you willing to tolerate? Together, these sanitation methods can help to prevent new weeds from entering your fields .

Key points

• Scout your weed seedbank by soil sampling in early spring and identifying weed species that are likely to germinate during the growing season.
• Reduce your weed seedbank through stale-seedbed technique, management to encourage seed predators, and soil management to increase weed seed decay.
• Condition your weed seedbank to reduce weed seedling emergence during the current growing season by flaming instead of cultivating early in the season, doing primary tillage at night, and sending large flushes of weed seed deep into the soil profile.
• Prevent new weed seeds from entering the weed seedbank by growing a healthy crop with a good stand, target weed species with long-lived seeds for spot-weeding, keep field borders free of weed problems, keep equipment clean, use clean seed sources, and consider adapting harvesting equipment to recover weed seed.

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Weed watch: weed species emergence is based on soil temperature

Karen Renner and
Doug Buhler
MSU Crop & Soil Sciences

Weed species start and stop germinating at specific temperatures as long as there is adequate soil moisture. Seeds won't germinate in warm soil if there is no soil moisture. What is the first summer annual weed to emerge in the spring? Most of us would guess common lambsquarters or smartweed. The minimum soil temperature for common lambsquarters germination is 36 °F, the maximum 95 °F, and the optimum 68 °F. Common ragweed will germinate when soil temperatures reach 50 °F; the optimum soil temperature for common ragweed germination is 68 °F. In contrast, the optimum soil temperature for redroot pigweed germination is 85 ° to 95 °F. Remember, most weeds germinate from the top inch of soil, so these are soil temperatures very near the soil surface.

Why is the time of weed emergence important?
For sugarbeet growers, postemergence herbicides must be applied when weeds are 1/4 to 1/2 inch in height. Common lambsquarters and smartweed will be the “trigger” weeds in early planted sugarbeets. Common ragweed and velvetleaf are two other weed species that germinate early, and are “trigger” weeds when soil temperatures reach 68 °F. What about annual grasses? Giant foxtail will emerge first, followed by fall panicum. Large crabgrass is considered a late emerging grassy species with optimum germination at soil temperatures of 85 ° to 95 °F.

For corn and soybean growers, most weed species are emerging in mid-May through mid-June. Rotary hoeing, cultivation, or postemergence herbicides will be controlling a broad spectrum of weeds.

For dry bean growers, tillage prior to planting controls most of the early emerging summer annual weeds. When fields are heavily infested with common lambsquarters, delaying planting to allow the majority of common lambsquarters to emerge and be controlled by tillage is a common strategy in organic production. Alternatively, if redroot pigweed is a predominant weed problem, planting a field early will allow the crop to be ahead of the weed and the crop will be very competitive.

The relative sequence of germination times for common weeds is shown in Figure 1. Figures 2 and 3 provide more detail on the relative time of emergence of fall panicum, giant foxtail, and large crabgrass (Figure 2), and common lambsquarters, common ragweed, common waterhemp, and redroot pigweed (Figure 3). The narrow, dark bar shown for each weed species in each figure shows the time of peak emergence. The wide broad band depicts the time during which each weed species emerged. This research was conducted in Ames, Iowa (Buhler and Hartzler), which may be a bit warmer than Michigan. However, the sequence of emergence for these weed species would not change. You can see from Figure 3 why common waterhemp is such a problem in Iowa. It starts emerging at about the same time as redroot pigweed but peak emergence is later in the season and waterhemp keeps emerging into August.

Keep a weed watch on your fields in 2002. Improve weed management strategies on your farm by knowing which weed species you have and when each species starts and stops emerging.

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Managing cover crops for improved water efficiency in organic vegetable systems

Sieglinde Snapp
MSU Horticulture

As organic growers gear up for the 2004 growing season, it is important to review the multiple paybacks from careful water management. There are many environmental and production reasons to look over pipe and sprinkler packages and fix problems with pressure regulators and replace outworn or old parts, and conduct routine maintenance such as sprinkler-head replacement. Sprinklers should be rotating properly, nozzles not worn or blown out with proper pressures at the nozzles and pipes free from leaks. Drip irrigation should be checked for clogs and leaks as the season progresses. In Michigan recently revised information has been provided on recommended irrigation practices. See the 2003 Irrigation Water Use Generally Accepted Agricultural and Management Practices (Irrigation GAAMPS) at: http://www.michigan.gov/mda/0,1607,7-125-1567_1599_1605-69180--,00.html. Irrigation scheduling is key to water efficiency, as described in the Irrigation GAAMPS.

