Fruit Pest News
Volume 8, No. 6 April 17, 2007
A weekly, online newsletter whose goal is to provide all interested persons with timely information on diseases and insects of commercial fruit and vegetable crops 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. Strawberries: Watch for Angular Leaf Spot
3. Blueberry: Twig Blight and Freeze Injury
4. Strawberry Plant Dip for Anthracnose Control
5. Suggestions for Insect Control in Short-Crop Peaches
6. Apple: Fire Blight Reports
7. Apple: New Theory on Shoot Blight Spread
8. Davidson County Pheromone Trap Catches
1. Current Conditions
The aftermath of the freeze still unfolds. The status of the current crop is becoming clearer, but the effects of the freeze on the health of the plants will take some time to discern. The Memphis and Chattanooga areas had some survival of some blossoms and young fruit and some strawberry crops were saved by freeze protection. We will continue to address pest management needs for fruit plantings with harvestable crops. Growers whose fruit crops were lost will want to use minimal spray schedules, as discussed in last week's issue. In those crops, the idea is to target only those pests that pose a threat to the foliage or the future health of the plant. (SB)
2. Strawberries: Watch for Angular Leaf Spot
The Easter freeze could cause problems with angular leaf spot, caused by the bacterium Xanthomonas fragariae. This disease is promoted by cold temperatures and tends to flare after a freeze. The water that is used for freeze protection aids dispersal and infection of tissue by the bacteria. This disease does not usually cause yield losses, but can cause severe quality problems because of a discoloration of the berry cap (calyx). Click here to see images of this and other symptoms.
Dark, watersoaked lesions first appear on the lower surface of the leaf, becoming angular as they enlarge and become delineated by veins. On the upper leaf surface, lesions appear brown and necrotic, and may be so numerous that the necrosis is generalized. These symptoms are difficult to distinguish from common leaf spot and leaf scorch. One identifying characteristic is the translucent nature of lesions when leaves are held up to a bright light; looking from the backside, light will be visible through the lesions. Berry caps may become infected, darkened, have angular lesions and are unappealing. Vascular infection and wilting by X. fragariae may lead to plant death. This systemic infection may be confused with wilt of anthracnose or Phytophthora crown rot; however, crown tissue infected by X. fragariae does not become discolored.
The bacteria primarily enter the field via infected planting stock, and may persist in the field by overwintering or oversummering in infected plants and dead leaves. In the Southeast, problems have not persisted from one year to the next in annual plantings. The pathogen cannot survive freely in the soil, but can survive on transplants in cold storage for one year and on plant debris through long dry periods. Healthy plant tissues are more likely to become diseased than stressed tissues. Losses can be substantial if a large portion of the fruit calyxes are infected and unsightly.
Registered copper compounds provide some control of the peduncle and calyx infections. In fields with a known problem, apply copper fungicides when cool, wet weather is predicted. Repeat applications at 7 to 10-day intervals. Discontinue if phytotoxicity appears, usually after 4-5 applications. (SB)
3. Twig Blight and Freeze Injury on Blueberry
Symptoms of blueberry twig blight, caused by Phomopsis vaccinii, can begin to show shortly after budswell and continue throughout the spring. Twig dieback resulting from the recent freeze may also be showing.
With twig blight, individual buds turn brown and die, followed by browning of the bark around the bud as the fungus moves from the blighted bud into the twig. The infection usually advances inside the twig until most or all of the flower buds on a twig are killed. The dieback does not progress into the older wood, making twig blight easy to distinguish from stem blight, caused by Botryosphaeria dothidea. Freeze injury can also resemble twig blight. Twig blight lesions usually continue to enlarge and may be centered around a bud. There is usually a distinct border between the live and dead portions of the cane, with twig blight. Freeze injured shoots tend to have a more gradual border.
It is helpful to prune out and destroy the twigs infected with twig blight, but this should be done prior to the bloom period, for maximum benefit. Many spores are released from infected twigs beginning shortly after bud break. Those that land in opening buds germinate and invade the twig. However, all is not lost if you have not done this. Removing infected twigs between this time of year and August is helpful in that it reduces twig blight in next year's crop. That is because dead twigs continue to produce spores, which land on and infect buds that become next year's flowers.
Preventive fungicide applications may be needed in plantings in which twig blight has been a problem in the past. Captan, Ziram, Cabrio, and Pristine are the most effective fungicides for twig blight.
The highbush varieties Murphy and Harrison are highly susceptible to twig blight. Croatan is moderately susceptible, while Reveille, Cape Fear, Bluechip, and Wolcott are relatively resistant. Some rabbiteye varieties are susceptible, especially Delite. (SB)
4. Strawberry Plant Dip for Anthracnose Control
Strawberry anthracnose sometimes enters a field on infested plants. The causal fungus may be present on the crown, root, and stem surfaces, or it may be internal, as infections that are not yet visible. Research has shown that the incidence of anthracnose in the field can be greatly reduced if transplants are dipped in appropriate treatments before planting, to kill the surface spores. These treatments will not rid the plants of anthracnose infections, because they are internal and beyond the reach of the chemicals.
