Fruit Pest News
Volume 10, No. 12 July 24, 2009
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. Strawberry Anthracnose
2. Carryinig Over Plasticulture Strawberries
3. Cucurbit Powdery Mildew Season
4. Bitter Rot of Apple
5. Why Do You Fumigate Your Strawberry Ground?
6. Plum Curculio Activity
7. Pheromone Trap Catches
1. Strawberry Anthracnose
We have had another report of strawberry anthracnose - this one in some day-neutral varieties planted this spring. Plants from three nurseries comprised the planting, and it is not known if the anthracnose originated with one of the nurseries or the farm environment. We earlier had a report of anthracnose in a plasticulture field at the end of the season. (SB)
2. Carrying Over Plasticulture Strawberries
With the increasing cost and regulation of fumigation, there is increased interest in carrying plasticulture strawberries over the summer for a second year or at least for harvesting tips for propagation. Beware of anthracnose and Phytophthora crown rot if you are trying this. Both of these are deal-breakers. Anthracnose should be suspected if lesions are found on petioles or stolons, and samples should be submitted to the plant diagnostic lab. For Phytophthora crown rot, look for dying or stunted plants, and send the crowns to the lab for confirmation. (SB)
3. Cucurbit Powdery Mildew Season
We have had a couple of reports of cucurbit powdery mildew, and it's that time of year. As reported earlier, we have a new registration for this disease, Switch fungicide. It represents a new class of chemistry for this use. Since resistance problems have ended the effective life for the strobilurins (Quadris, Cabrio, Flint) against this disease, another class was needed. The strobilurin fungicide Pristine has a second ingredient that offers some protection against powdery mildew, but is in short supply this year. The zoxamide fungicide Quintec can be used on melons. Sulfur and the sterol inhibitors Nova and Procure make up the remaining recommended powdery mildew materials.
The sterol inhibitor fungicides have also experienced some loss in effectiveness at certain locations. With the threat of resistance to the sterol inhibitors in mind, you should rotate to sulfur when using one of these materials.
The strobilurins provide control of other diseases such as microdochium blight and downy mildew and, because of this, still have some utility in cucurbits. On the other hand, sulfur, Quintec, and the sterol inhibitors are specific to powdery mildew and should be tank mixed with broad-spectrum fungicides such as chlorothalonil or mancozeb. Switch has activity against Alternaria leaf blight and gummy stem blight, but not microdochium blight or downy mildew, and should be tank mixed with chlorothalonil or mancozeb. Remember that sulfur is strictly a surface protectant and coverage of both sides of the leaves is needed for good control. (SB)
4. Bitter Rot of Apple
Bitter
rot is the most potentially explosive of the apple fruit rot diseases. We sometimes
get reports of growers, especially homeowners, losing the majority of their fruit
to this disease. The restrictions placed on the most effective group of fungicides,
the EBDC's, have increased our problems with bitter rot. The disease can move so
rapidly because infection can occur in as little as 5 hours of wetting at 79-82 F.
At 80 F, lesions can develop and produce spores within 11 days of infection. Fruit
remain susceptible right up until harvest.
Identification. Bitter rot is recognized by round,
sunken lesions on the fruit. When very young fruit are infected, the lesions
appear as tiny gray-brown flecks, which usually do not develop further until fruit
begin to ripen. Fruit infections occurring a month after petal fall begin as small,
round, slightly sunken areas that are light to dark brown in color. As the lesions
enlarge, concentric rings of spores or their fruiting bodies form around the center.
Decay lesions extend in a cone-shaped pattern toward the core, observed by cutting
the apple in half through the decayed area. This V-shaped lesion distinguishes bitter
rot from white rot, which has a cylindrical decayed area.
Cultural
control. Bitter rot is controllable if trees are well-pruned and air circulation is good in
the orchard. The removal of excess growth improves drying conditions and penetration
of sprays into the canopy. Try to prevent the buildup of inoculum by removing overwintered mummified
fruit, if feasible, or even diseased fruit during the growing season. Leaving
fire-blighted shoots on the trees can increase fruit rot problems, because the
fungi can colonize them. Do not allow prunings to pile up near the orchard. Prunings
can be left on the orchard floor if they are chopped with a rotary or flail mower,
which removes the bark on which the fungus can reproduce.
