Fruit Pest News

Volume 3, No. 15   June 17, 2002

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:

    Tree Fruit: Plum Curculio

    Tree Fruit:  Degree Days for Oriental Fruit Moth in Nashville

    Tree Fruit: Degree Days for Codling Moth in Nashville

    Apple: The Leaf Blotches - Necrotic, Alternaria, Glomerella

    Tree Fruit: Pheromone Trap Catches and Biofixes

Plum Curculio

Plum curculio adults overwinter in leaf litter around orchards. They become active and mate during warm spring weather (70F or higher) and start laying eggs in the small fruit. Control of this pest is best achieved with sprays at petal fall and first cover on apples. On stone fruit, begin sprays at petal fall and repeat every 10-14 days as long as new damage appears. The problem from this pest is often worse where apples and stone fruit are grown together. Feeding scars on apples look like tan bumps while the oviposition scars are crescent-shaped. Where these crescent-shaped scars appear, the eggs were crushed by the growing fruit. Most of the fruit that have larvae burrowing into the fruit will drop to the ground. The mature larvae exit the fruit and enter the soil beneath the trees to pupate. The adults start to emerge from the soil to feed on fruit sometime in June. They can make small feeding holes (a few millimeters wide) in apples up until harvest. Cold autumn weather will cause them to seek overwintering sites. (FH)

Degree Days for Oriental Fruit Moth in Nashville

On June 16, the degree day total in Nashville for Oriental fruit moth (OFM) was 1707 DD after biofix. Treatment for second generation OFM should have been started at 1,400 DD after biofix with a second spray 14 days later. This is for moderate to high-density OFM orchards. An insecticide application for third generation OFM can be made at 2,300 DD after biofix if trap catches exceed 5 moths/trap/week after 1,900 DD after biofix and fruit damage caused by the second generation is detected. (FH)

Degree Days for Codling Moth in Nashville

On June 16, the degree day total in Nashville for Codling moth (CM) was 1323 DD after biofix. This is about 12.5% egg hatch. Extremely low-density CM orchards (like Nashville site) may not require an insecticide application (i.e., pheromone trap catches never exceed 3 moths per trap per week between 800 to 1,600 DD after biofix). Low density CM orchards may require 1 insecticide application at 1,400 DD after biofix given no sign of damage by first generation larvae and pheromone trap catches are between 3 to 7 moths per trap per week between 800 and 1,500 DD after biofix. We should be at 1,400 DD on June 19 (Wednesday). Moderate to high-density orchards will have fruit damage and/or higher pheromone trap catches requiring two insecticide applications 14 days apart starting at 1,100 DD after biofix (or starting June 7 in Nashville).  (FH)

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)

Pheromone Trap Catches and Biofixes

Nashville (Davidson County) Pheromone Trap Catches for 2002

Biofix for RBLR in Davidson County estimated as March 14

Bradley County Pheromone Trap Catches

Codling moth biofix was April 14

Putnam County Pheromone Trap Catches

Obion County Pheromone Trap Catches

(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