Soybean Foliar Insecticides, Perhaps a Big Mistake– (John Obermeyer, Rich Edwards, and Larry Bledsoe)
- Insect defoliation to soybean may be approaching treatment levels.
- Insecticides affect all arthropods in the field, good and bad ones.
- An outbreak of plant suckers is possible after treating soybean fields.
|
Foliage defoliating insects, e.g., Japanese beetle, grasshoppers, bean leaf beetle, are active in most soybean fields throughout the state. Some fields, but mostly areas of fields, are looking pretty tattered and producers may desire to put an end to this attack on their crop that has gone on for weeks. We are aware that some seed producers are treating soybean fields for western corn rootworm beetles to reduce the rootworm threat to next year’s inbred corn. Applying insecticides from now until crop maturity may lead to devastating results.
Lady beetle larva feeding on soybean aphid
|
Lurking in most soybean fields are spider mites and soybean aphid. Most populations of spider mites have been subdued with the recent rains and high humidity of recent weeks. This was addressed in Pest&Crop #16. Soybean aphid continues to be found with regularity in northern Indiana, albeit low populations. Reports concerning soybean aphid continue to substantiate that natural predators, mainly lady beetles, are keeping this potential pest in-check.
Treating soybean with an insecticide for the remainder of the season may tip the balance in the favor of spider mites and/or soybean aphid. In other words, natural enemies (a.k.a., good bugs) recover slowly from broad-spectrum insecticides compared to mites and aphids. In general, toxic levels of insecticide are absorbed by ingestion (eating treated leaves) and/or contact (walking over treated areas). Mites and aphids are both sucking insects and ingest only internal plant fluids. Except for mature females, they are relatively stationary on the bottom sides of leaves; obviously a difficult location to get thorough coverage. As well, surviving mites and aphids can repopulate fields at break-neck speed, certainly outpacing natural enemies.
Even if a field is at or approaching a treatment threshold, carefully consider the impact on other potential pests and their natural enemies. Gee, this advise sounds like integrated pest management. Happy scouting!
back to top
Potato Leafhopper Numbers High, Natural Reductions Are Possible– (John Obermeyer, Rich Edwards, and Larry Bledsoe)
- Leafhopper populations should be evaluated after higher humidities and cooler temperatures.
- Fungal pathogens may flourish and naturally control leafhoppers.
|
Potato leafhopper populations have been high in most alfalfa fields this summer. Hopefully pest managers have been carefully monitoring leafhopper numbers before yield and quality have been lost. Yellow alfalfa indicates poor management of this pest!
Good news may be forthcoming. With “cooler” temperatures forecasted after this stifling spell of heat and humidity, insect disease may come to our rescue. The fungal pathogen Zoophthora radicans is favored by cool and wet conditions to multiply and spread throughout leafhopper populations. Once the environment favors the disease, leafhopper populations may crash within days. Typically the conditions that favor this pathogen occur in later July or August. Watch for discolored and/or slow moving leafhoppers while obtaining sweep counts. Should you suspect the presence of diseased leafhoppers, consider holding off treatment and re-evaluating in a couple days.
back to top
Black Light Catch Report
back to top
|