Monitoring bitter rot. Orchards should be scouted regularly
for this and other fruit rots. In orchards in which this disease has been a problem,
or in highly susceptible varieties, inspect the trees each week, beginning in early
June. Highly susceptible varieties include Golden Delicious, Fuji, Arkansas Black,
Granny Smith, Empire, and Yellow Newton. Almost as susceptible are Gala, Stayman,
Jonagold, Jonathan, Grimes Golden, Ginger Gold, and Braeburn. Among the least susceptible
are Delicious, Rome Beauty, and Winesap, but no variety has a high level of resistance.
Inspect
as many fruit as is practical (this exercise provides another case for keeping trees
trained to a manageable height). If more than 3 infected fruit are observed on any
tree, a change in the control program may be needed. The needed change may be in
the tree training and other cultural practices mentioned above.
Or it may be in the spray program. The spray interval may need to be shortened (especially
if the weather is rainy), the fungicide choice may need to change (a bitter rot fungicide
should be used in each cover spray), or the application method may need adjustments.
Chemical
control. The need for fungicidal protection against bitter rot is greatest from
midseason until harvest, although some fruit infection can occur as early as petal
fall. Where bitter rot has been troublesome in the past, use an EBDC fungicide (Dithane,
Manzate, Penncozeb, or Polyram) as long as the label allows (until 77 days before
harvest). Tank mixing with captan after petal fall will improve control of white
rot and black rot.
Captan, ziram, and thiram are good bitter rot materials,
and should be used at full rate where problems with bitter rot are expected.
The addition of a 1/2 rate of Topsin M helps with control of sooty blotch and
flyspeck, as well as white rot and black rot. The strobilurin fungicides, Flint and Pristine, are
as effective against bitter rot as captan, thiram, and ziram. The strobilurins
are more expensive, but do not require the addition of Topsin M to attain good
control of sooty blotch and flyspeck. Cover sprays should be applied
at 10- to 14-day intervals, using 10-day intervals during wet, rainy periods. (SB)
5. Why Do You Fumigate Your Strawberry Ground?
As supplies of methyl bromide dwindle under the Critical Use Exemption program, strawberry growers who have used or plan to use this fumigant should prepare for changes. New growers probably will not be able to get methyl bromide, and they will need to consider one of the alternatives. Existing growers may be able to get methyl bromide, but they should plan on using virtually impermeable film (VIF) and the lower rates of methyl bromide that this film allows while maintaining control. No one will be able to obtain methyl bromide in a few years, so we need to learn to do without it.
There are two questions you need to ask yourself:
1) Do I really need to fumigate? If you use a good crop rotation, or are moving onto new production land, then the need to fumigate is minimal. It might not even be needed at all. For many growers, though, rotations are not practical, and the same crop has been on the same fields for years, making fumigation the answer to reduce pathogens and weeds. Rob Welker, Methyl Bromide Alternative Project Coordinator at NC State, says that if you are unsure of your problems and have been fumigating simply because it is part of the plasticulture system, then try leaving some of your production unfumigated and see what the results are. You might be surprised. In an on-farm strawberry trial in the western piedmont of North Carolina, a nonfumigated treatment yielded statistically the same as the methyl bromide treatment. For most cases, however, he has seen approximately 20% reduction in yield when strawberries have not been fumigated.
2) If my crop benefits from methyl bromide fumigation, what is the fumigant doing that is beneficial? Is it controlling diseases? nematodes? annual weeds? perennial nutsedge? This knowledge helps you select the proper alternative to methyl bromide. Most of them are not as broad spectrum as MB. If you do not already know what pests are a problem on your farm, leaving an unfumigated area will provide the answer. If annual weeds are the only pest that methyl bromide has been controlling for you, that problem can be controlled with herbicides that have been labeled for plasticulture strawberries in recent years. However, don't assume that weeds are the only problem based on a visual observation of the treated and untreated areas of the field. There may be root diseases that are not obvious, as weeds are. You may need assistance from your university specialists in determining the cause of yield differences between the treated and untreated areas.
