Fruit Pest News

Volume 5, No. 17  July 13, 2004

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. First Reports for the Year

    2. Clearwing Borers

    3. Grape Berry Moth

    4. Apple: Bitter Rot

    5. Grape: Botrytis Bunch Rot

    6. Peach: Brown Rot

    7. Peach: Rhizopus Rot

    8. General: Pheromone Trap Catches

1. First Reports for the Year

First reports for the year: anthracnose cane blight - blueberries, June 23, Overton County; necrotic leaf blotch - Golden Delicious apple, June 30, Williamson County; grapevine root borer - grape, July 1, Williamson County; European red mite - peaches, July 7, Wilson County.

2. Clearwing Borers

Borer control is very important in a number of fruit and vegetable crops. The clearwing moths (family Sesiidae) are especially damaging. Peachtree borers and lesser peachtree borers atack Prunus spp., dogwood borers attack apple, grape root borers attack grapes and squash vine borers attack cucurbits such as squash, pumpkin and gourds. All of these borers can kill the plants that they attack which makes control of these pests essential. The adult moths are day-flying and tend to mimic bees, hornets and wasps. Some have smoky wings like some wasps while others only have dark wing scales that outline the wing veins and leave the rest of the wing clear, thus improving the mimicry. Fortunately, clearwing moths cannot sting but predators such as birds get fooled and usually leave them alone.

Peachtree borers (PTB) usually bore into the lower part of the trunk of Prunus spp. Lessor peachtree borers (LPTB) tend to tunnel into scaffold limbs. Both can be detected by the gummy exudate coming out of the wounded areas of the bark. LPTB adult moths begin to emerge in April in Tennessee while PTB usually begin emerging in late May. Most egg-laying females of PTB emerge and lay eggs from mid-June to early September across the Southeast. Post-harvest trunk and scaffold sprays for PTB and LPTB should begin in early August. One application of Lorsban 4E or two applications of endosulfan (Thiodan 3EC or Phaser 3EC) should be made.

Dogwood borers attack the burr knots and graft union of apples. Lorsban 4E is the preferred insecticide, but Lorsban 50 W, Thiodan 3EC and Asanal XL can also be used. Moths lay eggs from mid-May through July so treatment in mid- to late-May is optimal. If Lorsban is used, apply with a handgun sprayer from no more than 4 ft. with a shielded sprayer to prevent drift onto foliage or fruit.

Grape root borers (GRB) attack the roots and base of the vines. Mix 4.5 pints of Lorsban 4E with 100 gallons of water and apply 2 quarts of the diluted spray mixture to the soil surface on a 15-square area around the base of each vine. Do not allow spray to contact fruit or foliage. Pheromone traps can be used to determine when the moths emerge. It is best to make the insecticide application before the pest emerges. The adult male moths started being caught in the pheromone traps in Williamson County on July 1. Make only one application per season or apply within 35 days before harvest. Late June or early July is good timing for this pest with earlier application possibly needed for the earlier maturing grape cultivars.

Squash vine borers start laying eggs on squash, pumpkin and gourds in late spring (June) when the vines start running. The creamy white larvae can be found in vines now. The larvae feed inside the vine for four to six weeks before leaving the vine to burrow into the soil to pupate within a silken cocoon. The new moths emerge two to three weeks later giving rise to a second generation of larvae during August. This pest is much more damaging in backyard gardens where insecticide is only used infrequently or not at all. Sprays for cucumber beetles in commercial plantings seem to keep this pest at least partially under control. (FH)

3. Grape Berry Moth

Moths have recently been caught in a Williamson County vineyard site. With some grapes already ripe and other varieties still maturing, this is a critical period for protecting grapes. Be mindful of pre-harvest intervals when spraying close to harvest.
(FH)

4. 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, Fuji, 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, and should be used at full rate where problems with bitter rot are expected. The addition of a 1/2 rate of Topsin M helps with control of sooty blotch and flyspeck, as well as white rot and black rot. 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)

5. Botrytis Bunch Rot of Grape

A Botrytis fungicide should be applied before bunch closing and at veraison on tight-clustered French hybrids such as Vignoles and Seyval, and most vinifera varieties, especially Pinot Noir, Riesling, and Chardonnay. Removal of leaves around clusters before bunch closing has been shown to reduce losses to Botrytis, by improving the drying conditions in the cluster.

The most effective fungicides for control of Botrytis bunch rot are 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)  

6. Brown Rot of Peach

Remember that special attention to brown rot is needed in orchards in which bird or insect damage is severe, hail damage has occurred, and in which trees are planted closely or are surrounded by woods. 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. The registration of Pristine fungicide has alleviated a problem with resistance management for brown rot. Since resistance to the benzimidazoles developed in brown rot, Topsin M cannot effectively be used for control. Until Pristine was labeled, there were no fungicides as effective as the DMI's (sterol inhibitors) with which to rotate. After using a DMI (Orbit, Elite, Indar) for two applications, rotate to Pristine for one application before returning to a DMI. Pre-harvest fungicides should not be applied more often than every 7 to 10 days. Orbit, Indar, Elite, and Pristine have 0-day pre-harvest intervals. (SB)  

7. Rhizopus Rot of Peach

Rhizopus rot is a common post-harvest rot of peach that can spread rapidly in containers of non-cooled fruit. It is characterized by a fluffy, black fungal growth on a rotted area of the fruit. Before the mold is produced, Rhizopus rot can be detected by an easy slippage of the skin from the rotting flesh. Skin slippage does not readily occur over brown rot lesions.

Brown rot fungicides used during the pre-harvest period are not effective against Rhizopus rot. Botran 75W is somewhat effective, but should be tank mixed with a brown rot fungicide and cannot be used within 10 days of harvest. Scholar 50W provides good control of Rhizopus rot, but can only be used after harvest, as a dip or through spray nozzles in the packing line. As with brown rot control, avoid puncturing fruit skin, and store harvested fruit at less than 40 F. (SB)

8. General: Pheromone Trap Catches

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, Professor and Extension Entomologist

fahale@utk.edu

Both authors available at:

615-832-6802

fax 615-781-2568

Plant and Pest Diagnostic Center

5201 Marchant Drive

Nashville, TN 37211