Fruit Pest News

Volume 5, No. 14  June 15, 2004

A weekly, online newsletter whose goal is to update Extension agents and growers of commercial tree fruit and small fruit crops

on diseases and insects in Tennessee.

Text appearing in blue or red can be clicked to link to other web sites. Be aware that much of the linked information is produced in other states and may not be applicable to Tennessee.

In This Issue:

    1. First Reports for the Year

    2. Sooty Blotch Appears

    3. Brown Rot of Peach and Other Stone Fruits

    4. The Apple Leaf Blotches: Necrotic, Alternaria, and Glomerella

    5. Vegetable Corner -- Pest Sightings

    6. Study on Pesticide Exposure on Farms

    7. Tree Fruit: Pheromone Trap Catches and Insect Activity 

1. First Reports for the Year

First reports for the year: crown anthracnose - matted row strawberries, June 3, Dickson County; lesion nematode (Pratylenchus penetrans) - blackberries, June 4, Sumner County; Alternaria leaf blotch - apples, June 10, Wilson County; sooty blotch - apples, June 14, Davidson County. (SB)

2. Sooty Blotch and Flyspeck Appear

Sooty blotch made an early appearance at the Nashville office on June 14. The almost constant wet, cloudy weather we have had lately is ideal for the development of sooty blotch and flyspeck.

Several fungicides provide protection against sooty blotch and flyspeck, and some even provide curative (postinfection) activity, as well. Topsin M, Flint, and Sovran will eradicate infections if used within 100 accumulated wetting hours (AWH) after infection. AWH's are the total of periods of rain or dew lasting at least 4 hours. You can stretch out your spray interval this time of year, and still obtain control of sooty blotch and flypseck by taking advantage of the kickback activity of one of these materials. However, stretching your spray interval much beyond 21 days could jeopardize your control  of  other diseases, for which postinfection control is not available. (SB)

3. Brown Rot of Peach and Other Stone Fruits

The 2- to 3-week period prior to harvest is a critical period in the life of a peach. This is the period in which it is most susceptible to brown rot, the most important disease of peaches in Tennessee. Fungicide sprays just before and during the harvest period are very important. Apply effective fungicides such as Indar, Elite, Orbit, or Pristine beginning at 2-3 weeks prior to harvest and repeating at 7- to 10-day intervals through harvest. Adjust spray intervals as needed based on weather conditions, inoculum carryover, and the amount of physical injury to the fruit. Try to rotate your fungicide classes every third application, if applicable. For example, use a sterol inhibitor (Indar, Elite, or Orbit) for two applications, followed by a strobilurin (Pristine).

Injuries to fruit that can increase brown rot problems include hail, frost cracks, bird feeding, and insects such as Oriental fruit moths, Japanese beetles, green June beetles, hornets, and wasps. Breaks in the fruit skin make it easier for the fungus to enter and begin the rot process. Wet, warm weather aids dispersal and germination of the fungal spores. The spores come mainly from mummified fruit from the previous year, and the spores are carried to fruit by wind, rain, and certain insects.

Some brown rot is not apparent at harvest and develops in storage. Storing the fruit in a cooler after harvest slows the development of infections. Try to avoid injuries to the fruit during the harvesting operation, as post-harvest brown rot can begin at these sites. We have a good peach crop in many areas; let's try to keep it! (SB)

4. The Apple Leaf Blotches: Necrotic, Alternaria, and Glomerella

During the summer in Tennessee, three apple diseases can occur, all having similar names and symptoms. Let's compare these diseases and their controls.

Necrotic leaf blotch is actually not a disease, but a physiological disorder. It occurs on Golden Delicious and its sports. The affliction often occurs in waves during the summer. It tends to be more severe when hot, sunny weather follows several days of mild, cloudy weather. Large, irregular-shaped, necrotic (brown) spots appear suddenly on green leaves (click here to view an image). Most affected leaves soon turn yellow and fall from the tree. Defoliation can be significant. Although necrotic leaf blotch is not caused by a fungus, severity is decreased by a regular fungicide program (see below).

Alternaria leaf blotch, caused by the fungus Alternaria mali, affects Red Delicious and related varieties such as Empire. Alternaria leaf blotch is a problem in the higher elevation areas of Tennessee. Symptoms (click here) include small, circular necrotic spots on the leaves. The leaf spots may have a purplish margin and, thus, resemble frogeye leaf spot and captan injury. Alternaria leaf spot is aggravated by European red mites. Control consists of mite control, fungicide spray programs, and adequate tree spacing and other cultural practices that enhance drying conditions.