Remember that neither methyl bromide nor any other fumigant controls diseases other than those borne in the soil: Anthracnose, Botrytis, angular leaf spot -- none of these are controlled by fumigation. In assessing your farm's disease control needs by fumigation, only consider Phytophthora crown rot and the black root rot complex. When you consider that nematodes are not the problem in our fine-textured soils that they are in the coastal plains, the potential pest spectrum controllable by fumigation in Tennessee looks narrow! All the more need to leave an untreated area to determine the benefit of methyl bromide fumigation.
In summary, most of us fumigate simply because we've been told we should. Find out if you really do need to.
Please let us know if we can help you in your efforts. Contact your county Extension agent or Steve Bost (address at end). (SB)
6. Plum Curculio Activity
Detection of plum curculio adults has traditioanlly
been difficult. Since about 1993, entomologists have been evaluating the use of
the Tedders trap for plum curculio monitoring. The black Tedders trap mimics the
trunk of a tree. The plum curculio adults crawl up the structure and at the top
they enter a funnel that opens into the trapping container. Plum curculio larvae
develop in fruit during the spring and early summer. In July, adults start emerging
from the fruit. Recently, I have been catching adults in the trap from July 7 to
the present.
I put my Tedders trap at the Ellington Agricultural Center
next to a peach tree and I wrapped the trunk of the tree with a white plastic trash
bag. The plum curculio will be more attracted to the black upright Tedders trap
than the white tree trunk. According to Dr. Russ Mizell at the University of Florida,
making the tree trunks white reduces competition with the trap so that the trap catch
increases by 35 percent (http://ufinsect.ifas.ufl.edu/weevil-trapping.htm). Dr.
Mizell also notes to organic gowers and backyard gardeners that perhaps one to three
traps placed around each whitewashed or white wrapped fruit tree will reduce damage
from plum curculio in small plots.
Early season feeding and oviposition
(egg laying) by plum curculio on apple produces raised russeted bumps (feeding) and
cresent shaped russeted scars (oviposition). Most of the apples with larvae in
them will drop to the ground during June drop. The plum curculio also makes cresent-shaped
oviposition wounds on stone fruit. Plum curculio larvae are legless and they can
be found in stone fruit at harvest. Also, spores of brown rot fungi can be transferred
into the stone fruit during feeding.
This time of year, it is probably
second generation plum curculio adults that are active. Since the apples are not
growing as rapidly, the plum curculio adults make small round holes with a hollowed-out
cavity in the apples where they feed. This provides an entryway for fruit rot organisms.
They will feed on fruit until the fall when the cooler weather and shorter day length
leads them to move to hibernation sites. Feeding by adults on maturing peaches will
produce strands of clear gummy material that emerges from the fruit. (FH)
7. Pheromone
Trap Catches and Biofixes (FH)
Nashville (Davidson County) Pheromone Trap
Catches for 2009
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), beet armyworm
(BAW), squash vine borer (SVB), fall armyworm (FAW)
| OFM | RBLR | OBLR | CM | GBM | VLR | BCW | DBM | AW | CL | BAW | SVB | FAW | |
|
3-13 (Put out RBLR trap) |
-- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| 3-20 | -- | 29* | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
| 3-23 | -- | 14 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
|
3-30 (put out BCW trap) |
-- | 9 | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- | -- |
|
3-31 (put out OFM, CM, VLR, OBLR traps) |
-- | 10 | -- | -- | -- | -- | 0 | -- | -- | -- | -- | -- | -- |
| 4-2 | 4** | 2 | 0 | 0 | -- | 0 | 0 | -- | -- | -- | -- | -- | -- |
|
4-3 (put out AW trap) |
-- | -- | -- | -- | |||||||||
|
4-8 (put out GBM, DBM, BAW, FAW, SVB, CL traps) |
12 | 19 | 0 | 0 | -- | 0 | 2 | -- | 4 | -- | -- | -- | -- |
| 4-13 | 9 | 17 | 0 | 0 | 4*** | 0 | 0 | 0 | 7 | 0 | 0 | 0 | 0 |
| 4-20 | 4 | 7 | 0 | 0 | 5 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 4-27 | 6 | 0 | 0 | 0 | 16 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 5-4 | 2 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 5-11 | 0 | 0 | 4**** | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 5-18 | 5 | 0 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 5-21 | 3 | 12 | 23 | 0 | 4 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 5-26 | 7 | 29 | 10 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 6-1 | 7 | 96 | 38 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 6-10 | 10 | 4 | 18 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 0 |
| 6-15 | 3 | 2 | 6 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 6-22 | 6 | 2 | 2 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 6-30 | 5 | 2 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 7-7 | 8 | 7 | 16 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 0 | 0 |
| 7-15 | 5 | 16 | 16 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| 7-24 | 2 | 11 | 6 | 0 | 3 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
* Biofix for RBLR in Davidson County estimated as prior to March 20 (trap not
out early enough).
