Current insect conditions and late planting concerns

  • By Ron Hammond, Andy Michel, Mark Sulc
  • June 1, 2011
  • 291
                        
Alfalfa Weevil and Armyworm – We have received reports of significant defoliation by alfalfa weevil on alfalfa. Normally at this time and height of alfalfa, we would recommend cutting as your best option to control the pest. However, because of the heavy rainfall, saturated fields, and the continued forecast for rain, this is probably not possible. Because alfalfa weevil can cause a significant amount of yield and forage quality loss, you might have to make the decision to apply an insecticide to stop the feeding, if at all possible to get on the field. If so, using the lightest equipment possible will help to reduce the amount of damage to the alfalfa crowns and standing crop. This is just one of those years where you might be damned if you do, or damned if you don’t. Be very careful with soil conditions, as permanent stand loss in the wheel tracks will occur if the soils are too soft when taking a sprayer over the field, which might be worse than losing this one harvest to weevils. If weevils are present and you can’t get on the field, once you do cut the crop, be sure to watch the regrowth very carefully, as a rescue treatment may be needed if weevils survive on the stubble. Additionally, we have also received reports of armyworm at economic levels in wheat. However, before applying an insecticide, especially if adding to a fungicide application, you should first scout your wheat for this insect. Slugs – Wet cool springs are often associated with slugs, and obviously these are the conditions we have had. Of more importance is that while most fields have not been planted, the slugs have hatched and have begun their growth. Thus, when fields finally get planted, start to germinate, and finally emerge, the slugs will in all likelihood be at a growth stage where their feeding can cause economic injury. Keep in mind that it is only in fields that have slugs will we see problems. The weather conditions do not cause slugs to show up. But when planting late into fields with known slug populations and previous problems, you should plan on monitoring your crops. Because of the ability of slugs to cause significant problems with soybean emergence, soybeans should be watched closely. It would be helpful to scout for slugs prior to planting into problem fields by searching underneath crop residue and the top soil level to see if slugs are present. If necessary, application of a molluscicide might become necessary. At this time of year, one thing that you should hope for is warm and dry weather that will help the crops emerge faster and begin quicker growth. The better the growing conditions the lesser the chances of heavy feeding injury. See http://ohioline.osu.edu/ent-fact/pdf/0020.pdf for more information on this pest and differences in injury between corn and soybean. Western corn rootworms – Larvae usually hatch in late May or early June. In general, late planting tends to reduce the likelihood of economic problems of corn rootworms, perhaps because of the lack of corn root development and thus feeding sites for the larvae. Along with what has appeared to be lower rootworm populations over the last one to two years, we would hope for even less injury for this pest this year. See http://ohioline.osu.edu/ent-fact/pdf/0016.pdf for more information on this insect pest. Black cutworms – Fields having spring weeds and planted late this spring might be more susceptible to black cutworm injury this year. Corn is at most risk when planted into fields that have large populations of winter annual weeds. Although we usually see more problems in no-till fields, tillage just before planting will not provide control of newly hatched larvae that are already present; thus, growers should not assume that any late tillage immediately before planting will control this pest over the next few weeks. And with the larger cutworm populations that we think we have this year, don’t assume that you will get good control from any Bt hybrid that you might have planted. Large infestations of black cutworms can often overwhelm Bt hybrids. Also, previous history suggests that the various insecticide seed treatments at either the low or high insecticidal rates do not offer acceptable control. We recommend that growers plan on scouting for this pest in any late planted fields where weeds were late tilled or in no-till situations. Rescue treatments are usually the best management tactic if scouting confirms economic populations. See http://ohioline.osu.edu/ent-fact/pdf/0035.pdf for more information on this insect pest. European corn borers – This is one insect where late planting tends to increase potential problems with the second generation. In regular years, we often suggest Bt hybrids specifically for late planted fields for control of possible problems. However, numbers of this insect have been relatively low over the past few years, so it remains to be seen how much problem we have this year. See http://ohioline.osu.edu/ent-fact/pdf/0015.pdf for more information on this insect pest. Bean leaf beetles and Mexican bean beetles on soybeans – Early-planted soybean fields are most at risk for early-season feeding by both these insects. Because most soybean planting will be later this season, we don’t anticipate large economic infestations across the board with these insects this spring. However, any soybean fields that did get planted on time that are the only fields emerged in an area should be monitored closely in case those fields act as a trap crop, being the only soybean fields available. Later planted fields might be another story if we have a build-up of the second generation. However, because the majority of the fields will be later planted, the late summer generation of these two insects will hopefully be distributed over many fields. See http://ohioline.osu.edu/ent-fact/pdf/0039.pdf for more information on these defoliating pests.


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