Aphids on corn leaves
Article is taken from https://agcrops.osu.edu/newsletter/corn-newsletter/2024-26/insects-were-quiet-summer-until%E2%80%A6notes-corn-leaf-aphid-spider by Kelley Tilmon, Amy Raudenbush, Andy Michel
Corn Leaf Aphids
Corn leaf aphids are making an unusual appearance this year in field corn, reaching high numbers in our test plots and in other locations in Ohio. This outbreak is not restricted to Ohio, but appears to extend throughout the Midwest and also into the coastal southern US and also southern Canada. Other aphid species may be in the mix on corn, but corn leaf aphid is the dominant species. We do not recommend spraying for aphids in field corn regardless of numbers, because there won’t be an economic return with the relatively low value of the crop per acre. Sweet corn and popcorn may be a different story – if in doubt, contact specialty crop entomologist Ashley Leach leach.379@osu.edu The good news is that in most cases the natural enemies are taking care of the aphid populations. In the outbreak pockets we’ve been observing, lady beetle larvae and adults, syrphid larvae, lacewing larvae/adults, parasitoids, and insect-killing (entomopathogenic) fungus abound, and are knocking back populations as they build. The fungus is especially effective, and humid weather and rain will give it a boost.
Lady beetle larva feeding on corn leaf aphids. Photo credit: Amy Raudenbush.
Spider Mites in Soybean
Hot and dry weather encourages spider mites, and last week we received a few calls about spider mites in soybean. These are too small to count, so our treatment guidance is based on how much damage has progressed. Spider mite feeding makes characteristic stippling patterns on the leaves. If the stippling is minor and restricted to the lower canopy, no action is required. If the stippling is heavy on the lower canopy and progressing to the middle canopy, and if mites are still present, treatment is advised. As with corn leaf aphids, humidity and rain will encourage fungal disease to decimate the mite populations. That’s why it’s important to check mites are still active. The easiest way to do this is to tap stippled vegetation over a piece of black construction paper. That’s right: black, not white. Their little bodies reflect off the black, for some reason. Tap the vegetation, and look for little grains of dust that move [and use a hand lens, if you have one]. If they aren’t there or aren’t moving, chances are that you don’t have a problem – continue to keep an eye on the field, especially if you haven’t had rain for a while. If you do need to spray, avoid pyrethroid products, except those that contain bifenthrin. Most pyrethroids [for example, Warrior] can actually flare mite populations. There are also some good miticides available – abamectin and etoxazole [for example, Agri-Mek and Zeal, respectively – if using a generic, check your brand for use on soybean]. Chlorpyrifos (Lorsban and generics) has historically been an alternative, but it’s availability is uncertain as it has been yanked back and forth in the world of pesticide regulation. Though the situation is confusing, our best advice is that existing stocks of chlorpyrifos can still be used in soybean.
Visit the MSU/OSU Field Crop Insect Pest Management Guide for a comprehensive list of products (including trade names) and management guidelines in our major field crops. And as always, check your label for most current rules.
https://aginsects.osu.edu/sites/aginsects/files/imce/2021%20IPM%20Guide%20Online%20Version.pdf
Fall Armyworm
A few years ago, a very unusual fall armyworm outbreak in forage and turf took us by surprise. Though it’s definitely too early to panic, we’ve observed some fall armyworms in some of our corn test plots. We have 14 Ohio counties participating in a fall armyworm flight monitoring program, and monitoring has just begun. The Lepidoptera Network will begin publishing fall armyworm data in the C.O.R.N. newsletter next week – so keep your ear to the ground.
Soybean Aphid
And remember the soybean aphid? This being a favorable aphid year in general, we have found countable numbers of aphids in some of our soybean test plots. While we don’t expect huge trouble, keep half an eye on your soybean plants. Examine underneath leaves in the top canopy – if damage is available from the road, you are far too late. The well-tested and well-supported threshold for soybean aphids is an average of 250 per plant, which gives you a week of lead time to treat before economically relevant populations develop.