Fruit Pest News

Volume 5, No. 18  July 27, 2004

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. Vegetable Corner

        1.a. Squash Beetle and Mexican Bean Beetle

        1.b. Cucurbit Powdery Mildew Reminder

        1.c. Late Blight in Tennessee and a Comment on the Tomato Spray Schedule

        1.d. New Host for Phytohphtora capsici

    2. Grape: Bitter Rot

    3. General: Pheromone Trap Catches

1. Vegetable Corner

1.a. Squash Beetle and Mexican Bean Beetle

The coccinellid or ladybird beetles are primarily predaceous and thus considered beneficial insects. There are two plant feeding species (squash beetle and Mexican bean beetle) in this beetle family and they can both be found in Tennessee vegetable crops.

We have received samples of squash beetle adults during the last week. The adult is 11/32 inch long with a yellowish-brown legs and body. It has four small spots on the prothorax (area directly behind the head) and 12-14 different size larger spots on the wing covers. The larvae of both the squash beetle and the Mexican bean beetle are yellow and covered with forked spines. Both the larvae and adults of these species are plant feeders. Squash beetles primarily skeletonize the foliage of cucurbits but are also known to feed on the blossoms and pods of lima beams and cowpeas, on lima bean foliage, and on corn silks.

Mexican bean beetle adults are yellowish to copper red with 16 spots on the wing covers. The yellow eggs are laid in a cluster. It is the most injurious pest of beans (lima, snap, pole, kidney, etc.). It can also attack cowpea, soybean, clover, alfalfa and some leguminous weeds. They feed on the underside of the leaf between the veins. The tissue that is left turns brown and the skeletonized leaves can give the field a burnt cast. The pest can even feed on pods and stems and in severe infestations some of the plants can die before a crop is produced. The adults migrate to ditches, fence rows and brushy areas later in August or September to overwinter under plant debris. The adults start to emerge to feed on newly emerged seedlings in the spring. (FH)

1.b. Cucurbit Powdery Mildew Reminder

As powdery mildew season gets cranked up, remember that we no longer recommend the strobilurins (Quadris, Flint, Cabrio, Pristine) for control of this disease because of the prevalence of resistant strains. Use Nova, Procure, or sulfur in a tank mix with a basic fungicide such as mancozeb or chlorothalonil, preferably the latter during powdery mildew season. For further information on this topic, see the May 25 issue of Fruit Pest News, and for information on cucurbit spray programs, see the June 22 issue. (SB)

1.c. Late Blight in Tennessee and a Comment on the Tomato Spray Schedule

Late blight was recently found in some tomato fields in East Tennessee, and is also present in Western North Carolina. The tomato growing regions of East Tennessee and the Cumberland Plateau should consider themselves under an alert. The recent dry weather has diminished the late blight threat, but periods of frequent rains could re-ignite the epidemic.

What to do: Tomato growers who are not already on a once-per-week fungicide spray program should begin this practice. The use of mancozeb or chlorothalonil each week for general disease control is the best protection against late blight. Every other week, a strobilurin (Quadris or Cabrio) can be added, for additional early blight control. For fields in which late blight is present, a specialized fungicide such as Acrobat, Gavel, or Tanos can be added to the mancozeb, chlorothalonil, or strobilurin. For fields in which bacterial diseases are present (most of them fall into this category), copper or Actigard should be used in each application, in addition to the fungicides. These materials should have been used from the beginning, in alternation. An example would be Actigard + mancozeb followed by copper + mancozeb. It may be necessary to continue bacterial disease control through harvest.

If Botrytis gray mold becomes a problem, the new fungicide Endura can be added. With all of the new products for tomatoes, designing a spray program can seem daunting. If you have any questions, feel free to contact me. (SB)

1.d. New Host for Phytophthora capsici

Phytophthora blight, caused by Phytophthora capsici, is a major threat to the production of cucurbit and pepper crops. Since some of the solanaceous crops such as tomato and eggplant are slightly susceptible, it is recommended that they not be used as rotation crops in infested fields. Now it appears that you can add beans to the list of taboo rotation crops. Infected commercial lima bean pods from West Tennessee were recently submitted to the lab. Snap beans were found to be hosts in Michigan last year. (SB)

2. Bitter Rot of Grape

If you are seeing a rot of mature berries (8% sugar or above), the culprit is probably bitter rot. Black rot, which has a similar appearance, occurs in green berries. Bitter rot can be a particular problem to wine grapes because of the unpleasant flavor it can impart to the wine. Catawba is particularly susceptible.

The causal fungus usually invades a berry from the pedicel (berry stem). As the berry rots, concentric rings of fungal fruiting bodies appear. Within a couple of days, the berry softens and is easily detached. Berries that do not fall off continue to dry and become firmly attached. When shriveled, the berries look much like berries affected by black rot or other fruit rots.

The bitter rot fungus overwinters on fallen leaves and berries and in the bark of year-old canes. The disease cycle on fruit starts shortly after flowering, when the fungus invades the natural warts on the berry stems and remains latent until the berry reaches maturity. It then invades the stem and moves into the berry, where a rot forms and spores are produced on the surface. Spores that are splashed to injured fruit cause new infections.

Generally, broad-spectrum fungicides such as Benlate, captan, ferbam, and mancozeb are effective in controlling bitter rot. Used around bloom time and afterward, these materials help prevent pedicel infections. Late season sprays are needed to prevent secondary infections. (SB)

3. 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