Fruit Pest News

June 18, 2001

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. Apple: Sooty Blotch Appears

    2. Peach: Brown Rot Control

    3. Blackberry Rosette: Continue To Watch For It

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

    5. General: Assistance With Pest and Problem Identification

1. APPLE: SOOTY BLOTCH APPEARS

Sooty blotch appeared at the Nashville office on June 18. Hopefully, you have included Benlate or Topsin M in some recent cover sprays. These benzimidazole fungicides will eradicate existing sooty blotch and flyspeck infections that are not yet visible. If sooty blotch and flyspeck have not yet appeared in your orchard, now would be a good time to use Benlate or Topsin M. One of these materials should be tank mixed with ziram or captan. Flint and Sovran are also very effective against sooty blotch and flyspeck, but their eradicative ability is less well known than the benzimidazoles. (SB)

2. 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, or Orbit, beginning at 2-3 weeks prior to harvest and repeating at 7- to 10-day intervals. Adjust spray intervals as needed based on weather conditions, inoculum carryover, and the amount of physical injury to the fruit.

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)

3. BLACKBERRY ROSETTE: CONTINUE TO WATCH FOR IT

These rosettes should have been removed in the spring, before the blossoms opened, releasing the spores. Removing and destroying the rosettes now would still be worthwhile, since some spores are still being released. Use Benlate or copper at 10-14 day intervals. However, do not expect fungicide applications to control rosette in this year's crop. Fungicides applied this year control rosette in next year's crop by protecting the new primocanes. Any rosettes you see this year arose from infections that occurred on primocanes last year.

Fungicidal control may have a place even if you do not currently have rosette, if you are growing a susceptible variety. Shawnee, Cherokee, Comanche, and Black Satin are examples of very susceptible varieties. (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. Low levels of this disorder have already been seen this year, about 2 weeks ago. 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 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.

*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. ASSISTANCE WITH PEST IDENTIFICATION

With our variable weather patterns this year, now would be a good time to walk through your orchard or small fruit planting and scout for potential disease, insect, or weed problems. If you need help in identification of pests or growth problems, don't hesitate to call on the University of Tennessee Agricultural Extension Service. Digital images of the pests or growth problems can be submitted to the Plant and Pest Diagnostic Lab at Nashville via our special web site. If we are unable to ID the specimen, we enlist the assistance of other professionals, whom we allow to view the images.

How to Use the Service. The Distance Diagnostics service is free to all Tennesseans, as is our regular diagnostic service. If you have a digital camera, you can take the images yourself. If you do not have a digital camera, most county Extension offices have one, and you can ask the agent to take the image with his/her camera. Only Extension agents and experiment stations can access our system and make a submission.

For problem diagnosis samples, you can take the specimen to the county office for photographing, but onsite images are preferred. This is because the specimen is fresher, more realistic, and in its natural habitat. It is good to obtain images close up and from a distance. For lowing-growing types of plants, a view of the whole field is helpful. Please provide us with as much information as you can, such as the distribution (pattern) of the problem in the planting, the plant variety name, and chemicals used. For photographing tiny insects, a few county offices even have stereoscopes with camera attachments.

Take advantage of this service. Distance Diagnostics can provide you with a rapid response and allow you to make timely control measures. (SB)

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, Associate Professor and Extension Entomologist

fahale@ext1.ag.utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211