Water management is a key component of producing high quality vegetables in coarse soils. Often organic vegetable production relies on well drained, sandy soils. This allows early production, facilitates tillage and enhances soil aeration which is critical to root growth and development of many vegetables – ultimately influencing yields and produce quality. In the upper Midwest rainfall can prove inadequate or erratic during the summer months, thus many growers use supplemental irrigation. In tomatoes maintaining sufficient soil moisture is critical during the flowering and fruit expansion period. Managing water in potatoes also requires particular attention to the tuber initiation and bulking time periods, to maintain sufficient soil moisture in the top 18 inches of soil. Less frequent but deep watering (e.g., two times a week) has been found to enhance fruit quality in some tomato varieties by providing a slight stress. However, the soil type will greatly influence the recommended frequency of irrigation. Heavier, fine soils will have water-holding capacity that supports a longer time period between irrigation.

Organic matter for improved water efficiency
Irrigation is not the only tool to improve water management: organic growers use practices that build up both "active" (short-term) and long-term pools of organic matter. This promotes efficient water management through improved infiltration and water-holding capacity. For example, an increase in soil organic matter from 1 to 1.5 percent can improve water holding capacity by approximately 20 percent . A soil well-buffered with organic matter has a large reservoir that supplies nutrients and water on an ‘as needed basis,’ while providing a well-aerated environment. This is the foundation for a uniform growth rate that produces high quality fruits and tubers. Long-term research on organic corn, wheat and soybean systems in Pennsylvania and potato-based rotations in Maine have shown that in dry years some organic systems can produce between 10 to 35 percent higher yields than conventional production systems. In high rainfall years no differences in yields were detected between organic and conventional management (Lotter et al., 2003; Alford et al., 1996).

Cover crop management for water efficiency
Overall, sandy soils have excellent water infiltration properties. Yet, localized problems can occur in sandy fields with poor infiltration, soil crusting and compacted or cloddy sites. Careful tillage management and timing of tillage will help address these problems. A preemptive means to enhance soil quality across uneven fields is to grow a substantial cover crop. Incorporating cover crop residues will improve soil structure and water infiltration at these sites. It may be worthwhile for growers to consider applying irrigation to a cover crop. This will greatly increase cover crop growth during dry spells in the spring, and provide subsequent benefits for a cash crop. Winter cover crops can dry out the soil in the spring, which can be a problem if irrigation is not available.

There are substantial enhancements in organic matter that can be achieved by allowing a cover crop to grow in the spring for as long as possible before mowing or tillage operations. Early growth of cover crops is limited in cool weather, only when the degree days start to accumulate above 40˚F for rye and hairy vetch, or 50˚F for most other cover crops is significant growth achieved. It is important to remember that early in the spring much of the plant growth may be belowground as roots. Large amounts of root growth may be occurring out of sight. Allowing the cover crop to grow for a few more warm days in the spring will increase the amount of biomass incorporated (Figure 1). Note that this figure presents biomass accumulation in a winter cover crop planted late in the fall. An earlier established cover crop would produce more biomass and have a better chance of winter survival as well.

Timing of cover crop incorporation
After residues are incorporated, it is important to wait sufficient time before planting a vegetable. This is most critical for small seeded vegetables, such as carrots. There needs to be a wait of at least three weeks after a cover crop is incorporated and tillage conducted, before a crop is planted. This will prevent any potential negative impact from allelopathic toxins released as residues decay, or immobilization of nitrogen. Large seeded crops, such as potato tubers, are not affected much by residue decomposition processes. Only a week or two delay after cover crop incorporation is necessary before a potato crop is planted. More information on cover crop management in Michigan vegetable and field crop systems is presented in extension bulletins which can be accessed at   http://web4.msue.msu.edu/veginfo

-S.S. Snapp and D.R. Mutch. 2003. Cover crop choices for Michigan vegetables. Michigan State University Extension Bulletin. E2896 (New).

-D.R. Mutch and S.S. Snapp. 2003. Cover crop choices for Michigan. Michigan State University Extension Bulletin E2884 (New).

The future of water efficiency: Reduced tillage systems for organics?
Conservation tillage is where the amount of tillage is reduced, and the maximum stubble or plant residues are left on the soil surface as mulch. Under a conservation tillage system, minimum soil disturbance increases soil water-holding capacity and plant residue mulch decreases water loss by evaporation. Above and below the mulch the temperature is generally decreased, by 1 to 6 degrees. This can delay plant development and be a problem in a wet, cold spring if vegetables are transplanted or planted into a strip-till residue system. However, for vegetables that are not targeted at the earliest market, a soil moisture conserving system such as this can be just the ticket in a dry summer. Mowed rye can be used to transplant tomatoes or direct seed pumpkins. These systems are experimental for organic production, as weed management can be challenging. Conservation tillage requires modification of current bed preparation and planting equipments; even harvest equipment may need to be altered. However, there are incentives. Not only do on-farm trials in the Northeast show that enhanced soil moisture holding capacity is possible, but increased soil organic matter and soil quality will build up remarkably over time in reduced tillage or strip-tilled systems.

