Fruit Pest News

Volume 4, No. 21   September 15, 2003

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.

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.Strawberry Anthracnose and Phytophthora Update

    2. Blueberry Leaf Rust

    3. Pumpkin Fruit Rots 

    4. Insects -- Grape Berry Moth, Wasps, Yellowjackets, Hornets, Lady Beetles

    5. Pheromone Trap Catches and Biofixes

Figure 1. Phytophthora crown rot in strawberry plug bed.

1. Strawberry Anthracnose and Phytophthora Update

 Since the last issue of Fruit Pest News, anthracnose has been confirmed in three Tennessee plug beds of Chandler strawberries that were stuck with runner tips from Ghesquire Farms, Ontario, Canada. To compound the misery, Phytophthora crown rot has also been found in some shipments (also from Ghesquire) of both Chandler and Sweet Charlie. The presence of Phytophthora negates one of the alternatives that was available in the battle against anthracnose-infected plants: the use of Sweet Charlie, which has a high level of resistance to anthracnose. Many TN growers devote a certain portion of their plasticulture planting to Sweet Charlie. Unlike anthracnose, which does not survive for long in the soil, Phytophthora is very long-lived. Although it lacks the explosive potential of anthracnose in damaging a crop, Phytophthora poses a long-term threat.

Should I Even Try?

There are many factors to consider in deciding whether to plant infected plants and attempt to make a crop. The potential effect on your market of taking a year off from strawberry production is chief among them. Others include: the money already spent on the crop; the loss of income by foregoing the crop; the potential of producing inferior quality berries; the cost of attempting to control the two diseases; the feasibility of controlling the two diseases successfully; whether alternatives to the use of infected plants are available; and the prospect of long-term contamination of the soil with Phytophthora.

It does not appear that plants of any variety are available, other than perhaps bare root plants. Ghesquire's bare root plants originated from micropropagated plants, so are assumed to be free of anthracnose. However, planting bare root plants is not for everyone. They require hand planting, adequate labor for quick planting, cooling facilities for holding prior to planting, and adequate water for all-day sprinkler irrigation for up to two weeks after planting. They should be planted 5 days sooner than plugs, which would be around September 20, for bare root plants.

Anthracnose. It is difficult to control this disease on the vegetative parts of the plant, i.e. stolons and petioles. The fungicides we use for this disease work best in protecting the fruit; efforts to slow spread on other parts of the plant have not succeeded. However, the use of infected plants does not necessarily spell doom, if the weather during harvest is not too hot and wet. If you choose to plant infected plants and want to follow a spray program, the most effective program would be a tank mix of captan with either Quadris or Cabrio, alternated on a 7- to 10-day schedule with captan applied alone. Switch® is as effective as Quadris or Cabrio, and does not need to be tank mixed with captan. Please keep the following in mind:

This spray program would be an expensive endeavor, as it would need to be continued throughout the fall and spring.
These fungicides have yearly use limitations on the labels that would be exceeded if they were applied this frequently for this long.
It is useless to apply these fungicides only once or "every once in a while." They do not cure infected plants; they are protectants, and newly-emerging plant tissue must be sprayed to be protected from anthracnose.

If you choose to proceed to the field with plants from a bed containing infected plants, my opinion is that you should discard (bury) obviously infected plants to minimize plant mortality in the field, reserve the fungicide uses for the spring, and hope for favorable weather during harvest.

Phytophthora. If anthracnose were the only disease to consider, making a decision regarding whether to proceed with planting might not be too difficult for some growers. However, it appears that plants of both Chandler and Sweet Charlie have some Phytophthora. Planting infected plants will result in contamination of the soil for many years. How much of a problem is that? Recurrences of Phytophthora problems seem to vary with location and with the grower's attention to soil drainage problems. Methyl bromide is effective, but the alternative fumigants do not appear to be as effective. Ridomil can be applied through the drip, but is expensive, and there has been one case in South Carolina of resistance to Ridomil.

