May 1, 2008
In this issue
§ Insects to watch 2008 - Part III - soybean aphid
§ S-B-A and K….what’s the link?
§ Weed control in soybeans can benefit from preemergence soil-applied herbicides
§ Delayed preemergence and early postemergence herbicide applications in corn
§ Allocating fertilizer resources for crop production
§ Managing higher priced fertilizer inputs
§ Fusarium head blight risk assessment models and DON prediction model
§ Regional reports
§ Weather
Next issue May 8
Christina DiFonzo, Entomology
Last season was a banner year for worms and beetles, but
where were the soybean aphids? Chris DiFonzo, the self-proclaimed soybean aphid
queen (that’s me) predicted an aphid outbreak for 2007. Where was the outbreak?
Will the prediction for 2008 be equally as accurate? Let’s recap the 2007
season. In the winter of that year, entomologists in the
The Northcentral Aphid Suction Trap network consists of over 40 traps in 10 states, running in the summer and fall. Fall catches of soybean aphid are important because they consist of winged males and females leaving soybean for buckthorn, the overwintering host. The females land on buckthorn and have daughters; the daughters mate with the males (in human terms, mating with their uncles), and lay eggs. The egg stage allows soybean aphids to survive the cold northern winters. In general, a large fall flight predicts an aphid outbreak the following year, in this way:
At the end of 2006, dozens to hundreds of winged soybean aphids were captured in the suction trap network (Table 1), The numbers may not seem high, but remember the trap is a vertical PVC pipe drawing in air 25-30 feet above ground. It is sampling a small amount of air overall, so the trap catch is a tiny fraction of the aphids actually flying from soybean to buckthorn.
In the winter of 2006-07, entomologists sampled buckthorn for soybean eggs. Eggs were found at numerous locations, hundreds on branches at some locations. Again, this may not seem very impressive, but aphid eggs are very small and generally difficult to find. Finding eggs at all, much less multiple eggs on a bud or branch, is significant. Because of the fall suction trap counts and egg numbers, we predicted an outbreak.
A spring freeze in April damaged buckthorn buds across the
In
Aphid numbers increased slowly until early July. Then unseasonably hot weather and minimal canopy resulted in very hot temperatures at the soil surface. In research plots, the ground was too hot to sit on. That same week, the building aphid numbers took a dive. Soybean aphids can survive hot weather when they are under a cool plant canopy, but they likely cannot tolerate 90-degree days when plants are still small. The population growth rate appeared to slow, and perhaps predators had a chance to catch up. Fields were essentially aphid-free until August, until winged aphids blew in from surrounding states. Some fields went over threshold, but for most fields it was too late to build aphid populations.
Surrounding states, northern
What about 2008? Table 1 shows that the suction trap catches
in the fall of 2007 were considerably lower than at the same locations in 2006,
with one exception,
|
State |
Fall catch 2006 |
Fall catch 2007 |
Reduction 2006-07 |
|
|
196 |
1 |
99.9% |
|
|
1472 |
10 |
99.9% |
|
|
133 |
2 |
98% |
|
|
42 |
31 |
26% |
|
|
32 |
2 |
94% |
Christina DiFonzo, Entomology
With the high cost of fertilizer this season, many producers are making decisions about how much to purchase, how much to apply, and which fields to treat. As you make these decisions, consider that insects as well as plants are affected by fertilization.
In 2000, when soybean aphid (SBA) was first found in
In 2004 and 2005, graduate student Abby Walter sampled
plants from symptomatic (yellow) and nearby green areas in commercial fields in
southwest
Answer: Yes. In commercial fields, the average number of aphids per leaf was 50 percent greater on the plants with severe yellowing compared to plants growing in green areas of the same field. Plants from deficient and non-deficient areas had the same aphid number per plant. However, the K-deficient plants were stunted and had fewer leaves per plant, so that aphid density was higher. This is why aphids appeared to “drip off” of symptomatic plants.
Answer: Yes. In field cages infested with soybean aphids on June 1, populations went over the economic threshold and injury level (EIL) earlier, and increased to a much higher level, on plants growing in unfertilized plots (dashed line) compared to plants growing in K-fertilized plots (solid line).
Answer: Yes. Aphids on plants growing in unfertilized (deficient) plots reproduced at an earlier age (approximately nine days) and produced more nymphs (nearly 90 per female) than aphids on plants growing in K-fertilized plots (first reproduced at 11 days, 60 nymphs total).
