Vol. 1, No. 6 - June 24, 2004
In this issue
Next issue posted July 15. Read previous issued through our calendar of issues.
Weed management systems in organic vegetable production
David Hillger, Botany and Plant Pathology, Purdue University
Are you spending your summer trying to control weeds? Does it feel like no matter how many times you cultivate you still have weed problems? Maybe your weed management system needs to be adjusted. The effective management of weeds in organic vegetable production depends on the integration of practices that prevent the germination and establishment of weeds, increasining the ability of the crop to compete with weeds, and controlling within-season outbreaks. While conventional farmers often focus almost exclusively on controlling with-in season outbreaks of weeds, primarily with herbicides, organic farmers need a more balanced approach in which all three areas (prevention, crop competition, control of within-season outbreaks) are used. Indeed, ignoring any one of these areas can place greater strain on the remaining areas and may explain why you’re spending so much time this season hand-weeding or on a tractor. In the following paragraphs we provide a brief overview of these areas and suggest places to go to find more detailed information.
Prevention
Wees require favorable environmental conditions to germinate and for seedlings to survive. Preventive tactics seek to alter the environment so that weed see germination and survival are reduced. Crop rotation, which is arguably the most important tool for prevention, allows farmers to vary tillage, seedbed preparation, cultivation and to include cover crops in their weed management strategy. Crop rotations also allow farmers to utilize plants with different growth habits and canopy structure (e.g. a vegetable crop followed by a grain crop or a cool-season vegetable followed by a warm-season vegetable). A diverse and well-planned crop rotation system can prevent the selection of weeds adapted to specific conditions and prevent rapid increases in weed densities that are often seen when crops are not rotated.
Competitive crops
There is considerable evidence that crops and cultivars vary substantially in their abilities to compete with weeds. For example, vegetable crops, including tomatoes, tend to be less competitive and often require stronger prevention measures and more intense cultivation than grain crops. Thus, farmers can limit the effect of weeds by selecting more competitive crops and varieties. Farmers also can limit the effect of weeds on the crop by altering row spacing and crop density to increase the ability of the crop to suppress weed growth. Weeds that emerge earlier in the growing season generally decrease yields more than weeds that emerge later. Relatively small advantages in early growth can greatly reduce the effect of weeds on crop growth and yields. Transplanting crops such as tomatoes can give them a substantial growth advantage over newly emerged weeds.
In addition to choosing competitive crops, transplanting, and manipulating crop planting density, farmers may be able to increase the proportion of nutrients and water taken up by the crop relative to weeds. In irrigated crops, the placement of irrigation lines can affect competition between weeds and the crop. For example, California growers have also shown that burying the drip irrigation line 15 to 20 cm below the surface of the bed will provide moisture to the crop but limit the moisture available to weeds on the surface (Gaskell et al. 2000). Researchers are currently investigating whether the placement and timing of organic fertilizers including composts and mulches can be manipulated to insure that the crop takes up a larger proportion of nutrients.
Within-season control
Prevention and crop competition can reduce weed densities. However, it is often necessary to control weeds during the season. To be effective, most cultivation must be conducted early in the season. In tomatoes, the critical weed-free period is four to five weeks after transplanting. By reducing the competition of weeds during this period, growers can reduce the negative affects on yields caused by weeds. Weeds that germinate during the season can be controlled with a variety of methods. The simplest, but most time consuming is hand removal. Mechanical cultivation is the more common approach on larger farms. The growth of organic and low-input agriculture has triggered an increase in the availability of equipment for mechanical weed control (Bond and Grundy 2001; Bowman 1998). Cultivation implements that are used to uproot, dismember and bury weeds and can be grouped into three categories: 1) inter-row, 2) near-row and 3) full-field and in-row tools. Inter-row tools such as shovels, sweeps, rolling cultivators, rotary tillers are designed to dig moderately deeply between crop rows (5-10 cm) and can uproot and bury larger weeds. Near-row tools such as vegetable knives, disk hillers, spyders, basket weeders, and brush weeders cultivate 5-12 cm from the crop to a depth of less than 5 cm. Full field and in-row tools such as weeding harrows, rotary hoes, rubber-finger weeders, spinners, and torsion weeders are designed to disturb the soil surface layer and uproot weed seedlings. Cultivation using rolling cultivators or disc hillers can be used to mound soil next to the base of the tomatoes, effectively covering small weeds and allowing the tomatoes to develop roots further up the stem.
