Sunday, March 1, 2015

Squash bugs are likely culprits attacking zucchini

Squash bugs suck the juice out of plants through their needle-like mouthparts. The adults are colorful, more than a half-inch long with the underside trimmed in orange to orange-brown stripes. UC Statewide IPM program/Courtesy photo

Question: Last year, my zucchini plants had yellow specks on the leaves that turned brown and then black as they became crisp and dry. What happened?

Chances are you had squash bugs, Anasa tristis. These insects (true “bugs”) suck the plant juices through their needle-like mouthparts.

Look for the colorful adults, more than half an inch long with the underside trimmed in orange to orange-brown stripes. (You may confuse them with stink bugs, similar in appearance though wider and rounder, that feed on tomatoes and legumes, not cucurbits.)

Sanitation is your best form of prevention. Remove zucchini plants after harvest or as soon as they have passed their prime. Keep your garden free of debris that may be overwintering sites for the bugs.

With spring, the adult bugs fly from their winter sites in search of squash and cucumber plants to feed, mate and lay eggs. From this hatch of eggs, a second generation of bugs will overwinter and produce eggs the following spring.

Adult bugs can be trapped beneath boards placed on the soil in spring. (Another entertaining snack for chickens!) When your plant is growing, look under the leaves for the eggs, in clusters and bronze in color. Remove and destroy these.

Question: I’ve been reading up on composting. Some of the sources talk about keeping a balance between green stuff (good sources of nitrogen, or N) and brown (for carbon, C). What happens to the N in the green plant material (such as green grass clippings) when they become dry and brown? Where does the nitrogen go?

The nitrogen remains in the material even after it turns brown. Drying (and turning brown) delays breakdown a little, but otherwise doesn’t change subsequent availability of the nitrogen from the material after it is returned to the soil or to a compost pile.

Lawn grass clippings are typically N-rich, have a relatively low C:N ratio, and breakdown quickly. By the way, I’d encourage you to leave the clippings on the lawn — that will reduce somewhat the fertilizer N required to keep the lawn looking nice.

If you are collecting clippings from someone else’s lawn, make sure they aren’t using herbicide (which they may do unknowingly with some “weed and feed” preparations.) A friend of the Garden Doctor nearly destroyed her tomato seedlings when she repotted them with homemade compost. After consulting with Yolo County farm adviser Gene Miyao, she concluded that there might have been some toxics in that pile, the likely source being lawn clippings.

The “recipe” for a successful compost pile is intended for gardens where the typical brown stuff is sawdust or autumn leaves. But our California recipe may include avocado peels, coffee grounds and banana peels. These look brown but are excellent sources of nitrogen. So it is good that you are remembering the chemistry behind the recipe.

I’m planning to replace my front lawn with native plants. What options are available to get rid of grass? What about perennial weeds? Should I use herbicide?

Congratulations on replacing your water-hungry lawn with native plants! That’s an excellent choice since most cities are now charging for water use. A great resource for choosing natives is UC Davis Arboretum’s “All-Stars” list, available online and as a printed pamphlet.

The All-Star plants have been chosen for their low maintenance, drought tolerance and attraction for beneficial wildlife. Remember, even drought-resistant natives need water until established in the site, as do all plants.

Once established, the native plants should be relatively pest-free and even attract beneficial insects that attack pests. In contrast, you are replacing a lawn that may have many perennial and annual weeds.

During the coming hot summer months, solarization is an excellent choice for removing a lawn so that when you plant the natives this fall there will be fewer weeds or weed seeds. Visit the UC Davis IPM site at for complete guidelines on soil solarization.

Solarizing will work better if you remove existing turf by moistening the lawn and skimming the shovel beneath the grass roots. After you plant your new garden, be alert for perennial weeds that may have survived or reseeded. As perennial weeds reappear, continue to cut at the soil line and eventually the weeds will die from carbohydrate starvation.

Don’t forget to mulch! The Central Park Gardens are a good example of successful weed control by mulch. It benefits from regular applications of bark mulch. You might like to visit and see the meadow there — a little bit of paradise that was once a parking lot.

— Send questions, addressed to the “Garden Doctor,” by email to [email protected], 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
Stop by and chat with us on Saturdays at the Davis Farmers Market.



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