**Biofix for OFM in Davidson County was April 2.
***Biofix
for GBM in Davidson County was April 13.
****Biofix for OBLR in Davidson County
was May 11.
Putnam County Pheromone trap Catches for 2009
Tufted Apple Bud Moth (TABM)
| OFM | RBLR | OBLR | CM | VLR | TABM | |
| 3-16 | -- | 10* | -- | -- | 0 | -- |
| 3-18 | -- | 31 | -- | -- | 0 | -- |
| 3-20 | -- | 2 | -- | -- | 0 | -- |
| 3-23 | -- | 2 | -- | -- | 0 | -- |
| 3-25 | -- | 0 | -- | -- | 0 | -- |
| 3-27 | -- | 6 | -- | -- | 0 | -- |
| 3-30 | -- | 11 | -- | -- | 0 | -- |
|
4-1 (put out OBLR, TABM traps) |
||||||
| 4-3 | -- | 10 | 0 | -- | 0 | 0 |
|
4-10 (put out OFM trap) |
-- | 11 | 0 | -- | 0 | 0 |
| 4-13 | 4 | 3 | 0 | -- | 0 | 0 |
|
4-17 (put out CM trap) |
12 | 9 | 0 | -- | 0 | 0 |
| 4-20 | 10 | 0 | 0 | 2** | 0 | 0 |
| 4-22 | 4 | 0 | 0 | 0 | 0 | 1 |
| 4-24 | 7 | 2 | 0 | 2 | 0 | 2*** |
| 4-27 | 4 | 0 | 0 | 1 | 0 | 0 |
| 5-1 | 5 | 0 | 0 | 0 | 0 | 0 |
| 5-8 | 11 | 0 | 0 | 1 | 0 | 14 |
| 5-15 | 1 | 0 | 0 | 0 | 0 | 15 |
| 5-18 | 3 | 0 | 0 | 1 | 0 | 12 |
| 5-22 | 5 | 14 | 0 | 0 | 0 | 22 |
| 5-25 | 2 | 16 | 3 | 2 | 0 | 1 |
| 5-29 | 0 | 30 | 3 | 1 | 2 | 6 |
*Biofix for RBLR in Putnam County estimated as prior to March 16 (trap not out
early enough).
**Biofix for CM in Putnam County was April 20.
.**Biofix for
TABM in Putnam County was April 24.
Obion County Pheromone Trap Catches for 2009
| VLR | RBLR | OBLR | CM | OFM | |
| 5-1 | 3* | -- | -- | -- | -- |
| 5-12 | 42 | -- | -- | -- | -- |
| 6-1 (Note: missing data [--] prior to June) | 14 | 22 | 2 | 0 | -- |
| 6-18 | 7 | 14 | 1 | 0 | 2 |
| 6-22 | 6 | 14 | 1 | 0 | 2 |
| 6-27 | 4 | 2 | 1 | 0 | 3 |
| 7-22 | 5 | 4 | 0 | 0 | 6 |
*Biofix for VLR in Obion County was May 1.
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 2009 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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