Pest Report for July 12, 1999

Remember to thank all my sources for info if you run into them including Dave Handly 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 CONDITIONS
POTATOES
CORN
CUCURBITS
CRUCIFERS
GREEN BEANS and DRY BEANS
TOMATOES
PEPPERS

CROP CONDITIONS:

They are pretty much the same all around New England. Some locations have had at least some rainfall and areas with good thunderstorms are getting a little more caught up on water. With irrigation and rain, warm season crops are doing great. The heat has been hard on greens and lettuce.

I just got back from a farm inspection tour of six places down east. I saw the type of farming that I think is the heart of organics...local growers selling to their community. Keep up the good work.

Jim Dwyer reports that aphid populations continue to be low, but activity is picking up slowly. His scouts are currently finding mostly potato aphids with the occasional buckthorn aphid and the trace wingless green peach aphid. They have found Colorado potato beetles active throughout their scouting range. Large and small larvae are now being found in many fields. Several fields are at or above the recommended threshold levels for larvae, which are as follows:

This makes it difficult for organic growers who are using Bt for CPB control. If you have a large number of large larvae you probably need to come in with rotenone to knock them down. The Bt really is only effective on the small larvae. Remember, timing with the Bt is important so you do not get the large larvae

Late Blight:

No potato late blight has been found as of this date anywhere in the state of Maine. With the varied rainfall and micro-climating, conditions in some areas have been conducive for the development of the disease. Most stations have been reporting a 5-day spray schedule. Some stations have been reporting longer schedules. This is an important time to be scouting for potato late blight! Conditions have been conducive for late blight development. Please scout! The earlier the disease is found, the more options that you have for control.

European Corn Borer in the County:

Peak moth flight appears to have occurred late last week. Moths are still active and laying eggs in some areas, but activity is dropping. All growers are strongly urged to continue to scout for ECB.

Damage from untreated borers or escapes will appear as a wilting branch on the plant with a small entry hole visible. The small entry hole will usually be at a leaf axil and have frass, which will look like sawdust on the hole. Damage should start to appear late next week.

Potato Leafhopper:

Adult potato leafhoppers are continuing to be found throughout the state. This is a situation that warrants close scrutiny and careful scouting. I still have not seen nymphs and have only seen one field with a very large population of adults.

Tarnished Plantbug:

Tarnished plantbugs are currently active in many fields. The populations in some fields are some of the highest that we have seen in recent years. These insects are generally not an economic threat, but at high populations, they can cause problems. Symptoms of plantbug feeding are wilting leaflets with a small brown "sting" mark at the base of the leaflet.

(From UMEXT report, see "http://pmo.umext.maine.edu" for update) Some early corn is being harvested this week in southern and central Maine from plantings started under plastic mulch. High temperatures continue to push corn development where lack of water is not a problem. Weeds are becoming a problem in many fields.

Corn Earworm: Moth captures increased in most southern locations this week, resulting in a 5 day spray interval being recommended at Gorham, Lisbon, Jefferson and Nobleboro, and a 6 day spray interval being recommended in Auburn, Cape Elizabeth, North Berwick and Poland Spring. A single spray for corn earworm was recommended in Hollis and Wells. We have found more corn earworm larvae feeding on tassels and chewing into ears as a result of moths that arrived before silking corn was available and laid eggs on corn foliage. We recommend a spray on silking corn in any field where corn earworm larvae are found on the foliage or tassels. Fields that are not yet in silk should not need to be sprayed for corn earworm.

Corn Earworm may be blown up with storms in large numbers at anytime now. Rather than depend on Extension reports from their traps set up your own trap and keep a close eye on it!! Numbers can vary within regions. Silking corn should be protected at a 4-7 day interval, depending on flight levels in your location. Note: non-target moths also can be captured in pheromone traps. The distinctive features of corn earworm moths are:

• if they are alive, bright green eyes
• light tan or buff color on both body and wings, wingspan about 1 ½ inches
• Single darker spot toward the front of the forewing (the one on top).
• Hindwing (underneath) is lighter, and has a dark border at the tip.
• antennae are NOT feathery.

Gypsy moths often show up at this time of year—they are larger, dark brown, and have feathery antennae.

For more information on setting up your own trap and identifying corn pests call the MOFGA office or your local Extension office for their Corn Pest Bulletin.

European Corn Borer: We continue to catch high numbers of European corn borer moths in pheromone traps in some locations. These pose a threat to all silking corn, and sprays have been recommended for silking corn in Fairfield, where more than five moths were caught, and sprays were not yet needed for corn earworm. Larval feeding on foliage and tassels was variable from site to site. Sprays were recommended in Auburn, Gorham, Jefferson, Lisbon and Nobleboro, where injury levels exceeded the 15% threshold for fields at pretassel to silk.

Fall Armyworm: We have caught our first fall armyworm moths in pheromone traps in Wells and Biddeford this week. This helps to confirm the early larval feeding injury we found in two fields last week. Feeding injury is still very low, and is added to European corn borer injury when scouting. If 3 or more fall armyworm moths are caught in a pheromone trap in a week a spray is recommended to protect all silking corn, if it is not being sprayed for corn earworm. This was the situation this week in Biddeford.

Bacillus thuringiensis (Javelin, Condor) is a pesticide that is registered for corn pest including ECB and CEW and is approved for organic certified farms. It can be used in a sprayer. Next week I will give some details on a new applicator that is being tested in New England that includes these materials in an oil base and has been shown to be much more effective than spraying.

