Fruit Pest News

Volume 3, No. 23   September 16  , 2002

An 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.

Fruit Pest News will be produced every two weeks until the end of the growing season.

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. Apple: Late-Season Pests and Fruit Damage Sampling

    2. Strawberry: Disease Control in the Fall

    3. Pumpkin: Fruit Rots

    4. Grape: Need Help with Pierce's Disease

    5. Apple: Southern Blight on Young Trees

    6. Tree Fruit: Pheromone Trap Catches and Biofixes

General: The late-summer weather has been very dry, providing good harvest conditions for apples and good soil conditions for planting plasticulture strawberries. The cool front that entered the region on September 12 provided relief from the 90+ temperatures we had been having, and brought scattered showers to much of the state.

The last issue of Fruit Pest News will be available on September 30. It will contain a subject index for the 2002 issues.

1. Apple: Late Season Pests and Fruit Damage Sampling

We are still catching some moths in pheromone traps. Oriental fruit moth and redbanded leafroller have been very active lately. Obliquebanded leafroller trap catches have picked up since the end of August in Nashville while tufted apple bud moth have also increased at the Putnam County site. Continue to monitor traps. The later harvested apples may need further protection prior to harvest.

Pheromone traps and orchard pest monitoring during the growing season can give the on-farm information needed to better mange your crop. Harvest is another time when valuable information can be gathered that will help you make storage and future pest control decisions. Sample for fruit quality with a random sample of 50-100 fruit from several representative bins of each block. Grade the fruit for size and quality and note the cull factors for each downgraded fruit. You can get a good idea of how the fruit will grade out. Soluble solids and pressure tests will help to determine optimum length of storage for each block of fruit. High temperatures and drought prior to harvest will effect fruit firmness and fruit storage potential.

Close examination of each cull will let you determine your level of pest control and fruit handling. What percent of fruit culls had insect or disease damage, small size, or bruises from rough handling? Pests like codling moth and Oriental fruit moth that tunnel into the fruit will often cause fruit to drop. Many of these fruit will not be harvested. Other pest damage that occurs more on the outer skin will often remain on the tree. While much early season insect damage from plant bug and plum curculio will be shed at June drop, much of the damaged fruit can remain on the tree. Hand thinning will remove some of this damage. Typical damage seen are smooth or russetted indentations (plant bugs) or russetted bumps and fan shaped marks (Plum curculio). Low levels of plant bug damage may not be enough to downgrade the fruit on the packing line while the larger plum curculio marks are more obvious and will often cause a downgrade. The good thing is that this damage does not effect storage or soundness of the fruit. Fruit with the skin fed upon by leafrollers and tufted apple bud moth can shrink more in storage due to moisture loss. If leaves are webbed over the feeding area, the red skinned apples will remain green or yellow on the shaded, fed upon area of the fruit.

What you will often find is that bruises are one of the most common problems that could potentially cull fruit. After protecting fruit for the whole season, it seems a shame for fruit to get bruised from a lack of tender loving care at harvest. If too many bruises are occurring at harvest, consider incentives to lower this damage while still keeping productivity at a high level. (FH)

2. Strawberry Disease Control in the Fall

Plasticulture strawberry fields are now being planted, and disease control is one of the many things that must be considered. Botrytis is thought to begin building up in fields in the fall, and an application of a Botrytis fungicide may be helpful, although there is not universal agreement as to when that application should take place. An application in early November would help prevent fungal colonization of plant parts that get killed by winter weather. Colonization could occur as early as the plant establishment stage, or even during rooting of the tips in the plug production beds. When planting in the field, the use of plug-type plants with water-wheel planters is advisable, as this practice would avert the need for sprinkler irrigation during establishment. Repeated wetting of the plants would encourage Botrytis colonization of the dead tissues. Botryticides that could be used in the fall include Elevate, Rovral, and Switch. Rovral may only be used one time.

Hopefully, you purchased anthracnose-free plants so that applications of anthracnose fungicides will not be needed. If anthracnose does appear (I would like to hear about it, if it does), a regular spray schedule that includes captan, Switch, or Quadris will be needed.

Chandler strawberries generally have sufficient resistance to common leaf spot that chemical control is not needed. Some matted-row varieties occasionally require control measures. This disease is most likely to be a factor during cool, wet weather. Nova is our most effective fungicide against common leaf spot. (SB)

3. Pumpkin Fruit Rots

Pumpkins, gourds, and winter squash are an important commodity for apple growers. Some apple orchardists grow pumpkins and sell them at their stands to complement their apple sales. Others purchase pumpkins for resale at their stands. In either case, post-harvest rots can be a problem. Rotten pumpkins don't sell, and you don't want them to rot in Mrs. Customer's house, either.

Most efforts to control post-harvest rots of pumpkins, gourds, and winter squash should have already taken place. Most of the rots that appear in storage actually began in the field, during the production of the fruit. However, there are some steps you can take to lessen the development of rots after harvest.

