Fruit Pest News
Volume 10, No. 1 March 24, 2009
An 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. Of Cloudy Weather and Greenhouse Bedding Plants
3. Maneb Cancelled
4. Vegetable Disease Control Recommendation Changes for 2009
5. Fruit Disease Control Recommendation Changes for 2009
6. Other Disease Control Product News
7. Early-Season Apple Fungicide Sprays
8. Suggested Strawberry Fungicide Spray Schedule
1. Current Conditions
Redhaven peaches at Nashville are already at the late bloom stage, Golden Delicious apples are at pink tip, blackberries are at 1-inch shoot, early blueberry varieties are in bloom, and some grape varieties are at bud break while others are still fully dormant. Most of the state had frosts on Friday and Saturday mornings, requiring frost protection in strawberries. The week of overcast weather from March 9 - 16 caught greenhouse vegetable growers by surprise (see article below). There is an important peach spray coming up soon - the petal fall spray is needed for good control of catfacing insects and scab. Also, include copper or oxytetracycline if bacterial spot is a concern. Stormy weather is in the forecast for the next several days, but no frosts. (SB)
2. Of Cloudy Weather and Greenhouse Bedding Plants
As growers of greenhouse vegetable transplants can now attest, persistent cloudy weather can wreak havoc on a crop. The absence of sunshine during the week of March 9 - 16 caused damping-off (seedling disease) problems that, for some growers, will be difficult to overcome. Poor drying conditions caused by constant cloudy weather favor the activity of microbes that cause seedling disease problems, which include root and stem rots and a plethora of associated symptoms.
Such problems are sometimes best resolved by starting over, if the production schedule allows. Seriously affected seedlings cannot be saved, and treatments are limited for even mildly affected seedlings. Float systems seem to be bearing the brunt of the damping-off assault, and there are NO chemical treatments for these systems. Biocontrol products can be used, but keep in mind that these products work best as preventives and under low-disease pressure conditions.
The primary causal organisms for seedling diseases are Pythium, Rhizoctonia, and Fusarium. For Pythium control, Previcur Flex can be used, but only for tomatoes, peppers, leaf lettuce, and cucurbits. For Rhizoctonia control, Terraclor can be used only as a pre-seeding preventive treatment on tomatoes, peppers, broccoli, cabbage, cauliflower, and brussels sprouts.
Preventive sanitation steps are key for greenhouse production of vegetable plants, because of the lack of effective rescue products for seedling disease. The medium needs to be kept free of contamination during storage and filling of trays. Watch for dirty containers, surfaces, hands, seeding trays or anything else that the medium contacts, as these are probably the most common source of the causal fungi.
Base your watering practices on the need for water, rather than on a schedule, so that the medium does not stay too wet. During extended cloudy periods, be especially cautious of watering too frequently. And think twice about growing your transplants in a float system, as you will be helpless against seedling disease. (SB)
3. Maneb Canceled
Maneb fungicide, sold under the names Maneb and Manex, will no longer be available as the result of a business decision by United Phosphorous, the registrant who produces the technical material. Existing stocks are already in low supply. The closely-related EBDC fungicide mancozeb is still available. However, maneb is labeled for more vegetable crops than mancozeb, leaving an EBDC void on some crops such as pepper. The mancozeb label will soon be expanded to fill those needs, but the EPA is not expected to approve that supplemental label until late summer. Bravo 720 is a broad-spectrum protectant whose label was just expanded to include some of the crops losing maneb, such as pepper; however, Bravo (chlorothalonil) does not enhance the bacterial spot-controlling properties of copper as maneb does.
To fill the need for a tank mix partner for copper that will enhance its bacteria-controlling properties, plans are underway to pursue a Section 18 label for mancozeb on peppers. Several states, including Tennessee, are collaborating on a proposal for this label, and it is hoped that it will be approved by EPA in time for use season. I will keep you posted on the progress of this Section 18. (SB)
4. Vegetable Disease Control Recommendation Changes for 2009
5. Fruit Disease Control Recommendation Changes for 2009
6. Other Disease Control Product News
7. Early-Season Apple Fungicide Sprays
Scab sprays should be applied early to prevent primary scab infections and thus break the disease cycle. Also, it is important to avoid early infections on sepals (calyx), as these are difficult to detect and can provide secondary inoculum throughout the early part of the growing season.
