Fruit Pest News
Volume 7, No. 12 May 31, 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. Raspberry Bushy Dwarf Virus
2. Effect of Rain on Fungicide Wash-Off
3. Matted-Row Strawberry Disease Control After Harvest
4. Peach Scab
5. Apple: My Trees Have Fire Blight. What Do I Do Now?
6. Apple Scab: Summertime Control
7. Oriental Fruit Moth
8. Pheromone Trap Catches and Biofixes
1. Raspberry Bushy Dwarf Virus
The recent discovery of raspberry bushy dwarf virus (RBDV) in raspberry fields in Ohio should remind us of the threat of this disease here. RBDV has been a problem in Pacific Northwest bramble production for several years. The virus can affect plant vigor and survival. Symptoms may include small, dry, and mishapened berries, foliar chlorosis, and premature dying of fruiting canes before or during harvest.
It may be advisable to avoid the purchase of raspberry or blackberry plants from the Northwest because of the prevalence of RBDV. This is a pollen-transmitted virus that can easily spread once introduce into a field. There are no resistant blackberry or black raspberry varieties. The red raspberry cultivars Willamette, Haida, Heritage, and Latham are reported to be resistant to the disease. (SB)
2. Effect of Rain on Fungicide Wash-Off
If rain is forecast on or around the day you plan to make a fungicide application, it is best to spray before the rain, rather than after. Disease-control products work best in a preventive mode. They need to be in place, working to protect the plant tissues while they are wet. But that begs the question, "Just how durable are those protective covers? How soon do I need to re-apply a fungicide after a rain?" The following article was written for apple growers by Dr. Jim Travis, Pennsylvania State University plant pathologist. The guidelines he provides should apply to all crops, although the example products may not apply. (SB)
If you are using protectant fungicides, you need to consider the effect of rain on wash-off of the materials. The strobilurin (Sovran, Flint) and sterol inhibitor (Nova, Procure, Rubigan) fungicides are absorbed into the leaf and fruit tissue after application (once the residue has dried) and are not affected by rain wash-off. The protectant (Dithane, Manzate, Penncozeb, Captan, Ziram, Thiram, copper) fungicide residues can be affected by rain. A general rule-of-thumb for the effect of rain on washing off protectant fungicides follows.
This rule has been used for many years to provide growers with general guidance. Newer protectant fungicide materials may be less subject to wash-off, but information is limited.
3. Matted-Row Strawberry Disease Control After Harvest
Harvest has
wound down, and now it is time to take steps to produce a healthy bed of plants for
next year's crop. Proper renovation is the most important step in producing a vigorous
crop. When new growth emerges after renovation, fungicide applications may be necessary,
especially in rainy weather. Anthracnose is the greatest threat, since this disease
can prevent bed fill and can debilitate established plants. However, the runner
phase of anthracnose, which affects stolons, petioles and crowns, is difficult
to control. Efforts to control anthracnose on these vegetative parts of the
plant, even with effective fungicides such as Quadris and Switch, may lead to disappointing results.
Resistant varieties such as Delmarvel do not need control measures.
Nova fungicide is registered for use on strawberries. In my field trials, I have found Nova to be very effective against common leaf spot and Phomopsis leaf blight, but that it does not control anthracnose or Botrytis. Phomopsis can be a problem in hot weather, whereas common leaf spot is a problem on certain varieties in cool seasons. Below is a summary of the results I have obtained with field trials on the leaf spot diseases.
Summary of Strawberry Foliar Fungicide Trials
Amount of Disease Control
|
Product |
Leaf Blight |
Leaf Spot |
| Topsin M | moderate | moderate |
| Captan, Thiram | fair | moderate |
| Nova | good | good |
| Quadris | moderate | good |
Please note the following:
4. Peach Scab
I have not yet seen peach scab symptoms, which usually begin appearing around this time. Peach scab has a 40-day latent period, which means that symptoms do not appear for 40 days after infection. Control is not needed on varieties that are within 40 days of harvest, since any infections that occur will not have time to develop before harvest. This does not mean that early-maturing varieties will not have scab if it is not showing at this time (a 40-day latent period could be in progress, and could expire before harvest).
