As we approach cotton planting season, one of the common questions is whether standard imidacloprid seed treatments will control wireworm and darkling beetle injury to cotton seedlings. In short, imidacloprid seed treatments are designed primarily for thrips control. While they may provide some activity against secondary pests, they are not effective against wireworms below ground.
However, when
adequate soil moisture is present to activate the seed treatment, we have seen
imidacloprid help suppress injury from above-ground Blapstinus darkling
beetles. These beetles are about 1/4 inch long and are commonly observed
chewing and girdling stems of young cotton seedlings at the soil surface.
If darkling beetle
activity and stem injury are present, a foliar pyrethroid application is the
most effective treatment option. Another common question is whether
foliar-applied imidacloprid will control these beetles. Because imidacloprid is
systemic, beetles must feed sufficiently on treated plants to receive a lethal
dose, which limits its effectiveness in this situation. If targeting darkling
beetles, a pyrethroid is the better foliar option. Imidacloprid generally
performs better as an at-plant, in-furrow treatment than as a foliar spray
against early-season pests.
For thrips
management, imidacloprid seed treatments continue to provide good control and
may be sufficient under low to moderate thrips pressure, particularly in areas
south of Lubbock. However, high thrips numbers are already being observed in
northern areas on the limited vegetation available under ongoing drought
conditions. These thrips will readily move to cotton as soon as seedlings
emerge. As a result, early-planted cotton may require an additional foliar
treatment on top of the seed treatment.
For foliar thrips
control, both acephate and dicrotophos (Bidrin) remain effective options. In
our region, acephate continues to provide good control, unlike some
areas of the Cotton Belt where thrips populations have developed reduced
susceptibility. Although acephate is effective and relatively inexpensive, it
has shorter residual activity and is less rainfast than Bidrin. Those factors
should be considered when making treatment decisions. Vertento is another effective
option for thrips and provides a different mode of action than acephate and Bidrin.
However, it is going to be more expensive than those products.
When both thrips and
darkling beetles are present, a tank mix of acephate and a pyrethroid should
provide effective control of both pests.
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| Blapstinus darkling beetle |
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| Blapstinus beetle injury |
