Corn IPM Newsletter No. 1 — June 26, 2025

2025 SWEET CORN PEST SEASON BEGINS!

Insect Pests Active in Early Corn

The 2025 University of Maine Cooperative Extension Integrated Pest Management (IPM) program for sweet corn is getting underway. We have set up pheromone traps at volunteer farms to monitor the adult (moth) stages of European corn borer, corn earworm and fall armyworm, and have begun scouting the fields for feeding injury by insect larvae. We’ll share the information we collect along with management recommendations through this newsletter. It will also be posted on the Highmoor Farm web page blog. If you would prefer to receive this newsletter via e-mail, give us a call at 207.933.2100 or send an e-mail message to david.handley@maine.edu.

SITUATION

Getting corn seeded was challenging due to rain-soaked soils this spring. Early planted corn under plastic mulch or rowcovers is in the late whorl to pre-tassel stage in the southern part of the state. Insect traps were set up last week and field scouting for feeding damage was initiated this week. All of the major insect pests are active, but so far numbers have been well below control thresholds. Growers with early corn at pre-tassel or beyond should initiate scouting for the presence of pests.

European Corn Borer: Pheromone traps for moths are set up in the grassy borders around cornfields. To monitor corn borer feeding, we examine 100 corn plants in each field, typically twenty plants in a row at five different locations. This provides a good estimate of the total amount of injury in a field. Most locations saw flights of European corn borer moths this week. Pheromone trap catches indicate that moths are now active and laying eggs on the leaves of corn plants. We have found larval feeding in late whorl and pre-tassel corn at most sites, but below the recommended spray threshold of 15% injury, so no sprays have been recommended (see table below).

In the early stages, European corn borer feeding damage looks like small “pinholes” in the leaves. Whorl stage corn only needs to be sprayed if fresh feeding injury is found on 30% or more of the plants scouted. Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15% because larvae feeding at this stage are more likely to move into the ears. On the tassels, feeding damage first appears as chewing and brown waste found in the small florets. After the tassel emerges from the whorl, the larvae chew into the stalk just below it, often causing the tassel to fall over. Sprays during the pre-tassel stage, when both moths and larvae are present, target the larvae before they can move into the protection of the stalks and ears. Good spray coverage of the entire plant provides effective control of larvae as they move from around the plant. Rotating the type of insecticide used also improves control. Materials registered for controlling European corn borer include Bacillus thuringiensis products (XenTari®, Dipel DF®); Avaunt®, Coragen®, Warrior II®, Lannate®, Baythroid®, Asana®, Radiant®, Delta Gold®, Mustang®, Sevin XLR® and Intrepid®. Newly hatched European corn borer larvae are very small and translucent with shiny black heads. They emerge from small egg masses that look like a tiny clump of overlapping fish scales on the undersides of corn leaves. European corn borer overwinters in Maine, and is usually the first pest to become a significant problem.

Growers should start scouting whorl to pre-tassel stage corn for feeding injury now. Varieties of corn genetically modified to produce the Bt toxin (e.g. Bt corn, Attribute® varieties), shouldn’t need to be sprayed for European corn borer.

Corn earworm: Corn earworm generally appears in Maine in late June to early July, but the actual date varies greatly. We have caught single earworm moths in several locations this week. The arrival of this pest is only a concern for fields with corn in the silk stage. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths are caught at a site, all silking corn in the fields should be protected with a spray. These moths lay eggs on the fresh silks, and the larvae move directly into the ears of corn. When corn earworm moths cannot find silking corn to deposit their eggs on, they may lay eggs on the leaves or tassels of younger corn. The larvae will feed on the foliage and tassels, similar to armyworm, until the ears become available. This damage should be counted, along with any borer or armyworm damage, to determine if a spray is warranted. In many states, corn earworm larvae have become resistant to some products in the IRAC group 3A insecticides, e.g. Warrior, Asana, Pounce, Brigade, Hero, Declare, Delta Gold, Mustang, Fastac, Baythroid. It is recommended that these products should not be used alone to control CEW. Combining them with another material from a different IRAC group (e.g. Lannate, Coragen or Blackhawk /Radiant) will improve effectiveness.

Fall armyworm: We have caught single fall armyworm moths in pheromone traps at several locations this week. Fall armyworm moths fly into Maine from southern overwintering sites and tend to lay their eggs on the youngest corn available. The young larvae initially chew large, ragged holes in the leaves, and later may bore into developing ears. We have not yet found any larval feeding damage in the field. Larvae can also move into the ears through the silk channel, behaving similarly to corn earworm. Pheromone trap catches will indicate if there is a threat to silking corn. However, corn is often on a spray program for corn earworm when fall armyworm is present, and both insects should be controlled.

Squash vine borer: One moth was caught in a pheromone trap in Gray this week, indicating that egg laying will begin soon. Squash vine borer moths are black and orange and resemble wasps. They lay their eggs at the base of squash plants. The larvae bore into the base of the plants, causing vines to wilt and collapse. Growers should be on the lookout for vine borer symptoms and protect squash plants if moths or damage are seen. See the New England Vegetable Management Guide for control options.

Potato leafhopper alert: We expect leafhoppers will soon be active in vegetable and berry fields. These small, bullet-shaped insects feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow-streaked. Beans are often the first crop to show symptoms, but other crops are also susceptible, including potatoes, peppers, eggplant, strawberries and raspberries. To scout for leafhoppers, brush the leaves of the plants with your hand. The small, whitish adults can be seen flying off the plant. Look for small, light green leafhopper nymphs on the underside of injured leaves. They are about 1/16 inch long. When touched, they will crawl sideways in a crab-like manner. Control options for potato leafhoppers are listed in the New England Vegetable Management Guide.

Striped cucumber beetle: We have been finding high populations of striped cucumber beetles in cucumber, squash and pumpkin plantings. These black and yellow striped beetles feed on the foliage and can kill young seedlings and transplants. They also spread bacterial wilt, a disease which can kill plants later in the season. Control options for striped cucumber beetles are listed in the New England Vegetable Management Guide.

Do-It-Yourself IPM: To get the most accurate information about the pest situation on your farm, you should monitor the fields yourself on a regular basis. Pheromone traps and lures are available that can give you an accurate, early warning of the arrival of all the major insect pests. Traps and lures can be purchased from pest management supply companies such as Gempler’s (1.800.382.8473) or Great Lakes IPM (517.268.5693). You may also want to download a copy of our fact sheet Managing Insect Pests of Sweet Corn at our website.

Garlic IPM Newsletter: Dr. Peyton Ginakes has begun a weekly IPM newsletter for garlic. You may find the newsletters on the Highmoor Farm blog for garlic. You can also sign up to receive this newsletter as well as other resources.

 

Sincerely,

David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259
207.933.2100

UMaine Extension Diagnostic Research Lab
Pest Management Unit
17 Godfrey Drive
Orono, ME 04473
1.800.287.0279

CEW: Corn earworm (Only fresh silking corn should be sprayed for this insect.)
ECB: European corn borer
FAW: Fall armyworm

Thresholds apply only to corn with exposed fresh silk. Lengthen spray intervals by one day if maximum daily temperature is less than 80°F.

European Corn Borer Thresholds

Whorl stage: 30% or more of plants scouted show injury.
Pre-tassel-silk: 15% or more of plants scouted show injury.
Silk: 5 or more moths caught in pheromone traps in one week.

IPM Web Pages:

Explore Integrated Pest Management in Maine — UMaine

Integrated Pest Management — UMass Amherst

Pestwatch Report — PennState

Where brand names or company names are used, it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

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