Fruit Pest News
Volume 8, No. 9 May 8, 2007
A weekly, online newsletter whose goal is to provide all interested persons with timely information on diseases and insects of commercial fruit and vegetable crops 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 Disease Update
3. Critical Period for Grapes
4. New Formulation of Kocide
5. Error for Sevin in Strawberry IPM Guide
1. Current Conditions
Some shower activity has helped, but we are still basically in a moisture deficit mode. Last spring was considered a dry one, but consider these facts: The rainfall totals for all Tennessee reporting stations for the March through April period of 2006 was 86.6% of average, whereas the same period for 2007 was 46.5% of average. Dry springs such as this can portend of upcoming problems with certain insect-transmitted diseases such as tomato spotted wilt virus and the aphid-borne mosaic viruses. These diseases are difficult to control with insecticides and may justify the planting of resistant varieties.
Strawberry harvest seems to be going well for most farms. The first state report for strawberry anthracnose for the year was May 1, in Montgomery County. It's good to see some varieties of blackberries and raspberries blooming nicely. (SB)
Apple scab: The first state report of apple scab for the year was on May 8 in Davidson County. Hopefully, you’ve been able to stay ahead of primary scab this year. If you have scab in blocks with little crop, it would be best to get the lesions under control before you reduce or eliminate fungicide applications from the block. Scab could defoliate trees early and cause reduced winter hardiness and a high potential inoculum level for 2008. Many orchards probably had a full primary apple scab program before the freeze, and scab should not be a problem for the 2007 season, even if you are seeing a few lesions. Once primary scab season is over, which should be soon, you can reduce further control measures if you have primary scab under control.
Powdery mildew: Just as with apple scab, powdery mildew left uncontrolled can lead to reduced vigor and winter hardiness. As with apple scab, most commercial blocks have had some mildewcides in their programs already this year, so mildew might not be of concern in most blocks with no crop. Although mildew does not cause the drastic defoliation that scab does, it can reduce winter hardiness of buds. Leaving it uncontrolled can lead to a higher inoculum potential for the 2008 season. Sulfur will provide inexpensive control of powdery mildew and, as a bonus, provides control of sooty blotch and flyspeck, if fruit are present. Do not apply sulfur within two weeks of an oil spray.
Cedar-apple rust: Severe leaf rust infection can lead to premature defoliation and weakening of trees. Many materials applied to control primary scab will provide some control of leaf rust. Captan is weak against rust. The cedar galls are almost depleted of spores. If you have applied a rust fungicide recently, it should get you through the rust period.
Fire blight: There have been some cases of fire blight. They seem to have begun in blossom clusters prior to the freeze. It's doubtful that the freeze caused increased fire blight severity. The presence of blossom blight increases the risk of shoot blight through increased inoculum. Vigorous shoots are more likely to be susceptible to fire blight, so a shoot blight epidemic is a real possibility in a no-crop year because of the added shoot vigor. Where fire blight is active on no-fruit blocks, applications of low rates of copper (0.2-0.6 lb of metallic copper per acre, depending on tree size) are recommended. If some fruit russeting can be tolerated, copper can also be useful in blocks that have fruit. Recommended coppers include Cuprofix, Kocide, and C-O-C-S. (SB)
3. Critical Period for Grapes
Secondary buds are now at the pre-bloom stage of growth, i.e., the 10 to 14 days prior to the beginning of the opening of the blossom buds. Apply a black rot fungicide now. This is the most critical period for control of black rot disease. If black rot can be controlled during the immediate pre-bloom period, bloom, and immediate post-bloom stages of growth, successful control should be possible throughout the season.
Traditionally, it has been thought that successful black rot control required beginning the spray program at the 1- to 2-inch shoot stage. Recent research conducted in New York and here in Tennessee has shown that this is not the case, because the black rot fungus does not become active until later. This year, vine growth stages are highly variable because of the freeze. Some buds are just beginning to emerge, while other shoots are at the pre-bloom stage. Use the more advanced stages to guide your spray decisions -- most pests are now active because of the late date.
Choose a fungicide(s) based on the history of disease problems in the vineyard, using an efficacy table such as the one in the regional spray guide. 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 theses diseases. The sterol inhibitors or sulfur should be used where powdery mildew is expected. Strobilurins have the broadest spectrum of activity, but are more expensive and are limited to 4 applications per year. (SB)
4. New Formulation of Kocide
Kocide is a well-known copper product that is used for control of bacterial and fungal diseases of fruit and vegetable crops. DuPont Crop Protection has introduced a new formulation of Kocide 3000 for the 2007 season. This formulation has a finer copper hydroxide grind than previous Kocide formulations. Kocide 3000 has more copper ions available to provide disease control at a lower rate. The environmental benefit is less metallic copper applied per acre.
According to the company, improvements made with Kocide 3000 include:
5. Error For Sevin in Strawberry IPM Guide
The editors of the regional IPM guide, http://www.smallfruits.org/SmallFruitsRegGuide/Guides/2006/StrawberryIntegMgmtGuidefina12Jan06.pdf , have issued the following correction in the guide: All uses for Sevin should indicate a 7-day PHI and not a 1-day PHI. If you have printed this manual out, make this change on page 7 (cutworms), page 8 (strawberry clipper), and page 20 (sap beetle and slugs and snails). (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 2007 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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