Fruit Pest News
September 4, 2001
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. Strawberries: Switch Fungicide Receives Registration
2. Apples: Weather Alert
3. Apples: Prevent Storage Decays
4. Apples: Late-Season Pests
1. SWITCH® FUNGICIDE RECEIVES REGISTRATION FOR STRAWBERRIES
Switch fungicide has received federal registration by the EPA for control of Botrytis gray mold in strawberries and onions, as well as Alternaria purple blotch in onions. Switch is a prepack mixture of two novel active ingredients, cyprodinil and fludioxonil. Neither active ingredient belongs to a family of compounds currently registered on strawberries. As a result, Switch will provide aid in preventing the development of resistance to fungicides in fungal pathogens.
Switch is an effective Botryticide, and contains both a systemic (cyprodinil) and a surface protectant (fludioxonil) ingredient. In a recent California trial, Switch provided residual control of gray mold for 7 to 10 days. I have found that Switch also is very effective against strawberry anthracnose. The manufacturer, Syngenta Crop Protection, plans to submit anthracnose for inclusion on the label as more data becomes available.
Switch is a 62.5 percent wettable granules formulation labeled at 11 to 14 ounces per acre on strawberries. It is classified by EPA as a reduced-risk pesticide. (SB)
2. WEATHER ALERT: COSMETIC APPLE STORAGE DISEASES
The recent mild, rainy, cloudy weather will provide plenty of apple
scab, sooty blotch, and flyspeck pressure to apples. Although these diseases can develop after apple harvest,
in storage, they are the result of infections
that took place in the orchard before harvest. Their appearance can reduce the marketability of the fruit.
Storage scab is sometimes
referred to as 'pinpoint' scab because of its small size, from barely visible up
to 1/8 inch in diameter. The lesions are black and often shiny because of the intact
cuticle. They are circular and differ from scab lesions that develop in the orchard
by a darker color and a definite border.
Late-season scab that becomes visible
before harvest closely resembles storage scab. Late-season scab lesions often remain
viable in storage and enlarge by forming a fringe of olive-green mycelia around the
margin of the scab spot.
At optimal temperatures for the scab, sooty blotch,
and flyspeck fungi (roughly 62º to76º F), about 8 to 10 days are required for symptom
development after infection. Symptom development does not occur below 48º F.
Control
of these cosmetic storage diseases must take place before harvest; that is, infection
must be prevented on the tree. In selecting fungicides, preharvest intervals for
the fungicides in question are a primary consideration. Then consider what diseases
to target. In orchards in which sooty blotch and flyspeck is active, Benlate, Topsin
M, Flint, or Sovran are good choices. Benlate or Topsin M should be tank mixed with
captan, not only for resistance management purposes, but also for bitter rot control.
Where scab has remained or has become active, Dr. Turner Sutton, North Carolina State
University, suggests using dodine (Syllit) at 1.5 to 2 lbs/acre plus captan at 5
lbs/acre. Flint or Sovran would also play a valuable role. (SB)
3. PREVENT APPLE STORAGE DECAYS
The
previous article discussed cosmetic apple storage diseases. Other storage diseases
such as blue mold, caused by Penicillium expansum, and gray mold, caused by
Botrytis cinerea, involve decays that actually reduce marketable yields. Unlike
the cosmetic storage diseases, most of the decay disease infections occur in storage,
mostly through wounds. Control tactics differ for the two types of storage diseases.
However, certain late-season fungicide sprays in the orchard can help reduce both
types. Applied at 14 days before harvest, a tank mix of either Benlate or Topsin
M with either captan or ziram helps control storage decays and sooty blotch and flyspeck.
If
you have had problems in the past with storage decays, you are encouraged to visit
http://www.wvu.edu/~agexten/orchardmon/om082100.htm
for details on control. The article was written by Alan Biggs, West Virginia University,
and David Rosenberger, Cornell University. (SB)
4. LATE-SEASON ORCHARD PESTS
Spider Mites
If European red mites or
two spotted spider mites have not been too much of a problem look to the weather.
These summer mites prefer hot, dry weather. Many areas of the state have had lots
of rain with a good number of rainy, overcast days. Wet foliage can lead to fungal
diseases for the mites just like it can lead to more disease pressure for the apples.
Some cultivars such as red delicious seem to have more problems from mites almost
every year. If these problem cultivars have low mite populations then the weather
is definitely in your favor for mite suppression. It might also be a good year for
beneficial insects. I have seen high numbers of green lacewings flying about. They
lay tiny white eggs that are attached to leaves and twigs with a threadlike, white
stalk. The larvae are predaceous and feed mainly on aphids. Predaceous mites will
do a better job of controlling spider mites populations if the pest mites do not
reach real high numbers. That means that if weather or other factors limit the population
growth of the pest mites to moderate levels, the predaceous mites will be better
able to manage the remaining mite populations.
Late Season Sprays
If
a late season spray is to be applied, be sure to check the preharvest interval (PHI).
It will probably be necessary to choose a pesticide with a short PHI. Examples
of the range of PHI are Sevin with a 3 day PHI, Imidan has a 7 day PHI, Confirm has
a 14 day PHI and Auvant has a 28 day PHI. (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, Associate 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