Glomerella leaf blotch was first found in Tennessee in 1998. The two orchards in which it was found were the first North American reports of this disease. It has since been found in Georgia and North Carolina, but its distribution is still very limited. Symptoms (click here) resemble necrotic leaf blotch of Golden Delicious. However, Glomerella leaf blotch has only been found on Gala and Ozark Gold. Also unlike necrotic leaf blotch, Glomerella can infect the fruit, causing a bitter rot type of infection. The fruiting bodies of the Glomerella fungus on the surface of the rot have a black color, whereas those of Colletotrichum acutatum bitter rot have a salmon color. Appropriate fungicides for control of Glomerella are provided below. As with Alternaria leaf blotch, Glomerella is most severe where tree spacing or branch spacing is inadequate, or other conditions exist that interfere with drying conditions. Note: Necrotic areas on leaves of Gala can also be caused by Abound injury.

*The EBDC fungicides have a 77-day preharvest interval.

As you can see, the 3 blotches have different cultivar spectra and the chemical control specifications are different in some cases. If you find any of these blotches, we would be interested in knowing about it, and would be glad to assist you in selecting control products. Please let me know. (SB)

5. Vegetable Corner - Pest Sightings

Flea beetle damage is evident on many vegetable plants, especially eggplant. They produce small holes in the leaves and can transmit Stewart's wilt in sweet corn.

Squash vine borer larvae have been found tunneling in squash vines. In home gardens, some plants can be saved by making a longitudinal cut in individual vines to extract the larva. Commercial growers need to use protective insecticide sprays to prevent the borers from boring into the vine.

Diseases at retail outlets - Diseases are being brought into home gardens on transplants purchased at retail outlets. From gardens, these diseases can be spread into commercial fields -- by wind, wildlife, tools, equipment, or soil water.  Bacterial spot of tomato and Pythium root rot of pepper have been found recently. If you find what you think is a diseased plant, ask for a refund from the retailer. If you would like a confirmation, ask your county Extension office to send it to us. Please try to send us the nursery tag, also. I plan to try to take action to stop the distribution of diseased plants to garden outlets.

6. Pesticide Study Shows No Exposure for Farm Families

Spoused and children who live on farms where pesticides were applied generally did not have appreciably increased exposure to those pesticides, according to a study conducted by the Universtiy of Minnesota. The $2 million project is the most comprehensive study to date of pesticide exposure for farm families. Ninety-five farm families in Minnesota and South Carolina provided urine samples for four days after pesticides were applied on their farms. Much of the health research that previously has been conducted with farm families and pesticides has used questionnaire-type surveys. By analyzing urine samples in the recent study, scientists were able to obtain an actual measure of the participants' exposure to the pesticides. There was no indication that pesticides applied to the field were translocated to family members.

The study also measured the amount of exposure for the pesticide applicators. The results varied, depending on the amount of exposure of the applicator to the pesticide. Exposure was detected by the analytical techniques in cases in which there was direct skin contact, such as spills or repairing equipment.

This study shows that, with proper precautions, the use of pesticides on farms poses little to no threat to those who do not handle the pesticides. (SB)

7. Tree Fruit: Pheromone Trap Catches and Insect Activity

Adult moth activity has been down at most locations over the last ten days or so, except for redbanded leafrollers at the Smith County orchard site. Continue to monitor fruit and foliage for signs of larval feeding damage. More of these larval populations will complete their development and begin to pupate and produce moths in the coming weeks. Be looking for this increase in moth activity. Timing of cover sprays can be fine tuned by using pheromone traps and degree day models.

Japanese beetle adults can be found feeding on the foliage of many types of trees and shrubs. Feeding on peach foliage produces leaves that have clear window pane areas where one side of the leaf has had the tissue removed.

Brood X of the 17-year periodical cicada has been active in large numbers in many East Tennessee counties. Middle and West Tennessee growers were generally spared damage from this insect. If you have been spraying for cicadas in fruit orchards, take note that the worse of the egg laying damage may be over. Check to see if the females on fruit trees are still laying eggs. If not, further pyrethroid insecticide sprays targeting these pests may not be needed and regardless, millions of cicada adults will be dying of natural causes soon.

 (FH)

The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm

Contacts:

Steve Bost, Professor and Extension Plant Pathologist

scbost@utk.edu

Frank Hale, Professor and Extension Entomologist

fahale@utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211