Remember, I want growers to email me with any observations they make, especially early sightings of insects or diseases. I also want to thank all the university folks who allow me to borrow from their reports, including Ruth Hazzard and Sonia Schoelmann from U Mass, Vern Grubinger from UVM, and all those great U Maine folks (Steve Johnson, Dave Handly, Jim Dill, Jim Dwyer and others).

It is raining again today and it is unusual that in mid July we do not welcome the water. But, last week we had over 3 inches! It is also unusual that in July we wake up to 42 degree mornings over and over. Needless to say, crops are about 10 days or more behind schedule.

The night temperatures in 40’s and 50’s have slowed growth in corn, peppers, tomatoes, melons and other crops—not a big help when crops are already delayed. The plus side is, early blight of potato and tomato does not develop when leaf wetness periods (ie, dew or rain) occur at temperatures below 55 oF. Similarly, bacterial leaf spot of pepper is halted by periods of several nights at <55 oF. In general, foliar diseases are slowed by low humidity and cool nights. However, since it’s July, don’t count on this lasting too long!

Check new plantings now for potato leafhopper (Empoasca fabae) damage. Leafhoppers feed primarily on the underside of strawberry leaves, causing them to yellow between the veins and become curled and distorted. Feeding activity is most serious during the late spring and early summer. Leafhoppers are 1/8 inch long, green, bullet-shaped insects that take flight quickly if disturbed. The nymphs are light green and do not fly. Nymphs are easily identified by their habit of moving sideways when disturbed. Insecticides should be applied only when large populations of nymphs are noted on the leaves or symptoms become apparent. See past Pest Reports for details on control materials.

As foliage grows back after renovation, keep an eye out for feeding of strawberry rootworm (Paria fragariae). Strawberry leaves attacked by strawberry rootworm beetles are riddled with small holes. Some leaf damage occurs in May, but most occurs in August. Heavy infestations can reduce plant growth or kill plants.

Although adults of the strawberry rootworm feed on the leaves of strawberry, root-feeding by the larvae is more damaging to strawberry production. Adult strawberry rootworms are brown to black or copper-colored, shiny, oval-shaped beetles with four blotches on the shell-like wing covers. They are 1/8 inch long. The larvae are grubs that are 1/8 inch long, creamy white, with three pairs of legs. Adult strawberry rootworms overwinter in mulch and soil crevices, and become active in May and June. Adults feed primarily at night and hide in soil or mulch during the day. They chew small holes in leaves, and females lay eggs on older leaves near the soil surface. Larvae burrow into the ground to feed on strawberry roots from late spring to early summer. New adults begin emerging in mid-summer, and these beetles feed on strawberry foliage through early fall. Scouting for the presence of adult beetles is best done after dark using a flashlight to examine plants. No threshold has been established for this insect, but a population of 10 to 20 beetles per square foot is considered high. As with all the root feeding insects, control of the root feeding stage is very difficult. Therefore, control measures for strawberry rootworm should be directed toward the adult stage. If feeding injury is observed in May or June, an insecticide spray at this time will reduce the number of egg laying females and, therefore, the number of grubs feeding during the summer. When the next generation of adults emerges in July or August, control measures may be needed again. The only control that really works for organic growers is to rotate out of the field after one or two years of picking.

Mexican bean beetle has arrived in snap beans. I have not seen a lot but did see them in Albion. Look for coppery brown, spotted adults that look like large ladybeetles, yellow-orange egg masses, or bright yellow, oval spiny larvae. A beneficial insect, Pediobius foveolatus, is now commercially available for Mexican bean beetle control. This small, non-stinging, parasitic wasp attacks and kills Mexican bean beetle larvae. The parasite does not overwinter here, but provides excellent long-season control of the beetles. This wasp has been tested in snap beans and soybeans in New Jersey and Maryland. A single release, timed so that wasps can attack bean beetle larvae, can provide control. Wasps reproduce in the field and are still present when the second generation hatches out. To pronounce Pediobius, say "pee-dee-oh-bee-us". To purchase Pediobius contact:

The Beneficial Insect Company (NC), 336-973-8490

For more information, you can contact: Carol A. Holko, Maryland Department

of Agriculture, Plant Protection and Weed Management Section, 410-841-5920

Scout each new bean planting for potato leafhopper by checking the undersides of leaves. Damage is greater in plants that are infested early in their growth. Thresholds are two hoppers per foot of row in seedlings, five per foot of row after seedling stage. Rotenone does not work on leaf hoppers. Concentrated pyrethrum materials are the best thing organic growers have. The two I know of are Pyrenone and Pyrenyl.

Potato leafhopper numbers are still high in both potato and eggplant too. Check undersides of leaves for adults or nymphs. On eggplant, University of Connecticut recommends a threshold of one to 1.5 leafhopper per leaf. This year leafhoppers are worse than usual and numbers may be high enough to cause damage if uncontrolled.

The good news is that the potato crop continues to grow rapidly and no late blight has been found anywhere in the state.

The rains have been extremely variable, with some locally intense rainfall. Field scouting has and continues to be difficult because of the wet conditions. The moist, damp conditions have continued to create excellent disease conditions and the current long range forecast is calling for a continuation of the shower activity. With the conditions being excellent for both plant growth and disease development please do not let your guard down.

We strongly encourage all growers to be carefully scouting all potato fields for potato late blight. This is a critical time for all growers to be scouting carefully. The sooner that a late blight infection is found, the more options that you the grower will have for control.

European Corn Borer:

We are continuing to catch corn borer moths in pheromone traps.