The azoxystrobin products, Quadris and Abound, are labeled for use as strawberry plant dips. Wash soil off roots before dipping. Mix 5-8 fl oz of Quadris or Abound per 100 gal of water. Dip plants by immersing completely for 2 to 5 minutes. Plant treated plants as quickly as possible. The hydrogen dioxide product, OxiDate, is also labeled for this use. Mix 1 gal per 100 gal of water, immerse, remove, and allow to drain. Do not rinse. Plant as soon as possible after treatment. Use personal protective equipment as specified by the labels when dipping. (SB)
5. Suggestions for Insect Control in Short-Crop Peaches
Dr. Dan L. Horton (University of Georgia) recently sent out some management options for treating savageable crops. It is important to protect these blocks as economically as possible. In short-crop peach blocks consider alternate-row-middle (ARM) cover sprays. He suggests using 2.25 to 2.5 lbs Imidan 70W or 12 to 14 ozs esfenvalerate (Asana XL, Adjourn) in these ARM cover sprays. When using ARM, modestly shorten cover spray intervals by a day or two. (FH)
6. Fire Blight Reports
To add insult to injury, fire blight is appearing in some apple orchards. Some blossom infections occurred during the warm period, and symptoms began to appear just as the freeze hit during Easter weekend. The freeze had nothing to do with those cases. The timing may cause some growers to mistake fire blight for injury caused by the freeze. The blighted clusters and shoots should be able to serve as inoculum sources for spread to shoots, as in other years. Note: Death of shoots bearing blighted blossom clusters is not true shoot blight -- Shoot blight results from infection of the young leaves on a shoot. (SB)
7. New Theory on Shoot Blight Spread in Apples
Aphids have been suspected of being involved in the spread of fire blight
to apple shoots. Recent research at Penn State indicated no association between
aphids and shoot blight spread. Attention has shifted to potato leafhoppers.
Some researchers have suspected that potato leafhoppers can vector or facilitate
the spread of fire blight on shoots, according to Dr. Turner Sutton at North
Carolina State University. This insect does not overwinter in Tennessee. They are thought to overwinter in the southern
half of the Gulf States in pine trees. Each spring they fly north with the prevailing
winds.
If shoot blight appears, Dr. Jim Walgenbach (North Carolina State University) suggests
that growers consider controlling potato leafhoppers with an application of Provado,
especially on cultivars susceptible to fire blight. (FH)
8. Nashville
(Davidson County) Pheromone Trap Catches for 2007
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), armyworm (AW)
| OFM | RBLR | OBLR | CM | GBM | VLR | BCW | DBM | AW | |
| 2-22 (caught one RBLR in last year's trap) put out new trap | -- | 1 | -- | -- | -- | -- | -- | -- | -- |
| 2-26 | -- | 0 | -- | -- | -- | -- | -- | -- | -- |
| 2-28 | -- | 1* | -- | -- | -- | 1 | -- | -- | -- |
| 3-2 | -- | 3 | -- | -- | -- | 0 | -- | -- | -- |
| 3-12 | -- | 50 | 0 | -- | -- | 0 | -- | -- | -- |
| 3-14 (Put out OFM, CM, OBLR, BCW) | -- | 26 | -- | -- | -- | 0 | -- | -- | -- |
| 3-20 | 0 | 33 | 0 | 0 | -- | 0 | 0 | -- | -- |
| 3-21 | 1 | 7 | 0 | -- | -- | 0 | 0 | -- | -- |
| 3-26 | 20** | 34 | 0 | -- | -- | 0 | 0 | -- | -- |
| 3-27 (put out AW trap) | 8 | 4 | 0 | 0 | -- | 0 | 0 | -- | -- |
| 3-30 | 12 | 16 | 0 | 0 | -- | 0 | 0 | -- | 0 |
| 4-2 | 18 | 18 | 0 | 0 | -- | 0 | 0 | -- | 1 |
| 4-3 (put out DBM, GBM) | 10 | 1 | 0 | 0 | -- | 0 | 0 | -- | 0 |
| 4-5 | 11 | 0 | 0 | 0 | 4*** | 0 | 0 | 0 | 0 |
| 4-10 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 4-17 | 2 | 1 | 0 | 0 | 2 | 0 | 0 | 0 | 0 |
* Biofix for RBLR in Davidson County was February 28.
**Biofix for OFM in Davidson
County was March 26.
***Biofix for GBM in Davidson County was April 10.
Bradley
County Pheromone Trap Catches for 2007
| OFM | CM | |
| 3-26 | 1 | 0 |
Putnam County Pheromone trap Catches for 2007
| OFM | RBLR | OBLR | CM | VLR | |
| 3-19 | 1 | 9* | 0 | 4*** | 0 |
| 3-21 | 1** | 3 | 0 | 2 | 0 |
| 3-23 | 2 | 6 | 0 | 1 | 0 |
| 3-26 | 2 | 15 | 0 | 2 | 0 |
| 3-28 | 4 | 7 | 0 | 1 | 0 |
| 3-30 | 2 | 14 | 0 | 0 | 1 |
| 4-2 | 6 | 32 | 0 | 0 | 0 |
| 4-6 | 2 | 28 | 1 | 1 | 0 |
| 4-13 | 0 | 2 | 1 | 0 | 0 |
*Biofix for RBLR in Putnam County estimated as March 2 (trap not out early enough).
**Biofix
for OFM in Putnam County March 21.
***Waiting to verify biofix for CM, many unknown
moths being caught in these traps that can easily be mistaken for CM..
Obion
County Pheromone Trap Catches for 2007
| OFM | RBLR | OBLR | CM | VLR | |
| 3-19 | 0 | 17* | 0 | 0 | 0 |
| 3-26 | 5** | 89 | 0 | 1 | 0 |
| 4-11 | 0 | 0 | 0 | 0 | 0 |
*Biofix for RBLR in Obion County estimated to be on March 2 (trap not out early
enough).
**Biofix for OFM in Obion County on March 26.
(FH)
The Fruit Pest News URL is: http://web.utk.edu/~extepp/fpn/fpn.htm
Contacts:
Steve Bost, Professor and Extension Plant Pathologist
Frank Hale, Professor and Extension Entomologist
Both authors available at:
615-832-6802
fax 615-781-2568
Plant and Pest Diagnostic Center
5201 Marchant Drive
Nashville, TN 37211
Copyright 2007 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.