CROP CONDITIONS
   PESTS:
COLORADO POTATO BEETLES
LATE BLIGHT
LEAFHOPPERS
EUROPEAN CORN BORER
CORN EARWORM
BLOSSOM END ROT IN TOMATOES

CROP CONDITIONS:

The dry conditions continue for many growers around the state but for many lucky ones scattered showers have brought up to an inch of rain. Crop growth is slow or even cooked in the dry spots and is picking up in the fields that got water. Disease pressure is still low, but the summer insects are showing up.

A note on marketing: if the media contacts you about the drought, let them know the positive side of the story this season. Low insect and disease pressure, sweet berries, early crops—yes we have a drought on our hands, but we are coping. Let them know there will still be some early, delicious, local fruits and vegetables this season! Disasters make good news, but not good business.

Colorado Potato Beetles:

In the county, adult beetles continue to emerge and lay eggs. CPB eggs are continuing to hatch and small and large larvae can now be found in some fields. The more south you head the more CPB you find. In the southern part of the state the beetles are in the 3^rd and 4^th instar (big). Remember, Bt only works on the small instars. The economic thresholds for CPB are as follows: large larvae - 75/50 plants; small larvae - 200/50 plants.

There is no late blight yet anywhere in the state, but microclimate varies widely and growers are advised to scout their fields. If you typically have late blight problems a copper fungicide is advised as soon as conditions are ripe. Remember for those who typically have a problem with late blight, if you want to protect your plants you must get on a regular spray schedule to keep new plant tissue covered with the fungicide.

They have now been observed in several locations in Maine. There is still no word as to the severity of the infestation. Most years they are not a problem, but they can become a very major pest and this happened recently enough that we are all still scared.

Potato leafhopper does not over winter in Maine, but must fly in from southern states. These small, bullet-shaped insects feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow. In severe infestations the leaves get burned edges. Symptoms are often first noticed on beans and potatoes, but leafhoppers feed on many vegetables, flowers and fruits. To scout for leafhoppers, brush the leaves of the plants with your hand. The small, whitish adults can be seen flying off the plant. Examine the underside of leaves for small light green leafhopper nymphs. They are about 1/16^th of an inch long (tiny). The best product is Pyrenone, but it is very hard to find this year because of a crop failure of the pyrethrum ingredient. Rotenone has not worked well. The best I can suggest at this time while I hunt for a solution is to get the most concentrated pyrethrum product you can find. If anyone knows of a good product or knows someone with a supply of Pyrenone let me know.

European Corn Borer:

In the county they are very concerned about a severe infestation of the potato crop with ECB this year. (Remember, the ECB does not only attack corn; it goes after about 300 other things too.) The report from Jm Dwyer up north says they are catching European corn borer moths in their traps in Southern and Central Aroostook. They expect the first egg masses to be hatching late this week (6/24-6/26). They expect an increased egg hatch mid to late next week. The larvae are most vulnerable from the time the eggs hatch till the larvae enter the stalk. This will be about 3 days. The timing of insecticides for control is critical, especially when using Bt. A new formulation of Beauvaria is being released soon and is likely to be registered in Maine quickly for the ECB. I will keep you informed.

Scouting for corn borer eggs is difficult but, with careful inspection, very possible. Carefully inspect the undersides of the leaves for a whitish area that will resemble a single fish scale. Flagging several egg masses can be used to monitor egg hatch. The economic threshold for European corn borer is an average of 1 egg mass per 15 plants. Please scout and let me know!

In the more southern part of the state the ECB is more of a concern for corn. Moths were caught in nearly all locations this week. Feeding injury was variable from location to location and has not yet required a spray, but the numbers suggest larvae will be appearing in all fields soon and may exceed threshold. Protective sprays are recommended if feeding injury exceeds 30% of 100 plants examined in a field at whorl stage, or 15% if the corn is at pretassel or beyond. Look for pin holes in the leaves as they unfold.

There is also a threat from this pest to silking corn. Moths may lay eggs on leaves close to the developing ear, and the larvae could move directly into the ears through the silk channel. This could not be detected by field scouting. Therefore, corn entering the silk stage should be sprayed for ECB if any fresh larval feeding is observed on the plants or 5 or more moths are caught in traps. Bt products such as Dipel 2X or Condor are the best choice but timing is critical.

Pheromone trap catches of corn earworm were relatively widespread in southern Maine this week, but numbers were low. The corn earworm moth lays its eggs only on green silk. So, corn with no silk or corn with silk gone by is not at risk. If you have corn in the green silk stage it is at risk of corn earworm attack. We are involved in a study of a method to control this difficult. Ruth Hazzard from U. Mass has developed an applicator that can squirt a mixture of Bt and vegetable oil into the silk channel. I will talk more about this soon.