Regardless of the tools you use, a successful weed management program will need to include prevention, crop competition and within-season control. A careful consideration of your weed management system may help you identify and compensate for weaknesses in any of these three areas and develop a system that works best for your operation.
Literature cited
Bond, W. and A. C. Grundy. 2001. Non-chemical weed management in organic farming systems. Weed Research 41: 383-405.
Improving soil water holding capacity
Eileen Kladivko, Agronomy Department, Purdue University
Water holding capacity refers to the amount of water held or “stored” in the soil and available for plant use. After a good soaking rain, when the soil is completely saturated, some of the water drains quickly under the influence of gravity and is lost from the rooting zone. The soil water content at the time rapid drainage ceases is often called the “field capacity.” Some of the remaining “stored” water is available for plant use while some is bound tightly to soil particles and not available. The difference between the water content at field capacity and that at “wilting point” (water content at which plants can no longer extract water from soil and thus permanently wilt) is what is usually called the “water holding capacity” or “plant available water.”
Generally, our goal is to have the largest possible water holding capacity for a given soil, as long as aeration is adequate. Good soil aeration usually requires about 10% of the bulk soil volume (or 20% of the soil pores) be filled with air shortly after a heavy rainfall event. Compacted soils or heavy clay soils may hold too much water and suffer from aeration problems after rain events. But as long as aeration requirements are met, a larger water holding capacity is of value whether in rainfed conditions or under irrigation, since irrigation could be applied less frequently.
Water holding capacity is determined by several factors, some of which are beyond our control but some of which can be managed. Management practices designed to improve soil structure are the main way to improve water holding capacity. The major contributing factors are discussed below.
Texture
Soil texture is the major determiner of water holding capacity of a soil. The large pores in sandy soils allow water to both infiltrate and drain quickly, leaving smaller amounts stored within the soil profile. Loams, silt loams, and clay loams have a broader range of sizes of pores, many of which store water for longer time periods. In most cases there is no practical way to change the soil texture, and so other practices should be used to try to increase water-holding capacity of sandy soils.
Increasing the organic matter content of the soil will increase the amount of water held in the soil, and usually some of that increased water content is available to plants. The main way in which organic matter increases water holding capacity is through its influence on soil structure and aggregation. Organic matter helps build soil aggregation and tilth, producing a mixture of pore sizes that retain water in the plant available range. For sandy soils, organic matter is key for producing some medium pore sizes that will retain water. For heavier soils, organic matter helps aggregate the soil and reduce the influence of compaction and fine pores that retain water too tightly to be taken up by plants.
Periodic “feeding” of the soil microorganisms with fresh organic materials is necessary to increase soil organic matter content. Organic matter can be added in the form of manures, composts, etc., or it can be grown on-site such as by green manures and cover crops. Grasses and other plants with fine roots are particularly effective in building soil aggregates. Refer to the articles by S. Snapp and D. Mutch in the April 29 issue of the Newsletter for more details on cover crops.
Depth of rooting zone
Infiltration
Structure and aggregation
Soil structure is related to all of the factors already discussed. Good soil structure will have a mix of sizes of pores that allow for water infiltration, drainage, and storage. A lack of root-restricting layers and other compaction features will enable roots to develop freely and access water deeper in the profile. A well-aggregated surface will allow rapid water infiltration.
Improving soil structure involves organic matter additions, as discussed earlier, as well as appropriate tillage practices. Excessive tillage destroys soil aggregation and decreases soil organic matter content. No-till has been an excellent way to improve soil structure for agronomic crops. The lack of tillage means that tillage pans are not formed, and the macropores formed by soil biota, including earthworms, remain intact and build up with time in the system. Surface residue cover provides organic material for aggregate formation near the soil surface. As discussed in the article by S. Snapp in the April 29 edition of the New Ag Network, reduced tillage systems for organic vegetables may become more viable in the future and provide similar soil structure and water efficiency benefits as with agronomic crops.
