Garden Doctor: ‘Crop’ rotation can help control pests

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* Propagation from cuttings, 9-10 a.m. Saturday, March 16, Grace Garden at United Methodist Church of Davis, 1620 Anderson Road

* Backyard and worm composting workshop, 10 a.m.-noon Saturday, March 23, Woodland Community College, 2300 E. Gibson Road, Woodland

Question: I was turning the soil in my raised beds and I found dormant “caterpillar” looking things in the soil. They are moving now that they have warmed up. What should I do about them? I grew tomatoes in the beds last year and the year before it was squash.

Answer: The Garden Doctor can’t answer your question exactly, without seeing one of the critters from your raised beds. If you find any more, you could email a photo to our office (see below) or bring one to the UC Master Gardener table at the Davis Farmers Market.

When the Garden Doctor was just a girl, both home gardeners and farmers practiced crop rotation to deal with problems such as yours. It is still a good idea, although a little more challenging with the limited space in a raised bed. It is definitely a good idea to consider what is planted from one year to the next. (If your memory isn’t what it used to be, a garden journal becomes an essential tool.)

Try to avoid repeating crops from the same plant family from one year to the next in the same soil. For example, it isn’t a good idea to plant peppers, eggplants or potatoes in soil that has just had tomatoes. They are all members of the Solanaceae family, and some pests may persist from one crop to the next.

You should avoid using an insecticide in any case until you have a positive identification of your “pest.” It may, in fact, be a beneficial insect, such as the larvae of a soldier beetle, which is not harmful to crops and eats aphids and other pests.

Question: Something has eaten the leaves on my radishes and chard until only the ribs remain. What should I do?

Answer: This sounds a lot like the damage caused by cabbage worms, because hungry caterpillars may not be so choosy about what they eat. If this is the problem, you should be able to find some inch-long light green caterpillars that can be picked off by hand and even brown droppings from the caterpillars. (Look carefully; the caterpillars look a lot like what is left of your plants.) The plants themselves may be too far gone to save.

For prevention, be aware of the pretty white moths that may lay eggs beginning in late autumn and early winter on newly planted seedlings. Look at the underside of leaves, especially on cabbage and broccoli plants, for the tiny eggs that are stuck on the leaves. You can wash these off with water. An effective but more costly solution is to spray Bt (Bacillus thuringiensis) on the young plants. Bt is a bacteria that affects only the caterpillars.

Question: There are whiteflies on my grapes and on ornamentals in my yard. What can I do about them?

Answer: Whiteflies are tiny sapsuckers. Leaves of infested plants may turn yellow, get sticky and have black sooty mold. Whitefly eggs are laid in circles or partial circles on the lower surface of mostly full-sized leaves. They are found in vegetables, ornamentals and citrus and if disturbed the adults fly into the air.

Management of whiteflies can be controlled by natural enemies: bigeyed bugs, dustywings, lacewings, lady beetles (lady bugs) and pirate bugs are natural predators. Parasitic wasps are another natural enemy. The beneficials, however, can be hampered by ants or dust and killed by insecticide sprays.

Further management includes removing insect-infested plant material by plucking leaves or pruning branches. Proper sanitation when pruning is essential. Clean pruning shears after each cut in a solution of bleach, discard prunings in trash cans, not in compost piles or your municipal green waste program, keep dust to a minimum by planting ground covers, and avoid insecticide sprays when at all possible.

Much like aphids, whitefliesalso can be controlled by a blast of water. By spraying the underside (underside is the critical element here) of infected leaves, the blast will wash the eggs, larvae or nymphs to the ground where they will die. Hose down the plants once a week to keep these populations at a low level.

Also like aphids, whiteflies often attract ants to their honeydew residue. Ants will help spread the whiteflies to new uninfected areas. Be sure to rid the plants of ants by placing ant stakes around the trunk of infected plants or wrap trunks of plants with a sticky barrier product.

You can learn more about control of pests by viewing the UC Davis Integrated Pest Management website at www.ipm.ucdavis.edu. Another way to find answers to pest questions is to come to the UC Master Gardener table at the Davis Farmers Market in Central Park, Fourth and C streets, from 8 a.m. to 1 p.m. Saturdays. We have lots of convenient Pest Notes on all the favorite pests there.

— Send questions, addressed to the “Garden Doctor,” by email to mgyolo@ucdavis.edu, voice mail to 530-666-8737, or regular mail to UCCE Master Gardeners, 70 Cottonwood St., Woodland, CA 95695. Be sure to include your contact information, because any questions not answered in the Garden Doctor column will be answered with a phone call or email to you.

You can request the Yolo Gardener newsletter delivered by email and learn more about the Master Gardener program in Yolo County at http://ceyolo.ucdavis.edu/Gardening_and_Master_Gardening.