Be sure to begin your brown rot sprays within 2 weeks before harvest for each variety. (SB)
5. Fire Blight: Managing Affected Trees
Following are some reminders for management of fire blight at this time of year. Efforts to limit secondary spread by cutting out fire blight strikes are most successful if the strikes are removed immediately after they appear. By this time in Tennessee, it is too late for strike removal to effectively reduce the rate of spread of the epidemic. Pruning of fire blight shoots during the growing season should be limited to light to moderate cases. Extensive pruning of heavily blighted trees is neither practical nor desirable, as the result would be the stimulation of new, succulent tissue, which is very susceptible. However, young trees and high density, dwarf-tree orchards should be followed closely and strikes should be removed immediately, regardless of the severity of the outbreak. In such trees, the infection can spread internally to the rootstocks and cause tree death.
Classical recommendations for growing-season removal of fire blight strikes include making the cut 8 to 12 inches below the blighted area and sterilizing the pruning tool between each cut. We now know that this approach is not appropriate because of the systemic nature of the bacterial infection. If the infected shoot is associated with the main trunk or a major scaffold limb, you may want to try the "ugly stub" cut, leaving a two-inch stub for winter removal.
Other practices to keep in mind: Excessive tree vigor should be discouraged. Use management systems that promote early cessation of tree growth without adversely affecting tree vigor. Maintain good control of sucking insects, as they can transmit the causal bacterium to healthy shoots. Remove from the orchard and destroy the fire-blighted shoots and limbs, since they can serve as a source of inoculum. If the amount cut cannot be removed quickly, there may be too much blight present for the cutting operation to be effective. (SB)
6. Apple Scab: Summertime Control
The thunderstorm activity we have been experiencing may be encouraging secondary apple scab. At this time of year, control of the fruit phase of scab is key. Fungicide use should center on captan. Use the full labeled rate. You can tank mix the captan with an SI (Nova, Procure, or Rubigan) to obtain curative activity in the leaves, but captan is needed for good control of scab on the fruit, where the SI's are weak. Remember that we want to minimize the use of SI fungicides to delay the development of resistance to them. Use a full rate, if you do decide to use an SI. You can also use Flint, Sovran, or Pristine to obtain some curative activity in the leaves, but they are rather weak on fruit scab and are limited to 4 applications per year. Dodine (Syllit) is very effective against fruit scab if resistance to dodine has not developed in the population.
These weather conditions also favor sooty blotch and flyspeck. With that in mind, selection of captan, Flint, Sovran, or Pristine for the scab sprays will serve to control these fungi also. The SI's and Syllit will not control sooty blotch and flyspeck. (SB)
7. Oriental Fruit Moth
In the Southeast, early season insecticides for plum curculio,
plant bugs and stink bugs usually provide excellent control of OFM. a pheromone
trap threshold of 10 moths/trap/week should be used after third cover. In peach,
first generation OFM larvae feed primarily on tender vegetative growth. subsequent
OFM generations feed inside the fruit.
Pheromone trap catches and degree-day
(DD) models can be used to decide if and when to spray. The biofix is determined
by trap catches when two or moths are first caught in the spring. The biofixes for
Bradley, Putnam, Obion, and Davidson Counties were March 29, March 31, April 3 and
April 4, respectively. Begin to accumulate daily DD (base temperature of 45 F) when
the male flight (biofix) occurs. In peach for low OFM-density orchards, a single
insecticide application can be applied against OFM at 600 DD after biofix. A low
density OFM orchard is one in which less than 0.5 percent of the fruit was damaged
by OFM the previous year and pheromone trap catches do not exceed 10 moths/trap/week
anytime before the accumulation of 500 DD after biofix. In moderate to high-density
OFM orchards, two insecticide applications are applied 14 days apart, the first at
