Fruit Pest News
Volume 6, No. 9 May 17, 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. Observations
2. Grape Cane Gallmaker
3. Grape: Time for Botrytis Spray
4. Blackberry: Watch for Orange Rust
5. Apple: Fire Blight Breaking Out
6. Apple IPM: Sooty Blotch and Flyspeck
1. Observations
The weather has been dry for the last two weeks, interrupted only by some thunderstorm activity last Saturday. This is a boon for the strawberry growers, who are in the harvest period. Weather has been good for harvesting, with the exception of last week's few hot days. Strawberry anthracnose has managed to make itself felt. Despite the dry weather, I saw a patch last week that had an appreciable amount of anthracnose. First reports for the year during the past week: frogeye leaf spot of apple -- May 10, Davidson County; orange rust of blackberry -- May 11, Fentress County; rusty spot of peach -- May 12, Obion County. (SB)
2. Grape Cane Gallmaker
This small brown weevil (1/8 inch) moves to grapes in April from wooded or brushy areas, where it overwinters. The females chews holes lengthwise on the new shoots (beginning when shoots are 10-20 inches long) just above the node. An egg is placed in the hole next to the node. The shoot splits and a brownish swelling forms around the split which is 3/4 to 1 inch long. The weevils probably continue laying eggs into May. When the larvae are mature, they pupate within the gall and adults emerge by August. They seek overwintering sites by late summer and there is only one generation per year. Since most of the galls are formed beyond the grape clusters, yield loss is minor. The canes with galls can produce a crop next year. If pruning is desired, remove the canes with galls prior to mid-July to remove the immature weevils before they can become adults and move to their overwintering sites. (FH)
3. Grapes: Critical Period for Disease Control
The pre-bloom to early bloom period is a critical time for controlling black rot and other diseases. Early bloom is the time for the first application of a Botrytis fungicide. Botrytis bunch rot can be a problem in tight-clustered French hybrid or Vinifera varieties. With recent fungicide registrations, we have several classes of chemistry available to us in our efforts to combat resistance in the Botrytis fungus.
Scala 5SC is a new fungicide in a new chemical class for grapes (mode of action group 9). Scala, Vangard 75WG, Elevate 50WG, and Rovral 50WP are botryticides that do not provide black rot control, so an effective fungicide should be added to the tank. A sterol inhibitor (Nova, Elite, Bayleton, etc.) should be used because of their locally systemic activity. Since the sterol inhibitors are not effective against Phomopsis or downy mildew, an effective product such as mancozeb or captan should also be applied. The recently-labeled Pristine 38WDG is effective against all of these diseases, with only a slight sacrifice in Botrytis activity.
For Botrytis control, Vangard is used at 10 oz per acre at early bloom and at berry touch, veraison, or preharvest (20 oz per acre per year, 7-day PHI). See the label for precautions for use near aquatic areas. Elevate is used at 1 lb per acre at early bloom, bunch pre-close, and veraison, up to and including the day of harvest (up to 3 applications). Rovral 50WP may be applied at 1.5 to 2 lb per acre at early bloom, prior to bunch closing, veraison, and preharvest (7-day PHI). Although the Rovral label allows 4 applications, it is suggested that no more than 3 applications be made, in light of resistance problems that have occurred in other areas. Scala is used at 18 fl oz per acre when used alone and at 9 fl oz per acre in tank mixes (36 fl oz per acre, 7-day PHI). (SB)
4. Watch for Orange Rust in Blackberries
Orange rust can be very
destructive to blackberries and black raspberries. Most of the blackberry varieties
that we grow in Tennessee are moderately to highly resistant to orange rust. However,
some varieties, such as Navaho and Kiowa, are quite susceptible.
The fungus causes
plants to be so stunted and weakened that they produce little or no fruit. The fungus
is systemic in the plant, and is perennial inside the below-ground parts. Once a
plant is systemically infected by orange rust, it is infected for life. It is
for this reason that removal of infected plants is recommended, to prevent spread
of the fungus to other plants.