Answer: Probably. Abby found that the proportion of the amino acid asparagine was greater in phloem sap from deficient plants. Aphids feed on phloem sap, a poor source of nutrition because it is low in nitrogen in the form of amino acids. Asparagine is a non-essential amino acid that is an important nitrogen source in the aphid diet; aphids can convert asparagine into essential amino acids lacking in their diet! How do aphids do this? They have friendly symbiotic bacteria living in their guts that do the job for them. So, K-deficient plants do appear to be nutritionally better (i.e. aphid candy), which may partially explain the quicker and greater reproduction on such plants.
So what? First, this research demonstrates that crop fertility can effect the population of, and damage from, an insect pest. If you need a reason to spend time and money soil sampling and following recommendations for applying potash to build soil K levels, reducing the impact of soybean aphid is a good one. Second, even if you don’t plan to apply potash, this research still provides you with valuable information to select which fields to scout first and more often. Fields with a history of K deficiency, or a soil type susceptible to deficiency, or fields planted after alfalfa are all at greater risk for an aphid outbreak.
In 2007, a very low aphid year in
If you are a glutton for punishment, and want to read a journal article about this research, visit:
http://www.ingentaconnect.com/content/esa/envent/2007/00000036/00000001/art00004
Christy Sprague, Crop and Soil Sciences
The use of postemergence (POST) glyphosate in Roundup Ready
soybeans has been the primary weed control program used by many
One way to help overcome some of these concerns is to implement the use of a soil-applied or preemergence (PRE) herbicide into your soybean weed control program. Using a planned PRE residual herbicide followed by a POST glyphosate application can result in more consistent weed control, reduces the size and number of weeds present at the POST application timing, and offers greater flexibility in the POST application window. One of the concerns that many producers have in implementing a PRE herbicide is the economics. While a PRE herbicide may increase the cost of your weed control program, resulting benefits often make up for the cost by increasing weed control and yield. Below are some of the benefits realized by PRE followed by POST weed control programs.
Using a PRE herbicide will control a number of weeds that would have emerged and competed with the crop as it becomes established. While early-season competition may not be a factor if the POST application is timed appropriately, (remember that weeds can increase in size in a number of days and if you are trying to spray a large number of acres or you become delayed in your applications due to rain) early-season weed competition can become a problem. Remember, for timely POST applications to avoid yield losses due to early-season weed competition MSU recommends weeds should be controlled before they are 4-inches in height in 7.5- and 15-inch rows and 6-inches in height in 30-inch rows.
Several weed species have continual emergence or emerge only
later in the season. These species can include: annual grasses, giant ragweed (southern
In
Control of perennial weeds is more effective in the later stages of growth (bud to flower stage). Because PRE residual herbicides will provide initial control of annual weeds, the POST glyphosate application may correspond more appropriately to the stage of growth needed for perennial weed control.
One possible long-term benefit from including a PRE herbicide in your weed control program is the implementation of herbicide resistance management strategies. A PRE herbicide would include another mode of action into the weed management program and reduce the number of weeds present for the POST application. Ultimately, these two benefits will relieve the selection pressure of a glyphosate-only weed management system. This has become a much greater concern as we see more glyphosate-resistant weeds being reported around the United States.
Wes Everman, Crop and Soil Sciences
Preemergence herbicides should be applied as soon after planting as possible because delayed application increases the risk of poor herbicide performance, especially for grass control. However, there can be challenges for herbicide application following planting, such as high winds and rainfall. Therefore, it is likely there will be situations where corn has emerged before preemergence herbicides have been applied. In fields with emerged corn and no herbicide applied, growers have two primary options: to use an herbicide program typically applied before emergence; or switch to a total postemergence strategy. There are several possible herbicide programs with each strategy.
When herbicide application is delayed until after crop emergence, rotary hoeing is recommended. The rotary hoeing may be done before or after the herbicide application, but must be done when the weeds are very small. If the delayed application includes Banvel/Clarity, Distinct, Marksman (or other herbicides containing dicamba) or Prowl/Prowl H2O/Pendimax, crop safety will be greater if the rotary hoeing is done before herbicide application.
Herbicides typically applied preemergence are listed in
Table 1K (pg. 46) in the 2008 Weed Control
Guide for Field Crops. Many of these herbicides are also labeled for
application after corn emergence. Axiom and Princep7 should only be applied
before corn emergence. To avoid confusion, tank mix combinations are not
included in this table. Details on the specific restrictions for tank mixtures
can be found on herbicide labels. Some herbicide labels allow application to
emerged corn using 28 percent liquid nitrogen fertilizer as the herbicide
carrier; however, we advise that all herbicide treatments to emerged corn be
applied with water as the carrier. Applying herbicides to emerged corn with 28
percent liquid nitrogen as the carrier, poses a risk of severe crop injury.
