Planting this season has been tedious, and tough planting conditions can have a negative impact on yield. This is all the more reason to protect the crop from pests and make the most of every opportunity to maximize yields. In order to do this, we have to first understand that late-planted soybeans can have some significant insect concerns.
When you’re looking at soybean stands, be sure to examine the skips found in rows to determine why no seedlings exist in those areas. If you expect it could be planter issues, and poor seedling vigor and soil crusting have been eliminated as causes, be sure to consider the possibility of insects.
Bean leaf beetles overwinter as adults beneath plant residue. While we might think the harsh winter many experienced would lead to a lower than normal population in the spring, it is possible that the plentiful snowfall in many areas may have provided insulation for the beetles to survive.
Bean leaf beetles makes holes in the leaf surface and hide on the underside of soybean leaves when disturbed, making them difficult to find. They attack first planted fields the hardest; however, late planted soybeans may be more desirable for feeding if near earlier planted bean fields. Scouting procedures and treatment thresholds vary by state. Generally at VE to VC, the first generation ranges from 2-4 beetles per plant. With second and third generation beetles, most plants can handle up to 50% defoliation before treatment is needed. Late generation bean leaf beetles can feed on pods, which is more of a concern.
With a harsh winter in most areas, stink bug populations should be lower than normal. Overwintering stink bugs typically like no-till and cover crops areas. They can be found anywhere on the plant, and during flowering, they can be tough on late planted soybeans. Stink bug control generally needs to be considered from pod development to seed fill. Scout weekly using a sweep net or by inspecting individual plants. Overall counts to consider control vary by region, but generally 1 insect per foot of row is a good average.
The late planting of soybeans combined with cool temperatures should limit aphid densities early in the season, but time will tell. Economic thresholds vary, but a general rule is around 250 soybean aphids per plant, with at least 80% of plants infested and conditions favorable for populations to increase. Late June to early July in the Midwest states is typically a good time to start scouting. Symptoms often resemble early drought stress. Populations can jump quickly in mild conditions, so continue to scout throughout the mid to late growing season.
Grasshoppers overwinter as eggs, and they hatch in early June, feeding well into October. Grasshoppers generally move into soybean fields from field margins so scouting margins can help determine possible outbreaks. Consider field margin treatment if 15 nymphs or 8 adults per square yard are observed. Thresholds within a field vary from state to state, but generally treatments should be considered when 40% or more defoliation occurs before flowering.
Caterpillars of numerous species can defoliate soybean plants. When scouting try to estimate defoliation in various parts of the field to establish a good average. During vegetative growth, treatment should be considered if defoliation reaches or will reach 30%. During podding stages, consider treatment if defoliation has reached or will reach 20%. These numbers are general and vary by region and yield expectation.
Subsurface insects that can cause a soybean stand reduction include wireworms, seedcorn maggots and white grubs. There are no rescue treatments for subsurface insects. Plant soybeans treated with an insecticide or use an in-furrow insecticide to help minimize the possible need for a replant. If replanting is considered, be sure to check with your crop insurance provider about any provisions that may affect your replanting decision.
We have a way to go, but we can still maximize the yield potential that remains. Remember that scouting your fields is the best way to catch pests early and make a plan to control them. Also, understand the importance of application timings when it comes to insect treatments. Untimely applications can be expensive and offer a poor return on your investment. Remember to always read and follow label directions.
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Abiotic and biological factors to anticipate
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ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. It is a violation of federal and state/provincial law to use any crop chemical product other than in accordance with its label. The distribution, sale and use of an unregistered pesticide is a violation of federal and/or state law and is strictly prohibited. It is your responsibility to confirm prior to purchase and use that a product is labeled for your specific purposes, including, but not limited to, your target crop or pest and its compatibility with other products in a tank mix.
Sources:
https://cropwatch.unl.edu/watch-late-season-insects-late-planted-corn-and-soybeans
https://aces.illinois.edu/news/late-plantings-impact-corn-and-soybean-insects
https://soybeans.ces.ncsu.edu/stink-bug-economic-threshold-calculator/
https://extension.entm.purdue.edu/fieldcropsipm/insects/bean-leaf-beetle.php
https://extension.entm.purdue.edu/fieldcropsipm/insects/soybean-grasshopper.php