The
time to control orange rust is in the spring. Your queue to take action is the appearance
of weak, spindly new shoots with pale green to yellowish leaves. Such plants should
be removed before they begin to produce the orange-colored, blister-like pustules
on the lower leaf surface. The orange pustules contain spores that spread to other
plants and cause new infections that may not become apparent until the following
spring.
The fungicides Nova, Pristine, and Cabrio can be used for control of orange rust. These fungicides help prevent leaf infections. They will not cure a systemically-infected plant. Begin applications soon (the orange pustules should mature and release their spores sometime in the month of May) and continue every 10 to 14 days until mid-summer. For Nova, the maximum amount is 10 oz per acre per year, and the rate per application is 1.25 to 2.5 oz per acre. Cabrio is labeled at 11 - 14 oz per acre, Pristine at 18 - 23.5 oz per acre, and the sum of the number of applications for these two materials cannot exceed four. (SB)
5. Fire Blight Breaking Out
Fire blight appears to be severe this year. Blossom blight and shoot blight are appearing in several varieties, even Red Delicious, to some extent. It is too late to use streptomycin, except where secondary blossoms are open. Otherwise, streptomycin will not help you control this outbreak.
Should you cut out infected shoots? This has been debated for some time because of inconsistent results. The operation should be conducted as soon as possible after the fire blight strikes appear. If it is not possible to complete this task within a couple of days, it is probably best to let nature take its course. Remember that the job will need to be repeated as new symptoms appear.
The ugly stub method. The late Dr. Paul Steiner claimed that the old method of making a cut 10 to 12 inches below the symptom was useless, because the bacterium is usually systemic much further down the limb than that. It does no harm there, because of the natural resistance of the tree. Making a cut, however, breaches this natural defense, and a small canker almost inevitably forms around the cut (in Dr. Steiner's opinion). By making two cuts, the canker and its associated bacteria can be eliminated. The first cut is in 2-year-old wood, 2 to 4 inches above the supporting limb. A canker may form around the cut surface of the stub, but the second cut removes the stub at the supporting limb. This is done during the dormant season, when the bacteria are not active (paint or flag the stubs to make them easier to find).
Alternatively, you could wait until the dormant season and make one cut, and save a lot of work. But the ugly stub method allows those who wish to prune out fire blight during the growing season a method of doing so without leaving cankers around the cuts. If you feel you should prune at this time, the ugly stub method would probably be the way to go. (SB)
6. Apple IPM: Sooty Blotch and Flyspeck
One of the goals of this newsletter is to teach IPM techniques. Disease control is included in IPM, just as insect control is. We may be able to reduce the number of fungicide sprays by timing them well, with the help of predictive models that use information from weather-monitoring equipment.
Sooty blotch and flyspeck is a disease complex for which we have such a model. The only parameter it uses is hours of leaf wetness, caused by rain or dew. This disease is different from most, in that the speed at which infections develop is determined by wetness, not temperature. Using this model, you can eliminate two to four fungicide applications per year. Since the model does not apply to the summer rots, I don't recommend that you reduce your number of fungicide applications where these diseases are a problem. However, even in these locations, you can reduce the number of applications of Topsin M, Flint, or Sovran, since these materials are used primarily for control of sooty blotch and flyspeck.
Using a leaf wetness recorder, accumulated wetting hours (AWH) can be used to determine when a fungicide with post-infection activity (Topsin M, Flint, or Sovran) should be used to arrest the development of infections. Research in North Carolina showed that symptoms appear at 275-300 AWH and the workers suggested that a fungicide should be applied at about 3/4 of that time (225 AWH). Researchers in New York have suggested that the time for the fungicide application should be at about 1/3 of the incubation period (100 AWH), and the count is not begun until 21 days after the last scab spray, which is typically first or second cover. The New York system makes sense, because of the protection against sooty blotch and flyspeck provided by the last scab spray. In Kentucky, 175 AWH was suggested and, as in North Carolina, the count is begun at 10 days after petal fall. Do not include wetting periods of less than four hours.
How well does it work? In validation trials conducted in Iowa, Wisconsin, and Illinois, the warning system saved an average of 2.5 fungicide sprays per season. The researchers calculated that the savings would be $3,125 per year for a 50-acre orchard. (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, 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
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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