Fruit
Volume 4, No. 13
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
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
In This Issue:
1. Apple: Summer Disease Control Program
2. Apple: Powdery Mildew
3. Apple: Necrotic Leaf Blotch of Golden Delicious
4. Blackberry Rosette: Continue to Watch for It
1. Apple: Summer Disease Control Program
Your summer disease control program is, no doubt,
well underway. The so-called summer diseases take a greater toll on
Your choice of fungicides will depend to some extent on what diseases have historically been a problem in your orchard. If bitter
rot has been a problem, captan should be a major
component of your summertime spray program.
Captan has had a 4-day re-entry interval in the past. The re-entry interval has been changed on the Captan 80WDG label, allowing workers to enter the treated area in 24 hours.
Remember that management of diseases with fungicides is improved if cultural practices that reduce inoculum and enhance coverage are used. (SB)
2. Powdery Mildew of Apple
Powdery mildew is usually thought of as a dry-weather disease. However, high humidity caused by frequent rains can also contribute to mildew problems by favoring spore production and germination. Powdery mildew will continue to spread as long as there are new leaves developing on apple trees. When terminal growth stops, the potential for spread of powdery mildew will decrease. On susceptible varieties, apply effective mildewcides such as the sterol inhibitors, the strobilurins, or sulfur every 10 to 14 days until terminal growth stops. (SB)
3. Golden Delicious Growers - Protect Against Necrotic Leaf Blotch
Necrotic leaf blotch can strike with great suddenness. A prevention program should be begun right away on Golden Delicious and its bud sports, because a remedy is not possible after the disorder appears. Although necrotic leaf blotch is not a disease, certain fungicides will help control it. In the past, we relied on the EBDC fungicides (Dithane, Manzate, Penncozeb, etc.) for control. However, with the current label restrictions (77-day PHI and 3 lb/acre maximum rate), the EBDC fungicides are no longer useful for managing necrotic leaf blotch. Ziram or thiram should be applied on a 10-14 day schedule from mid-June through early August. Tank mixing with captan will improve the control of certain other diseases. Foliar sprays of zinc oxide are also effective for prevention of necrotic leaf blotch.
Necrotic leaf blotch begins as broad necrotic areas on green leaves. The green turns to yellow and the leaves fall from the tree. The affliction can occur in several "waves" throughout the summer. It is usually most severe when a period of overcast, rainy weather is followed by sunny weather. (SB)
4. Blackberry Rosette: Continue to Watch for It
Rosette (double blossom) disease is the scourge of blackberries. It has the potential to destroy a blackberry planting. If it is present in your planting, it should be readily apparent as bare berry caps; i.e. berries that do not develop. Click here for an image. The sepals (the green, leaf-like structures that enclose blossoms) are abnormally long and pointed and may have a pink to purplish color. The infected fruit clusters usually consist of multiple shoots, rather than the normal single shoot. Such growths are known as rosettes or witch's brooms.
These rosettes should have been removed in the spring, before the blossoms opened, releasing the spores. Removing and destroying the rosettes now would still be worthwhile, since some spores are still being released. The fungus is not systemic in the plant, so only the side stems showing disease symptoms have to be removed. Use copper at 10-14 day intervals. However, do not expect fungicide applications to control rosette in this year's crop. Fungicides applied this year control rosette in next year's crop by protecting the new primocanes. Any rosettes you see this year arose from infections that occurred on primocanes last year.
Fungicidal control may have a place even if you do not currently have
rosette, if you are growing a susceptible variety.
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