Vertebrates: As corn ripens, vertebrate pests, as well as insect pests, may become a problem. Birds will feed in recently seeded fields as well as in ripening corn. To protect corn from birds, visual deterrents such as scare eye balloons or noise deterrents such as recorded distress calls may be effective. Deer will feed on young corn, and raccoons, skunks and porcupines will feed on ears of mature corn. Electric fencing is effective as a deterrent for these pests. For recommendations on electric fencing or other animal deterrents contact Edwin B. Butler, the USDA’s State Director of animal damage control at (207) 622-8263.

For an update on sweet corn pest scouting at different sites in Maine go to the web site mentioned above.

Also, try calling the Pest Management Hotline: (207) 933-4647 for uptdates.

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 forrates, application instructions and safety precautions. Users of these products assume all associated risks.

Winter squash and pumpkins are vining and filling in between rows, in early fields.

Cucumber beetles are present at low levels in some fields, but growth has outsripped the need for concern about feeding damage. Beetles are attracted to blossoms (along with bees), but do little damage. Beetles do need to be controlled in wilt-susceptible crops such as melons and cucumbers.

Squash bug adults and eggs have been reported but not damaging yet.

Now is the time to watch for the arrival of powdery mildew. This was reported in pumpkin from one field in Mass., but was not found in any other scouted fields of winter squash or pumpkins. However, it has been reported on summer squash throughout New York State. Sysmptoms are often found first on summer squash or zucchini. Look for small white tuffs of spores. They start out being about a ¼" in diameter but get larger and are usually on the undersides of the leaves. When PM spreads and gets going in a field you will find the spores on the upper surface as well.

Imported cabbageworm, diamondback moth, and cabbage looper are being reported. Scout cabbage family crops regularly. Bt products are recommended for the caterpillars. This material does not control adults and has no protective value. So spraying is only recommended when caterpillars are found. It is much more effective on small caterpillars so keep up the scouting.

Scout for potato leafhoppers, which are now being reported in beans. Symptoms are similar to potato, with bronzing of the whole leaf as well as marginal burn. The threshold for seedlings is 2 leafhoppers per foot of row. After three trifoliate leaves develop, the threshold is 5 leafhoppers per foot. Also watch for Mexican bean beetle at this time.

Hot, humid conditions with warm nights and long dew periods dominated the past week, and provided ideal conditions for development of early blight and Septoria leaf spot .

Symptoms of foliar diseases are beginning to show up in the field. The major foliar diseases in tomato can be confusing to tell apart. Here is a description of each.

Early blight, caused by the fungus Alternaria solani, is characterized by brown to brownish-black lesions on foliage which form distinctive concentric rings as they enlarge. These lesions may be surrounded by a yellow halo. The lesions tend to form on older leaves first and work their way up the plant to the newer growth. These symptoms eventually grow to cover the entire leaf and under favorable conditions may lead to defoliation, which will reduce yield. Tomato fruit can be infected as well; fruit lesions are dark brown and leathery and tend to occur at the stem end of the fruit, and may be covered by a velvety mass of black spores.

Septoria leaf spot caused by the fungus Septoria lycopersici, develops under similar weather conditions as early blight. As a result, the diseases often appear together in the field. However, the symptoms are distinct. Symptoms from Septoria infection appear as numerous small tan spots surrounded by brown tissue. Small black pepper-like fruiting bodies, called pycnidia, form in the center of each spot (these can be seen with the naked eye, but are easier to see with a 10X lens). Infected leaves will turn yellow, then brown, and eventually whither and fall off, also resulting in reduced yield. Fruit is not directly infected by the fungus.

The spots of Septoria leaf spot usually stay fairly small, 1/8 inch in diameter or less, while early blight lesions can get much larger, ½ inch in diameter or more.

Crop rotation can help control both these diseases. Decomposition of last year’s crop is essential. If you put tomato debris in the compost pile make sure it gets hot enough to kill the spores or do not use the compost on tomatoes. Septoria leaf spot can be carried in the seed...use hot water treated seed. If you raise your on seedlings, sterilize the containers. A mulch helps reduce splashing spores from the soil and picking off infected leaves helps reduce splashing spores too. Good air movement is important. If you spot the diseases early again this year you may want to consider a copper based fungicide.

Bacterial canker, caused by the bacteria Clavibacter michiganensis subsp. michiganensis, can be seed-borne and is also carried over in infected tomato debris. What we typically see in the field are symptoms of "secondary infections" of the foliage, which include marginal leaf scorch (brown leaf margins) which have yellow band on the inner edge of the scorched tissue. These tend to appear first on older, lower leaves but may be found anywhere the plant. We may also see symptoms of systemic or primary infections, which include wilting of leaflets on one side of a leaf, and downward turning of lower leaves.

Bacterial leaf spot is present in some fields—reported primarily where non-resistant specialty varieties are being grown for processing. Copper sprays and good growing conditions seem to be helping plants to outstrip the disease. So many resistant varieties of bell peppers are now available that these now dominate in fresh market pepper fields and we have not seen BLS. Green peach aphids are present but are far below threshold levels --- held in check by many beneficials. Delaying insecticide applications in peppers until the second ECB flight begins helps conserve natural enemies and keep aphids down. Monitor for aphids by examining the underside of four leaves per plant on 25 plants. The average is your total divided by 100. The threshold is 10 aphids per leaf.

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