Fruit Pest News
April 9, 2001
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. What a Difference a Week Makes!
2. Strawberry Anthracnose Reminders
3. Apple: Fire Blight Alert
4. Grape: Early Season Disease Control
1. WHAT A DIFFERENCE A WEEK MAKES!
Temperatures did an about-face, swinging from unseasonably cool to hot. Apple trees that spent 15 days in the tight cluster stage of growth (because of the extended cool weather) passed through the pink tip stage in 1 day. The beginning of bloom is a significant event in the course of fire blight control (see article below). Matted-row strawberries went from no blossom buds visible to open blooms in a few days. Only 1 blueberry cultivar out of a planting of 10 cultivars at the Plant and Pest Diagnostic Center was in bloom on April 4 . . . 9 of the cultivars are in bloom today. Delicious and Golden Delicious are in full bloom. In East Tennessee (Sevier County), a block of Braeburns are in full bloom, and other cultivars are on the edge of bloom.
Damage from the freezes of late March appears to have been light. Frost protection on plasticulture strawberries really paid off. On matted-row strawberries, I have seen freeze-damaged blossoms that weren't even visible as buds when the low-20's temperatures occurred, but they are few in number. Apple and peach leaves are emerging crinkled because of the freeze that occurred while they were in the bud.
Rainfall has been light, even during all the overcast weather we had. This will help us with diseases such as gray mold of strawberry and cedar-apple rust of apple. Cedar galls here at the Center have still not produced the orange tendrils, indicating spore release, but are poised to do so during the next shower . . . the brown "horns" are evidence. (SB)
2. STRAWBERRY ANTHRACNOSE REMINDERS
For those who may not have gotten the word, Tennessee has again been granted a Section 18 label for the use of Quadris fungicide for control of anthracnose. Tennessee Farmers Cooperative has distributed copies of the label, which must in the possession of the user when applying the product, to their dealers. Copies can also be obtained from me.
If anthracnose inoculum is present in the field, these warm days and nights we are having could cause infections of the blossom clusters or petioles if moisture is available. It has been dry in most areas, but there are some chances for some thundershowers this week. An application of Quadris or another anthracnose fungicide (captan or thiram) at this time is advised if you think that anthracnose may be present in your field.
Quadris can be applied at 7 to 14 day intervals, no more than 3 consecutive applications before alternating to another anthracnose fungicide for at least 1 application. If rainfall activity increases, protection against both anthracnose and Botrytis may be needed as often as once per week. Quadris does not have adequate activity against Botrytis, and should be tank mixed or alternated with effective materials.
If apple trees are located near your field, remember that Quadris is extremely phytotoxic (burns) certain apple varieties. Use extreme care to avoid drift to apple trees, and do not use spray equipment that has been previously use to apply Quadris to spray apple trees. Even trace amounts can cause unacceptable phytotoxicity. (SB)
3. FIRE BLIGHT DISEASE ALERT
Warm weather and blooms don't mix. Not for the apple grower, anyway. The warm weather of the last few days and nights and predicted for the next several days and nights has caused an explosion of the fire blight bacterium on the surfaces of the trees, according to the MaryBlyt program for fire blight management. All that is needed for infection is an open bloom and moisture. And a dew may be all that is needed to satisfy the moisture requirement.
Fortunately, things have been pretty dry during this spate of warm weather. The MaryBlyt program that I am operating here at the Plant and Pest Diagnostic Center indicates that infection occurred yesterday, April 8, as did a program being operated by a cooperator in East Tennessee. I suspect this happened in other areas, also. If you were caught unprepared by the sudden warm temperatures and didn't get your streptomycin spray on your susceptible varieties, you may still be safe. The dew that occurred yesterday and triggered the infection warning on the program was only a moderate one, and may not have caused much infection. Also, last year was a light fire blight year for many areas, and inoculum may be low. But I would advise spraying susceptible varieties now. The forecast is for continued very warm weather, and dews can be unpredictable.
The MaryBlyt program indicates infection when 4 conditions occur: (i) any blooms are open; (ii) rain or dew occurs; (iii) the average temp for the day is 60 or above; and (iv) there have been enough accumulated heat units to allow colonization of the blossoms by the bacteria. The risk of infection is rated as "low," "medium," "high," or "infection." These ratings correspond to any one, two, three, or four of the previously-mentioned conditions, respectively. All the program needs from the operator is the high and low temperature for each day beginning at green tip, and rainfall or dew for each day beginning at first open bloom. (SB)
4. EARLY SEASON GRAPE DISEASE CONTROL
Grapes have begun growth and many are at the 1-inch bud stage (and growing rapidly) at which the first black rot spray is recommended. Other diseases such as Phomopsis cane and leaf spot and powdery mildew can also begin activity at this stage of growth. Choose a fungicide(s) based on the history of disease problems in the vineyard, using an efficacy table such as the one on page 17 in the small fruit spray guide, PB1197. Sterol inhibitor fungicides can be used in the early sprays, but keep in mind that they do not provide control of Phomopsis or downy mildew. The multi-site inhibitors (e.g. captan, mancozeb, maneb, ziram) are better choices for control of Phomopsis and black rot. The sterol inhibitors can be tank mixed with the multi-site inhibitors to provide control of powdery mildew and systemic control of black rot. Strobilurins have the broadest spectrum of activity, but are more expensive and are limited to 4 applications per year.
Considering the arsenal of fungicides available to the grape grower, it is a good idea to become familiar with the classification of the products, as listed on page 34 of the spray guide. (SB)
The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm
Contacts:
Steve Bost, Professor and Extension Plant Pathologist
Frank Hale, Associate Professor and Extension Entomologist
Both authors available at:
615-832-6802
fax 615-781-2568
Plant and Pest Diagnostic Center
5201 Marchant Drive
Nashville, TN 37211