May Gardening Topics

Powdery Mildew:

Powdery mildew fungus is a common disease on many plants and produces a white powdery appearance on leaves and sometimes other green parts. It can be found on roses, dahlias, chrysanthemums, peas and squash. Some rose varieties are so susceptible that you would be better off removing the plant. A homemade spray with baking soda may be used for control. To each gallon of water, add 2.5 teaspoons of light horticulture oil (or salad oil) and four teaspoons of baking soda. Use a fine spray on affected plants, but sparingly as some plants may show some sensitivity. More control methods are available in the UC Pest Note on Powdery Mildew.

Ants in the house:

The first step of ant control is to clean up any food crumbs, spills or leaks that might attract the ants. Store your food in tight containers. Keep the ants outside by caulking cracks and crevices. Use baits that contain boric acid. Place baits in locations that are not accessible to pets or children. Control with baits can take several weeks; ants take the bait back to the nest where it is effective. The UC Pest Note on Ants or the Ant Quick Tips has additional information.

Carpenter Bees:

These bees are similar in appearance to bumble bees and are about an inch long. They do not sting. They are considered beneficial insects because they pollinate many plants and trees. For their nests, they tunnel into unpainted softwoods such as pine, fir and redwood in house or garden structures. Adults overwinter in the nests, emerge in the spring, mate, deposit food in the tunnels and lay eggs. The tunnels are sealed with wood pulp and the new adults chew their way out. After the bees emerge, fill the holes with steel wool and wood filler. Apply paint to the surface to prevent re-entry. Further information is available in the UC Pest Note on Carpenter Bees.


Earwigs are third only to snails and slugs in causing plant damage. While they are beneficial because they eat insects such as aphids, unfortunately they also feed on soft plants. Earwigs can do quite a lot of damage if there is a high population. They feed at night and hide in moist, tight-fitting places during the day. Trap them by putting out moistened, tightly rolled newspaper or corrugated cardboard in the evening. In the morning dispose of the paper and the trapped insects. Another method of control is a covered container such as a small margarine tub with holes cut halfway up the sides. Pour in about an inch of soy sauce and a thin layer of vegetable oil in the container and bury up to the holes. Empty as needed. Other control methods are described in the UC Pest Note on Earwigs.


Gophers are also called Pocket Gophers. They make their presence known with crescent shaped mounds of dirt in the garden. Snacking on plant and tree roots as they tunnel through the soil, they are active year round and can have up to three litters a year in well watered areas. They also gnaw on irrigation lines and divert water into their tunnels, making it difficult to properly water plants. Adults live about three years. Homeowners can use several methods to control them. Locating the main tunnel is the first step. Placing Macabee or box traps or poison baits are explained in detail in the UC Pest Note on Gophers. Another method involves excluding them with wire fencing. Ultrasonic devices and chewing gum have been tested and are not considered to be effective.


As summer nears and efficient watering practices become more important, mulching is an effective technique to keep soil temperatures even, to retain moisture in the soil and to prevent weeds from germinating. Mulching with organic matter such as chipped tree trimmings, compost, or barks not only reduces water usage but also improves the organic content and texture of soil. Apply at least two to three inches of material (three to six inches of larger bark pieces), keeping it several inches away from the trunks of trees and shrubs to prevent crown rot. Renew every few years as it decomposes and enriches the soil.

Eugenia Psyllid:

This psyllid has been a real problem in California. New leaves on the infected Eugenia look very much like peach leaf curl. The leaves also may become discolored. Thanks to the diligent work of the entomology researchers in biological insect control at UC Berkeley, there is a parasitic wasp called Tamarixia. It was released in Santa Clara County in 1993. The wasp is known to go as far as 45 miles and is found throughout the county. It is essential that no insecticide be used on the Eugenia. The Tamarixia wasp can not do its job if it's poisoned. For more information see the UC Pest Note on Psyllids.

Fire Blight:

Fire Blight shows up in spring with blackened branches and twigs that have a scorched look. It strikes pyracantha, cotoneaster, toyon, flowering pear and crabapple, mountain ash, hawthorn and fruit trees (apple, pear, loquat and quince) and more. Fire Blight spends the winter in cankers or wounds on the plant and resumes bacterial growth in the spring. There may or may not be oozing from the canker. It is spread by insects, rain, or pruning. The infection can extend into limbs, trunks, or root system and may kill the tree. Prune the infected branch about 8-12 inches below the visible damage. Spraying with a very weak Bordeaux mixture during bloom may help. The UC Pest Note on Fire Blight contains more information.


Fuchsias come in many forms with sizes from small hanging baskets to 12 foot bushes and in hundreds of varieties. They bloom from early summer to first frost and the colors range from white, blue-violet, purple, pink, red to almost orange. Fuchsias like cool summer temperatures, filtered sunlight, moisture in the air, and overhead watering or misting. Feed with a complete fertilizer in light doses every few weeks. Pinch out the tips to keep it full. Prune in late February by cutting out about the same amount that grew the previous summer. Leave two fat buds on each branch. Spider mites can cause stippling of the leaves and the fuchsia gall mites distort leaves and shoots. Spider mites can be discouraged by overhead watering and use of a soap spray on all leaves. Trim off the gall mite damage and use a soap or oil spray on clean foliage. More control information on Fuchsia pests is at UC information on Fuchsias.

Snapdragon Rust:

Rust is a big problem for snapdragons. Springtime's mild and moist days favor rust. It forms unsightly dark brown or rust colored pustules or blisters on the leaves and stems. The rust spores are spread by the wind. Overhead watering is not recommended. Keep the foliage dry. Keep your plants growing vigorously by watering and feeding them properly. Try resistant varieties, but be aware that most will get rust anyway. Remove infected plants as soon as possible to avoid spreading the fungus. More rust information may be found at UC Pest Notes on Rust.

Soil Solarization:

Soil solarization can be used to control diseases, nematodes and weeds. The area to be solarized should be level, free of clods and visible weeds, and be as smooth as possible. Make a shallow trench around the area and water the whole area well. Lay down transparent plastic on the soil. Do not use black or other colored plastic. Anchor it to the ground by placing the plastic's edges into the trench and then fill the trench with soil. The highest soil temperatures are in June and July, but good results can be obtained from late May through September. Leave the soil covered for 4 - 6 weeks. This process controls most diseases, weed seeds, and nematodes. Refer to the pest note on soil solarization.

Verticillium wilt:

Verticillium wilt is a soil-borne fungal disease and damages the water conducting tissues. The damage is characterized by affecting one side of the plant. The leaves may wilt and turn brown, dying upward from the base of the branch to the tip. Dead leaves often fall, but may not. Mildly affected plants may survive if fertilized and encouraged into vigorous growth. The fungus can live for years in the soil. Soil solarization may eliminate it from infected soils. Soil rotation with cereals or broccolis can reduce the pathogen. Avoid high nitrogen fertilizers. Plant Verticillium wilt-resistant varieties of tomatoes, potatoes or strawberries. Refer to the UC information on Tomato, Potato, and Strawberry.

Funny Question of the Month

There is a bird's nest in my hanging basket, how do I water the plant? Answer: Very carefully!