Fruit Pest News

Volume 5, No. 7  April 27, 2004

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. Address Correction for Small Fruit Spray Schedules

    3. Apple: First Fire Blight

    4. Apple: Cedar-Apple Rust

    5. Disease Infection Periods

        5.a. Fire Blight of Apple

        5.b. Apple Scab

        5.c. Grape Black Rot

1. Current Conditions

We just completed a five-day period of rain. The frequent showers and storms coincided with a period in which disease organisms were beginning to become active, such as black rot of grape and cedar-apple rust of apple. There have been no frosts lately, and most crops are looking good. At Nashville, blackberries are blooming, apples are at petal fall to first cover, and peaches are at shuck fall. (SB)

2. Address Correction for Small Fruit Spray Schedules

In last week's issue of Fruit Pest News, the article "Designing an Early-Season Fungicide Spray Program for Grapes" contained an incorrect link to the Small Fruit Spray Schedules. The correct URL is http://www.utextension.utk.edu/publications/pbfiles/PB1197.pdf . A printed copy can also be obtained from your county Extension office. I apologize for the error, especially since the link used took you to the vegetable publication, which takes a long time to download! (SB)

3. First Fire Blight

The first report of fire blight comes from southeast Tennessee, on April 23. It was observed on Golden Delicious and Jonagold, but not on Gala. Look for wilting of shoots or side spurs associated with blossoms, where the bacteria enter. Most apple cultivars are now at petal fall and are no longer subject to blossom infections, unless tag-on blooms remain. (SB)

4. Cedar-Apple Rust

Perfect weather for cedar-apple rust infections occurred on Wednesday, April 21 through Sunday April 25. The intermittent showers and constant cloudy weather promoted production and dispersal of the spores. Also, light rains are less effective than heavy rains for washing spores out of the air. Apples are at a very vulnerable stage of growth for infection of leaves and fruit by this fungus.

The sterol inhibitors have very effective kick-back activity. While the length of curative activity is listed as 3-4 days for most sterol inhibitor fungicides, research has shown that one of them, Nova, has as much as 7 days of curative activity. If you have not already applied one of these materials since the rains, you should do so right away. Use a full labeled rate and tank mix with a protectant fungicide. (SB)

5. Disease Infection Periods

Infection periods and other disease progress reports for the first 25 days of April 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)

5.a. Fire Blight of Apple

The table below shows some of the results produced by the MaryBlyt program. Infection occurred on April 8 and symptoms of that infection occurred on April 22. The MaryBlyt program uses high and low temperatures and rain or dew for each day.

* Stage of growth: P = pink tip, B = bloom, PB = post-bloom (all petals fallen)

** B = blooms open, I = Inoculum potential > 100% (determined by accumulated temperature), W = wetting event, T = avg.daily temp > 59°F

5.b. Apple Scab

The results of two predictive models, the modifed Mills and the Cornell, are shown below. Both models are based on the length of time the leaves stay wet at each temperature. These models use temperature and leaf wetness data (not shown). These models can be used to apply curative fungicides after infections occur or, by entering weather forecasts, to time fungicide applications for best effect. (SB)

5.c. Grape Black Rot

The grape data uses the Spotts model, which is based on the length of time the leaves stay wet at each temperature. This model uses temperature and leaf wetness data (not shown). These models can be used to apply curative fungicides after infections occur or, by entering weather forecasts, to time fungicide applications for best effect. (SB)

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