References
Lotter, D.W., R. Siedel, W. Liebhardt. 2003. Am. J. Alt. Ag. 18:146-154.

A.R. Alford et al., 1996. The ecology, economics and management of potato cropping systems: A report of the first four years of the Maine Potato Ecosystem Project. Extension Bulletin 843, Univ. of Maine.

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General information on cover crops

Dale R. Mutch
Kellogg Biological Station/
Land and Water Program
and MSU IPM Program
3700 E. Gull Lake Drive
Hickory Corners, MI 49060

269-671-2412, ext.224
mutchd@msue.msu.edu

Cover crops are a key component to sustainable agriculture. The cover crop/IPM program at Michigan State University/W. K. Kellogg Biological Station (MSU/KBS) in Hickory Corners, Michigan provides research and demonstrations on cover crops in several farming systems. Early research/demonstrations primarily focused on incorporating cover crops into field crop (corn, soybean, wheat and alfalfa) systems. In the last four years, we have expanded into cherries, tomatoes, cucumbers, sugar beets, summer squash, zucchini and pumpkins.

MSU/KBS has sandy loam soils. Our on-site research is complemented by five on-farm research projects a year. This year we have cover crop projects in:

1) Gratiot County (evaluation of oilseed radish following pickles)
2) Tuscola County (evaluation of several oilseed radish cultivars on sugar beet cyst nematode populations)
3) Newaygo and Oceana counties (evaluation of four oilseed radish cultivars and oriental mustard on phytophora root rot control and management)
4) Berrien County at the Southwest Michigan Research and Extension Center (SWMREC) (an eight cover crop species evaluation on tomato and summer squash growth and quality).

Cover crops serve many beneficial purposes for organic farmers. They are especially important for maintaining and improving soil quality. Some other benefits from using cover crops include nitrogen management and weed suppression.

Nitrogen management
Cover crops can either provide nitrogen for future crops or recycle nitrogen. Good legume cover crops for nitrogen production are red clover, hairy vetch, crimson clover and cowpea.

§   Red clover can be frost seeded into small grains such as spelt, wheat or cereal rye in March. A 12 lb/A rate will often provide you with over 100 lbs. of N/A the next season.

§   Hairy vetch, a winter annual cover crop, seeded at 30 to 40 lbs/A in August can provide over 100 lbs/A of nitrogen. Hairy vetch can be bulk seeded with shallow incorporation or drilled. It fits best when you are growing a short season crop such as green beans, cucumbers, pickles or small grains. Note: hairy vetch will often re-grow the next season due to hard seed coats.

§   Crimson clover is an annual red clover that will winter kill during cold winters (2002-03) or survive the winter if it is mild. If winter killed, crimson clover will produce about 30 to 40 lbs/A of nitrogen. This can be doubled when it survives the winter. Seed crimson clover at 15 lbs/A following a short season such as described above. It can be killed rather easily with tillage.

§   Cowpea is a cover crop we are trying to fit into Michigan farming systems. It is a summer cover crop that will winter kill in Michigan. We have been seeding it at 60 to 80 lbs/A. We do not have enough data yet on the nitrogen produced by cowpea. Potato leafhopper has been an insect problem on cowpea and can stunt its growth. Cowpea should be seeded when there is no risk of frost and when the soils have warmed up. Since it winter kills, no tillage is needed to control it in the spring.

Legume cover crops, as described above, are primarily used to provide nitrogen for next year’s crop. Crops such as sweet corn, field corn, leafy vegetables, peppers, tomatoes, etc. will all benefit from legume cover crops grown the prior season.

Sometimes we want to recycle nitrogen to decrease nitrate leaching and runoff from our fields. These cover crops are referred to as non-legumes. They are characterized by being fast growing cover crops. Good recycling nitrogen cover crops are oats, cereal rye, wheat, spelts, buckwheat, oilseed radish and oriental mustard.

§   Oats seeded in August at 1.5 to 2.0 bushels/A can recycle about 20 to 30 lbs. N/A. We like to seed oats after a legume crop was grown. Oats establish fast and the roots take up the nitrogen rather than the nitrogen leaching.

