Fruit Pest News

In This Issue:

1. New Schedule for Fruit Pest News

2. Grape: Botrytis Bunch Rot
3. Apple: Bitter Rot
4. Peach: Brown Rot
5. Tree Fruit: Insect Trap Count Updates

1. NEW SCHEDULE FOR FRUIT PEST NEWS

For the remainder of the growing season, Fruit Pest News will be issued every two weeks. The weekly schedule will return at the beginning of the 2002 growing season. See you on July 23!

2. BOTRYTIS BUNCH ROT OF GRAPE

Botrytis bunch rot is particularly troublesome on tight-clustered French hybrids such as Vignoles and Seyval, and most vinifera varieties, especially Pinot Noir, Riesling, and Chardonnay. Hopefully, you made an application of a Botrytis fungicide before bunch closing, when berries within the cluster begin to touch. Another application is needed at veraison (beginning of fruit ripening), and another application can be made prior to harvest, if needed. Removal of leaves around clusters before bunch closing has been shown to reduce losses to Botrytis, by improving the drying conditions in the cluster.

Three fungicides are registered for control of Botrytis bunch rot: Rovral, Vangard, and Elevate. Realize that these products are effective ONLY against Botrytis. You need to apply other appropriate fungicides for control of black rot, bitter rot, the mildews, etc., all of which will continue to be active throughout the summer. It is also important to remember that these Botrytis fungicides are prone to resistance development in the pathogen population. It is therefore strongly recommended that none of these materials be used more than 3 times per year, despite the fact that the Rovral label allows 4 applications (the Vangard label limits its use to 2 applications per year, at the 10 oz/A rate). Try to alternate the 3 products, if possible.

Rovral 50WP is used at 1.5 to 2 lb/A, with a 7-day pre-harvest interval. Vangard 75WG is used at 10 oz/A, with a 7-day PHI. Although Vangard is classified as a reduced-risk pesticide, it is toxic to fish and should be used with caution around aquatic areas (see label). Elevate 50WG is used at 1 lb/A, and has a 0-day PHI. (SB)  

3. BITTER ROT OF APPLE

Bitter rot is the most potentially explosive of the apple fruit rot diseases. We sometimes get reports of growers, especially homeowners, losing the majority of their fruit to this disease. The restrictions placed on the most effective group of fungicides, the EBDC's, have increased our problems with bitter rot. The disease can move so rapidly because infection can occur in as little as 5 hours of wetting at 79-82 F. At 80 F, lesions can develop and produce spores within 11 days of infection. Fruit remain susceptible right up until harvest.

Identification. Bitter rot is recognized by round, sunken lesions on the fruit. When very young fruit are infected, the lesions appear as tiny gray-brown flecks, which usually do not develop further until fruit begin to ripen. Fruit infections occurring a month after petal fall begin as small, round, slightly sunken areas that are light to dark brown in color. As the lesions enlarge, concentric rings of spores or their fruiting bodies form around the center. Decay lesions extend in a cone-shaped pattern toward the core, observed by cutting the apple in half through the decayed area. This V-shaped lesion distinguishes bitter rot from white rot, which has a cylindrical decayed area.

Cultural control. A feared disease, bitter rot is controllable if trees are well-pruned and air circulation is good in the orchard. The removal of excess growth improves drying conditions and penetration of sprays into the canopy. Try to prevent the buildup of inoculum by removing overwintered mummified fruit, if feasible, or even diseased fruit during the growing season. Leaving fire-blighted shoots on the trees can increase fruit rot problems, because the fungi can colonize them. Do not allow prunings to pile up near the orchard. Prunings can be left on the orchard floor if they are chopped with a rotary or flail mower, which removes the bark on which the fungus can reproduce.

Monitoring bitter rot. Orchards should be scouted regularly for this and other fruit rots. In orchards in which this disease has been a problem, or in highly susceptible varieties, inspect the trees each week, beginning in early June. Highly susceptible varieties include Golden Delicious, Fugi, Arkansas Black, Granny Smith, Empire, and Yellow Newton. Almost as susceptible are Gala, Stayman, Jonagold, Jonathan, Grimes Golden, Ginger Gold, and Braeburn. Among the least susceptible are Delicious, Rome Beauty, and Winesap, but no variety has a high level of resistance.

Inspect as many fruit as is practical (this exercise provides another case for keeping trees trained to a manageable height). If more than 3 infected fruit are observed on any tree, a change in the control program may be needed. The needed change may be in the tree training and other cultural practices mentioned above. Or it may be in the spray program. The spray interval may need to be shortened (especially if the weather is rainy), the fungicide choice may need to change (a bitter rot fungicide should be used in each cover spray), or the application method may need adjustments.

Chemical control. The need for fungicidal protection against bitter rot is greatest from midseason until harvest, although some fruit infection can occur as early as petal fall. Where bitter rot has been troublesome in the past, use an EBDC fungicide (Dithane, Manzate, Penncozeb, or Polyram) as long as the label allows (until 77 days before harvest). Tank mixing with captan after petal fall will improve control of white rot and black rot.

Ferbam is also very effective against bitter rot, and can be used until 7 days before harvest. However, ferbam produces a gray residue that is unsightly on fruit. Other disadvantages of ferbam are increased cracking on Stayman, and russeting on certain varieties if ferbam is applied in the pink through first cover sprays. Russeting is not a problem when ferbam is used after the first cover spray. Like the EBDC's, ferbam applied alone may not provide adequate control of white rot or black rot.

Captan, ziram, and thiram are good bitter rot materials. The new strobilurin fungicides, Flint and Sovran, appear to be slightly less effective at the rates commonly used. Cover sprays should be applied at 10- to 14-day intervals, using 10-day intervals during wet, rainy periods. (SB)

4. BROWN ROT OF PEACH

Remember that special attention to brown rot is needed in orchards in which bird or insect damage is severe, and in which trees are planted closely or in which woods surround the orchard. Post-harvest losses to brown rot can be significant, especially if harvested fruit are not kept cool. Try to minimize post-harvest losses by using care in the picking and handling of fruit to avoid punctures. Any break in the skin of the fruit enables brown rot to more easily cause infection.

A good pre-harvest spray program also minimizes losses at harvest and after harvest. There currently is a dilemma in that our 3 most effective brown rot fungicides (Orbit, Indar, Elite) belong to the same chemical class, the sterol inhibitors. As a result, resistance to these fungicides may develop. Brown rot resistance has developed to the benzimidazoles (Benlate, Topsin M), causing these formerly outstanding materials to be unreliable in many southeastern peach orchards. We should make every effort to minimize the use of the sterol inhibitors, preferably by alternating them with Abound, which belongs to the strobilurin group. Pre-harvest fungicides should not be applied more often than every 7 to 10 days. Orbit, Indar, Elite, and Abound have 0-day pre-harvest intervals. (SB)  

5. TREE FRUIT: INSECT TRAP COUNT UPDATES
Codling Moth

Be on the lookout for codling moths. We should be catching codling moths in the pheromone traps sometime in July. We have not caught any since April 13 for Obion Co., April 23 for Davidson Co., May 4 for Putnam Co. (only one caught) Obion Co. (traps put out April 9), May 6 for Bradley Co. (last date that we received trap data).

                                                                                    Obion Co.

The 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

615-832-6802
fax 615-781-2568
Plant and Pest Diagnostic Center
5201 Marchant Drive
Nashville, TN 37211