This risk is increased under cool, cloudy conditions prior to application, a
common occurrence in
For several years, MSU has demonstrated the importance of
timely herbicide applications to prevent the loss of yield in corn. We have
shown that it is necessary to control weeds before they reach four inches of
growth to prevent measurable yield reduction. Two-pass herbicide applications
(preemergence followed by postemergence or two postemergence) or timely single
postemergence applications with residual control are most effective at
preserving yield and maximizing gross margin. Information about the
effectiveness and economics of preemergence and post emergence herbicide
programs can be found in the summary of Commercial Herbicide Program
Comparisons found on the MSU Weed Science website at http://www.msuweeds.com/publications/.
Herbicide options for total postemergence weed control are dependent on the
hybrid planted in the field. Many postemergence herbicides can be used on any
corn hybrid, while others such as
Darryl Warncke, Crop and Soil Sciences
The price for potash will be considerably higher this year than last year and supplies will be tight. Potash may be allocated based on past use. This is the result of an increasing worldwide demand for potash. Faced with this situation, farmers need to evaluate how they can best use the funds they have allocated for fertilizer inputs. Soil test results are an excellent guide for deciding how much lime, nitrogen, phosphorus and potassium to apply on each crop in each field. Collect soil samples and test as soon as conditions permit or work from recent soil test information, within the last 2 to 3 years.
Look first at the soil pH. If it is below 6.0, the best first investment is for lime. In many situations, the return on invest is best with lime, both short and long term. When the soil pH is below 6.0, applied fertilizer nutrients or indigenous soil nutrients are not used as efficiently by crops.
Nearly 70 percent of soils in
In contrast to phosphorus, less than 25 percent of the soils
in
This can be especially beneficial when planting corn no-till or into high residue fields. Another approach is to reduce the amount of K2O recommended and applied to each field by a set amount, for example 25 lb K2O per acre. In this way, the impact on field yields from having to apply less potash on a whole farm basis will be minimized and return on investment in potash will be optimized for the resources available.
Darryl Warncke, Crop and Soil Sciences
Increasing worldwide demand for nitrogen, phosphorus and potassium has brought about significant increases in the costs of these materials for the 2008 growing season, especially potash. The supply of potassium may also be limited. Faced with this situation, farmers may have to make decisions on how to get the best return from the fertilizer they are able to purchase. Following are some suggestions.
1. Soil test. A soil test indicates the available nutrient status of the soil, the need for lime and how much nitrogen, phosphorus and potassium are needed for the crop to be grown. Test results from samples collected within the last two to three years can be used as a guide. For fields where no soil test information is available, collect soil samples as soon as possible and have them tested.
2. Apply lime where needed. Maintaining the soil pH between 6.0 and 6.8 improves nutrient availability and crop growth. In many situations, the return on invest is best with lime, both short and long term. When the soil pH is below 6.0, applied fertilizer nutrients or indigenous soil nutrients are not used as efficiently by crops.
3. Take credit for nutrients contained in manures, composts or other materials applied to crop fields. Nutrients contained in these materials are readily available and can offset the need for purchasing any additional fertilizer. Have manures and compost analyzed for the nutrient content.
4. Apply phosphorus
only where needed. As the result of past buildup, 70 to 75 percent of
5. Focus of
potassium. Only 20 to 25 percent of
6. Band-apply nutrients. Band applied nutrients are used more effectively than broadcast nutrients. In high P testing soils, early growth from banded fertilizer comes more from nitrogen and potassium than phosphorus. Overall, reducing phosphorus in favor of nitrogen and potassium may prove beneficial.
7. Apply P and K first to fields most in need. The crop yield response to incremental additions of potassium or other nutrients can be characterized as the “curve of diminishing returns.” This means that the increase in yield from the first increment of potassium added (say 50 lb K2O per acre) is greater than the second. And return from the second increment is greater than from the third, and so forth. Eventually the cost of an additional increment of potassium is greater than the value of the yield increase. This being the case, it is better to apply or allocate potash first to fields with lower soil potassium values, where there will be a good yield response, than to those fields that have close to adequate levels.
8. Reduce amount of K applied uniformly across all fields. In fields that need K, applying slightly less, e.g. 25 pounds per acre, than is needed will have only a minimal, if any, effect on net income. Work from soil test results.