If you choose to proceed to the field with plants from a bed containing infected plants: Discard all trays with visibly diseased plants and a set of trays surrounding each diseased one. After planting, apply Ridomil Gold EC in the drip at 1 pint per treated acre (This would be 1/2 pint per actual acre if 1/2 of the ground is covered in plastic mulch). Ridomil does not need to be applied to the soil prior to planting. The label allows up to 3 applications per year. Some will be needed in the spring.

GET A DIAGNOSIS ON QUESTIONABLE CHANDLER PLANTS. Phytophthora-infected tips fail to root and then die. Some begin root formation and then die slowly (Figure 1). Chandler plants with anthracnose can display similar symptoms. Dying Sweet Charlie plants can be assumed to have Phytophthora, since this variety is resistant to anthracnose. Send suspect plants to the diagnostic center (address below). (SB)

2. Blueberry Leaf Rust

The clinic received a sample of leaf rust of highbush blueberry from northeastern Tennessee. This disease, also referred to as hemlock-blueberry rust, causes little damage because of its late appearance in the season. Spores that infect blueberry must be produced on hemlock trees, thus the late infection on blueberry. Infected leaves have reddish to brown spots. Yellow pustules may develop on the underside of the leaf. Control is not warranted. (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. Insects

Grape Berry Moth

Another grape berry moth (GBM) trap was put at a Middle Tennessee commercial vineyard in Williamson County in July. A better location was needed because of the poor trap catches at the Davidson County location where there are currently no cultivated grapes. Moths were caught at the Williamson County location throughout July and into early August before tapering off. A peak emergence occurred around July 18. Trap catches have picked up again in September.  (FH)

Wasps, Yellowjackets, Hornets and Even Asian Multicolored Lady Beetles

All of these pests are increasing in number to peak populations in the fall. They are attracted to ripe fruit, especially grapes, apples, raspberries and peaches. The wasps, yellowjackets and hornets are best managed by timely picking, disposing of over-ripe fruit, covering food and sweet drinks, and using screen to keep most of them out of retail markets. The use of sprays with short preharvest intervals and baiting is not very effective this time of year because populations are just too high. Chemical control may not be cost effective and spray residue can be a concern.

Asian multicolored lady beetles build up during the spring and summer feeding on aphids and other insects. In general, they are effective predators and help control aphids and leafhoppers in trees, shrubs, gardens, and other crops. They have even been reported feeding on a newly introduced pest, the soybean aphid, in Michigan soybean fields. All these abundant pests provide this lady beetle with plenty to eat and populations can soar. This is the same lady beetle that makes a nuisance of itself by moving into houses in October to find a place to overwinter.

In Michigan, these lady beetle adults were first reported feeding on fall raspberries and over-ripe grapes in the fall of 2001. The adult beetles can contaminate fruit at harvest and can remain hidden in the fruit in cold storage. The beetles will warm up and move around when the fruit is put out on shelves for sale. While some will leave the fruit, others can remain in the fruit when purchased. They can excrete a defensive chemical that can taint the fruit with a very disagreeable odor and an unpleasant, bitter taste. These off-flavors can be a big problem in juice or wine. Care should be taken to avoid picking these lady beetles whenever possible. Insecticides used for the control of other late season pests such as Japanese beetles should give some control of Asian multicolored lady beetles. Be sure to check the preharvest intervals so that pickers can safely re-enter and harvest as needed. (FH)

5. Pheromone Trap Catches and Biofixes

Nashville (Davidson County) Pheromone Trap Catches for 2003

* Biofix for RBLR in Davidson County estimated as occurring on March 8

                                                                  Williamson County (Nolensville) Grape berry Moth Pheromone Trap Catch

Bradley County Pheromone Trap Catches

*Biofix for redbanded leafroller in Bradley County estimated as occurring on March 8
**Biofix for codling moth in Bradley County was April 5 (2 caught)

Putnam County Pheromone Trap Catches

*Biofix for Putnam County estimated as occurring on March 8

Obion County Pheromone Trap Catches

*Biofix for RBLR occurred prior to trap placement, estimated as occurring on March 8
(FH)

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@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