There are several different strategies for scheduling scab sprays. The selection of a spray program (what fungicide to use and how often) depends on factors such as other disease organisms present and the ability to obtain good coverage of the trees with the sprays. If cedar-apple rust or powdery mildew are a threat, it is probably best to control scab with a sterol-inhibiting fungicide (Nova, Procure, Indar, or Rubigan), because control of all three diseases would be obtained. Tank mixing with mancozeb, metiram, or captan would improve the protectant ability and discourage the development of resistance to the sterol inhibitor (SI). Do not use captan within 2 weeks of an oil spray.
The 3- to 4-day curative (kickback) activity of the SI fungicides makes them useful for a first application in case some scab infections occurred prior to that time. The SI/protectant combination provides security in an extended spray program of up to 10 day intervals during primary scab season.
Where cedar-apple rust or quince rust are problems, mancozeb, metiram, or ziram should be used as the protectant, to be mixed with the SI. The strobilurin fungicides Flint and Sovran can be used in lieu of the SI's, but I recommend reserving these materials for use during the summer. They may only be applied 4 times per year, and they play a more valuable role during the summer than during the spring.
Powdery mildew inoculum may be abundant in blocks in which mildew was active last year, since we did not have the type winter needed to reduce inoculum. If weather conditions are favorable (cool, wet) for mildew, disease pressure could be high on susceptible varieties. Be sure to use an SI on such blocks, beginning at tight cluster to pink.
Note: If rust and mildew are not particular problems, it may be advisable to begin the season with two sprays of Syllit, Vangard, or Scala, rather than an SI. Although resistance to the SI's in the apple scab fungus has not been confirmed in the Southeast, it can occur, and some growers have experienced problems controlling scab with these materials. Other fungicides can be tank mixed with Syllit, Vangard, or Scala for rust (mancozeb or metiram) or mildew (sulfur or thiophanate methyl) control. (SB)
8. Suggested Strawberry Fungicide Spray Schedule
Below is a recommended spray schedule to follow for springtime disease control in strawberries. The exact design of a spray schedule can vary depending on disease control needs and products available. However, the principles illustrated below should serve as a good general guide for management of the two most common diseases, Botrytis and anthracnose.
| Application no. (At weekly intervals) |
Product |
Discussion |
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If anthracnose is not present |
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| 1 (early bloom) |
Elevate |
Botrytis is the primary target. This fungus is known for "getting used to" a fungicide and developing resistance to it. Try to include 3 chemical classes, as in the example, to keep Botrytis off-balance. Scala represents a 4th chemical class for Botrytis control. You can substitute it for any of the three. These materials can be applied in any order. |
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2 |
Switch |
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3 |
Pristine |
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| 4+ (through harvest) |
Repeat sequence; program may be relaxed somewhat during harvest |
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| If anthracnose is present |
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| 1 - 4+ (prior to harvest) |
Follow above schedule during bloom, with captan or thiram included in each application. |
The activity of anthracnose, if present, is low during bloom. The use of captan or thiram will provide adequate protection during this time. Thiram and captan are interchangeable because they are equally effective against Botrytis and also against anthracnose. Thiram has an advantage over captan in that thiram has a deer and rabbit repellency property. Thiram does not fit the harvest period because of a 3-day preharvest interval. Captevate® is a premix of captan and Elevate, and may be used in lieu of a tank mix. NOTE: The strobilurins (Quadris, Cabrio, Pristine) are limited to 5 applications per crop, either individually or collectively. For this reason, beware of using the strobilurins during bloom because you don't want to use up part of your allotment before the harvest period, which is a critical time for anthracnose control. The seasonal limit for Switch is 56 oz/A (4-5 applications). Use captan alone if the tank mix partner (Switch or the strobilurins) scheduled for that week has reached its limit. |
| Harvest period |
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1 |
Captan plus either Quadris, Cabrio, or Pristine |
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2 |
Captan plus Switch |
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3+ |
Repeat harvest sequence |
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(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
Soil, Plant and Pest Center
5201 Marchant Drive
Nashville, TN 37211
Copyright 2008 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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