Cool weather promotes seed/seedling pest issues

May 2, 2022 11:46 AM
Blog Post

Today during our Crops Team meeting, many field agronomists shared that cool soil temperatures and rain have delayed planting in Iowa, but there are some very determined farmers getting acres planted around the state. These cool and wet conditions during spring are favorable for a few seed and seedlings pests. The main concern during cool, wet conditions is that plant and insect development is slow, potentially leading to prolonged feeding on seeds or small plants that may result in substantial losses.

We encourage you to scout fields (whether you’ve planted or not!) to assess pest activity and potential plant injury. One thing in common with these early-season pests is that rescue treatments are not likely to be effective. Therefore, knowing whether pests are in the field prior to planting provides the opportunity to make proactive management decisions. If significant stand loss occurs, replanting might be necessary to reach ideal final stands. Read more about replanting considerations from Mark Licht here:

Here are the top spring pests to keep in mind:

Grubs. There are several grub species in Iowa that overwinter within and around crop fields. The last couple of springs, we confirmed grub activity in several central Iowa fields that had stand losses. Just last week Ashley found grubs while doing some soil sampling in western Iowa. They are in the final instar before pupation and therefore easy to see when poking around soil. Grubs are always in a c-shape and creamy white (with a dark butt). Some grub species have multi-year lifecycles and can be persistent pests. Read more about Japanese beetles in corn and soybean.

grub found in cropfield.
Grub found with soil sampling. Photo by Ashley Dean, Iowa State University.

Wireworms: Wireworms can be pests in corn, particularly when fields are recently transitioned from pasture and CRP. The multi-year lifecycle contributes to persistent feeding within fields. Start looking for wireworms in well-drained soil on ridgetops or hillsides. Read more about wireworms.

Typical wireworm injury to corn. Photo by Meaghan Anderson.

Seedcorn maggot. Earlier this year, we posted an ICM News article about seedcorn maggot emergence. They develop at lower temperatures than most insects, so adult flies are likely emerging and laying eggs around the state right now. Read more about seedcorn maggot management.

seedcorn maggot and pupa.
Seedcorn maggot and pupa. Photo by Brian Lang.

Millipedes, isopods, and slugs: In some springs, we hear about millipede and isopod plant injury (in addition to slugs and snails). All of these pests prefer to feed on decaying organic matter and tend to build up in no-till fields, but seed and seedlings would be acceptable food in wet soil conditions. Read more about millipedes and isopods and slugs.

slug on soybean.
Slug feeding on soybean. Photo by Brian Lang.


Erin Hodgson Professor

Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated...

Ashley Dean Agriculture and Natural Resources Extension Specialist II

Ashley is an education extension specialist for field crop entomology at Iowa State University. She coordinates the Iowa Moth Trapping Network, the Regional Corn Rootworm Monitoring Network, and the Iowa Pest Alert Network. She also develops educational resources for field crop pests in Iowa and ...