Fruit Pest News

Volume 6, No. 3  April 5, 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. Current Conditions

    2. Apple: Early-Season Fungicide Sprays

    3. Strawberry Fungicide Reminder

    4. Strawberry Plant Dip for Anthracnose Control

    5. Vegetables: Changes in Disease-Control Recommendations for 2005

    6. Fruit Insect Photographs

    7. Tree Fruit: Pheromone Trap Catches and Biofixes

1. Current Conditions

Plant development continues to run slightly behind normal, but the cool weather has not seriously damaged the strawberry, peach, or blueberry crops through frost. At Nashville, Golden Delicious apple trees are at tight cluster, Red Delicious is at green tip, and Tifblue blueberries are beginning to bloom. Rainy weather with seasonal temperatures are forecast for the next week. (SB)

2. Early-Season Apple Fungicide Sprays

Many trees are now at tight cluster. For many orchards, this is the time for the first fungicide application. Scab control at this time is a must. If scab was abundant last year, the first application should be made at green tip. Scab should be treated early to prevent primary scab infections and thus break the disease cycle. Also, it is important to avoid early infections on sepals (calyx), as these are difficult to detect and can provide secondary inoculum throughout the early part of the growing season.

There are several different strategies for scheduling scab sprays. The selection of a spray program (what fungicide to use and how often) depends on factors such as other disease organisms present and the ability to obtain good coverage of the trees with the sprays. If cedar-apple rust or powdery mildew are a threat, it is probably best to control scab with a sterol-inhibiting fungicide (Nova, Procure, or Rubigan), because control of all three diseases would be obtained. Tank mixing with mancozeb or captan would improve the protectant ability and discourage the development of resistance to the sterol inhibitor (SI). Do not uses captan within 2 weeks of an oil spray.

The 3- to 4-day curative activity of the SI fungicides makes them useful at tight cluster in case some scab infections occurred prior to that time. The SI/protectant combination allows you to space the applications 7 to 10 days apart.

Where cedar-apple rust is a problem, mancozeb or ziram should be used as the protectant, to be mixed with the SI. The strobilurin fungicides Flint and Sovran can be used in lieu of the SI's, but I recommend reserving these materials for use during the summer. They may only be applied 4 times per year, and they play a more valuable role during the summer than during the spring.

Overwintering of powdery mildew is highly dependent on winter weather. Since we did not have prolonged cold temperatures this winter, there should be abundant inoculum in orchards that had mildew last year. If weather conditions are favorable (cool, wet) for mildew, disease pressure could be high on susceptible varieties. Be sure to use an SI on such blocks (see previous paragraph regarding the use of strobilurins). (SB)

3. Strawberry Fungicide Reminder

In this strawberry bloom season, remember to pace yourself on the use of strobilurin fungicides (Quadris, Abound, Cabrio, Pristine). They are limited to 5 applications per crop, either individually or collectively. The most important role of this class of fungicides in strawberry production is control of anthracnose, and the critical time for anthracnose control is the harvest period. If your field has a history of anthracnose, you should reserve most of your allotment of strobilurins for the harvest period. Why? -- If you apply a strobilurin every 7 days during harvest, with a maximum of 2 consecutive applications before rotating, you could make 4 applications of strobilurins during a 5-week period. Granted, Switch is just as effective against anthracnose, but it, too, has a 5-application limit per crop, and is needed for Botrytis control during bloom.

If anthracnose is suspected of being present, I would minimize the use of strobilurins during bloom. Captan or thiram, tank-mixed with the Botrytis materials, should handle the light anthracnose activity that is likely to occur during bloom. (SB)

4. Strawberry Plant Dip for Anthracnose Control

Strawberry anthracnose sometimes enters a field on infested plants. The causal fungus may be present on the crown, root, and stem surfaces, or it may be internal, as infections that are not yet visible. Research has shown that the incidence of anthracnose in the field can be greatly reduced if transplants are dipped in appropriate treatments before planting, to kill the surface spores. These treatments will not rid the plants of anthracnose infections, because they are internal and beyond the reach of the chemicals.

The azoxystrobin products, Quadris and Abound, are labeled for use as strawberry plant dips. Wash soil off roots before dipping. Mix 5-8 fl oz of Quadris or Abound per 100 gal of water. Dip plants by immersing completely for 2 to 5 minutes. Plant treated plants as quickly as possible. The hydrogen dioxide product, OxiDate, is also labeled for this use. Mix 1 gal per 100 gal of water, immerse, remove, and allow to drain. Do not rinse. Plant as soon as possible after treatment. Use personal protective equipment as specified by the labels when dipping. (SB)

5. Vegetables - Changes in Disease Control Recommendations for 2005

The following changes were made to the disease control section of the UT Publication 1282, Commercial Vegetable Disease, Insect and Weed Control.

                                                * MOA Group - Mode of action group, also known as resistance management group.

(SB)

6. Fruit Insect Pest Photographs

A Michigan State University web site I gave earlier in Fruit Pest News is no longer working. Fortunately, a much better gallery of insect images can be found at a West Virginia University site. The address is:
http://www.caf.wvu.edu/kearneysville/wvufarm9.html (

FH)

7. Pheromone Trap Catches and Biofixes

Pheromone traps are used to determine the starting point of degree-day models (biofix) and to guage the intensity of populations of fruit pests. The degree-day model predicts percent of adult emergence and egg hatch for each of the generations of the pest. The biofix date is determined using pheromone traps to detect the first sustained catch of two or more of the specific pest moths in the spring.

In Bradley County, the biofix for redbanded leafroller was March 12. In Nashville, the RBLR biofix was March 16.

In Bradley County, the biofix for Oriental fruit moth (OFM) was March 24 (28 moths caught in four traps). In Nashville, one OFM was caught on April 4. When I catch two or more, I will set the biofix.

The grape berry moth (GBM) biofix was set at April 4 since four moths were caught in Nashville.

The biofix in Obion County for OBLR and CM has been tentatively set for April 4 until it can be confirmed. The RBLR trap was put out too late to set a biofix for RBLR. It is estimated as being March 12. (FH)

Nashville (Davidson County) Pheromone Trap Catches for 2005
Oriental fruit moth (OFM), redbanded leafroller (RBLR), obliquebanded leafroller (OBLR), codling moth (CM), grape berry moth (GBM), variegated leafroller (VLR)

* Biofix for RBLR in Davidson County estimated as occurring on March 12.
**Biofix for GBM in Davidson County is April 4.

Bradley County Pheromone Trap Catches for 2005

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


Putnam County Pheromone trap Catches for 2005

*Biofix for RBLR in Putnam County on March 21.


Obion County Pheromone Trap Catches for 2005

*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).
***Biofix for CM in Obion County on April 4 (waiting for confirmation).

(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, 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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