Eric Sideman's Pest Report
August 16, 2003

(View List Of All 2003 Pest Reports)

The Pest Report is a service to MOFGA Certified organic growers and others who contact MOFGA requesting it. I have been putting it together for the past 3 or so years. I do it by garnering information from Extension publications in northern New England, modifying their information to meet organic guidelines, and combining that with field reports I get from our local Extension folks, MOFGA inspectors and my own farm visits. I especially want to thank Ruth Hazzard and the other folks in Massachusetts for their excellent Vegetable Notes, Vern Grubinger in Vermont and Mark Hutton and David Handley here in Maine.

CORN

Corn Earworm Numbers on the Rise
Corn Borer and Armyworm Also Higher This Week

Main season corn harvest continues between rainstorms in much of the state. The frequent rain has slowed field operations and encouraged weed problems at many farms, but plant growth overall has been good. Recent weather patterns have encouraged the movement of moths into the state, resulting in significant increases in populations of corn earworm, corn borer and armyworm in many locations.

European Corn Borer: Pheromone trap catches of moths have risen in several locations, perhaps signaling the beginning of a second generation. While sprays for European corn borer to protect silking corn could have been recommended in most locations, all fields with silking corn are already being sprayed for corn earworm. European corn borer feeding damage exceeded the threshold in Cape Elizabeth, Dayton, Dresden, Litchfield, New Gloucester, Poland Spring and Wells. Fields with European corn borer damage should only be sprayed if fresh feeding injury is found on 15% or more of the plants scouted in a field.

Corn Earworm: Corn earworm moth numbers were very high in all locations this week, putting all fields on a three or four day spray intervals to protect silking corn. This is the highest level of moths we have seen this season, so growers are strongly encouraged to keep up with their control schedules. Fields that are not silking do not need to be protected from corn earworm.

Fall Armyworm: Fall armyworm moth trap catches were slightly higher this week. The threshold of three moths per week in silking corn was exceeded in about half of the fields scouted, but all of these sites are already spraying for corn earworm. Larval feeding continues to increase in younger fields not being sprayed for corn earworm and has exceeded the control threshold in several locations. When found, this injury is combined with any European corn borer injury to determine if protection is needed. The control threshold is 15% for corn at pre-tassel and beyond.

Picnic beetles can become a problem during the late summer on silking corn. These beetles are about * inch long, black with orange spots. They can often be found on stalks and ears that are infested with European corn borer, feeding on sap at an entry or exit hole. They are also known to feed on the silks. While this does little damage, customers may object to finding the insects in their bags.

Sincerely,

David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm Pest Management Office
P.O. Box 179 491 College Ave
Monmouth, ME 04259 Orono, ME 04473
(207) 933-2100 1-800-287-0279

Sweet Corn IPM Weekly Scouting Summary

Biddeford 123 115 0 10% 3 day spray interval recommended on silking corn
Cape Elizabeth I 191 5 12 3 day spray interval recommended on silking corn
Cape Elizabeth II 354 7 15 39% 3 day spray interval recommended on silking corn
Dayton I 45 2 2 4 day spray interval recommended on silking corn
Dayton II 88 12 6 30% 4 day spray interval recommended on silking corn
Dresden 117 62 10 25% 3 day spray interval recommended on silking corn
Farmington 28 12 5 4 day spray interval recommended on silking corn
Jefferson 15 1 0 6% 4 day spray interval recommended on silking corn
Lewiston I 42 35 8 8% 4 day spray interval recommended on silking corn
Lewiston II 7 89 10 3% 4 day spray interval recommended on silking corn
Lisbon 24 41 6 4 day spray interval recommended on silking corn
Litchfield 104 7 12 15% 3 day spray interval recommended on silking corn
Monmouth 83 6 7 4 day spray interval recommended on silking corn
New Gloucester 52 15 22 17% 4 day spray interval recommended on silking corn
Nobleboro 16 19 0 4% 4 day spray interval recommended on silking corn
North Berwick 135 37 0 7% 3 day spray interval recommended on silking corn
Oxford I 55 12 2 4 day spray interval recommended on silking corn
Oxford II 47 14 1 4 day spray interval recommended on silking corn
Poland Spring 63 9 3 29% 4 day spray interval recommended on silking corn
Waldoboro 43 0 0 3% 4 day spray interval recommended on silking corn
Warren I 15 34 0 6% 4 day spray interval recommended on silking corn
Warren II 7 1 0 3% 4 day spray interval recommended on silking corn
Wayne 55 91 0 4 day spray interval recommended on silking corn
Wells 68 9 4 15% 4 day spray interval recommended on silking corn

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

Corn Earworm Spray Thresholds for Pheromone traps

Moths caught per week Moths caught per night Spray Interval:

0.0 to 1.4 0.0 to 0.2 No spray
1.5 to 3.5 0.3 to 0.5 Spray every six days
3.6 to 7.0 0.6 to 1.0 Spray every 5 days
7.1 to 91 1.1 to 13.0 Spray every 4 days
More than 91 More than 13 Spray every three days

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

(NOTE: I put Dave's spray schedules here only for your info and to see the moth counts, but those using Zea-Later only need to do it once. --ES)

(modified from Sweet Corn IPM Newsletter No. 7 August 13, 2003)

CABBAGE

Once the infection takes off spores are produce in large numbers and are wind blown and carried by water. The spores are carried in the seed and the fungus can live long periods in the soil in a saprophytic stage outside a host. Long rotations will work in fields well isolated from other crucifers. Using certified disease-free and hot water treated seed is a key control practice. Copper (Champion, WP) is labeled for this but needs to be sprayed early and on a schedule to keep new tissue covered.