Additional reading
Magdoff, Fred, and Harold van Es. 2000. Building soils for better crops, Second edition. Sustainable Agriculture Network Handbook Series, Book 4
Illinois Natural History Survey, Champaign, Illinois
Scientists and Extension educators at the University of Illinois, Illinois Natural History Survey, and University of Wisconsin have joined forces to stimulate greater focus on organic issues and facilitate development of multi-disciplinary, cross-institutional research and education projects pertinent to organic systems. Current participants include specialists in soil fertility, vegetable entomology, crop protection, soil invertebrates, weed ecology, plant pathology, biological control, composting, sustainable agricultural systems, marketing of organic products, and economics aspects of organic systems. In 2002, the Survey designated six acres assigned to it on the University of Illinois Cruse Tract in Champaign for long-term research on organic production systems. With help from an advisory group of experienced organic growers and a USDA grant, the research group has initiated a research program at this field site, which is being developed following organic certification guidelines.
The initial research will focus on organic transition. “Transition period” is an arbitrary term with a regulatory dimension for organic systems. Transition from conventional to certified organic production usually takes three years to complete based on the National Organic Program standards requirement that no prohibited materials be applied for three years before harvest of the first organic crop. From an ecological perspective, however, this transition is a period of substantial change. Instead of synthetic fertilizers and pesticides, the grower now relies on biological and ecological processes to build soil organic matter, provide plant nutrients and regulate populations of pest and beneficial organisms. As crop diversity and organic soil amendments increase, these shifts promote increased biodiversity of organisms within the cropping system. A goal of organically managed systems is to achieve balance of soil biological processes so that nutrient availability is greater during times of plant growth and loss of excess nutrients into the environment is minimized. Because this balance may not be present yet in transitioning systems, crop yields may be affected and nutrient loss can occur. Gaining a better understanding of the changes in biological systems that occur during transition to organic production is a major goal of the Illinois project.
The Champaign project is comparing three farming system transition schemes that differ in management intensity (crop rotation, tillage) and organic matter inputs. The different approaches to transition that the three farming systems represent are:
1)
A high-intensity (high disturbance) system similar to what a vegetable grower might follow,
2)
A medium-intensity system similar to what a cash grain producer might follow and
3) A low-intensity (low disturbance) ley system that represents what a grower with extra land might choose with a focus on soil building rather than income-generating crop production during transition.
A second objective of the project is to develop science-based information products (from the project’s own research and other sources) on organic and transitioning production systems, products relevant and accessible to organic producers. An advisory board of organic growers is assisting the research team to refine objectives, lend expertise in farming systems management, provide input on the relevance of experimental approaches, and evaluate the results.
What is the take-home message about this project? Longer-term information will be available to help growers smooth the transition to organic production. Because many of the findings from the organic transition project will not be known until the certification year, however, the research group is also conducting short-term experiments that can provide beneficial information to organic growers more quickly. For example, entomologist John Shaw is currently evaluating the efficacy of 10 organic products for control of squash/pumpkin insect pests in an on-farm trial in Northern Illinois and another 24 organic products for control of cabbage pests in Champaign. In addition, Shaw and greenhouse specialist Janeth Moncada, have compared an experimental compost-based potting mix with commercially available organic potting mixes as a medium for growing organic transplants of several vegetable and flower crops. The results of these experiments will be available later this year.
Liz Maynard, Dept. of Horticulture and Landscape Architecture
Fred Whitford, Purdue Pesticide Programs, Purdue University
Chris DiFonzo, Dept. of Entomology, Michigan State University
Ed White, Office of the Indiana State Chemist
Vinegar or acetic acid?
First a clarification of the terms. Vinegar is a fermentation product produced by the feeding of bacteria on alcohol and typically contains 4% to 8% acetic acid along with low concentrations of other organic compounds. Vinegar can be concentrated by distillation or freezing to produce solutions containing higher concentrations of acetic acid. The acetic acid is presumably the compound responsible for vinegar's weed-killing effects. Solutions of pure acetic acid in water are not considered vinegar. Most pure acetic acid available today is produced using synthetic chemical processes. It is available in both concentrated and dilute solutions, and is used in a wide variety of industrial processes, as well as in food processing. As used in this article, and in most other cases, the terms vinegar and acetic acid are not interchangeable.
