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?
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):
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):
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:
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:
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).