CUCURBITS: 1999 CLYD SURVEY (In Mass.) In the summer of 1998, an apparently "new" disease of cucurbits was observed in squash and pumpkin fields throughout Massachusetts and in upstate New York. This disease, which was named Cucurbit Lethal Yellowing Disease, or CLYD, is characterized by unusual symptoms, including sudden wilt, scorched, blighted or yellowing leaves, and curling or stunting of young foliage at the growing tips (Figs. 1-2). Affected plants eventually wither and die. CLYD was first observed in early to mid-July on several Massachusetts squash/pumpkin farms. Diagnostic analysis at the UMass Plant Disease Diagnostic Laboratory revealed no clear association of symptomatic plants with known pathogens, although some (approx. 30%) of the plants did have a small amount of bacteria in their vascular tissue, indicating the presence of the bacterial wilt pathogen (Erwinia tracheiphila). The root-infecting fungus Pythium was also isolated from about half of the diseased specimens. However, these particular symptoms had not previously been associated with bacterial wilt or Pythium.

What causes CLYD? There have been several hypotheses about the cause of this disease. The diagnostic labs at UMass and Cornell University speculated that bacterial wilt, exacerbated by Pythium, heat stroke, drought, or a combination of these factors, may have contributed to the CLYD symptoms. Dr. Thomas Zitter at Cornell noted that the disease was similar to a cucurbit disease called "yellow vine", which had shown up in cucurbit crops in Oklahoma and Texas in 1989. Dr. Zitter coined the name CLYD for the Northeast version of the disease. Although the cause of yellow vine was (and still is) uncertain, Dr. Benny Bruton from the USDA Agricultural Research Service at the University of Oklahoma discovered a bacteria-like organism (BLO) in the vascular system of most of the affected plants. . Is CLYD caused by the same organism that was isolated from Oklahoma and Texas crops? We don’t know. Recently, Dr. Zitter revised his hypothesis regarding CLYD, and now believes that the bacterial wilt pathogen E. tracheiphila is the causal agent. Dr. Robert Wick, Associate Professor of Microbiology at UMass and head of the Plant Disease Diagnostic Clinic, suggests that we may be seeing new strains of the bacteria.

CLYD Survey. The actual cause of the symptoms we saw last season remains a mystery. This summer, the UMass Vegetable Team is conducting a survey of cucurbit crops to determine how widespread the disease is, and what is the cause. We will visit farms that report symptoms, and take samples for analysis at the UMass Disease Diagnostic Clinic and at the University of Oklahoma. Financial support for the survey comes from the UMass IPM program and from the New England Vegetable and Berry Growers Association.

Call us! If growers notice any cucurbit crops exhibiting these unusual symptoms, please call the UMass Plant Disease Diagnostic Clinic at (413) 545-1045 or 545-1667, or the Vegetable IPM office at 545-3696.

CLYD is characterized by sudden wilt or collapse of the entire plant. One of the unique symptoms associated with CLYD is a yellowing, curling or, stunting of young foliage at the growing tips, resulting in a "tufted" appearance.

Also observed is yellowing of the mid-leaves and older leaves; very often the veins remain green. Leaves often look scorched and blighted, either along the margin or in the interveinal regions. Drawings by Arne Christensen (Mail and Internet Version).

The current dry conditions increase the likelihood of blossom-end rot in tomatoes. This is a physiological disorder which sometimes causes serious losses. The early symptoms, which often go unnoticed, appear as water-soaked lesions on the blossom end or bottom of the fruit. The affected tissue breaks down and the area becomes sunken, dark brown or black, and leathery. This can happen at any stage during fruit development.

Blossom-end rot is caused by a lack of sufficient calcium in the fruit tissues. The disorder begins when the demand for calcium in the fruit exceeds the supply. This can occur even when there is an ample supply of calcium in the soil, stems, and leaves of the plant. Calcium is an immobile element, which means that once it is located in one part of the plant, it can not move to another. Actively growing parts of the plant such as developing fruit must have a continuous supply.

Field conditions which can bring about blossom end rot include the following:

Blossom-end rot can best be reduced or prevented by advance planning and close attention to details:

The beetle is out in full force now. Small plants can be completely killed by this critter because they can build up in giant numbers over just a few days. If you need to spray use a concentrated pyrethrum spray and spray very early (5 am) in the morning when it is cool and the beetle is inactive. If you spray later or in the evening when they are warm they will fly off as you walk up the row and return later. Be sure to get under the leaves.

(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.)