9. Apply preplant nitrogen close to planting time. This will minimize the length of time nitrogen is at risk of lost by leaching or denitrification before crop demand increases.
10. Use a presidedress soil nitrogen test for corn to determine need for more nitrogen. Some soils can provide significant amounts of available nitrogen, especially where cover crops or animal manures or a previous legume crop is incorporated prior to planting.
Diane Brown-Rytlewski
Plant Pathology
Two models have been developed to serve as decision aids for
growers to determine whether an application of fungicide should be made to
control Fusarium head blight (FHB). The Penn State Model and the Ontario
DONcast model are described in this article. Through research funded by Project
GREEEN in 2006-2007, both the
Scientists have developed scab risk assessment models
through projects with the U.S. Wheat and Barley Scab Initiative. The
The
The
The final decision to apply a fungicide should be made as
close to flowering as possible. You should monitor local weather conditions
during the week before flowering to help you decide whether infection is likely
to occur in your area.
The DONcast model, developed at the
Before the head emerges from the boot, it is protected from Fusarium. The head is most vulnerable to infection from the time that flowering begins to the early milk stage. After mid-milk, it becomes more difficult for the fungus to infect the kernel and damage is less severe. The most severe head blight epidemics have involved multiple infection periods and cultivars susceptible to spread of the fungus throughout the head. Depending on the fungicide used, the window for management of head blight extends from heading to 50 percent flowering, with the optimum period of fungicide application being at Feekes 10.5.1 (about 15-25 percent of heads flowering).
Fusarium head blight has the potential to cause significant losses in both quality and yield. Discounts tend to start at lower ppm DON levels in white wheats than in red wheats. When and if a fungicide should be applied for FHB depends on the level of risk the grower is willing to accept. Although considerable effort is ongoing to develop FHB resistant varieties of wheat, the use of fungicides to control FHB and reduce levels of deoxynivalenol (DON) is still a primary management strategy. Timing of the fungicide application is especially challenging. Growers have an application window of only a few days for effective control of FHB and DON. Unlike some of the common foliar diseases of wheat, by the time scab symptoms are visible, the window for fungicide treatment is already closed. Models are meant to serve as decision aids to help growers decide whether or not an application of fungicide to control FHB is warranted.
The April 17, 2008 Field CAT Alert contained a partial
budget analysis to help you determine whether an application of fungicide was
likely to be economical. A table of fungicides currently registered in
Ned Birkey
This weather has allowed fields to dry out and planting to begin. However, scattered rain and even light hail occurred on Monday, April 28. The Enviro-weather station in Dundee recorded 25ºF yesterday morning. April had warm and cold weather, with both rain and snow and was generally wetter and cooler than normal. Although soil temperatures have dipped below 50ºF, now that May is here, farmers will keep planting.
Alfalfa is growing nicely with most stands about 8 to 10 inches tall. I have not seen any alfalfa weevil feeding of any significance. Stands are generally thinner due to the harsh winter weather. We will have less alfalfa harvested this year as some fields went into wheat last fall or will be planted to corn this spring. I anticipate that several new fields will be planted this fall.
Corn planting started last week and is at full speed ahead now that fields are drying out. No corn is emerged and soil temperatures are no longer a factor as the forecast is favorable. Lots of triple stack corn was sold this past winter. One farmer was audited this past year for compliance with the Bt refuge.
Oats were “mudded” in a couple of weeks ago.
Soybean planting has also started, though none have emerged. Lots of treated seed sold this winter. We will likely be getting the soybean aphid suction trap up and running by next week, once the new supplies arrive.
Wheat is at Feekes’ growth stage 5. Most fields have had nitrogen applied and are nice and green, with very good stands.
Although planting is behind the pace of the past several years, there are several new tractors and planters out there and none are smaller than the ones they replaced. This will be an interesting year with all the winter talk of using fungicides and insecticides post applied to corn and soybeans to increase yields.
Bruce MacKellar
Unexpectedly dry conditions over the past two weeks have
allowed many producers to catch up with tillage work. This should be considered
a major plus because there was a lot of moisture in the forecast during this
period. Rainfall accumulations with the last cold front were widely variable
throughout the region. While the majority of the area received at least some
precipitation, some areas received very little. The rainfall totals are running
about 1.5 inches behind normal over the last two weeks in many southwestern
The earliest planted commercial corn fields could easily be rowed by early last week. While very few acres had actually emerged by early Wednesday morning, the temperatures were cold enough that chilling injury in addition to the direct frozen emerged tissue could potentially be an issue. Excellent soil moisture conditions have allowed for a great deal of corn to be planted in the last couple of days.
