Fruit Pest News

Volume 3, No. 16    June 24, 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:

    1. Peach: Brown Rot

    2. Peach: Fungicide Trial Results for Brown Rot

    3. Apple: Sooty Blotch/Flyspeck Prediction

    4. Cherry Leaf Spot

    5. Tree Fruit: Degree Days for Oriental Fruit Moth in Nashville

    6. Tree Fruit: Degree Days for Codling Moth in Nashville

    7. Tree Fruit: Pheromone Trap Catches and Biofixes

1. 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)

 2. Fungicide Trial Results - Brown Rot of Peach

The biological fungicide Serenade, consisting of the bacterium Bacillus subtilis, was compared to the standard brown rot fungicide Orbit in a peach trial at the Plant and Pest Diagnostic Center in 2000. Treatments were applied on 22 June, 29 June, and 5 July. Peaches were harvested on 28 June and 6 July. Fruit were evaluated for rots during a 7-day incubation period at room temperature following harvest. Treatments were applied with a CO-2 sprayer with an adjustable nozzle at 40 psi. The variety Redhaven was replicated three times in a randomized complete block design.

Fruit rot incidence at harvest time was not recorded, but the more severe measure of 7-day storage was used. As shown in the table below, Serenade was not effective against either brown rot or Rhizopus rot. Orbit provided control of brown rot. (SB)

* Data represent combined results from both harvests (28 June and 6 July).

After each harvest, approximately 40 fruit from each plot were stored at

room temperature and diseased fruit were counted and removed every

2-3 days for 7 days. Numbers within columns followed by same letter are

not significantly different (P=0.05).

3. Sooty Blotch/Flyspeck Prediction

Some of you may be interested in reducing the use of Benlate or Topsin M (benzimidazoles) for control of sooty blotch and flyspeck. If you don't need the benzimidazoles for control of other diseases, you can save money by applying them only when needed for control of sooty blotch and flyspeck. These materials will eradicate existing sooty blotch and flyspeck infections that are not yet visible. I have tested a predictive model developed by Sutton and Brown in North Carolina, and found that it saves Benlate sprays. A leaf wetness recorder is needed, or you can use the data obtained by other weather stations.

It works like this: The first symptoms of sooty blotch/flyspeck appear after around 275 hours of leaf wetness of 4 hours duration or longer, beginning with first rain that occurs 10 days after petal fall. Benlate or Topsin M should be added to the spray program at 225 hours. One of these materials is then included in the tank mix until harvest. In the mountains of North Carolina, symptoms have appeared as early as June 6 and as late as the third week of July. So, in a dry year, a grower routinely using Benlate or Topsin M could save 3 or 4  sprays. The weather station at Fletcher, NC expects to accumulate 225 leaf wetness hours this week. (SB)

4. Cherry Leaf Spot

Cherry leaf spot is a problem in wet weather wherever cherries are grown. Tart cherries are particularly susceptible. The disease first appears as small, purplish spots on the upper surface of the leaves. These spots eventually turn brown. Most spots are circular; however, when abundant, they often coalesce and form large, irregular dead patches. The spots later separate from healthy tissue and drop out, leaving a "shot-holed" appearance. Frequently, there are areas around the spots that remain green, giving the leaf a mottled appearance. Leaves turn yellow and fall off.

Fungicides used for cherry leaf spot are captan plus either Benlate or Topsin M in the early cover sprays. Sterol inhibitors used in the preharvest period for brown rot control are also effective against leaf spot. If there is wet weather after harvest, dodine or chlorothalonil may have to be used once or twice, beginning 2 to 3 weeks after harvest. (SB)

5. Degree Days for Oriental Fruit Moth in Nashville

On June 24, the degree day total in Nashville for Oriental fruit moth (OFM) was 1963.5 DD after biofix. 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 and fruit damage caused by the second generation is detected. (FH)

6. Degree Days for Codling Moth in Nashville

On June 24, the degree day total in Nashville for Codling moth (CM) was 1539.5 DD after biofix. 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. 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)

7. 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