Eric Sideman's Pest Report
July 4, 2003

(View List Of All 2003 Pest Reports)

COLORADO POTATO BEETLE

SWEET CORN

European Corn Borer: Pheromone trap catches indicate that we are experiencing a significant emergence of European corn borer moths. These moths are laying eggs on corn plants and the larvae are just beginning to feed on the foliage. European corn borer is the only one of the three major insect pests of corn that can successfully overwinter in Maine, and it is usually the first pest to become a significant problem. European corn borer feeding damage ("pinholes" in the leaves) has already been found in most locations scouted this week, but has only exceeded the control threshold in early fields at two locations (So. Berwick and Poland Spring). We expect to find increasing injury around the state soon. Corn in the whorl stage need only be sprayed if fresh feeding injury is found on 30% or more of the plants scouted in a field. Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15%. This is because larvae feeding on the later stages are more likely to move into the ears of the plant. We typically scout 100 corn plants in each field, examining twenty plants in a row at five locations throughout the field. This sample provides a reasonably accurate estimate of the total amount of injury in a field. Good spray coverage of the plant will provide the best opportunity to kill the larvae as they move from one part of the plant to another. Rotating the type of insecticide used may also improve control. Materials now registered for controlling European corn borer include Bacillus thuringiensis products (Dipel) and spinosad (Entrust).

Once early corn reaches the silk stage, as it has in a few locations this week, sprays may need to be based on the number of corn borer moths caught in pheromone traps rather than feeding injury. Moths will lay eggs on flag leaves of silking corn and the larvae can move into the ears without leaving any visible feeding injury on the leaves. If more than five moths are caught in a week in a field with silking corn, a spray (or treatment with the Zea-Later) will be recommended. This week sprays on silking corn were recommended in So. Berwick, Dayton, New Gloucester and Poland Spring.

NOTE: The Zea-Later was developed by Ruth Hazzard at UMASS and we (MOFGA) were part of a region wide trial. It is an oil applicator (mix of oil an Bt or maybe Entrust , which I will try this season) that makes it possible for organic growers to control corn pests (especially corn earworm) after they enter the silk channel. Each ear of corn has to be treated but the one time application has proven cost effective and doable. The Zea-Later can be purchased from Johnny's Selected Seeds (861 3900).

Corn Earworm: There has not yet been any capture of corn earworm moths in our pheromone traps. These insects usually arrive around the second week of July, but the actual date varies greatly. The arrival of this pest is only a concern for fields that have corn in silk. Fields not yet in silk do not need to be protected from corn earworm. When corn earworm moths start being 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 of younger corn. The larvae will feed on the foliage and tassels, similar to armyworm, until the ears become available. When larvae are found feeding on younger corn, the damage is accounted for along with any borer or armyworm damage to determine if a spray is warranted. We will be watching our traps closely to keep you informed as the situation changes.

Fall Armyworm: This is usually the last serious corn insect pest to arrive in Maine. The moths must fly in from southern overwintering sites, and tend to lay their eggs on the youngest corn available. When the larvae hatch, they chew large, ragged holes in the leaves, and may bore into developing ears. No fall armyworm moths have been captured yet and no feeding damage has been observed to date.

Other Pests of Note: Common Armyworm has been found in several cornfields. Like fall armyworm and cutworms, this caterpillar chews large holes in young corn. The larvae are light brown with yellow and black stripes running along the body. This insect is usually only present early in the season and the corn can often outgrow the injury. However, heavy infestations may require control. In general, when we see these pests causing significant injury in a field, we will count the injury along with our European corn borer scouting. So, if the damage from any of these pests, plus the injury from corn borer exceeds 30% of whorl stage plants or 15% of pre-tassel plants, we would recommend a spray to control them.

Common Stalk Borer: This pest is typically a problem early in the season and only around the edges of fields. The injury is similar to European corn borer, but the feeding holes are larger. The larvae are purple colored with white stripes. If high numbers of stalk borer are found in pre-tassel stage corn well within the field (not just along the edges) include the injury with corn borer for determining if a control is needed.

Do-It-Yourself IPM: The way to get the most accurate information about the pest situation on your farm is to 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 of the major insect pests. Pheromone traps and lures can be purchased from pest management supply companies such as Gempler's in Mt. Horeb, Wisconsin (1-800-382-8473) or Great Lakes IPM in Vestaburg, Michigan (517-268-5693).