§    Small grains such as spelt, wheat or cereal rye can be seeded late into the fall (October). These cover crops will recycle more nitrogen in the spring versus fall. If they are being used as a cover crop and you are not harvesting the seed, they should be tilled when they reach 10-15 inches tall.

§  Oilseed radish will winter kill. You should seed it in August after a short season crop. It will produce a large root and can recycle up to 40 lbs. of N/A.

§   Buckwheat is a rapid growing cover crop, but is very susceptible to frost and cold temperatures. It is a summer cover crop and should be planted at a 50 to 60 lbs/A rate. It is very good at extracting phosphorus from the soil.

Weed suppression
Cover crops can improve your ability to manage weeds.

§   Oilseed radish seeded at 20 lbs/A in August can reduce weed populations while providing excellent ground cover. Oilseed radish will winterkill in the fall after hard frosts. The cover crop program at MSU/KBS is testing four different cultivars of oilseed radish for influence on weeds, disease and nematodes. Oilseed radish seed is expensive.

§  Oats seeded at 1.5 to 2 bu/A in late August for lower Michigan will provide excellent cover, however, will not provide as good of weed control as oilseed radish. If you are further north you want to seed in early to mid August. Oats are susceptible to winter killing so early growth in the fall is important. In the spring, fall-seeded oat ground will be very mellow and easy to work. Oats are inexpensive and easier to find than oilseed radish.

§  Red clover can be effective in reducing weeds. Even though it is a perennial, it acts like a biennial and typically succumbs to disease pressure in its second year. Red clover influences weeds more after it has been established. You can clip and mow red clover and it will re-grow so mowing can help you to reduce weeds in your red clover seeding. The cost of red clover varies, however, it generally costs more than oats and less than oilseed radish. Red clover is a legume and it will produce substantial nitrogen as well as reduce weeds. Red clover is most effective when it is frost seeded into small grains in March.

§  Cereal rye is a great cover crop for weed control. Cereal rye produces allelochemicals (naturally produced compounds) that control and suppress weeds. Rye can be seeded late fall (October) and still provide excellent cover. Since it is a winter annual, rye will grow very rapid in the spring. Therefore, it must be controlled in the spring or it can grow up to four feet tall. We recommend controlling it with tillage when it is between eight and 15 inches tall. Cereal rye variety “Wheeler” is known to have allelochemicals and it costs more than other rye varieties.

§   Buckwheat is a rapid growth cover crop. It needs to be seeded after the risk of frost is over and soil temperatures are warm in the spring. Buckwheat needs to be controlled with tillage at flowering to avoid seed production and becoming a weed. It has a hard seed coat and will often re-germinate where it has been planted. Seed cost for buckwheat is reasonable.

§  Hairy vetch is a legume cover crop that can be seeded in August. It is a winter annual plant that will produce a lot of biomass in the spring. It is also a very good cover crop for nitrogen production. It will compete well with weeds as long as it gets established before the weeds do. It will survive most winters in Michigan. Hairy vetch should be controlled with tillage before it blossoms in the spring. Hairy vetch has a hard seed coat and can become a weed itself in fields where it was planted. Hairy vetch seed is expensive.

§  Crimson clover is an annual clover and a legume. It will establish easier and grow faster than red clover. Therefore, it is better for weed control when seeded in August versus red clover. In Michigan’s southern counties, crimson clover will survive most winters. Crimson clover produces nitrogen, but not as much as red clover or hairy vetch. Seed cost for crimson clover is about the same as red clover. Crimson clover is easier to control with tillage than red clover or hairy vetch.

Cover crops are an important component for our farming systems. For more information about cover crops, please check our web page at www.kbs.msu.edu/extension/covercrops

Selected reading
-Cover crop choices for Michigan. MSU Extension bulletin E-2884. Order E2884.
-Cover crop choices for Michigan Vegetables. MSU Extension bulletin E-2896. Order 2896.
-Managing cover crops profitably. 2^nd edition. Sustainable Agriculture Network Handbook Series. Order.

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We’d like to thank our nine growers who have agreed to report information for the 2004 New Agriculture Network. This week, we would like to introduce our Michigan team members.

Michigan

Rob Malcomnson is a young farmer who started from scratch in 1993, after returning from an internship at the Rodale Research Institute. His farm is located in Davison, Michigan. The 200 acres he farms is almost entirely rented ground. He owns six acres that are mostly pasture for steers, layers and broilers. In addition to the animals, he grows corn, beans, wheat, oats, rye, hay and some vegetables for the local market. He has always farmed organically, and is very active in the Thumb chapters of Organic Farmers of Michigan and OCIA.

