Fruit Pest News

In This Issue:

1. Current Crop Development
2. Strawberries: Quadris Cleared For Use By Tennessee Growers
3. Apples: Early-Season Disease Control
4. Status of Methyl Bromide and Replacement Options
5. Strawberries: Phytophthora Disease Control
6. Apples: Redbanded Leafroller Moth Activity

1. CURRENT CROP DEVELOPMENT

This morning's (March 26) 20 degree temperatures in Nashville, and similar temperatures predicted for tomorrow morning will take their toll on peaches. The Redhavens at the Plant and Pest Diagnostic Center are currently in bloom. Most blueberry cultivars have not quite begun to open their blossoms. The weather has been very cool and has slowed bud development. The very early-blooming blueberry cultivar O'Neal has just begun to bloom. Premier and later-blooming cultivars have not yet opened, but could still lose some buds at these temperatures. The apples here appear to be safe, with Red Delicious still at green tip, and Golden Delicious at tight cluster. (SB)

2. QUADRIS CLEARED FOR USE BY STRAWBERRY GROWERS IN TENNESSEE

Tennessee's application for a Section 18, specific exemption for Quadris fungicide on strawberries for anthracnose control has been approved by the EPA. We are grateful to the Tennessee Department of Agriculture and to the EPA for their prompt response to our request. Anthracnose causes losses somewhere in the state almost every year. The special label is effective immediately and expires October 15, 2001.

The labeled rate is 6.2-12.4 fluid ounces per acre, with no pre-harvest interval. The common rate is 9-10 fl. oz. per acre. Most strawberry growers use 100 gallons of water per acre. If you apply more than 100 gallons of water per acre, avoid diluting the concentration to less than 6 fl. oz. per each 100 gallons. For example, if you use 150 gallons per acre, use at least 9 fl. oz. of Quadris per acre.

Quadris is labeled at 7-14 day spray intervals, up to 4.6 pints (1.2 lbs. a.i.) per crop. The critical time for anthracnose control is during harvest, because of the susceptibility of the fruit. However, the occasional early appearance of hot, wet weather (favorable for anthracnose) justifies bloom-time applications of anthracnose fungicides as a preventive. These applications do not have to be Quadris, however. Captan or thiram should provide an acceptable level of control during the pre-harvest period while providing better Botrytis control than Quadris does. Quadris can be tank mixed with captan or thiram, but the manufacturer of Quadris discourages tank mixes and requires that Quadris not be applied more than 3 consecutive times before alternating to another fungicide.

There is another reason that there is no rush to purchase and apply Quadris: Copies of the Section 18 label, which must be in the possession of the user at the time of application, have not yet been distributed to the dealers by the manufacturer. (SB)

3. EARLY-SEASON DISEASE CONTROL IN APPLES

Although the first half of the winter was unusually cold, it probably was not sufficient to reduce significantly the overwintering populations of important apple pathogens. Following are some reminders for disease-control tasks for the early season.

Fire blight and blister spot: Late dormant applications of copper materials such as Kocide and C-O-C-S are known to be helpful in managing fire blight. I am not aware of any data indicating that such applications help with control of blister spot of Mutsu, but it stands to reason that they would. Both diseases are caused by bacteria that build up on the surfaces of the tree, a phenomenon referred to as epiphytic growth. The epiphytic portion of the population is vulnerable, because it can be reached with copper sprays. Copper can be harsh to the crop, and should not be applied after 1/4 to 1/2-inch green tip, a stage of growth that many trees may be past by now. Both pathogens live as epiphytes on resistant as well as susceptible cultivars and can move among them. If either of these diseases was present last year, you should spray blocks of resistant trees adjacent to susceptible trees. This strategy differs from that of streptomycin, which is intended only to protect susceptible plant tissues (the blossom for fire blight, the fruit for blister spot). The use of copper reduces the pathogen's exposure to streptomycin, thus helping to thwart resistance problems.

Apple scab. How soon you should begin sprays depends on how much scab you had last year. If you had considerable scab pressure last year, you should make your first spray at green tip. It is important to avoid early infections on sepals (the green part of the blossom bud), as these are difficult to detect and can provide conidial inoculum throughout the early part of the growing season. If you use a sterol inhibitor (Nova, Rubigan, Procure), use a tank mix partner such as captan or mancozeb to discourage resistance. However, do not use captan within 2 weeks of an oil spray. Given the limitations on the number of allowed applications of Sovran and Flint (4 per year), it may be advisable to forego using these materials in the spring. These strobilurin materials play a more vital role during the summer.

A fungicide spray at green tip is not necessary if you are sure that scab was not a significant problem last year. A broad spectrum tank mix should be applied at tight cluster to pink in all blocks. At that time, fungicides should be used that control not only scab, but also rust, powdery mildew, and black rot. The orange tendrils of the cedar apples have not yet developed, indicating spore production, but probably will begin during the next extended, warm rain.(SB)

4. STATUS OF METHYL BROMIDE AND REPLACEMENT OPTIONS

Methyl bromide is often as a soil fumigant in strawberry and tomato production and in fruit tree nursery production in Tennessee. The following article was written by Jimmy Upchurch, of Hendrix and Dail, Inc., and Jeff Kindhart, of the University of Illinois. It should be of interest to those of you who use methyl bromide or other fumigants, or who are considering using fumigants. (SB)

Present status. Currently, meetings are being held in Washington, D.C., to put together a bill that would extend agricultural use of methyl bromide. Growers interested in seeing methyl bromide remain on the market for agricultural use are strongly encouraged to contact their congressional representatives and urge their sponsorship of this legislation. Barring legislative intervention, methyl bromide production will be reduced again in 2003, and will be phased out by 2005.

