Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa
Help Desk Response: The spotted wing drosophila (Drosophila suzukii) is a relatively new pest of cherries and other soft fleshy fruits (strawberries, raspberries, blackberries, blueberries, etc). Unlike other vinegar flies that attack rotting or fermenting fruit, the spotted wing attacks maturing fruit. The name spotted wing drosophila comes from the single black spot at the tip of each wing of the male adult. Don't think though that you will be able to identify this fly by those markings without magnification because these adults are small, really small. The female is able to penetrate the skin of the fruit to lay her eggs and this act creates a small depression (“sting”) on the fruit surface. The eggs hatch and the maggots develop and feed inside the fruit, causing the flesh of the fruit to turn brown and soft.
An alternative to malathion with fewer negative environmental effects would be spinosad (e.g., Monterey Garden Insect Spray and see http://www.ipm.ucdavis.edu/TOOLS/PNAI/pnaishow.php?id=65); h
Since spotted wing drosophila attacks ripening fruit it is often not noticed in home garden situations until the fruit is being harvested. Sprays at this time will not protect the crop because maggots are already in the fruit. If only some of the fruit are infested, you can salvage some of the crop by harvesting immediately and sorting the fruit, removing any with “stings” on the surface. It is recommended that all infested fruit be removed from the tree and picked up from the ground. It should then be placed in a sealed plastic bag and disposed of in the trash or buried. Do not put the infested fruit in your compost pile as it may not get hot enough to destroy the eggs and larvae still in the fruit.
This blog was originally written by Emma Connery, Retired Master Gardener Program Coordinator, for publication in the Contra Costa Times April 2, 2011. Slight changes have been made to the original for this blog and are the full responsibility of the blog editor.
Help Desk of the UC Master Gardener Program of Contra Costa County
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Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
Cherry Tree Gardener: I am writing for help in identifying what is ailing our Japanese Fuji Cherry Tree. It is about 3 years old and had been doing very well until about a month ago. For about 2 months, we were watering it with water from our shower, but I have stopped. All of the leaves are hanging limply, but they have not yet fallen off. Thank you for your consideration and advice.
Before diagnosing your problem, could you please clarify the kind of cultural care you are providing to the tree?
1. You said that you had been watering it with water from the shower. Approximately how many gallons per week were you providing from the shower? When did you stop using the shower water?
2. How soon after you stopped using shower water did the symptoms appear?
3. Now that you have stopped using shower water, what kind of water are you providing to the tree?
4. How often are you watering now?
5. What type of watering system are you using? Drip? Spray? Soaker hose?
6. Did you fertilize the tree, or use any kind of insecticide or herbicide near the tree before seeing the symptoms?
We look forward to solving your problem.
Cherry Tree Gardener: Thanks for getting back to me. I really appreciate it. Here are responses to your questions –
1. You said that you had been watering it with water from the shower. Approximately how many gallons per week were you providing from the shower? When did you stop using the shower water? I put about 10 gallons of shower water per week. I stopped watering with shower water about 2 weeks ago.
2. How soon after you stopped using shower water did the symptoms appear? The symptoms started to appear about 4-6 weeks ago. When the symptoms appeared to be getting worse, I decided to stop watering with shower water. I thought maybe the soap in the water might be causing the symptoms.
3. Now that you have stopped using shower water, what kind of water are you providing to the tree? I water about 1-2 times per week using a hose. I give it a good watering each time, but I'm not sure how many gallons of water. If I had to guess, I'd say 3-4 gallons for each watering. The ground absorbs the water well.
4. How often are you watering now? 1-2 times per week.
5. What type of watering system are you using? Drip? Spray? Soaker hose? I just use a hose with no attachment.
6. Did you fertilize the tree, or use any kind of insecticide or herbicide near the tree before seeing the symptoms? I have not used any fertilizer, insecticides or herbicides.
Thank you again for your help. If you need any more information or pictures, please let me know.
MGCC Help Desk: Thank you for your speedy reply. We believe that your tree has not been receiving enough water through the hot part of the summer. Shower water (without harmful soaps or shampoos, see examples at http://ecologycenter.org/factsheets/greywater-cleaning-products/) is ok but appears that you will need even more water than you have usually applied. Since your tree is 3 years old, it probably has a fairly new and growing root system. During hot summer months, your tree will need a lot of water per month. The exact amount will depend upon what part of the county you live in and how big the tree is. For example, if you live in west county, say El Cerrito, and your tree at the drip line is 8 feet in diameter, it would need approximately 100 gallons during August, but if you live in Walnut Creek, your tree would need approximately 120 gallons in the same time period.
Also, the way you have been watering will deliver water only shallowly, and many of the roots will not have access to any water. The wilting is most likely a symptom of this.
We recommend that you water less often, but more deeply, to completely moisten the root zone (primarily at the drip line) down to a depth of 12 - 18 inches. If you dig into the soil with a screw driver near the drip line down to a depth of at least 12 inches, the soil should be moist but not sopping. If it is dry, you should immediately apply enough water to dampen the soil. Using a hose is fine as long as you deliver enough water. A soaker hose applied around the tree out to the drip line would be less work, and this type of slow watering helps the water go deep where it is needed. If you are able to sufficiently wet the root zone this way, watering every other week should be sufficient.
Once you have thoroughly wetted the root zone, we recommend that you also apply 3 - 4 inches of mulch or compost on top of the soil to reduce evaporation of water. Keep the compost (and water) away from the tree trunk by at least 4 inches, but otherwise spread it under the tree out to the drip line and a little beyond.
Since we believe that your tree is water stressed, it is good that you have not fertilized the tree. We recommend that you withhold fertilizer until next spring.
We believe that based upon the symptoms you provide this will take care of your problem. However, if it does not, please let us know so that we can look into other possible causes of the wilting and drying of the leaves.
Help Desk of the UC Master Gardeners of Contra Costa County
Note: The Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us//span>/span>