To learn more about IPM scouting techniques, insect identification and control thresholds, order the fact sheet Managing Insect Pests of Sweet Corn available from the University of Maine Cooperative Extension. Color pictures are provided to help with insect identification, and a chart with spray thresholds is supplied to post near your sprayer for easy reference. For copies of this free publication contact the Pest Management Office at 1- 800-287-0279.

The 2002-2003 New England Vegetable Management Guide is available from the University of Maine Cooperative Extension. The cost of the guide is $12.00. Checks should be payable to Cooperative Extension and sent to Highmoor Farm at the address below.

Sweet Corn IPM Weekly Scouting Summary

CEW: Corn Earworm (only fresh silking corn should be sprayed for this insect)
ECB: European Corn Borer
FAW: Fall Armyworm

If you have any questions about insect trapping or field scouting corn, we'd be happy to help. Call Highmoor Farm at 933-2100 or the Pest Management Office at 1-800-287-0279.

Pest Management Web Page: www.umext.maine.edu/topics/pest.htm.

Highmoor Farm Pest Management Office
P.O. Box 179
Monmouth, ME 04259
(207) 933-2100

491 College Ave
Orono, ME 04473
1-800-287-0279

Published and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the State of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment

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.

(Modified from Sweet Corn IPM Newsletter by David Handley, who is at Highmoor Farm)

EUROPEAN CORN BORER ON POTATOES

The best control is destroying crop residue at the end of the season to kill overwintering pupae. Entrust is labeled for ECB and should do a fine job.

THREE LINED POTATO BEETLE

I generally ignore them on potatoes, but this year I note that the Entrust did them in. Their favorite crop is the tomatillo, and they feed on lots of other plants in the tomatoe family.

PEAS- FUSARIUM WILT

The disease is caused by Fusarium oxysporum, which can persist in the soil for over 10 years. It is disseminated through the movement of contaminated soil, plant fragments, water, wind, tools, etc. It is commonly transmitted by contaminated and infected seed.

In my field I have three varieties of peas and only one variety of my snow pea has it. There seems to be lots of varietal resistance

PLEASE GET BACK TO ME IF YOU HAVE THIS PROBLEM AND TELL ME WHAT VARIETY OF PEA HAS IT IN YOUR FIELD.

The best control of Fusarium wilt of peas is varietal resistance. Of course, good cultural practices are necessary too. Rotation and sanitation is a must if you have this in your soil. Early planting so peas mature before the soil warms and the disease spreads rapidly helps, and good irrigation helps.

WATCH FOR ONION THRIPS

Identification: When they are immature they are from 0.5 to 1.2 mm, with an elongated, elliptical and slender body that is white to pale yellow. Their eyes have darker coloration and are easy to see. Immature thrips have short antennas. The difference between immatures and adults is that immatures do not have wings, so they cannot fly. The majority of immature thrips are found between the young leaf blades at the top of the plant. To observe them you need to separate the leaves from the neck. The pupae are pale yellow to brown and appear as an intermediate form between the immature and the adult. They have short antennae and the wing buds are visible but short and not functional. At this stage thrips do not feed. When they are adults they are pale yellow to dark brown and can be up to 2 mm. Adults have fully developed wings that are very different from other insects. They have a single longitudinal vein in which there are several hairs connected perpendicular to the vein. The wing appears as fringe with hairs. When at rest, the wings are folded along the back of the insect. Adults are more mobile than immatures and pupae because they can fly. They are attracted to yellow and white colors. They often will fly to one's clothes or land on exposed skin.

Direct seeding of onions prolongs the growing season in the field and the susceptibility to thrips infestation.

If the crop is going to be transplanted, the seedbeds should be distant from the old plantings and new plots to be planted. It is very important that onion seedlings are clean of thrips before transplanting to the field. Remove unharvested plant parts. Volunteer onion plants are an important source of infestation for thrips.

Thrips prefer to feed on the young plant tissue on the newest emerged leaves. When the leaf grows, the previous damage produced by the thrips enlarges, leaving empty spaces in the surface of the leaf. The appearance of the damage is silvery patches or streaks on the leaves that shine in the sun. When damage is severe, these small patches can occupy most of the surface of the leaf and the plant cannot adequately photosynthesize. The plant loses more water than normal through the damaged tissues and plant pathogens penetrate the injured plant easily. Plants are stunted, the bulbs are tiny and the crop dies very early.

Entrust is said to work well on thrips and I will try it this year if I get them again. Last year they stunted most of my varieties of onions (Copra was the worst and Greek Salad was the most resistant.

(Modified from a report last year by John Howell, Stephanie DeGray & Cornell University)

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)