Fruit Pest News

Volume 4, No. 14   June 17, 2003

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 and Flyspeck Appear

    2. Peach: Brown Rot

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

    4. Tree Fruit: Mite Update

    5. Tree Fruit: Pheromone Trap Catches and Biofixes

1. Sooty Blotch and Flyspeck Appear

Sooty blotch and flyspeck made an early appearance at the Nashville office on June 15. Researchers have found that these fungi develop independently of temperature, so the below-average temperatures that we have had this growing season have not slowed them down. Their rate of development depends entirely on wetness, and we have had plenty of that!

Several fungicides provide protection against sooty blotch and flyspeck, and some even provide curative (postinfection) activity, as well. Topsin M, Benlate (if available), 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)

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 through harvest. 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. 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)

4. Mite Update

If dormant oil sprays are used to kill overwintering eggs, European red mite (ERM) populations should initially be low in the spring. The mites can also be killed by low temperatures right after hatching in early spring. I do not know this to have happened this year. ERM are also more susceptible to acaracides at this time. On apple, the eggs start to hatch at tight cluster with 50 percent hatch by pink. All of the eggs will have hatched by bloom. The ERM develop quickly with the first eggs of the growing season hatching by late petal fall or first cover. The ERM populations will build best when temperatures are in the 70-90 F range under hot, dry conditions.

The twospotted spider mite (TSSM) has a wide host range and overwinters under bark scales on the tree trunk or in protected places such as beneath leaves on the ground. Thus, dormant oil sprays are not effective in controlling TSSM. These mites can be found feeding on broadleaf weeds and grasses as it warms up in the spring. As temperatures increase and the weed hosts mature, TSSM will move up into the trees to feed on foliage. These mites, like the ERM, do best in hot, dry, dusty conditions. I would not expect TSSM populations to really take off until we get over this relatively cool, rainy weather pattern. Inspect regularly for both ERM and TSSM, especially as more summer-like weather patterns become established. (FH)

5. Pheromone Trap Catches and Biofixes

Nashville (Davidson County) Pheromone Trap Catches for 2003

* Biofix for RBLR in Davidson County estimated as occurring on March 8

Bradley County Pheromone Trap Catches

*Biofix for redbanded leafroller in Bradley County estimated as occurring on March 8
**Biofix for codling moth in Bradley County was April 5 (2 caught)


Putnam County Pheromone Trap Catches

*Biofix for Putnam County estimated as occurring on March 8

Obion County Pheromone Trap Catches

*Biofix for RBLR occurred prior to trap placement, estimated as occurring on March 8
(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, 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