Pre-harvest control measures. Rots develop when disease-causing organisms, mostly fungi, enter the fruit surface. The best defense against this invasion is fruit rind tissue with strong cell walls. To obtain such "tough" fruit, the plant must be kept healthy during the growing season. Healthy leaves provide carbohydrates to the fruit, which strengthens the cell walls. Provide adequate calcium, avoid excessive nitrogen, and irrigate during dry periods. Follow a recommended spray program to control diseases and insects. Controlling foliar diseases helps maintain healthy leaves and reduces the populations of organisms that can infect the fruit. Crop rotation is important in reducing the populations of fruit-rotting organisms such as anthracnose and bacterial spot. Two years in a non-cucurbit crop should be allowed between pumpkin crops.

Post-harvest control measures. Damaged pumpkin skin allows easier entrance of the fruit-rotting pathogens. Handle fruit carefully to avoid injuries. It is helpful to wash the fruit after harvest and allow to dry. Some growers dip or spray the pumpkins in a 10 percent bleach solution. This practice can reduce infections in storage, but will not stop the development of infections that occurred in the field. Holding the pumpkins at 80-85 degrees F and 80-85% relative humidity for 7 to 10 days allows scratched areas to cure. After the curing period, the temperature and humidity must be lowered to the levels recommended for storage (50-55 degrees F and 50-70% relative humidity), to reduce the disease potential.

Store pumpkins in a dry, shaded area, out of contact with the soil (straw or hay works well). Avoid piling pumpkins, as this practice decreases air circulation around them. Check stored fruits regularly for rots, and discard affected ones. Storage life of pumpkins is typically two to three months. (SB)

4. Pierce's Disease of Grape - Need Help

We need help collecting grape leaf samples for testing for Pierce’s disease.  We are trying to determine its distribution in the state.  If you find any leaves that are suspicious of Pierce’s disease, please send some of them to the plant diagnostic lab in Nashville (address at bottom of this newsletter) and request the Elisa test for this disease.  Symptoms include drying of the leaf margins, sometimes with a yellow (on white-fruited varieties) or red (on black-fruited varieties) zone between the dead margin and the green portion of the leaf.  Fruit clusters shrivel and the cane matures unevenly, producing islands of green tissue surrounded by brown mature tissue. Vidal and Chardonnay are very susceptible. Let's hope for a severe winter to halt spread of the bacterium. (SB)

5. Southern Blight on Young Apple Trees

Southern blight is caused by the soil-borne fungus Sclerotium rolfsii and can occur on many types of herbaceous and even woody plants. Young apple trees are very susceptible, and southern blight can be a problem in nurseries and young orchard trees. The following is adapted from an article written by John Hartman, University of Kentucky, for Kentucky Pest News. (SB)

Symptoms and signs. The causal fungus strikes the lower stems and roots of apple trees, killing the bark and girdling the trees. The disease is characterized by the presence of a white, web-like mycelium, which often forms at the bases and on the lower stems of affected trees. Tree death usually occurs rapidly. Additional signs of the fungus, tan to dark brown spherical sclerotia, about the size of mustard seeds (1/16 to 1/8 inch in diameter), form in the mycelial mat. The fungus spreads from previously infected plants such as weeds or from infested decomposing plant material to new trees via sclerotia and mycelium in the soil. Sclerotia also serve as overwintering structures. The disease is most severe on 1- to 3-year-old trees. As the bark thickens, trees become resistant to infection.

Disease management. The key to managing southern blight is management of previous crops and weeds. Avoid planting sites where the disease has been severe on previous crops such clover, tomato, and soybean. The fungus can also exist as sclerotia in old pasture soils from previously infected weeds. Plow or till apple planting sites a year in advance to allow organic matter to completely decompose before planting apple trees. If southern blight is known to be present, and if the soil is not very erodible, use a moldboard plow. S. rolfsii is sensitive to the low oxygen levels found deep in the soil.

Keep the soil around the bases of trees free of dead organic matter that may serve as a food base for S. rolfsii. This includes orchard weeds that are killed by herbicides. Large dead weeds provide an ample food base for the fungus. Apple rootstocks differ somewhat in their susceptibility to southern blight. The most resistant rootstock currently used is M.9. No fungicides are currently registered on apples for southern blight control. In nurseries, fumigation with methyl bromide or chloropicrin is effective.

6. Pheromone Trap Catches and Biofixes

                                            Nashville (Davidson County) Pheromone Trap Catches for 2002

                                        Biofix for RBLR in Davidson County estimated as March 14

                                                        Bradley County Pheromone Trap Catches

                                                                    Codling moth biofix was April 14

                                                               Putnam County Pheromone Trap Catches

                                                                Obion County Pheromone Trap Catches

                                                                                                (FH)  

The Fruit Pest News URL is: https://webmail.utk.edu/redirect?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