Fruit Pest News

Volume 4, No. 11   May 27, 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. Peach Scab

    2. Disease Infection Periods

        2.a. Apple Scab

        2.b. Apple Sooty Blotch and Flyspeck

        2.c. Grape Powdery Mildew

        2.d. Grape Black Rot, Botrytis, and Downy Mildew

    3. Apple: Dogwood Borer

    4. Tree Fruit: Pheromone Trap Catches

1. Peach Scab

Scab symptoms are beginning to show in severe proportions in the orchard here at the office in Nashville. The grayish lesions are tiny now, but will enlarge and darken. Nothing can be done to prevent their development now. Furthermore, for varieties that are within 40 days of harvest, fungicide sprays will have no effect on the amount of scab at harvest. This is because peach scab has a 40-day latent period, which means that symptoms do not appear for 40 days after infection. Thus, any infections that may occur from here on will show only on fruit that mature later than 40 days afterward. Fungicides have no effect on these developing infections. (SB)

2. Disease Infection Periods

Infection periods and other disease progress reports for the first 26 days of May are presented below. The weather data upon which this information is based was collected on a Spectrum WatchDog system placed in Franklin, TN. This information may familiarize you with this method of timing the application of fungicides in an effort to improve control while reducing the number of sprays. Each disease is based on a different "model," or system of predicting infection. (SB)

2.a. Apple Scab

2.b. Apple Sooty Blotch and Flyspeck

Accumulated wetting hours (AWH) can be used to predict the appearance of sooty blotch and flyspeck on apple fruit, and the time at which a fungicide spray is needed for control. With this method, unnecessary applications of fungicides for control of these diseases can be avoided. Research has shown that sooty blotch and flyspeck will appear after about 260 - 300 AWH following the biofix of 10 days after petal fall. Wet periods are caused by rain or dew. Those wet periods of less than 4 hours are not included in this model. Benlate, Topsin M, Flint, and Sovran appear to be effective in arresting fungal development if used within 100 AWH after infection. Assuming the last scab fungicide application provides about 3 weeks of protection against sooty blotch, the need to use one of these fungicides may not occur for 6 weeks.

In the first 26 days of May, 121 wetting hours have accumulated at the station. (SB)

2.c. Grape Powdery Mildew

The risk for infection by conidial spores has been heavy throughout the month. With this predictive model, the infection risk for a given day is based on previous days' conditions. Once the infection risk develops to the heavy category, it can move down to the medium category only after several days of very cool or very hot weather. The index increases by 20 with each day having 6 hours between 70 F and 85 F. The index decreases by 10 on days with less than 6 hours between 70 F and 85 F, and on days with a maximum temperature greater than 95 F. The risk is determined by the following index values:

2.d. Grape Black Rot, Botrytis Bunch Rot, and Downy Mildew

* Black rot infection risk begins at a value of approximately 1.00.

3. Dogwood Borer

Dogwood borer on apples is a problem, especially on grafted trees. The moths lay their eggs on rough bark areas such as burr knots and graft unions. They feed beneath the bark and can girdle the tree.

In late April, the dogwood borer moths start to emerge. They do not all emerge at the same time. There is a peak emergence in late April and early May followed by a month or so of lower levels of emergence. Another peak emergence occurs in mid-July. One control option is to brush undiluted latex paint on the lower trunk before egg laying begins in the spring. This is not as effective as applying insecticide so I would still recommend applying a preventive insecticide spray to the bark in mid- to late-May.

Spray with Lorsban 50W, Lorsban 4E, Thiodan 3EC, Phaser 3EC or Asana XL. Lorsban is the preferred spray because of the long residual. The insecticide should be applied with a handgun sprayer from no more than 4 feet or with a shielded sprayer to prevent drift on foliage or fruit. (FH)

4. 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