Sweeping in alfalfa is always a good time

May 11, 2021 1:03 PM
Blog Post

I am always surprised to find insect abundance and diversity when scouting in alfalfa. It never disappoints. At any point in the growing season, one is likely to find 20+ species of potential pests feeding on foliage. However, finding a lot of different insects at one time doesn’t necessarily mean they are causing economic loss. Recently, ISUEO field agronomist Meaghan Anderson was sweeping in an alfalfa field with a bit of orchardgrass and found a bonanza of activity! What do you see in her sweep?

Meaghan's sweep.

First thing I notice is the stink bug. Iowa has several brown stink bugs and my best guess from the photo is the onespotted stink bug. I wouldn’t consider this bug a significant pest in Iowa. See a glamour shot with more detail from Hanna Royals (www.ipmimages.org):

onespotted stink bug.

Second thing I see are green insects that look like caterpillars. What you can’t see in this photo is the number of fleshy prolegs on the abdomen. Major clue! When there are 6 pairs of prolegs, it isn’t a caterpillar (butterfly or moth) but a sawfly. They are closely related to wasps and bees. My best guess is a grass sawfly. I wouldn’t consider this an alfalfa pest – they were probably more interested in the orchardgrass. For a close-up photo of sawfly prolegs, this elm sawfly photo by Steven Katovich is a beautiful example (www.ipmimages.org):

elm sawfly.

Tucked away under one of the sawflies is a weevil. This time of year, you can probably find alfalfa and clover leaf weevils in alfalfa. Clover leaf weevils are a bit bigger (>1/4 inches long); they overwinter as larvae and have brown heads. They are rarely pests in Iowa. Alfalfa weevils are smaller (3/16 inches long); they overwinter as adults; the larvae have black heads. Alfalfa weevils are active in Iowa now, read more about scouting and management here. Look at the clover leaf weevil larva Meaghan found:

clover leaf weevil.

Of course, I can’t forget about my favorite insects – the aphids. In Meaghan’s photo, notice there are mostly green and one pink aphid. They have long cauda’s and cornicles (at the end of the abdomen), and are the biggest aphids I see in Iowa. Read more about aphid management in alfalfa here. Joseph Berger (www.ipmimages.org) has a great photo of a pea aphid with two nymphs:

pea aphid.

Are you seeing any of these insects as you scouting alfalfa this week? Or maybe you are seeing a few different things? Send photos our way via Twitter (@erinwhodgson, @mjanders1, and @ashleyn_dean).


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...

Meaghan Anderson Field Agronomist in Central Iowa

Meaghan Anderson is a field agronomist in central Iowa and an extension field specialist at Iowa State University Extension and Outreach. Educational programming is available for farmers, agribusinesses, pesticide applicators, certified crop advisors, and other individuals interested in...

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 ...