INSECT and DISEASE

Summer 2011

 

Spotted Wing Drosophila, Drosophila Suzuki, is a new pest of concern along the west coast of the United States. First identified in California in 2009, it has now been identified north to B.C. Canada, in many areas along the I-5 corridor. Hot dry summers are expected to limit its spread into the interior portions of the country. It is a type of fruit fly, or vinegar fly is another common name. Unlike other types of vinegar fly which deposit their eggs in fully ripe fruit, this one deposits her eggs in the fruit just prior to the full ripe stage. The larvae are mature and ready to pupate in 6-10 days, when the fruit is just ripe and ready to pick, depending on temperature. This fruit fly infests many types of soft fruit, from blueberries to strawberries, domestic or wild, and many others in between. At this point the insect is not widespread, but is expected to become more established over the next few years. Learning to monitor and identify this insect will be your first best step to dealing with it. Currently, Spinosad insecticides are the recommended spray if they are present in your fruit plantings. Click here to learn more about the life cycle, identification, and monitoring of SWD (Spotted Wing Drosophila) http://swd.hort.oregonstate.edu/information_homeowners

 Contact your local co-operative extension service to see if the SWD fruit fly has been reported in your area.

Apple maggot and codling moth

Monitor both apple maggot and codling moth traps to determine when insect populations are increasing throughout the fruit development season, so you can apply control measures when they are needed and will be most effective. Surround and other types of insecticidal sprays will need to be re-applied periodically throughout the fruit ripening season. Read package labels for instructions.

Apple maggot control bags only need to be installed once. Just install them by the time the fruit is nickel size for season long prevention of egg deposit by apple maggot flies. Thinning the fruit at the same time will reduce the total number of bags you need to install, and allow the fruit to grow to a larger size. Unfortunately, the nylon apple maggot control bags we offer, which allow fruit color to develop normally, are not effective against codling moth. The tiny little caterpillars are able to chew through the mesh and make their way into the fruit. A paper type bag is effective, but will need to be removed for the last couple of weeks before harvest to allow color development.

There are other non-chemical techniques you can also use. Sanitation is one of the most important, for both apple maggot and codling moth control. Every week or two, beginning about 6 to 8 weeks after bloom, check fruit on trees for signs of damage. Look for pin-hole scars (where apple maggot eggs have been deposited) or slightly larger scars where the codling moth caterpillar chewed its way in (sometimes not very visible because it went through the blossom scar). As the caterpillar grows it pushes its “frass” (excrement) out of its entrance hole. Remove and destroy any visibly infested fruit before the larvae are old enough to crawl out and begin the next generation. This can be a very effective method for reducing the insect population, provided your orchard is relatively isolated. If your neighbors are not taking care of their trees, you may have to take additional steps. Also clean up dropped fruit as soon as possible after they fall because dropped fruit may have larvae in them. Removing infested fruit from the tree and promptly picking up dropped fruit from the ground is most critical in May and June, but should continue throughout the season.

Install more codling moth and apple maggot traps than are necessary to observe population fluctuations to trap more individual insects and help reduce total populations.

Spinosad, a broad spectrum natural insecticide derived from the metabolites of a common soil bacterium, is effective against codling moth, plum curculio, and currant worm caterpillars before they enter the fruit. Apply the first spray 2-4 weeks after bloom, or when you start seeing the pin hole scars. Start looking for the scars a week or so after catching increased numbers of adults in your monitoring traps. Reapply spinosad every 10-14 days, up to 6 times per year, following label instructions. New adult populations can emerge periodically throughout the growing season, up to 3-6 times depending on the insect and the length of your growing season.

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Some varieties of grapes, apples, gooseberry, currants and other fruits are susceptible to powdery mildew. There are chemical fungicide sprays available at your local nursery, or you may want to try the recipe on page 16 in our Raintree Owner’s manual. You can achieve a reasonable level of control using fatty-acid soap, oil (such as Neem), and powdered milk, but you will have to apply repeated sprays throughout the typical infection period, from June through August or September. To avoid having to spray choose varieties listed as being resistant or immune to powdery mildew.

 

Some varieties of grape produce clusters of berries that are very tight, which can be susceptible to botrytis (bunch rot). Thin fruit clusters to maintain better air circulation in the bunch. Serenade, a biological fungicide derived from Bacillus subtilis strain, may be effective as a spray. Botrytis also affects other fruits, including strawberry, raspberry, blackberry, blueberry, cherry, and pear. Keeping the fruit dry, and not in contact with other fruit will help minimize spread of the disease. Sanitation is very important. Clean up and discard infected fruit (compost piles are generally not hot enough to destroy the organism), as well as old leaves that have died back or have fungal lesions on them, to remove as much source of inoculum as you can.

 

If you have anthracnose lesions in the bark of your apple tree you can cauterize or excise new infections once the weather has dried out. To cauterize use a hand torch with a small flame, heat the bark until it begins to bubble, be sure to stop before it begins to turn black. Your goal is to cause heated cells to expand and rupture, not burn them. Apply heat to the entire lesion area, as well as about ¼” outside the lesion all the way around, to make sure you have destroyed all of the fungal organism. To excise the lesion, use a sharp blade, such as a utility blade or a grafting knife. Start at a point above the lesion about ¼” and press just hard enough to cut through the entire bark layer. Make an oval shaped cut with a point at the top and bottom around the lesion, about ¼” away, then pop or pry out the piece you have cut loose. Keep the pieces as you remove them so you can burn them and destroy the fungus when you are done. Clean the blade between each lesion with alcohol. Either cauterize or excise as early in the summer as you can to give the tree plenty of time to heal over the wounds.

By Theresa Knutsen