Pest Report for August 9, 1999

CROP CONDITIONS
SWEET CORN
Leafhoppers
POTATOES
TOMATO
Other Pests
Irrigation Guidelines

There will be a whole day of talks and demonstrations and a barbecue lunch will be sold. If you would like more info and a list of talks call the MOFGA office at 622 3118.

Remember to thank all my sources for info if you run into them including Dave Handley and Jim Dwyer from U Maine Extension, Ruth Hazzard and Sonia Schoelmann from U Mass Extension, Vern Grubinger from Vermont Extension, Clay Kirby from the Pest Management Office and the MOFGA certified growers who take the time to send me reports from the field. Please send along anything interesting you note in your fields.

CROP CONDITION
Not much has changed. If the crops got water then this has been one of the best growing seasons ever, if not it has been one of the worst. Disease pressure has been very low because of the dry conditions. Crop growth has been very fast because of the heat units.

CORN
Corn harvest is in full swing and quality is mostly very good, in spite of the extremely dry weather. The heat has pushed many varieties to mature ahead of schedule, so keeping up with the harvest has been a challenge in many fields. The warm, dry evenings have brought about a further increase in moth activity this week. The moths of all three major corn pests are most active at night, so high evening temperatures result in more flights. Alternatively, cool, rainy nights tend to slow moth activity.

Corn Earworm
Moth captures have significantly increased in many sites this week, putting many fields on a shortened spray interval. A four day spray interval for silking corn was recommended by the IPM program in North Berwick, Cape Elizabeth, Gorham, Poland Spring, Dresden, Wayne, Corinth and Milford, where large moth captures occurred this week. A five day spray interval for corn earworm was recommended in Wells, Hollis, Auburn, Lisbon and Monmouth. A six day spray interval was recommended in Biddeford and New Gloucester. A single spray on silking corn was recommended in Lewiston and Plymouth. Only corn that has reached the silking stage needs to be protected from corn earworm.

European Corn Borer
Numbers of European corn borer moths caught in pheromone traps continue to be very high in some locations. These moths are a threat to silking corn, so protection is recommended when five or more corn borer moths are caught in a week, and sprays are not needed for corn earworm. A single spray to protect silking corn from European corn borer has been recommended in Fairfield, Jefferson, Nobleboro, and Thomaston. Other locations where corn borer moth counts were high had already been put on a spray schedule for corn earworm. Larval feeding on corn was over the 15% threshold in Fairfield, Jefferson Nobleboro and Thomaston, and a single spray was recommended for those fields.

Fall Armyworm
Moth captures in pheromone traps continue to be low in most locations this week. Moths were caught only in Wells, Gorham, Auburn and Lewiston. Only Cape Elizabeth exceeded the threshold of three or more moths per week in silking corn, but that location is on a spray schedule for corn earworm. Fall armyworm feeding injury on pre-silking corn has increased in some locations, but is generally under the control threshold. Fall armyworm injury is added to European corn borer injury when scouting to determine whether management is necessary.

LEAFHOPPERS
Hopperburn has been reported around the state. Some potato plantings and beans are going down from earlier activity. If the leafhopper is ignored the crop quickly suffers because of clogging of the food conducting tissue. Potato leafhoppers remain active. Nymphs are found on the underside of leaves, light green, wedge-shaped, 1/8 to 1/4 inch long, very fast-moving and able to move sideways. "Hopperburn" --scorching of leaf margins followed by browning of the whole leaf -- can occur in green beans, potato, eggplant, and other crops.

POTATOES
Aphids:
Aphid populations are exploding, especially in the southern range of the potato growing region. Our scouts are continuing to find the green peach activity increasing; winged green peach are now being found in our yellow pan water traps throughout our scouting region. Seed growers are urged to be carefully scouting fields.

Colorado Potato Beetles:
Colorado potato beetle populations seem to be under control at this time. Our scouts are finding mostly adults and large larvae, with a few fields over threshold at this time.

Late Blight:
There is almost no blight reported in the state. Most of our disease forecasting stations are calling for a 5-day spray schedule, with the occasional longer spray schedule. The long range weather forecast continues to call for shower activity. Growers should be aware that local weather radar is available on the internet, which can be of great assistance in planning field work.

Potato Leafhopper:
Potato leafhoppers, both adults and nymphs, are now being found in Central Maine and Aroostook County. Several fields in Aroostook and Central Maine have exceeded the recommended threshold levels for potato leafhopper nymphs, which is when one finds an average of 10 nymphs per 100 leaves surveyed. All growers should be carefully watching this situation.

Flea Beetles:
Flea beetle activity has returned. All species of flea beetles overwinter as adults. In the spring they begin feeding and the females lay about 100 eggs each. The eggs hatch in about 10 days and the larvae feed on roots (and stolons and tubers of potato). There are 2-3 generations per year. If the populations are large, these insects should be controlled to avoid any potential tuber damage.

TOMATO
Water is critical for fruit growth and quality in tomatoes.

OTHER PESTS
Squash bugs are still being found on pumpkins and winter squash. Look on the underside of leaves for the gray nymphs and copper eggs. Imported cabbage worm and diamond back moths have been very active in cole crops. Sunscald has been a problem on peppers and tomatoes, causing tan patches on the fruit that turn black if fungi invade the wound.

There have been reports of European corn borer and common stalk borer attacking peppers. The larvae of these insects may feed within the stem, causing the plant to wilt and die, or the may bore into the fruit leaving a small entry hole. The wound often results in a fruit rot.

IRRIGATION GUIDELINES
Recent drought combined with shortages of water and heavy demands on machinery and time have forced growers to make choices about what crops to water. The following guidelines about what growth stage of a given vegetable is the most sensitive to drought stress and rooting depth of various crops may help in making water management decisions.

Critical watering times for vegetables:

Rooting Depth of Vegetables