October 19, 2001
COASTAL GARDENER
Franklin Laemmlen, Ph.D.
Q: How can I get rid of yellow jackets?
A: Summer and fall is yellow jacket season almost everywhere. There are several wasps, which are very active now provisioning the nests and feeding their young. Yellow jackets and paper wasps are very common on the Central Coast. These insects usually eat worms and plant nectar, but are readily attracted to meat and sweets. Paper wasps hang their nests from bush or tree limbs in a protected site. Yellow jackets usually nest in the ground or a hollow space such as a log or house wall. If you can find the nest, the wasps can be controlled with soapy water (the detergent acts as a wetting agent, and the wasps drown) or any of several insecticide bombs or sprays. Control is best done at night when the air is cool, all the wasps are at home and are reluctant to fly. For picnics, meat traps can be placed around, but away from the picnic site, so the wasps are drawn to that source of food rather than your hamburger. For wasp trap making suggestions contact the Coastal Gardener.
Q: I have planted potatoes in my garden. When can I start digging them?
A: Depending on the variety, potatoes take from 80 to 120 days to mature. As a “rule-of-thumb,” I suggest 100 days to start digging from the date of planting. If you like “new” potatoes, you can try digging early to check their size and maturity. At the time the plant blooms, there will be small edible tubers present, but the full crop potential of the plant is still several weeks away.
Q: Each year most of my walnuts get destroyed by a “worm.” Can I do something to prevent this?
A: Both codling moth and walnut husk fly will attack and destroy walnuts. Codling moth larvae are a pink ½ to ¾-inch long worm with a brown head. The walnut husk fly larvae are maggots. The body is white and somewhat pointed at one end. Walnut husk fly (WHF) normally must be controlled in July and August. When this fly wants to begin laying eggs, it is attracted to green round objects on the tree. Therefore, you can hang green styrofoam balls covered with “Tac” or “Tanglefoot” in the tree, starting in mid-June. Check them weekly. When WHF adults are found stuck to the styrofoam, it is time to spray. The adult female WHF is a tawny color with yellow markings. The wings are clear, with three distinctive dark bands. When the first flies are caught, spray the tree with diazinon, malathion or carbaryl. There is only one generation of adults per year, so 2-3 sprays, 15 days apart, should greatly reduce the infestation.
Q: My pittosporum is growing poorly. I have noticed that many of the leaves are notched on the edges. Are these two problems related?
A: They could be. The notching of the leaves is caused by feeding of the adult black vine weevil, Otiorhynchus sulcatus. The larvae of this insect feed on the roots and basal stems. Black vine weevils and their young feed on a wide variety of shrubs including privet, euonymous, azaleas, rhododendron, taxus, citrus, and other evergreens. High grub populations can severely stunt these plants by root feeding and may cause death. Where populations are small, no control is recommended. However, if populations build up, a soil drench and basal plant spray with diazinon or lindane will help reduce the population and improve plant vigor. There are other causes of plant decline, so check for diseases and other insects (scale) as well before making a final diagnosis.
Send your garden and landscape questions to: The Coastal Gardener, 624-A West Foster Road, Santa Maria, CA 93455.
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