Is it legal to use vinegar to control weeds?
The quick answer is yes, but with qualifying conditions. First, a review of the federal pesticide law is required. This law, called FIFRA (The Federal Insecticide Fungicide and Rodenticide Act) requires most pesticides be registered with EPA and obtain an EPA Registration Number before they are sold in the marketplace. A pesticide is defined in very broad terms as a substance intended for preventing, destroying, or mitigating a pest. Facilities that produce these registered pesticides are required to obtain an EPA Establishment Number that is used to track where the product was made. These rules require vinegar sold or distributed as an herbicide to have an EPA Registration Number, and the place where it was formulated to have an EPA Establishment Number. Registering a pesticide involves more than just filling out paperwork and paying EPA the fees. For conventional pesticides, it typically costs the registrant more than $180 million to perform the studies on human health effects, environmental fate, and food residues required to meet EPA approval.
As Paul Harvey would say, "And now the rest of the story." The Federal law provides a mechanism that exempts products from registration if they contain only certain specific ingredients that EPA has concluded will not pose unreasonable risk to public health or the environment. To fall under this exemption, the active ingredient(s) of the product must appear on the list of exempt substances (known as the "25(b) List"), and also, all inert ingredients must be on the list of minimal risk inerts (known as "4A Inerts"). Active ingredients are those that are responsible for the desired pesticidal effect. An example of an exempt product is one containing mint oil used to kill wasps and hornets. The product works like a pesticide, but is not required to be registered for use with EPA, because mint oil is on the 25(b) exemption list. Some other materials that appear on the list of exempt active ingredients are: cinnamon oil, citric acid, malic acid and white pepper. Neither vinegar nor acetic acid is on the 25(b) exemption list. Vinegar, at a concentration of less than 8% acetic acid, is on the list of minimal risk inert ingredients that do not require registration. Clearly, an herbicide containing vinegar as an active ingredient is NOT exempt from registration under these criteria, and must undergo the EPA registration process.
So far, we have been discussing registration with the EPA at the federal level. Individual states also require pesticide products to be registered within the state, and they may have their own set of rules to deal with product registration. For example, state regulations in Indiana, Michigan, and Illinois require the registrant to register all pesticide products, even those that may have been exempted under federal laws.
Are there any registered herbicides containing vinegar?
At the writing of this article, no herbicides containing vinegar listed as the active ingredient are registered with the EPA. Two herbicides containing acetic acid as the active ingredient are registered in Michigan, Indiana, and Illinois for non-cropland use: Burnout Weed & Grass Killer Concentrate and Burnout Weed & Grass Killer Ready-to-Use. These are not registered for use on cropland.
What about using vinegar sold for use as a food?
Up to this point, the discussion has centered on materials intended for use as pesticides and are sold or distributed as such. What about the case where a farmer buys a substance that is not intended for use as a pesticide, and uses it as a pesticide in his or her own operation?
For example, what about a farmer buying vinegar intended for human consumption, and spraying it to kill weeds? What if a homeowner uses vinegar to control weeds in the garden? These would be described by EPA as “production of pesticides for personal use” and would not require registration of the vinegar or the pesticide-producing establishment (i.e. the farm or the home). However, if the vinegar is to be sprayed on food or feed crops that will be sold, the technical issue of “tolerance” arises. Pesticide laws are not the only laws governing what may be applied to food or feed crops. The Federal Food Drug and Cosmetic Act prohibits contamination of food with materials harmful to human health. All pesticides (even those exempt from registration because they contain minimal risk active ingredients and inerts), and all other materials, require approval before they can be used on food, food crops, animal feed commodities, and food contact surfaces. In order to be approved, a “tolerance” for the material on particular crops must be approved, or an “exemption from tolerance” must be granted.
Before determining that it is OK to spray vinegar where it might come in contact with food or feed crops, it must be clear that vinegar either has a tolerance for this use or is exempt from tolerance. According to EPA staff, vinegar sold for human consumption is exempt from tolerance because it is a commonly consumed food. This means it is OK to spray vinegar meant for human consumption where it may contact food or feed crops. Vinegar could legally be sprayed on weeds by the farmer or homeowner.
