Fruit Pest News

Volume 6, No. 13  June 14, 2005

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 Update

    2. Brown Rot of Peach and Other Stone Fruits

    3. Apple: Summer Disease Control Program

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

    5. Tree Fruit: Plum Curculio

    6. Tree Fruit: Pheromone Trap Catches 

1. Apple Sooty Blotch and Flyspeck Update

The AWH's jumped this week in Middle Tennessee, with extended rainy period of Thursday through Sunday creating 57 hours of wetness. The table below shows the wetting hours that have accumulated since the biofix for each of the two models discussed in previous issues. First cover was considered to be 10 days after petal fall. As you can see, the target time to spray was reached on the same day (Sunday) with each model. The second cover spray will be applied at the same time for each of these models, and the results will be compared to a program in which the usual spray program was followed. That program is now at 3rd cover, so exactly one spray was saved by the models in this case. (SB)

AWH = accumulated wetting hours

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, 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)

3. Apple: Summer Disease Control Program

Your summer disease control program is, no doubt, well underway. The so-called summer diseases take a greater toll on Tennessee apple production than the spring diseases. The summer diseases are fueled by a continuing source of overwintered inoculum, and there are fewer effective fungicides from which to choose. Furthermore, it is more difficult to obtain good spray coverage during the summer than during the spring because of more dense foliage, fruit clustering, and limbs drooping under heavy crop loads.

Your choice of fungicides will depend to some extent on what diseases have historically been a problem in your orchard. If bitter rot has been a problem, captan should be a major component of your summertime spray program. Flint also performs well against bitter rot. If white rot has been a problem, captan or Topsin M should be relied on heavily. For sooty blotch and flyspeck, be sure to include Topsin M or a strobilurin (Flint, Sovran). Strobilurins are also a valuable component of a program if scab is still active. In Golden Delicious blocks, it is a good idea to include ziram or thiram to help protect against necrotic leaf blotch (see article below). Mancozeb provides good control of most summer diseases, but cannot be used within 77 days of harvest when used at the 3/4 lb per 100 gallon rate.

Captan has had a 4-day re-entry interval in the past. The re-entry interval has been changed on the Captan 80WDG label, allowing workers to enter the treated area in 24 hours.

Remember that management of diseases with fungicides is improved if cultural practices that reduce inoculum and enhance coverage are used. (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.

5. Plum Curculio

Plum curculio larvae are whitish and leggless with a brown head. The body is bow-shaped and a bit narrower at both ends. Mature larvae were found from unsprayed trees while pitting sour pie cherries this past weekend. There is a single larva per fruit and these fully mature larvae were 9 mm long. They will soon drop from the fruit to pupate in the top one or two inches of soil. Each larva excavates a small cavity in the soil and molts into the pupal stage about two weeks later. After an additional two weeks in the pupal stage, the adult emerges and the summer generation flies to the trees to feed on the fruit. Thus, the adult plum curculios should be emerging from the soil in a little over a month. On apples, the feeding damage from these summer adults appears as a small round hole through the skin of the fruit (about the size of a hole that you could make with the tip of a ball point pen). They use their curved snout to eat out a small cavity in the flesh of the fruit beneath the hole. (FH)

6. Pheromone Trap Catches

Nashville (Davidson County)
Oriental Fruit Moth (OFM), Redbanded Leafroller (RBLR), Obliquebanded Leafroller (OBLR), Codling Moth (CM), Grape Berry Moth (GBM), Variegated Leafroller (VLR), Black Cutworm (BCW)

* Biofix for RBLR in Davidson County estimated as occurring on March 12.
**Biofix for GBM in Davidson County is April 4.
***Biofix of BCW in Davidson County on April 12.
****Biofix for OFM in Davidson County on April 12.
*****Biofix for OBLR in Davidson county on May 13.

Bradley County

*Biofix for RBLR in Bradley County on March 12.
**Biofix for OFM in Bradley County on March 25.
***Biofix for CM in Bradley County on April 16.


Putnam County

*Biofix for RBLR in Putnam County on March 21.
**Biofix for OFM in Putnam County on April 6.
***Biofix for OBLR in Putnam county on May 11.

Obion County

*Biofix for RBLR in Obion County estimated to be on March 12 (trap not out early enough).
**Biofix for OBLR in Obion County on April 4 (waiting for confirmation since this was much earlier than other locations).
***Biofix for CM in Obion County on April 4 (waiting for confirmation).
****Biofix for OFM in Obion County on April 11.
*****Biofix for VLR in Obion County on May 3 (waiting for confirmation).

Other Pheromone Trap Catches for Davidson County
Diamondback Moth (DBM), American Plum Borer (APB), Cabbage Looper (CL), Armyworm (AW), Sod Webworm (SWW)

* Biofix of DBM in Davidson County probably earlier than April 20
**Biofix of APB in Davidson County probably earlier than April 20
***Biofix of CL in Davidson County on April 29
****Biofix of AW in Davidson County on May 2
*****Biofix of SWW in Davidson County on May 9

Knox County*
Tufted Apple Budmoth (TABM)

*The Knox County traps were put out by a first time cooperator still learning to identify. the moths. Correspondingly, the trap counts for May 2 remain suspect. We do know that the traps were put out too late to accurately determine a biofix for Oriental fruit moth (OFM) and redbanded leafroller (RBLR). The obliquebanded leafroller (OBLR), codling moth (CM), variegated leafroller (VLR) and tufted apple budmoth (TABM) catches are possible biofixes or at least early in their moth flights.

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

Copyright 2005 The University of Tennessee. All rights reserved. This document may be reproduced and distributed for nonprofit educational purposes provided that credit is given to University of Tennessee Extension.

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