Pests of the Season

WEED: Creeping spurge, Chamaesyce serpens. Creeping spurge is a summer annual broadleaf plant. It is found in the Central Valley, southern South Coast Ranges, and southwestern region. It inhabits agricultural lands and other disturbed places—like gardens, landscapes, containers and cracks in walkways. A weed that once established and has gone to seed is a difficult one to get rid of. The very small seeds are viable for several years, so it is important to control this weed before it goes to seed to reduce the seed bank in your soil. Avoid composting as seeds may not be destroyed. Mulching can help reduce the weeds. The flowers are tiny and occur at the stem tips and along the stems. Spurge species have a milky, sticky sap that can cause contact dermatitis in humans and animals so after a session of pulling it is good to wash your hands or wear gloves while handling. There are two other spurge weeds that are very similar in most respects: Petty spurge (Euphorbia peplus) and Spotted spurge (Euphorbia maculata). The spotted spurge has a maroon spot on the leaves which is very distinctive.

DISEASE: Peach leaf curl (Taphrina deformans). This is fungus disease that will show up when peach and nectarines break into leaf bud in the spring. The spores overwinter on the trees and infest the leaves. It is exacerbated by cool, moist conditions in a rainy spring. Infected foliage is distorted and reddened in spring and is the distinctive symptom of peach leaf curl. New leaves and shoots thicken, pucker, and may later die and fall off. If you allow an infection to go untreated for several years, it can lead to tree decline. To prevent peach leaf curl, treat susceptible trees with a preventive fungicide spray every year after leaves fall. It is usually recommended to spray three times after leaf fall and before spring bud break. Spray all parts of the tree to get all the spores which lurk on branches and buds. However, the most important spray in just before bud break before Valentine's Day. Treating after symptoms appear won't be effective. When planting, consider the few tree varieties resistant to the disease.

INSECT: Thrips, order Thysanoptera, are tiny (about 1 mm in length), slender insects with fringed wings that feed on plant leaves by puncturing the epidermal (outer) layer of host tissue and sucking out the cell contents. This results in stippling discolored flecking, or silvering of the leaf surface. Thrips feeding is usually accompanied by black varnish like flecks of frass (excrement). They discolor and scar leaf, flower, and fruit surfaces, and distort plant parts. Many species of thrips feed on fungal spores and pollen and are often innocuous. Certain thrips are beneficial predators that feed on other insects and mites. Thrips have several generations (up to about eight) a year. When the weather is warm, the life cycle from egg to adult may be completed in as short a time as 2 weeks. The Wester Flower thrips is the most common pest in our area and I have had intense infestations on dahlias and zinnias this past summer. Hot dry weather favors thrips and with cooler fall weather they are less of a problem. Spraying plants with water daily helps discourage them as they seem not to thrive with wet conditions. Biological control can help by using green lacewings, minute pirate bugs, mites, and certain parasitic wasps. Spinosad pesticide is also a control that lasts 1 week or more and moves short distances into sprayed tissue to reach thrips feeding in protected plant parts. For more information see: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7429.html#TABLE1