Fruit Pest News

Volume 6, No. 6  April 26, 2005

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. Current Conditions

    2. Blackberry: Watch for Orange Rust

    3. Strawberry: Phytophthora Crown Rot Found

    4. Pheromone Trap Catches of Diamondback Moth and American Plum Borer

    5. Grape: Climbing Cutworm

    6. Grape: Critical Period for Black Rot Control

    7. Tree Fruit: Pheromone Trap Catches

1. Current Conditions

"Blackberry winter" happened this weekend, and the weather remains cool. Good news for fire blight control, because this type of weather slows the buildup of the causal bacterium. Many cultivars of apple are at petal fall, which ends the period of susceptibility to fire blight blossom blight. Problem is, secondary blooms may continue to open. The year's first sighting of apple scab was made on April 22, on a crabapple tree, and the lesions were already producing spores. Shower activity and cool temps are forecast for this week. Provide protection against diseases that flourish in this weather, such as scab and powdery mildew of apple, common leaf spot of strawberry, and downy mildew and Phomopsis cane and leaf spot of grape. (SB)

2. Watch for Orange Rust in Blackberries

Orange rust can be very destructive to blackberries and black raspberries. Most of the blackberry varieties that we grow in Tennessee are moderately to highly resistant to orange rust. However, some varieties, such as Navaho, are quite susceptible.

The fungus causes plants to be so stunted and weakened that they produce little or no fruit. The fungus is systemic in the plant, and is perennial inside the below-ground parts. Once a plant is systemically infected by orange rust, it is infected for life. It is for this reason that removal of infected plants is recommended, to prevent spread of the fungus to other plants.

The time to control orange rust is in the spring. Your queue to take action is the appearance of weak, spindly new shoots with pale green to yellowish leaves. Such plants should be removed before they begin to produce the orange-colored, blister-like pustules on the lower leaf surface. The orange pustules contain spores that spread to other plants and cause new infections that may not become apparent until the following spring.

The fungicides Nova, Pristine, and Cabrio can be used for control of orange rust. These fungicides help prevent leaf infections. They will not cure a systemically-infected plant. Begin applications soon (the orange pustules should mature and release their spores sometime in the month of May) and continue every 10 to 14 days until mid-summer. For Nova, the maximum amount is 10 oz per acre per year, and the rate per application is 1.25 to 2.5 oz per acre. Cabrio is labeled at 11 - 14 oz per acre, Pristine at 18 - 23.5 oz per acre, and the sum of the number of applications for these two materials cannot exceed four. (SB)

3. Strawberries: Phytophthora Disease Control

A case of Phytophthora crown rot was submitted to the lab last week from a plasticulture field. The source of the infestation is not certain.

Be on the lookout for wilting plants with reddish-brown discoloration of crown interiors. See Figure 17. If these symptoms are found, it is a good idea to have the disease confirmed by a lab, because it is sometimes impossible to distinguish Phytophthora from anthracnose crown rot. We would also be interested in knowing where this disease occurs.

Control. If your field is known to have had Phytophthora in the past, you should begin fungicide treatments before symptoms appear. The products discussed below should help reduce losses not only to Phytophthora crown rot, but also to leather rot (a berry rot caused by the same fungus) and red stele (caused by a different, but related, fungus). Ridomil Gold and Aliette are systemic fungicides that are used in control of Phytophthora, Pythium, and the downy mildews of labeled crops. Their methods of application differ.

Ridomil performs best when taken up by the roots and translocated upwardly by the plant. The preferred method of application in strawberries is through the drip system. Ridomil Gold EC is injected into the drip system at the rate of 1 pint per treated acre. An actual acre would only receive 0.6 pint if the beds are 3 feet wide on 5-foot centers, because only 60% (3/5) of the ground would be treated. If you apply Ridomil with a sprayer, use enough water to move the fungicide into the root zone. An additional application may be made during fruit set or harvest.

Aliette is labeled for use against red stele and leather rot. Recent research has indicated that it is also effective against Phytophthora crown rot. Aliette is applied at 2.5-5.0 pounds per acre at 30-60 day intervals for red stele control and at 7-14 day intervals for leather rot control. Aliette can be applied through the drip system or through some sprinkler irrigation systems. A foliar spray is the preferred method of application of Aliette because of its downward systemic activity. Like Ridomil, Aliette can be applied on the day of harvest. Follow label directions carefully. (SB)

4. Pheromone Trap Catches of Diamondback Moth and American Plum Borer

In Nashville at the Ellington Center, pheromone traps were put out on April 18 for American plum borer, armyworm, Fall armyworm, beet armyworm, cabbage looper, diamondback moth, Squash vine borer and a turf pest, sod webworm. On April 20, five diamondback moths (pest of cabbage and other cole crops) were caught and four more were caught during the rest of the week. This pest was probably active prior to when the trap was first put out. These tiny moths have a series of diamond shaped white markings down the back where the folded wings come together. The small green larvae chew small holes in the leaves of cole crops. Inspect cole crops now for the presence of the small green diamondback moth caterpillars and their feeding damage.

The American plum borer is a wood-boring pest of plum, peach, cherry, persimmon, sycamore, basswood, tuliptree, sweetgum, oak and others. These pyralid moth borers have two generations per year. Three moths were caught on April 20, two on the 21st, one on the 22nd and none on the 25th. The second generation moth flight is expected by early September but pheromone trap catches will let us know the actual flight dates. No specific borer sprays are recommended for this pest in the spring or fall on stone fruit. Borer sprays for peachtree borer are recommended as a post-harvest trunk directed spray of chlorpyrifos or endosulfan in early to mid-August. This spray should also protect against the second generation American plum borer expected in late August or early September. (FH)

5. Grape: Climbing Cutworms

Climbing cutworm damage has been seen in grapes where leaves and flower buds are clipped. If more than one to two percent of the buds injured, a directed cutworm spray using carbaryl (Sevin) may be justified. Direct the spray in the late afternoon to the lower cane and surrounding soil. (FH)

6. Grape: Critical Period for Black Rot Control

Grapes are entering the pre-bloom stage of growth. This is the beginning of the most critical period for control of black rot disease. Be sure you don't miss this fungicide spray! (SB)

7. Nashville (Davidson County) Pheromone Trap Catches for 2005
Oriental fruit moth (OFM), redbanded leafroller (RBLR), obliquebanded leafroller (OBLR), codling moth (CM), grape berry moth (GBM), variegated leafroller (VLR), black cutworm (BCW)

* Biofix for RBLR in Davidson County estimated as occurring on March 12.
**Biofix for GBM in Davidson County is April 4.
***Biofix of BCW in Davidson County on April 12.
****Biofix for OFM in Davidson County on April 12.

Bradley County Phoromone Trap Catches for 2005

*Biofix for RBLR in Bradley County on March 12.
**Biofix for OFM in Bradley County on March 25.
***Biofix for CM in Bradley County on April 16.


Putnam County Pheromone trap Catches for 2005

*Biofix for RBLR in Putnam County on March 21.
**Biofix for OFM in Putnam County on April 6.

Obion County Pheromone Trap Catches for 2005

*Biofix for RBLR in Obion County estimated to be on March 12 (trap not out early enough).
**Biofix for OBLR in Obion County on April 4 (waiting for confirmation).
***Biofix for CM in Obion County on April 4 (waiting for confirmation).
****Biofix for OFM in Obion County on April 11.
*****Biofix for VLR in Obion County on April 25 (waiting for confirmation).

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 2005 The Unversity 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.