Availability. For the current growing season, established customers may be able to purchase methyl bromide. There will likely be about a 25% increase over last year's prices with an additional four to five percent increase coming in June or July. This price may remain fairly stable until the next legislated reduction in production which will come in 2003. Some companies will likely be supplying methyl bromide only to established customers. Those lucky enough to receive the product will be asked to reduce their consumption of methyl bromide by switching to products with lower levels of methyl bromide and higher levels of chloropicrin, and treating part of their acreage with alternative products such as Telone C-35. In other words, you will likely be strongly encouraged to purchase a percentage of your fumigation material as Telone C-35 and not all methyl bromide. Major accounts will likely not have difficulty obtaining methyl bromide for the 2001 crop season. Small growers may not be as lucky, especially if they are not established customers.

Costs. For growers that custom hire their fumigation done, this service will continue to be offered. It is estimated that fall 2001 prices will run about $1,950 per acre for methyl bromide fumigation (350 lbs/acre) and about $1,700 per acre for Telone C-35 (40 gal/acre).

Comparison. Methyl bromide mixed with either 2% or 33% chloropicrin has long been the standard of the industry. These mixes can control nematodes, weeds and soil diseases. The 67/33 mix, which contains 33% chloropicrin, is actually better for soil-borne disease control than the 98/2 mix.

Telone II and Telone C-35 are also soil fumigants, but both are weaker on weed control than methyl bromide mixes. While Telone II is also weaker on soil-borne diseases, Telone C-35 provides control levels similar to 67/33 methyl bromide mixes. Tarped applications of Telone II and C-35 normally provide fair to good weed control but fail to control some hard-seeded weeds. Nutsedge often escapes the Telone application. Anyone who has observed nutsedge growing through black plastic will tell you that this particular weed can be devastating to plasticulture systems. The herbicide Tillam can be use in tomatoes to enhance nutsedge control. (Jimmy Upchurch, Hendrix and Dail, Inc., Frankfurt, KY, and Jeff Kindhart, University of Illinois.)

5. STRAWBERRIES: PHYTOPHTHORA DISEASE CONTROL

Phytophthora crown rot, also known as vascular collapse, is becoming an increasing problem in plasticulture strawberry production. To lessen losses in infested fields, you should begin fungicide treatments before symptoms appear. The products discussed below should help reduce losses not only to Phytophthora crown rot, but also to leather rot (a berry rot caused by the same fungus) and red stele (caused by a different, but related, fungus).

Ridomil Gold and Aliette are systemic fungicides that are used in control of Phytophthora, Pythium, and the downy mildews of labeled crops. Their methods of application differ.

Ridomil performs best when taken up by the roots and translocated upwardly by the plant. The preferred method of application in strawberries is through the drip system. Ridomil Gold EC is injected into the drip system at the rate of 1 pint per treated acre. An actual acre would only receive 0.6 pint if the beds are 3 feet wide on 5-foot centers, because only 60% (3/5) of the ground would be treated. If you apply Ridomil with a sprayer, use enough water to move the fungicide into the root zone. An additional application may be made during fruit set or harvest.

Aliette is labeled for use against red stele and leather rot. I am not aware of data related to its effectiveness against crown rot, but it should at least be helpful in suppression. Aliette is applied at 2.5-5.0 pounds per acre at 30-60 day intervals for red stele control and at 7-14 day intervals for leather rot control. Aliette can be applied through the drip system or through some sprinkler irrigation systems. A foliar spray is the preferred method of application of Aliette because of its downward systemic activity. Like Ridomil, Aliette can be applied on the day of harvest. Follow label directions carefully. (SB)

6. REDBANDED LEAFROLLER MOTH ACTIVITY

The old pheromone traps from last year were still on the apple tree when I went out to replace them today (March 26). While putting out a new pheromone and sticky trap for redbanded leafroller, I found 8 fresh moths in the old sticky trap. The pheromone, put out sometime last August or September, still had enough left to draw in male moths. The last warm weather was on Friday, March 23. Some of these moths may have been caught then or during an earlier warm spell. It has been much too cold since Friday to expect moth activity. I also put out an obliquebanded leafroller pheromone trap. No other new moths were caught in last year's traps. The oriental fruit moth pheromone and codling moth traps will be put out as soon as I receive my recent order. I also ordered two minimum-maximum thermometers in case they are needed. (FH)

Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm

Contacts:
Steve Bost, Professor and Extension Plant Pathologist
scbost@utk.edu

Frank Hale, Associate Professor and Extension Entomologist
fahale@ext1.ag.utk.edu

Both authors available at:
615-832-6802
fax 615-781-2568
Plant and Pest Diagnostic Center
5201 Marchant Drive
Nashville, TN 37211