Fruit Pest News

Volume 7, No. 18  July 26, 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. Cucurbit Powdery Mildew Reminder

    2. Southern Blight of Vegetables

    3. Ozone Injury in Vegetables

    4. Grape: Bitter Rot

    5. Grape: Zeal Now Labeled

    6. Pheromone Trap Catches and Biofixes

1. 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 24 issue of Fruit Pest News, and for information on cucurbit spray programs, see the June 20 issue. (SB)

2. Southern Blight of Vegetables

The summer heat has brought on southern blight. This disease, also known as southern stem blight, is a serious disease of many vegetable crops, causing an almost certain death of affected plants. It is caused by the soil-borne fungus, Sclerotium rolfsii, and attacks a number of vegetable crops including bean, cantaloupe, carrot, potato, pepper, tomato, eggplant, sweetpotato, tomato, watermelon and others.

Southern blight is one of the most common causes of sudden wilting and death of a plant. Mild yellowing of the leaves may occur prior to wilting. Under humid conditions, a thin, white, fan-shaped mold forms on affected stem tissues and adjoining surface soil. Even under dry conditions, at least a trace of the white mold should be evident on the stem surface.  Soon after mold formation, seed-like bodies (sclerotia) develop in the mold. The sclerotia begin white, turning tan, then bronze. When the plant is pulled up, a brown, dry rot of the lower stem and upper roots is apparent. In vegetables in which the fruit contact the ground, such as pumpkin and cantaloupe, the fruit are rotted, beginning with the side of the fruit in contact with the soil.

The fungus overwinters as sclerotia in the soil and in plant debris. A characteristic of the fungus is that it is generally restricted to the upper 2 or 3 inches of soil and will not survive at greater depths. The fungus is more active in hot, wet weather, and it requires the presence of undecomposed plant residue to initiate infection. S. rolfsii is more active under acidic soil conditions. The fungus does not have a air-borne spore, so all infections result from contact of the plant tissue with soil. It is spread when infested soil particles are moved, as with cultivation. The fungal body is so strong that it is capable of growing across the soil surface to reach a plant, if old plant debris is available.

Control

•       In gardens, remove affected plants, including roots and a small amount of soil surrounding the plant. Be careful not to scatter debris as the material is removed. Place the material in a place that will not be used for a garden in the future.

•       Do not plant susceptible crops where southern blight occurred the previous year.

•       Control weeds, which can allow buildup of the fungus.

•       Prepare the land properly. The previous crop must be well decomposed prior to planting, and this may require disking or rototilling the field several times in the fall and in the spring.

•       Bury the previous crop litter with a moldboard plow to a depth below later cultivation equipment movements (8-12 inches). The crop litter should be below a 3 to 5 inch depth. None of the buried litter should ever be brought back near the soil surface during the current season by cultivation.

•       Do not throw soil with debris against plant parts during the growing season if southern blight is a problem.

•       Control foliar diseases since dead leaves on the ground may trigger infection. Weeds should also be controlled early in the season for the same reason.

•       Avoid using organic mulches where southern blight is a problem.

•       For commercial growers, soil fumigation is an option. It will reduce, but not eliminate, southern blight.

•       Terraclor (PCNB) can be used at planting time for tomatoes, peppers, potatoes, and beans. Refer to the label for proper use instructions. Terraclor will reduce southern blight when used preventively and cannot be used after planting. (SB)

3. Ozone Injury in Vegetables

Atmospheric ozone levels have been high lately, with television stations issuing alerts to sensitive people on some days. The same ozone can be harmful to some plants. The exposure of sensitive plants for 4 hours at levels of 0.04 to under 1.0 ppm of ozone will produce injury. Ozone is produced naturally in the upper atmosphere and by man, from the byproducts of the combustion of coal or petroleum fuels, as in internal combustion engines.

Sensitive vegetable crops include snap beans, carrots, sweet corn, gourds, cantaloupes, green peas, potatoes, pumpkins, squash, tomatoes, and turnips. Among fruit crops, grapes, peaches, and strawberries are sensitive. Cucumbers and peppers are considered resistant.

Symptoms can range from pale leaf color to bleached and the upper leaf surface may be stippled or flecked, especially on the highly-exposed areas of the leaf. Plant health is affected by the loss of photosynthetic area. Rapidly-growing plants are affected more than mature plants, and irrigated plants can be expected to show more symptoms than drought-stressed plants. In cucurbit crops that have covered the ground, ozone injury appears as pale-colored strips through the field, with the pale strips being the older, crown leaves of the row. The damage may later affect the younger leaves. (SB)

4. 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)

5. Zeal Now Labeled for Grapes

Etoxazole (Zeal miticide) by Valent is a mite growth inhibitor. Zeal has an unknown or non-specific target site of action and for resistance management purposes is placed in the Mode of Action Group 10B. The new Zeal label for February 2006 (EPA registration number 59639-138) has added grapes and the listed pests are Pacific spider mite and the two-spotted spider mite. Unfortunately when they submitted the grape portion of the new label, they forgot to add European red mite. Thus, they had to put together a FIFRA Section 2(ee) recommendation for Zeal (EPA Registration Number 59639-138) that adds European red mite to grapes.

For anyone with the old Zeal label (EPA registration number 59639-123), they will need the Supplemental Grape Label (Zeal Supplemental Label 59639-123) that adds grapes and the FIFRA Section 2 (ee) Recommendation label [EPA Registration Number 59639-123) that adds European red mite to grapes. Please take the time to have all the proper labels that you will need in your possession when applying a pesticide. (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.
***Biofix for GRB 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.

Programs in agriculture and natural resources, 4-H youth development, family and consumer sciences, and resource development. University of Tennessee Institute of Agriculture, U.S. Department of Agriculture and county governments cooperating. UT Extension provides equal opportunities in programs and employment.