We are able to find several fields in
Seed corn planting
will not begin until after this weekend. Many fields that will be planted early
are fit and ready to go. We look for a record number of acres of seed corn to
be planted in southwestern
Soybean planting
has also really picked up the pace. Most seed corn producers in
Growth was kicked into high gear for alfalfa and pastures following the week of warm weather since the last report. We are unsure how the freeze will effect subsequent alfalfa growth in the area. Alfalfa weevil larvae feeding was reported in the Paw Paw area in Van Buren County.
Wheat is mostly in the Feeke’s 5 growth stage at this point. Most fields have greened up nicely following N applications and were growing well. Not a lot of problems with winter annual weeds or leaf diseases at this point.
Fred Springborn and Roger Peacock
It has been quite dry for the past two weeks with light showers in the Montcalm area on the April 25. High temperatures have gone from quite warm last week with highs in the 70s to quite cool this week with highs in the lower 50s. Low air temperatures have been in the 30s and 40s with two notable exceptions of lows in the 20s. A low temperature of 21.9ºF was recorded on April 30 at the Montcalm Experiment Farm
Alfalfa growth progressed rapidly last week with many stands at 8 to 10 inches in height. Frost damage has been observed after the last two to three nights of very cool temperatures. The extent of the damage should be apparent in the next couple of days. Grasses are 10 to 12 inches and growing rapidly.
Approximately 5 percent of the corn crop is planted. Much tillage has been done. If the weather holds next week, we will see major progress.
Very limited planting of soybeans has occurred.
Wheat is in growth stage Feeke's 5-6. A significant portion of the crop has yet to be topdressed. Most fields look good.
Oat planting is nearly complete with much of the crop emerged.
Paul Gross
There has been very little rain over the region in the past two weeks. Field conditions vary a great deal with some fields still very wet. Soil temperatures have cooled this past week with several cold mornings. Temperatures have gotten down into the mid-twenties. Most farmers are able to start planting in pretty good field conditions. A good rain would be helpful as long as it comes easy.
Corn planting is well under way. Most farmers have been planting since late last week and this week. Most report good progress and planting conditions average.
There are a few acres of soybeans that have been planted. Growers are cautioned that with the low germination of some of this year’s soybean seed it may be a good idea to hold off and plant soybeans when the soil temperatures have warmed up. Planting into good conditions can help insure good stands.
Wheat is in Feeke’s 4-5 and generally looking good. Most nitrogen has been applied at this point. There are still herbicide applications that will need to be made. Know what growth stage your wheat is in as we are getting past the growth stage when growth regulator herbicides can be used safely.
The alfalfa crop is growing nicely with most of the fields between 6 to 8 inches. There is no reported alfalfa weevil feeding at this time. Some feel harvest will come early this year.
Oats planting is nearly complete. The early planted fields have emerged.
Sugar beets are planted with some beginning to emerge.
Bob Battel
The weather has been dry and cool. Most of the area received a light rain a week ago Thursday, April 24. We are in need of warmer air temperatures and a nice rain. The lack of moisture has allowed planting to progress rapidly. We received a heavy frost last Wednesday morning, as did the rest of the state.
Alfalfa’s new growth looks good. Most fields that have been walked are 8-14 inches, with better growth on lighter ground. Winter damage was light, and no insect damage has been reported.
Sugarbeet planting is pretty much done, and some fields have emerged. Other fields need a rain to emerge. A little frost/freeze damage was found in some low areas.
Corn planting is progressing nicely. Most farmers have at least half of their crop planted and several are completed or nearing completion.
Wheat is at Feekes 3, 4 and 5. Jointing may begin next week for the most mature fields. Ice sheeting damage is extensive. We have probably lost over 5 percent of our yield potential. Perhaps 1.5 percent of our acreage has been abandoned. Very low disease pressure to date. Using a foliar fungicide treatment at this time would not be recommended.
Some soybeans have been planted. We would expect soybean plantings to ramp up during the next several days, weather permitting, especially as corn planting wraps up.
Jeff
Andresen
Agricultural Meteorology
Geography
An area of low pressure over the central Great Plains
Thursday, May 1 is expected to strengthen and move towards
High temperatures will range from the mid-50's north to upper 60's south Thursday to a range from 56ºF north to the low 70's south Friday. Low temperatures will range from the upper 30's north to mid-50's south Friday morning to the mid-30's north to mid-40's south by Sunday.
Further ahead, medium‑range forecast guidance suggests
a series of upper air troughs moving from the western