Fruit Pest News
Volume 3, No. 3 March 25, 2002
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. Apples: Redbanded Leafrollers Found
3. Apples: Time for Copper Sprays
4. Apples: Good Pruning Job Needed This Year
5. Strawberries: How to Use the New Fungicides in a Spray Program
6. New Fruit Miticides
1. Current Conditions
Temperatures on the morning of Friday, March 22 were around 20 degrees in most areas and only slightly higher the next morning. Many peach trees were beginning to bloom at that time, and considerable blossom loss can be expected. In the blueberry variety planting at the Plant and Pest Diagnostic Center, only one variety, O'Neal, was in bloom at the time of the freeze. We have been experiencing strawberry blossom kill intermittently since December, as warm periods have caused some varieties to bloom and be killed by frosts. Apple trees vary from silver tip to tight cluster. Looking forward, frosts are possible this week on March 27 and 28. (SB)
2. Apples: Redbanded Leafrollers Found
Redbanded leafrollers have been active since traps
have been put out. A trap in Bradley County, put out March 14, caught 67 the first
night, 49 on 3-16, 18 on 3-17 and 14 on 3-18. The Nashville trap was put out March
15 and had caught 34 moths by 3-21 and 8 by 3-25. I have not caught any Oriental fruit
moths (OFM) in Nashville. I will be checking moths caught in Bradley County to confirm
whether they are OFM or not. (FH)
3. Apples: Time for Copper Sprays
Fixed coppers and Bordeaux mixture are applied at this time of year to reduce fire blight bacterial populations on the surface of apple and pear trees. By doing so, there will be fewer bacteria to be carried to the blooms on the feet of insects or by splashing rain. This job should not be delayed, because application after the 1/2-inch green tip stage can cause injury. Don't restrict the copper application to fire blight-susceptible blocks. The fire blight bacteria can be found on the surface of resistant varieties, too, since they don't require a susceptible host to multiply. (SB)
4. Apples: Good Pruning Job Needed This Year
Since we had a somewhat bad fire blight year last year, we really need to do a good pruning job going into the growing season. The fire blight bacterium is carried over from one year to the next in the cankers that the disease caused the previous year. Removing limbs containing cankers will reduce the inoculum, thus reducing the number of bacteria encountered by the streptomycin sprays at bloom. As a result, the chances for resistance to streptomycin developing in the bacteria is reduced.
Another reason for a good pruning job is that all the dead limbs and twigs caused by fire blight will create a breeding ground for the bitter rot, white rot, and black rot fungi. This killed tissue was invaded by these fungi last year, and they will produce spores this year and cause fruit infections. (SB)
5. Strawberries: How to Use the New Fungicides in a Spray Program
The strawberry fungicide arsenal has changed much in recent years. Since last growing season, two new registrations (Switch, Quadris) have been granted (see the March 11, 2002 issue of Fruit Pest News). Benlate is less available, since it has been discontinued by the manufacturer. Elevate was first registered two years ago. The strawberry label for Ronilan was discontinued, and the strawberry label for the related fungicide Rovral was severely restricted. Resistance to the benzimidazole fungicide Topsin M is becoming widespread. What strategy should you follow in designing a fungicide spray program?
The focus of the bloom sprays is on Botrytis control. Bloom time is the key time to prevent this fruit disease, and other fungal disease activity is low at that time (however, the bacterial disease angular leaf spot may require copper sprays). Use either Elevate or Switch as your primary Botrytis material. If anthracnose is known or suspected of being present, Switch would be the preferred material. Follow a 7 to 10-day schedule through bloom. Both labels limit the number of applications, so alternate after one or two sprays with a tank mix of Topsin M with either captan or thiram. I recommend that Quadris not be used during the bloom period. It is rather weak against Botrytis. Furthermore, the label only allows 4 applications per year, so reserve those applications for the harvest period, in case anthracnose appears. In severe anthracnose cases, Quadris should be applied once per week for 4 weeks during harvest. To comply with the alternation requirement, make a captan or Switch application between each Quadris application. Quadris can be tank-mixed with captan, but the requirement of alternating to a fungicide not related to Quadris for 1 application after the second application of the tank mix must still be satisfied. (SB)
6. New Fruit Miticides
The miticide, etoxazole
(Secure) by Valent has been granted "reduced risk" status on pome fruit,
cotton and strawberries by the EPA. This miticide is thought to inhibit molting
and thus is active against eggs and immatures, but not adults.
Another miticide,
bifenazate (Acramite 50WS) by Cromptom Corp. (Uniroyal Chemical), has ben registered.
It is labeled for use on apples, pears, peaches, nectarines, plums, prunes, grapes,
hops, and srawberries for control of twospotted spider mites and European red mites.
It has a 7 day preharvest interval on apples and pears; 14 days on grapes and hops,
3 days on peaches, nectarines, plums and prunes; and one day on strawberries. Only
one application is allowed per season. (FH)
The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm
Contacts:
Steve Bost, Professor and Extension Plant Pathologist
Frank Hale, Associate 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