August 21, 2009

Corn leaf aphids

Bird cherry-oat aphids

We have been receiving reports of aphids on corn the last few weeks in central and eastern Nebraska. Entomologists in the states to the north and east of us have also been reporting aphid problems. In some cases a high percentage of the plants were infested, and aphids could be found throughout the plant.

The aphids involved include corn leaf aphids and bird cherry-oat aphids. We are used to finding corn leaf aphids in whorl stage corn, and occasionally low numbers of aphids later in the season. The higher populations we are seeing this year are somewhat unusual.

Possible reasons for aphid problems in corn this year include the cooler weather we saw in July and the increased use of foliar fungicides in corn. Research from other crops indicates that some fungicides may inhibit the growth of insect-attacking fungi that normally help suppress aphids.

There is very little research on the economic impact of late season aphid feeding, so there are no economic thresholds developed for this situation. Now that corn is denting in many areas, it is likely that additional yield loss will be minimal.

Possible Stalk Rot Complications

Fields that were heavily infested with aphids late in the season may be at increased risk from stalk rots and should be watched carefully, and harvested first if stalk rots develop.

More Information

The NebGuide, Cereal Aphids, has additional information on the biology and identification of corn leaf aphids and bird cherry-oat aphids.

Bob Wright
Extension Entomologist, Lincoln