500 DD after biofix.
In apple, first-generation egg laying is usually low
and only one insecticide application between 400 and 500 DD after biofix is necessary,
which usually coincides with petal fall. (FH)
8. 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)
| OFM | RBLR | OBLR | CM | GBM | VLR | BCW | DBM | |
| 3-1 (put out RBLR, OFM, VLR traps) | -- | 0 | -- | -- | -- | -- | -- | -- |
| 3-2 | -- | 3* | -- | -- | -- | -- | -- | -- |
| 3-9 | -- | 15 | -- | -- | -- | 0 | -- | -- |
| 3-13 | 0 | 50 | 0 | -- | -- | 0 | -- | -- |
| 3-21 | 0 | 71 | 0 | -- | -- | 0 | -- | -- |
| 3-28 | 0 | 15 | 0 | -- | -- | 0 | -- | -- |
| 3-29 (put out GBM, BCW, & DBM traps) | 0 | 5 | 0 | -- | -- | 0 | -- | -- |
| 3-30 | 0 | 4 | 0 | -- | 0 | 0 | 0 | 2** |
| 4-4 | 24*** | 34 | 0 | -- | 0 | 0 | 0 | 2 |
| 4-6 | 5 | 14 | 0 | 0 | 1 | 0 | 0 | 1 |
| 4-7 | 14 | 4 | 0 | 0 | 3**** | 0 | 0 | 0 |
| 4-11 | 12 | 10 | 0 | 0 | 1 | 0 | 0 | 1 |
| 4-17 | 39 | 9 | 0 | 0 | 23 | 0 | 0 | 4 |
| 4-18 | 6 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 4-24 | 49 | 0 | 14^ | 0 | 2 | 0 | 0 | 3 |
| 4-27 | 9 | 0 | 15 | 0 | 0 | 0 | 0 | 4 |
| 5-3 | 13 | 0 | 25 | 0 | 0 | 0 | 0 | 1 |
* 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
| OFM | CM | |
| 3-29 | 3* | 0 |
| 4-3 | 26 | 0 |
| 4-5 | 0 | 1 |
| 4-10 | 16 | 0 |
| 4-17 | 19 | 5** |
| 4-24 | 17 | 17 |
| 5-1 | 17 | 2 |
*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
| OFM | RBLR | OBLR | CM | VLR | |
| 3-21 (put out RBLR & OFM) | -- | -- | -- | -- | -- |
| 3-24 | 0 | 0 | -- | -- | -- |
| 3-27 | 0 | 0 | 0 | 0 | 0 |
| 3-31 | 2** | 12* | 0 | 2*** | 0 |
| 4-2 | 1 | 3 | 0 | 0 | 0 |
| 4-7 | 6 | 23 | 1 | 1 | 0 |
| 4-10 | 1 | 16 | 0 | 0 | 0 |
| 4-15 | 9 | 60 | 6 | 0 | 1 |
| 4-17 | 0 | 13 | 1 | 0 | 1 |
| 4-21 | 3 | 14 | 0 | 0 | 0 |
| 4-28 | 10 | 3 | 2 | 1 | 0 |
*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
| OFM | RBLR | OBLR | CM | VLR | |
| 3-13 | 1 | 49* | 0 | -- | 2*** |
| 3-21 | 0 | 40 | 0 | 0 | 0 |
| 3-27 | 1 | 2 | 0 | 0 | 0 |
| 4-3 | 2** | 13 | 0 | 2**** | 0 |
| 4-17 | 1 | 18 | 3^ | 1 | 5 |
| 4-25 | 7 | 0 | 0 | 0 | 4 |
| 5-1 | 4 | 0 | 3 | 0 | 4 |
*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)
| SWW | AW | |
| 4-18 | 3* | 0 |
| 4-24 | 15 | 4** |
*Biofix for SWW in Davidson County for 2006.
**Biofix for AW in Davidson County
for 2006.
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 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.
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