Departments of Plant Pathology and Entomology
North Carolina Cooperative Extension Service
North Carolina State University

FRUIT
AND
VEGETABLES

North Carolina Pest News
Volume 12, Number 9, June 20, 1997
Stephen J. Toth, Jr. and Thomas A. Melton, editors

The information and recommendations in this newsletter are applicable to North Carolina
and may not apply in other areas.

From: Gerald J. Holmes, Extension Plant Pathologist

Foliar Diseases of Cucurbits

Several foliar diseases common to cucurbits (cucumber, watermelon, squash, etc.) have been recently diagnosed in the Plant Disease and Insect Clinic at North Carolina State University. These include anthracnose, powdery mildew and gummy stem blight. Disease pressure will increase as temperature and humidity rise and several other diseases (e.g., downy mildew, target spot, Alternaria leaf spot, bacterial leaf spot) may appear. All of these diseases can be very destructive and result in heavy losses if favorable conditions (warm, moist weather) persist and they are not managed properly.

Management begins with use of pathogen-free seed that has been treated to control seedborne diseases (e.g., anthracnose). Crop rotation should be practiced and sprinkler irrigation avoided. Survey fields weekly and have diseases diagnosed at the Plant Disease and Insect Clinic to be certain of the pathogen(s) involved.

Fungicide/bactericide selection should be based on the type of disease present, since each material has its own level of activity against specific pathogens (Table 1). Timing, coverage, and dosage are all very important to making the selected material actually work like it can.

Table 1. Fungicide/bactericide efficacy for control of cucurbit foliar diseases.

   
    ********************************************************************
                                            Foliar Disease
                             *******************************************
     Fungicide/               Powdery     Downy      Leaf
     bactericide              mildew      mildew     spot /1   Bacteria
    ********************************************************************
     Triadimefon                +++          -         -          -
     Benomyl                    +++          -        ++          -
     Chlorothalonil             +,-         +++       +++         -
     Copper                      +           +         +         ++
     Mancozeb                    +          +++       +++         -
     Maneb                       +          +++       +++         -
     Metalaxyl                   -          +++        -          -
     Sulfur                     +++          +        +,-         -
     Thiophanate-methyl         +++          +        ++          -
    ********************************************************************

    1/ anthracnose, gummy stem blight, target spot, Alternaria, etc.

    Key: +++ = high activity
          ++ = moderate activity
           + = some activity
           - = no activity

From: Kenneth A. Sorensen, Extension Entomologist

Fall Webworms on Pecans

Fall webworms are in Johnston County (small instar larvae). Expect fall webworms to be present over the next couple of weeks. Unsightly nests can be removed by hand when the nest are small in size. Applications of the Sevin or Bacillus thuringiensis (B.t.) can be directed into the nests. A second generation of fall webworms will occur in August; any action taken now will reduce the population later in the season.

Squash Vine Borers and Pickleworms

Squash vine borer adults have been collected over the last two weeks in pheromone traps in Johnston County. Squash is subject to attack by this pest.

Reports of pickleworms south of Charleston, South Carolina have been received. There is a grid system of traps set from Florida to North Carolina. In North Carolina, there are traps located in Brunswick, Sampson and Johnston counties. Populations of pickleworms are expected over the next three weeks. Traps will be used to make initial collections of pickleworms, then used to monitor populations throughout the growing season.

Thrips Threat to Vegetables

Epizootic conditions for thrips exist from small grains, and cool, wet weather which is favorable for thrips. All green plants that are located down wind from fields of small grains that are mature and being harvested are subject to thrips attack. These include cotton, peanuts, peppers, watermelons, beans, peas, cantaloupes, cucumbers, etc. High populations of thrips have been observed on sweetpotato transplants in Greene and Lenoir counties. As a result of thrips infestation, sweetpotato transplants are not becoming established and death of the transplants is occurring. Expected are the loss of several hundred acres, poor stands, and inefficiency in production due to small plants and the cool, wet growing conditions. Now stressed with hot, dry conditions, thrips have moved into small plants on a few leaves causing scarring and tissue breakdown (contributing to desiccation and the death of plants). Some control of thrips can be achieved with the use of Sevin or Thiodan on most of the crops; Lannate is also effective on some crops. Check product labels for crops on which these insecticides may be applied. These conditions with respect to thrips should persist for at least two more weeks. Growers should be advised to check their plants and delay planting around small grains if they are located down wind of these fields. Cabbage growers should also be alert as thrips will move from these fields into the heads.

Web page last updated on June 23, 1997 by Stephen J. Toth, Jr..

This Web version is a cooperative effort between the North Carolina Cooperative Extension Service and the Center for Integrated Pest Management