Fruit Pest News

Volume 7, No. 17  July 12, 2006

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. Vegetables: Phytophthora Blight Alert

    2. Apple: Bitter Rot

    3. Peach: Brown Rot

    4. Peach: Rhizopus Rot

    5. Clearwing Moths

    6. Pheromone Trap Catches and Biofixes

Current Conditions

 The extended hot, dry weather has been broken by thunderstorms in most areas of the state.  More are needed. A chance for showers continues for the next several days.

1. Vegetables: Phytophthora Blight Alert

We have begun seeing cases of Phytophthora blight (P. capsici) on cucurbit crops. If this year is like previous years, we will see more acres affected each year. This disease has serious implications for your ability to grow susceptible crops.

Phytophthora blight is a devastating disease particularly of cucurbit crops and peppers, but also tomatoes, eggplant, snap beans, and lima beans. The destructive nature of the disease and the long life (many years) of an infestation can prevent successful production of susceptible crops for many years. Because of the difficulty of controlling this disease after it occurs, prevention should be emphasized. The action to take when Phytophthora blight is first found in a field depends on the severity of the case. If the blight is widespread throughout a field, attention should be directed to prevention of spread to non-infested fields. Chemical control of Phytophthora blight in such severe cases is not very effective and not generally recommended. Prevention of spread consists of cultural practices such as cleaning equipment after working in an infested field. Certain disease-control products have activity against P. capsici and may be helpful in light cases of Phytophthora blight. Pre-plant soil applications of mefenoxam can suppress root and crown rot phases of the disease, unless resistance to this fungicide develops.  Other products are applied as foliar sprays to protect against airborne spores. The most difficult aspect of this disease to control is the fruit rot phase in crops in which the fruit lies on the ground, such as unsupported vine crops. The potential for disease-control products to be successful is highly dependent on the correction of soil drainage problems. Peppers and cucurbit crops are so susceptible to Phytophthora blight that it is risky to plant these crops in fields in which the disease has ever been known to occur. Some degree of control can be achieved with resistant pepper varieties and hard-rind pumpkin varieties, but cultural practices and chemicals would still be needed.

Be on the lookout for this disease, especially in irrigated fields. Dying plants and rotting fruit are the main symptoms. Be wary of borrowing or lending cultivation equipment, as this organism can be introduced into your field on anything that carries soil particles. (SB)

2. 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. You can use ferbam if you have some old product, but it is no longer being produced for used in apples or being marketed in this area. Ferbam also 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 strobilurin fungicides, Flint and Pristine, are as effective against bitter rot as captan, thiram, and ziram. The strobilurins are more expensive, but do not require the addition of Topsin M to attain good control of sooty blotch and flyspeck. Cover sprays should be applied at 10- to 14-day intervals, using 10-day intervals during wet, rainy periods. (SB)

3. 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. Refer to the June 14, 2006 issue of Fruit Pest News for information on a recommended spray program for brown rot. (SB)

4. 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)

5. Clearwing Moths

I have written about the importance of controlling the dogwood borer, a pest of various trees including dogwood, pecan, oak, and apple. The peachtree borer and lesser peachtree borer are clearwing borer pests of Prunus. There are pheromone traps to monitor for these clearwing borers as well as for the squash vine borer and the grape root borer. The pheromone that I have used for squash vine borer has only caught one squash vine borer moth so far this year and none last year. This pest should start laying its eggs on the cucurbit vines soon after they start to run, usually in June. Last year I caught grape root borers in the squash vine borer trap. This year, I caught one squash vine borer and two grape root borers in the squash vine borer trap on July 7. This is right about when I would expect catching the grape root borers.

Grape root borers can kill grape vines if left unchecked. Borers tunnel inside vines at or below ground level. All grapes are susceptible and there are two control options. Mounding uses layers of soil to make it more difficult for young larvae to reach the roots or for adults to emerge. Clean cultivation should be used and soil should be mounded one foot high and about 1.5 feet out from the base of each mound. These mounds should be out now and taken down between early November and late December. Alternately, a plastic mulch can be used to cover the soil three feet from the base of the vines.

Lorsban 4E can be applied to the base of the grape vine if possible before adult borers emerge and at least 35 days prior to harvest. Mix 4.5 pints of Lorsban 4E in 100 gallons of water. Apply two quarts of this dilution to the base of each vine. The spray should not contact fruit or foliage. Application can be made with flood nozzles and low pressure (40-60 psi). (FH)

6. Pheromone Trap Catches and Biofixes

Nashville (Davidson County) Pheromone Trap Catches for 2006
Oriental fruit moth (OFM), redbanded leafroller (RBLR), obliquebanded leafroller (OBLR), codling moth (CM), grape berry moth (GBM), variegated leafroller (VLR), black cutworm (BCW), diamondback moth (DBM)

* Biofix for RBLR in Davidson County was March 2.
**Biofix for DBM in Davidson County was March 30.
***Biofix for OFM in Davidson County is estimated to be April 3.
****Biofix for GBM in Davidson County was April 7.
^Biofix for OBLR in Davidson County was April 24.


Bradley County Pheromone Trap Catches for 2006

*Biofix for OFM in Bradley County on March 29.
**Biofix for CM in Bradley County on April 13.


Putnam County Pheromone trap Catches for 2006

*Biofix for RBLR in Putnam County estimated as March 3 (trap not out early enough).
**Biofix for OFM in Putnam county March 31.
***Waiting to verify biofix for CM, catch probably too early.


Obion County Pheromone Trap Catches for 2006

*Biofix for RBLR in Obion County estimated to be on March 3 (trap not out early enough).
**Biofix for OFM in Obion County on April 3.
***Waiting to verify biofix for VLR in Obion County, catch probably too early.
****Waiting to verify biofix for CM in Obion County, catch probably too early.
^Biofix for OBLR in Obion County.

Additional Pheromone Trap Catches in Davidson County for 2006
Sod Webworms (SWW), Armyworm (AW), Squash Vine Borer (SVB), Grape Root Borer (GRB)

*Biofix for SWW in Davidson County for 2006.
**Biofix for AW in Davidson County for 2006.

Knox County Pheromone Trap Catches for 2006
Tufted Apple Budmoth (TABM)

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

Copyright 2006 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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