Is vinegar allowed under the National Organic Program?
Is vinegar acceptable for use in killing weeds under the National Organic Program (NOP)? Naturally produced vinegar made from non-gmo plant materials is acceptable for use under the NOP. As described above, vinegar is a natural fermentation product of alcohol. The alcohol can be derived from various sources, including fruit, grain, and potatoes. Vinegar concentrated by distillation and/or freezing is acceptable for use in organic production. Synthetic acetic acid is not considered vinegar, and is not currently approved for crop production uses under the NOP.
Solutions containing acetic acid, including vinegar, like other acids, are corrosive. The more concentrated the acid is in the solution, the more corrosive, and the greater the hazard of the material. Solutions containing less than 10% acetic acid can cause mild irritation to the skin, severe irritation to the eye, and produce vapors irritating to the respiratory tract. Solutions containing higher concentrations cause more severe irritation or injury. Solutions containing over 10% are regulated by the federal Dept. of Transportation as corrosive materials.
Summing it all up
In summation, materials containing vinegar sold for herbicidal purposes must be registered with the EPA and used according to label instructions. The use of vinegar sold for human consumption on ones own farm or garden does not appear to violate federal pesticide and food safety regulations. As with the use of any material, the user should become informed about potential hazards of the material and recommended practices to avoid harm to oneself, others, wildlife and the environment. It is important to check with your state department of agriculture to make sure that the state agrees with the arguments presented here.
People who make pest management recommendations as a part of their professional responsibilities have additional issues to consider. In general, recommending the use of non-registered products is a risky business, even if the use is legal in particular circumstances. When there is limited information on efficacy, especially when used against multiple crops in varied situations, the recommender could be facing serious consequences when a recommendation results in garden, landscape, and crop injury and damage. Or, if the material does not work as expected, there is potential for an accusation that false claims were made. In some states, recommending an unregistered pesticide product can be grounds for enforcement action against the person making the illegal recommendation. Thus, it is important to really understand what your state will and will not allow when it comes to making such recommendations. Lastly, consider the impacts, both negative and positive, when it comes to putting your name to these types of recommendations.
References
Canadian Centre for Occupational Health and Safety. Chemical profile of acetic acid, solutions of 10% or less. CHEMINFO Record No. 752. <http://www.intox.org/databank/documents/chemical/acetacd/cie752.htm> Accessed 19 May 2004.
Organic crop budgets: A catalogue
Corinne Alexander and Jennifer Dennis
This article provides a catalogue of the available crop budgets for organic crops and discusses how a grower would use this information. Organic crop budgets have been developed in five states: California, Kansas, North Dakota, North Carolina, and New Jersey (see Table 1 for the catalogue). While all of these states have different growing conditions from Illinois, Indiana, or Michigan, these budgets can serve as general guides to the costs incurred in organic production. Growers and other users of this information need to recognize that these budgets have been developed to estimate the costs of a hypothetical average producer. Anyone using this information should make adjustments to the yields, prices, input costs, and input requirements. The organic crop production budgets shown can also serve as a template for creating budgets for the tri-state areas of Illinois, Indiana, and Michigan.
Production budgets enhance marketing and selling functions, including a better management of the product and an increased awareness when setting price points. Growers can use this production cost information in several ways. First, the grower can use this information for financial planning; to identify the profit margins associated with each specific crop, to estimate cash flows during the year, and to estimate the size of farm to earn a specific income.
Illinois updates on June 28
Northern
Illinois
Weather conditions have resulted in it being too wet to finish up soybean planting and rotary hoeing and cultivating corn. There is very poor germination in the cornfield that was planted first and it will be torn up and planted to buckwheat (or another short season crop). Current farming practices include cultivating corn and planting soybeans (first field planted June 19), as well as mowing thistle patches in wheat fields and hand-hoeing thistles in these same fields. Farming operations in the next two weeks will include finishing planting and rotary hoeing soybeans, cultivating corn, and cutting thistles in wheat fields and around farmstead.
Central Illinois
Since the last update, we’ve had excessive rain (6-7 inches) and heat. Now, it is cool and dry. Current farming practices included field cultivating, planting of the last summer planting of peppers and tomatoes and replanting of winter squash. Currently, we are making the beds for the fall plantings that will begin the first of July. We also planted sudan grass and grain rye for summer covers.