Currently we are catching ECB moths from St. Agatha through Central Maine. Moth counts are about the same this week as compared to last week. Egg masses are being found in all areas, however only in low numbers. The cool wet weather of the past few weeks has slowed development and most likely delayed egg laying. The modified growing degree-day accumulation is 901as of July 19. The model indicates that peak moth flight should be occurring, however, the cool wet weather should have a negative impact on the insect’s development.

We strongly encourage all growers throughout the state to be scouting potato fields for ECB activity. Please be aware that egg masses can be extremely difficult to find. The economic threshold for ECB is 1 egg mass per 15 plants scouted.

All the life stages can be found now. If you have done nothing about them on your potatoes you probably do not have leaves anymore. But, Bt has worked well when sprayed on time (young larval stage) and those of us who have also had to spray pyrethrum for the leaf hopper have gotten additional control from that. At this time, in most of the fields that I have seen where control (hand picking or Bt) was diligent the numbers are low enough to leave them alone now. Remember, potatoes can take quite a bit of defoliation without yield reduction, and you do want to leave Bt susceptible individuals out there to breed and keep their genes around. On the other hand, keep scouting your fields and if large populations of young larvae develop do not let them get out of hand.

Cucumber beetle numbers are currently low in most fields with crops of all ages. However, bacterial wilt symptoms are showing up in many vine crops. Symptoms include the sudden wilting of one vine or the entire plant; a yellowing, curling or, stunting of young foliage at the growing tips, resulting in a "tufted" appearance; or yellowing of the mid-leaves and older leaves, while the veins remain green. Leaves often look scorched and blighted, either along the margin or in the interveinal regions. These symptoms have been observed in pumpkin, cucumber, summer squash and zucchini.

These bacterial wilt infections came from cucumber beetle feeding on plants at the seedling stage. Once plants have 5 leaves, and are vining, flowering, and developing fruit it is unlikely that they will acquire damaging new infections. The most critical period for new infections with bacterial wilt from cucumber beetle is from the cotyledon to the 2 leaf stage. After the 3-4 leaf stage, beetle feeding is less likely to cause plants to wilt or develop other symptoms. Once wilt shows up, it is too late to take action.

It is time to watch for powdery mildew. Reports of powdery mildew on pumpkin and summer squash have come in from Berkshire and Norfolk Counties in Mass. However I have not yet in Maine. Look for whitish or grayish talcum-like fungal growth on the upper or lower surface of the leaves and on petioles and stems. Check 5 mid- or lower leaves at 10 locations in the field. Symptoms usually develop first on older leaves. Older plants will show it first. It can often be found on summer squash before it develops on winter squash or pumpkin. Fungicide applications should begin if powdery mildew is found on one leaf out of 50 anywhere in the field.

Options for organic growers include potassium bicarbonate (Armicarb 100), monopotassium phosphate (EksPunge), or oils (SMS Stylet-oil, Sunspray Ultra-Fine Spray oil).

Tomatoes are way behind last year. Even hoop house tomatoes are behind although they are being harvest now. Field tomatoes look like August this year.

Some diseases are beginning to show up. I have seen the beginnings of early blight (caused by the fungus Alternaria). Diane has told me that she has seen what I think may be leaf mold (caused by the fungus Cladosporium). And, in Mass they report bacterial canker. All three diseases start out affecting leaves, but early blight can infect fruit and bacterial canker can invade the vascular system.

Early blight is characterized by dark brown bull’s eye-like lesions on lower leaves. Later it will appear as rotting at the stem end of the tomato fruit. Early blight is carried from season to season on crop debris. Crop rotation is important and remember that if you put diseased plants into your compost pile it better get hot or do not use that compost on your tomatoes next year. Mulch helps because the initial infection is by splashing spores out of the soil. If the infection is early, picking of diseased lower leaves helps. Copper sprays will keep the disease from spreading if you keep the plants tissued covered.

Leaf mold causes pale yellow spots on the upper surface of leaves and a corresponding felt-like olive green growth on the underside of the leaf. The undersurface patches are spores, which are spread by air currents and watering. It is a disease that is more common in greenhouses where humidity is high or in rainy seasons. Night heat in greenhouses and good ventilation is the best control.

Canker causes marginal scorching, which eventually spreads throughout the foliage and stems. If canker is present, you may want to use a copper product at weekly intervals.

Obviously corn is going to be late this year. My transplanted corn is the only corn I have with silk now, which is in the wilt stage now.

Trap catches of moths continue to be low except in northern Maine where these are a concern for potato growers (see above). Larval feeding injury on corn foliage is low too but I have seen some around the state. Only spray (Bt) if you see damage.

Captures of corn earworm moths in pheromone traps increased in some coastal sites this week, but remained low at many inland sites. Remember, you only need to be concerned about corn in the silk stage and only when the moth is flying. Check the corn hotline (933 4647) for up to date reports on earworm flights in your area or put up your own traps. Injecting a mixture of Bt and corn oil into the silk channel has good but not perfect control. See previous Pest Reports for details.

Fall armyworm feeding damage has been seen in southern Maine fields. Look for ragged cut holes and edges on the corn leaves. Bt sprays work.

This bizarre looking disease has been found in a field this week and is likely to be more prevalent this year due to the wet weather. This fungus disease is easily recognized by the large galls which form in the ears, tassels, and on leaves. The young galls are silvery-white in color. When the galls mature they rupture into masses of powdery, black spores. This fungus tends to infect plants with prior injury, perhaps from cultivation or insect feeding. Smut usually affect only a few plants in a field and is not considered an economically significant problem. Pick off infected ears and destroy (cook them up...I hear that the smut galls are a delicacy).

(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.)