Fruit Pest News
Volume 4, No. 3 March 31, 2003
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. Current Conditions
2. Apples: Tips for Fire Blight Control During Bloom
3. Apples: Early-Season Fungicide Sprays
4. Peaches: Mycoshield Shortage
5. Strawberries: Phytophthora Disease Control
6. Plant Problem Diagnosis: Just a Mouse Click Away
1. Current Conditions
We had our first return to winter during a beautiful early spring. Cold, windy conditions occurred during the weekend of March 29 - 30. Temperatures in most areas were probably not low enough to cause serious damage. Peaches are in full bloom to early petal fall, apples are at tight cluster to pink tip, most strawberry varieties and several blueberry varieties have begun to bloom. Blackberry shoots are one to two inches long. The cool snap should help apple growers by reducing fire blight pressure going into the bloom period. Low temperatures slow bacterial multiplication and reduce the activity of the insects that carry the bacteria. (SB)
2. Apple: Tips for Fire Blight Control During Bloom
Many varieties are within days of the first open blooms. The bloom period is a key time for fire blight management in apple and pear. It is during bloom that many of the most damaging fire blight infections take place. It is also the time at which streptomycin sprays are most effective . . . in fact, we no longer recommend streptomycin after bloom (unless there is a hailstorm) because of its lack of effectiveness against the shoot blight phase. The following points should help you to use streptomycin efficiently.
3. Early-Season Apple Fungicide Sprays
Many trees are now at tight cluster. For many orchards, this is the time for the first fungicide application. Scab control at this time is a must. If scab was abundant last year, the first application should be made at green tip. Scab should be treated early to prevent primary scab infections and thus break the disease cycle. Also, it is important to avoid early infections on sepals (calyx), as these are difficult to detect and can provide secondary inoculum throughout the early part of the growing season.
There are several different strategies for scheduling scab sprays. The selection of a spray program (what fungicide to use and how often) depends on factors such as other disease organisms present and the ability to obtain good coverage of the trees with the sprays. If cedar-apple rust or powdery mildew are a threat, it is probably best to control scab with a sterol-inhibiting fungicide (Nova, Procure, or Rubigan), because control of all three diseases would be obtained. Tank mixing with mancozeb or captan would improve the protectant ability and discourage the development of resistance to the sterol inhibitor (SI). Do not uses captan within 2 weeks of an oil spray.
The 3- to 4-day curative activity of the SI fungicides makes them useful at tight cluster in case some scab infections occurred prior to that time. The SI/protectant combination allows you to space the applications 7 to 10 days apart.
Where cedar-apple rust is a problem, mancozeb or ziram should be used as the protectant, to be mixed with the SI. The strobilurin fungicides Flint and Sovran can be used in lieu of the SI's, but I recommend reserving these materials for use during the summer. They may only be applied 4 times per year, and they play a more valuable role during the summer than during the spring.
Overwintering of powdery mildew is highly dependent on winter weather. Since we did not have prolonged cold temperatures this winter, there should be abundant inoculum in orchards that had mildew last year. If weather conditions are favorable (cool, wet) for mildew, disease pressure could be high on susceptible varieties. Be sure to use an SI on such blocks (see previous paragraph regarding the use of strobilurins). (SB)
4. Peaches: Mycoshield Shortage
Due to production problems, there will be a severe shortage of the antibiotic product Mycoshield, which is used to control bacterial spot in peaches. For information on what course of action to take, refer to the article written by David Ritchie and Phillip Brannen for The Southeastern Regional Peach Newsletter at the following web site:
http://newsletters.caes.uga.edu/SRPN/
(SB)
5. Strawberries: Phytophthora Disease Control
Phytophthora crown rot, also known as vascular collapse, is becoming
an increasing problem in plasticulture strawberry production. To lessen losses in
infested fields, you should begin fungicide treatments before symptoms appear. The
products discussed below should help reduce losses not only to Phytophthora crown
rot, but also to leather rot (a berry rot caused by the same fungus) and red stele
(caused by a different, but related, fungus).
Ridomil Gold and Aliette are
systemic fungicides that are used in control of Phytophthora, Pythium, and the downy
mildews of labeled crops. Their methods of application differ.
Ridomil performs
best when taken up by the roots and translocated upwardly by the plant. The preferred
method of application in strawberries is through the drip system. Ridomil Gold EC
is injected into the drip system at the rate of 1 pint per treated acre. An actual
acre would only receive 0.6 pint if the beds are 3 feet wide on 5-foot centers, because
only 60% (3/5) of the ground would be treated. If you apply Ridomil with a sprayer,
use enough water to move the fungicide into the root zone. An additional application
may be made during fruit set or harvest.
Aliette is labeled for use against
red stele and leather rot. Recent research has indicated that it is also effective
against Phytophthora crown rot. Aliette is applied at
2.5-5.0 pounds per acre at 30-60 day intervals for red stele control and at 7-14
day intervals for leather rot control. Aliette can be applied through the drip system
or through some sprinkler irrigation systems. A foliar spray is the preferred method
of application of Aliette because of its downward systemic activity. Like Ridomil,
Aliette can be applied on the day of harvest. Follow label directions carefully.
(SB)
6. Plant Problem Diagnosis: Just a Mouse Click Away
As the new growing season unfolds, remember that getting a diagnosis of your plant problems can be done quickly with The University of Tennessee's Distance Diagnostics service. Operated by those of us located here at the Plant and Pest Diagnostic Center, at Nashville, the service offers diagnoses for plant problem images submitted to us over the internet. By asking your Extension agent to submit digital images of your sample to us, you may have a diagnosis within hours -- even minutes, if the agent telephones us and asks us to look at the image.
Photographs of plant problem samples and insect and weed specimens are taken with digital cameras, and the images are submitted to the center over the internet. If the center's diagnostician, Tom Stebbins, needs help with a sample, he asks other professionals to view the sample. Only those persons who are given a password can access the sample, for security purposes. Also, only Extension agents, experiment stations, and Tenn. Dept. of Agriculture plant inspectors can submit samples, for the same reason. The only thing needed to submit a sample is a digital camera. Some counties even have microscopes with camera attachments. Stereoscopes are helpful for obtaining images of insects.
Not all problems can be diagnosed from a distance (or in person, for that matter). In many cases, the diagnosis is inconclusive, and we suggest a sample be sent to us in the mail. But we may be able to offer some possibilities as to the cause of the problem based on the symptoms.
Our lab continues to operate as always, as far as examining specimens that are sent or brought to us. Remember, for either method of sample submission, we need background information to help us to make an accurate diagnosis, and thus help you. We look forward to serving you with this new system (or with the old). (SB)
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