John and Curtis Simmons operate a certified organic farm of 720 tillable acres in Lapeer County, Michigan. They started transitioning their farm in 1993. They are active members of the Thumb chapters of Organic Farmers of Michigan and OCIA, as well as the Lapeer Co. Soil and Water Conservation District. They raise corn, soybeans, dry beans, a variety of small grains and maple syrup. They participated in an organic farmer research design team at MSU’s Kellogg Biological Station in 1998 and 1999.

Matt Wiley farms 300 acres in Kalamazoo County, Michigan. His first year of organic certification was 1999. He rotationally grazes 150 ewes and grows 100 acres of soybeans and 100 acres of spelt. He has collaborated many times in the past with MSU researchers doing rotational grazing research.

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Illinois Report From Dave Campbell, Kevin Brussell and Jon Cherniss

Have there been any weather conditions that affected your cropping system?
Two rainfalls in the past two weeks totally 1.5 inches has been a big help in replenishing topsoil moisture. Oats are coming through and wheat is starting to take off. The past two weeks we’ve seen our typical spring rollercoaster of temperatures. We had a high of 84 degrees on the 18 th and we’ve also had a couple of mornings lately where we’ve received frost.

Wind, wind, and of course more wind, last couple of weeks not to wet or dry.

Two inches of rain last week.

What current farming practices are you involved in (i.e. planting cover crops, tillage operations, etc.)?
I’ve been field cultivating some ground that is going to corn. Volunteer wheat is being destroyed in these fields by field cultivating. Broadcast fertilizing of wheat is completed. Some cornstalk ground will be plowed up today that will eventually be planted to soybeans.

Mowing and turning in clover and grass covers for summer plantings in 4-6 weeks. Spading and bed shaping. Planting in green houses and fields. Finished spring plantings last week. Wondering if Canadian thistle will ruin the farm.

Waiting for the soil to dry

What farming operations are you planning to do in the next two weeks?
Field cultivating last year’s corn ground for the first time. It will be planted to beans this year.

Next week we will begin first succession of summer crops. Tomatoes, peppers, squash.

Disc cornstalks, plow clover and alfalfa, plant corn, plant soybeans, foliar feed wheat.

Do you have any questions to be addressed for the next conference call?

• Ideas on controlling Canadian thistle.
• Wondering if there is any oilseed radish available for cover crop seeding after wheat harvest. Also would like to know seeding rates recommended for oilseed radish as well as typical price for certified organic seed.

Indiana report
Gary Reding in Southeast Indiana reports 2.5 in. of rain in the last two weeks. There is still standing water in some pastures. This morning there was frost and temperatures are predicted to reach 75⁰F this afternoon. Last week cattle began grazing in the pastures, but the grass will probably grow faster than they can eat it, and he'll be baling some hay. In other parts of Decatur County the soil is a bit drier, and more corn has been planted than usual for this early in the season. He just saw the first flies.

David Swaim reports alfalfa looks great and is approaching initial budding in west central Indiana. Wheat stands look good. Earliest planted corn is now at second leaf stage. Locally, the majority of corn acres were planted by April 23. Operators are back in the field after rain late last week. Bean planting has just begun. As of Wednesday, April 28, a no-till field with wheat stubble from last season plus volunteer rye-grass (from last year’s cover crop study) that was killed prior to reaching 10 inches height, is still too wet to plant under the residue mat, even after strong drying winds.

Michigan report from Matt Wiley, Rob Malcomnson and John Simmons
All the farmers reported dry conditions in Michigan. However, in Southwest Michigan, the oak leaves are coming out. Farmers are working their ground and preparing for planting. Oats, clover and hay are finishing seeding. Grass is growing rapidly and is ahead of cattle grazing.

In the next two weeks, farmers in the Thumb area and east side of the state will be planting corn. One farmer stated that he is planting blue hybrid corn early to prevent conventional GMO corn pollination contamination. He is hoping to have his corn pollinated prior to GMO corn pollination.

We had a good conversation on controlling Canada thistle organically. Suggestions were:

• Tilling the field dry several times
• Planting thick alfalfa for three years
• Using vinegar to burn the above ground growth

The suggestion to use vinegar raised several questions.

• What concentration?
• Is it legal to apply?
• Is it economical?

If you know the answer to these questions, please let us know! You can e-mail us at: newagnet@msue.msu.edu

One farmer from Indiana indicated that grazing has eliminated Canada thistle on his farm. He noticed that thistle plants turned black or white after cattle fed on the buds and those plants died.

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