Fruit Pest News
Volume 9, No. 6 April 30, 2008
An 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. Attention Grape Growers: Critical Period for Black Rot Control
2. First Fire Blight
3. Leaf Spots on Vegetable Transplants
4. Fungicides for Botrytis Control on Greenhouse Tomatoes
5. Watch for Orange Rust in Blackberries
6. Scale Insects and Dogwood Borers
7. Pheromone Trap Catches and Biofixes
1. Attention Grape Growers: Critical Period for Black Rot Control
Grapes are at the pre-bloom stage of growth. This is the most critical period for control of black rot disease. If black rot can be controlled during the immediate pre-bloom, bloom, and immediate post-bloom stages of growth, successful control should be possible throughout the season. Be sure you don't miss this fungicide spray! (SB)
2. First Fire Blight
The first reports of fire blight come from Bradley and Davidson Counties, on April 29. Look for wilting and browning of blossom spurs or shoots associated with blossoms. Any symptoms you see this time of year are the result of blossom infections. True shoot blight will come later. Since the bloom stage is over, so is your use of streptomycin. This antibiotic is not effective against the shoot blight phase of fire blight. If tag-on blooms remain, it may be worthwhile to continue streptomycin applications or to remove the blooms by hand. (SB)
3. Leaf Spots on Vegetable Transplants
Those pesky brown spots and dead areas on leaves are the source of one of the most frequent errors made in greenhouse vegetable problem diagnosis. They are often assumed to be caused by fungi or bacteria. Truth be known, they are more often the result of low nutrition, low light, or low temperatures. Add to that the stress and low nutritional state that results from root rot diseases, and you have a rather lengthy list of possible causes of leaf necrosis other than foliar pathogens. You can probably think of other causes of leaf burn, also, but the ones mentioned here produce lesions that particularly mimic fungal and bacterial spots.
One tip for distinguishing foliar diseases from stress factors is the leaf color around the lesions....If the overall color is uniformly green and plant growth indicates good health, the lesions are more likely caused by foliar pathogens. However, if a nice green color is lacking, you will have to investigate further -- pale color, chlorosis, and poor growth could be caused by either foliar diseases or the other factors mentioned above. (SB)
4. Fungicides for Botrytis Control in Greenhouse Tomatoes
Botrytis gray mold control in the greenhouse is primarily approached through cultural practices, but growers often find that chemical supplementation is necessary. Historically, we have been hampered by a lack of labeled products for this use. Progress is slow, but we have added some products in recent years. It is getting to the point at which we can now actually rotate some products, so that we can head off resistance development in the fungus. Decree (fenhexamid) was recently registered and should be a major player in Botrytis control. It can only be applied 2 consecutive times before rotating to an unrelated fungicide. Scala and Serenade are registered products that would make suitable rotation partners. Scala must be tank mixed and the greenhouse must be ventilated for 2 hours after application to avoid plant damage. Serenade would be the product of choice for tank mixing with Scala if you are in rotation with Decree. Decree is limited to 4 applications per crop. Be sure to adhere to the resistance management requirements when dealing with Botrytis, as this fungus knows no bounds when it comes to adapting to a fungicide. Humidity management should always come first.
For control of Botrytis stem canker occurring on the lowest 24 inches of the stem, Botran may be directed to that area. However, the 10-day preharvest interval of this product may preclude its use after harvest begins. (SB)
5. 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)
6. Scale Insects and Dogwood Borer
Apples - Control of San Jose scale insects should not be overlooked because they
can build up to damaging levels on the branches. First generation crawlers are generally
active from petal fall to third cover and they are known to move to fruit. Start
sampling for crawlers at petal fall by making traps with double sided tape wrapped
around a small portion of an infested twig or wrapping the twig with black electrical
tape coated with a thin layer of petroleum jelly. When crawlers are caught in the
traps, treat with an insecticide such as Dimethoate 4EC/400, Diazinon 50WP, Guthion
50WP, Esteem 0.86EC, Centaur 70WP, Assail 30SG, or a summer horticultural oil.
Caution: Diazinon or oil applied with captan or Captec may cause phytotoxicity.
Dogwood
borer control is very important on apples. Apply insecticides (Lorsban 50W, Lorsban
4E, Thionex 3EC, Asana XL) with a handgun sprayer to the trunk, especially to burr
knots and graft unions. Moths can lay eggs from April through September. In Tennessee,
a peak moth emergence usually occurs in late April and another peak occurs in mid-July.
Treatment before July is optimal.
San Jose scale and white peach scale can
be a problem on stone fruit. Use sticky tape traps to monitor for scale crawlers
beginning prior to time of the 7 to 10 days after shuck split spray. Pyriproxyfen
(Esteem 35 WP) or buprofezin (Centaur 70W) should be applied at crawler emergence.
Proper spray timing is very critical for effective control.
Grapes - Grape
scale is another scale in which sticky tape traps should wrapped around the vine
to monitor for the crawlers that should be emerging by May. (FH)
7. Pheromone
Trap Catches and Biofixes (FH)
Nashville (Davidson County) Pheromone Trap
Catches for 2008
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 | CL | |
| 3-10 (Put out RBLR trap) | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| 3-13 | -- | 2* | -- | -- | -- | -- | -- | -- | -- | -- |
| 3-19 | -- | 5 | -- | -- | -- | -- | -- | -- | -- | -- |
| 3-31 | -- | 7 | -- | -- | -- | -- | -- | -- | -- | -- |
| 4-1 (put out BCW, OFM, CM, VLR, OBLR traps) | ||||||||||
| 4-9 | 0 | 2 | 0 | 0 | -- | 0 | 0 | -- | -- | -- |
| 4-11 (put out AW trap) | 2** | 0 | 0 | 0 | -- | 0 | 0 | -- | -- | -- |
| 4-17 (put out GBM, DBM, CL traps) | 0 | 0 | 0 | 0 | -- | 0 | 0 | -- | 0 | -- |
| 4-18 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 4-24 | 2 | 0 | 0 | 0 | 3*** | 0 | 0 | 0 | 0 | 0 |
| 4-29 | 2 | 16 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
* Biofix for RBLR in Davidson County was March 13.
**Biofix for OFM in Davidson
County was April 11.
***Biofix for GBM in Davidson County was April 24.
Bradley
County Pheromone Trap Catches for 2008
tufted apple bud moth (TABM)
| 3-18 (put out OFM trap) | OFM | CM | TABM |
| 4-6 (put out CM trap, TABM) | 0 | -- | -- |
| 4-12 | 0 | 1 | 4 |
| 4-14 | 0 | 0 | 2 |
| 4-19 | 0 | 1 | 0 |
| 4-21 | 0 | 0 | 23 |
Putnam County Pheromone trap Catches for 2008
| 3-16 (put out RBLR, OBLR, VLR) | OFM | RBLR | OBLR | CM | VLR |
| 3-21 | -- | 12* | 0 | -- | 0 |
| 4-1 | -- | 5 | 0 | -- | 0 |
| 4-13 | -- | 0 | 0 | -- | 0 |
| 4-22 | -- | 9 | 0 | -- | 0 |
*Biofix for RBLR in Putnam County estimated as prior to March 21 (trap not out early enough).
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
Soil, Plant and Pest Center
5201 Marchant Drive
Nashville, TN 37211
Copyright 2008 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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