Fruit Pest News
Volume 7, No. 10 May 17, 2006
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. Peach: Beware Resistance to DMI Fungicides in Brown Rot
3. Spray Equipment Web Site
4. Darselect Strawberry Will Rot
5. Grape Cane Gallmaker
6. Apple IPM: Sooty Blotch and Flyspeck
7. Don't Spare the Lime
1. Current Conditions
The weather has been wet and chilly for two weeks. In many areas, rains have occurred almost daily over this time. Strawberries have suffered. Incidentally, all berry rots are not Botrytis. Most of the rotting that you see during these extended rainy periods are general rots caused by opportunistic organisms on water-gorged berries. No spray program will help prevent that from happening. Covering the ground with straw or plastic has really paid off this year. Temperatures are supposed to approach normal over the next few days. (SB)
2. Peach: Beware Resistance to DMI Fungicides in Brown Rot
Peach growers in parts of Georgia and New York have been seeing a shift towards resistance to the DMI fungicides (Orbit, Indar, Elite, etc.) in the brown rot fungus. Growers in other states should be alert to this possibility in their areas. The DMI fungicides, also known as sterol inhibitors, are our mainstay for brown rot control. To discourage resistance development, consider these recommendations: (1) Alternate a DMI application with a strobilurin (Pristine, Abound). Pristine would be preferred because it consists of two active ingredients, one of which is a non-strobilurin. (2) Do not use the DMI's for blossom blight control. Reserve their use for the critical pre-harvest and harvest periods. (3) If conditions are not highly favorable for brown rot, Elevate (alone) or Topsin M plus captan should provide adequate control until conditions change, such as the harvest period drawing nearer. Brown rot sprays are begun at about 14 days prior to harvest and repeated at 7-day intervals. (SB)
3. Spray Equipment Web Site
You may be interested in this web site http://www.nysaes.cornell.edu/ent/faculty/landers/pestapp/grape.htm for information on spray equipment. The information sheets contained in it were written for the grape grower, but the information applies to other fruit operations as well. There is a work sheet for calibrating air blast sprayers, information on small sprayers for smaller plantings, and information on how spray volume affects pest control. Good information on sources of spray equipment is there, as well as other topics. (SB)
4. Darselect Strawberry Will Rot
Darselect strawberry was released two years ago and is being looked at by some growers. I have it in a small variety trial at Nashville. It is highly productive, but is proving to be quite susceptible to anthracnose and Rhizoctonia fruit rot. The incidence of these berry diseases is much higher for Darselect than for the other varieties present: Chandler, Camarosa, and Bish. The planting is in a matted-row system, which is more subject to Rhizoctonia fruit rot than is the plasticulture system, because of the difference in soil contact. Based on these results, I would reserve Darselect for plasticulture. If it is used in a matted-row system, generous use of straw mulch would be needed to prevent contact of the berries with the soil and thus reduce Rhizoctonia fruit rot. But when it comes to anthracnose, neither straw nor plastic mulch will appreciably reduce berry infections. (SB)
5. 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)
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. I conducted a trial last year in Williamson County. The New York system and the Kentucky/North Carolina system reached the threshold level at the same time and save one spray, the second cover spray. Control of sooty blotch and flyspeck by both of these programs was as good as the standard spray program. (SB)
7. Don't Spare the Lime
It keeps happening. We continue to see cases of low pH dashing hopes for a good yield. Over the last two weeks, I have found four cases of pH levels in the range of 4.2 to 5.0, on soil from problem areas of strawberry, blackberry, and squash fields. Soil pH can drop drastically after fertilizer applications, so be sure to test and know your pH before planting. It's too late to do anything about it, for that crop, when a problem appears. If it does appear, don't add any more fertilizer, because that will just make things worse! (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 2006 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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