Southern Illinois
Rain has delayed hoeing and cultivating of soybeans and corn, as well as the baling of alfalfa hay. Also, frequent rains have resulted in weeds sprouting. Current farming practices include baling second cutting of alfalfa hay, hoeing soybeans and cultivating corn and soybeans. Farming operations in the next two weeks will include combining wheat, baling hay, cultivating corn and soybeans, and hoeing soybeans.
Questions
Are there any ideas for a crop that can be planted in July, other than buckwheat?
Northwest Iowa (updated June 28)
We have finally enjoyed some dry weather and have been able to do some much needed cultivating. The beans look good with the rows really clean, but there are some very large lambsquarters in the middles, which are very hard to kill, even with a Buffalo cultivator. The replanted corn looks pretty, but is small, and weed control is excellent.
I have been cultivating and baling waterways. I will start to ridge corn shortly and lay the beans by after that. I have high school kids who will start walking beans this week, although there aren’t too many weeds to chop. I will also sidedress some liquid pig manure on some corn that followed triticale. It looks quite N deficient. I think the residue from the considerable volunteer triticale has really tied up the nitrogen.
West Central Iowa
Ron Rosmann reports that the heavy rains have subsided somewhat even though it is still raining some smaller amounts about every other day. Their soil types, good drainage, and fairly significant slopes allow the ground to dry out quickly. They are now cultivating corn the second time and are ridging it with the Buffalo cultivator. It is about two feet tall for the most part. The Buffalo cultivation system allows one to do an “extreme makeover” in weedy fields that one can’t get into because of too much rain. The mirror and anti-three point sway attachments available through Klingler Manufacturing of New Ulm, Minnesota helps a great deal in cultivating very close to the crop and not taking out the crop on steeper slopes. They also use a Buffalo guidance system some of the time, but for the money, the mirror and the anti-sway device are the most important and certainly the cheaper of the tools. They have been using the ridge-till system for over twenty years in our row crops of corn and soybeans. Three years of on-farm trials through the Practical Farmers of Iowa showed 7 to 10 times less weeds when compared to a conventional tillage operation when not using any herbicides.
They have had 175 pigs born in June in their organic hog operation. They are one-half Berkshire and one-half Chester White. All the pigs are completely white so that must be the dominant color.
Indiana
In Northeast Indiana, Dan Flotow’s farm is located outside of Fort Wayne, Indiana. He grows vegetables along with cut flowers and has a greenhouse with organic bedding plants, perennials, and hanging baskets. He’s been doing it about 10 years; switched to organic in the field about four years ago, and switched the greenhouse over last year. Because he operates a CSA, he does a wide variety of vegetables: sweet corn, melon, cukes, squash, lettuce, onion, potatoes, celery, broccoli, eggplant, tomatoes, including many heirloom varieties. Out of 60 varieties of tomatoes about 40 are heirlooms. The CSA is in its second year and has 42 members. Most people in the area are unfamiliar with CSAs, so there has been a lot of consumer education. Just now he is getting a lot of crops in the ground; there was a delay because it has been extremely wet. Last Monday the field was under water, and greenhouses had water in them. He had to ditch the field to get water off of the wet spot in the field. He purchased a compost tea brewer and is applying it every day in the greenhouse and in the field.
A question was asked about insect control in the greenhouse. Dan reported it is generally ok. They have beneficial insects, and, if necessary, use insecticidal soap, neem, sometimes rotenone or pyrethrum. Aphids were not a big problem this year. Right now the biggest problem is mealy bugs on the coleus.
As part of a discussion that arose on the call about wheat harvesting, Gary also had some comments on equipment that harvests only the heads of wheat. There had been two stripper headers in his county. He reported they do a tremendous job, and can suck heads off the ground if wheat is down on ground. One individual custom bailed the straw behind it; he baled it long and it was used for erosion mats. A place in southern Indiana made the erosion mats. Horse people also liked the “long straw.”
Michigan
Corn planting is completed. Soybeans are still being planted. Soybeans are germinating very fast in about four to five days after planting.