CURCURBITS

Bacterial Wilt-
Cucumber and melons are severely affected. Individual runners or whole plants wilt and die. Test for this by cutting the stem and then touch the cut ends back together or hang one end in a glass of water and look for a stringy slime. This disease is carried and spread by cucumber beetle feeding. Controlling the cucumber beetle is the only way I know to prevent this problem

Fusarium Wilt of watermelon and other melons
Damping off of young seedlings is possible, but what is seen this late in the season is whole plant wilt because they cannot carry the water demand of the developing fruit load. This is especially true when plants are under drought stress. There are a number of races of the species of Fusarium and great varietal resistance. So, you will often see one variety of melon go down while the one next to it stays healthy. Note the resistant varieties in your system. This is the best means of control. Fusarium is a long live soil organism and so rotation is not that effective and they have to be long.

Fusarium Crown Rot of squash
Wilting of leaves is the first symptom, but this late in the season you will see the entire plant wilting or more likely dead. If you move the soil away from the base of the plant you will see the crown has rotted and by now the plant is likely to have broken off or will break off easily about 2 inches below the soil line. Also, I have seen maggots from a muscid fly, the family of flies to which the house fly belongs. These are just feeding on the rotting tissue and did not cause the problem. The severity of this disease is heavily dependent on soil moisture and the density of the inoculum in the soil. A four year rotation will work well.

BRASSICAS: FLEA BEETLE AND CATERPILLAR UPDATE

A new generation of imported cabbageworms are hatching out, diamondback moth is going strong. Cabbage looper is present in the Connecticut Valley, which probably means it can also be found in other parts of the state. Keep a close eye on brassicas - especially underneath the leaves. Diamondback moths were found in a hoop house with mesclun greens in southeastern MA. These are not the preferred host, but they were causing small round holes in the leaves. And, keep in mind that the cabbage worms are active well into the fall.

--(modified from Mass Veg. notes story by Caryn Andersen and Ruth Hazzard)

TARNISHED PLANT BUG

Feeding: Adults and nymphs have piercing sucking mouthparts (stylets) which are used to penetrate plant tissues and suck up cellular contents. TPB select succulent, nutritious tissues such as new growth or newly forming fruits (just after blossoming). While feeding, the bugs secrete a toxic substance from their salivary glands which kills cells surrounding the feeding site. Usually the first signs of damage are small brown spots on young leaves. As the tissue grows, healthy tissue expands while dead tissue does not, which results in holes and distorted, malformed leaves, buds or fruit. Terminal shoots and flowers may be killed. Ribs and stalks may be discolored or die.

Damage. In strawberry, this distorted growth of fruits is known as cat-facing. In lettuce, TPB causes scars on ribs, which allow entry of pathogens and render heads unmarketable. In celery, feeding on tender stalks produced large, brown colored wilted spots and blacking of joints, know as "black-joint'. In beans, feeding on flowers causes them to drop, and feeding on seeds in young pods causes pitting and blemishing of pods. In tomatoes, eggplants and peppers, feeding may occur on flowers and stems, causing flower drop. (NOTE: IF YOU HAVE SEEN THIS PLEASE EMAIL ME AS I WOULD LIKE TO KNOW THAT I AM NOT ALONE, THANKS, ERIC). Fruits may also be attacked leading to indentations, bumps, or yellowing of the flesh where the fruit is "stung" by the piercing mouthparts of nymphs or adults. These could be confused with stink bug damage, but they do not have the white pithy areas beneath the skin that is typical of stick bug damage. It is not common to see this damage, but if the damage occurs it may help to determine the cause. In pepper and in basil, feeding in emerging leaves causes distortion and browning of leaves. In apples, adults feed on fruit buds and cause fruit dimpling and scabbing, or dropping off (abscission) of the buds. In water spinach, we see distortion of leaves and dieback of tips or leaf internodes.

Tarnished plant bugs attack a large variety of crops, weeds, flowers, and orchard crops. Weed hosts include wild carrots and other umbelliferous crops, redroot pigweed (and other amaranths), lambsquarters, mustards, shepardspurse, rocket, goldenrod, and mullein. Alfalfa is a favored host, and harvesting alfalfa often stimulates major lygus migrations into crops. Other legume hosts include vetch, lupine, and fava beans.

Management: Whole farm management should include removing sources of infestation outside the crop. Disk or rototill weeds along field borders to reduce weed hosts, or keep them mowed all season. However, disturbing non-crop areas by mowing can encourage movement of TPB into your crop, so it should be avoided at critical periods when the crop is vulnerable. There are natural enemies of TPB, including a parasitic wasp which was released for control of TPB in alfalfa (Peristenus digoneutis). This was released in New Jersey and has spread throughout the northeast, and can cause up to 50% mortality. However, it currently does not reduce the numbers sufficiently to prevent damage in key crops. Many vegetable crops can sustain a small population of TPB without economic injury.

--(Modified from Mass. Veg. Notes, Ruth Hazzard)

(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.)