Look for bagworms toward the end of the month. Early detection is important; caterpillars are cleverly disguised and can quickly defoliate plants before they are noticed. Bagworms prefer evergreens such as arborvitae, cedar, juniper, and pine. Tap a branch over a sheet of white paper; look for small, green caterpillars with a small cone of plant debris attached to them. As they grow, they enlarge this cone until it is two inches long. Fully grown caterpillars anchor the bag they constructed to a branch before they become adults. Females fill their bags with as many as 200 eggs after they mate. Hand pick the bags before the eggs hatch to prevent damage. Remove the tough silken threads attaching the bags to the plant. If left on, they can girdle the branches as they grow. Spray infested plants with Bacillus thuringiensis as soon as the caterpillars hatch if bags are too numerous to remove.
Don’t overfertilize your plants. This practice encourages aphid populations which feast on the tender, new growth that results from the abundance of nutrients. Heavy, frequent fertilization usually results in nitrate contamination of ground and surface water as well.
Be aware of your plants’ watering needs during periods of drought. Plant roots, particularly those of shrubs and trees, extend one to two feet below the ground. Deep, infrequent watering is the best approach. This can be done by laying a hose at the base of your plants on a slow drip or programming your automatic drip system to run for an extended period of time at infrequent intervals.
Watch for signs of Seiridium canker on your leyland cypress. Increasingly popular in the southeastern states as a fast growing windbreak and privacy screen, this hybrid evergreen can be easily stressed by prolonged drought or extreme cold, making it susceptible to canker. Watch for signs of resin oozing from cracks in the trunk or branches, dark brown to purplish patches on the bark, and yellow-brown foliage above the canker. Keep plants healthy and vigorous. Aside from adequate moisture, leyland cypress need at least 15 feet of space to minimize competition with other plants; existing plantings can be thinned by removing some of the plants. During drought provide deep, infrequent watering and avoid overfertilizing. Prune wilted or discolored branches or tips, cutting back to a healthy part of the branch. Severely infected trees should be removed and destroyed.
Keep an eye out for a new scale that has been attacking spruce and other conifers. Fiorinia japonica, a scale similar to the more commonly known elongate hemlock scale, has been found in increasing numbers in the Eastern U.S. The males are white and the females are tan or grayish with a dark area in the center. Crawlers begin emerging in May and continue to emerge sporadically through September. Avoid using chemical pesticides to control this insect which will harm beneficial insects. If control is necessary, use horticultural oil when crawlers are present.
Keep algae growth down in your garden pond. Too much light and excessive nitrogen and nutrients create conditions for algae to flourish. Sources of nitrogen include fish and other animal wastes, uneaten fish food, and decaying plants. Provide your pond with good plant coverage to filter out excessive light and avoid overfertilizing the plants and overfeeding the fish that inhabit the pond.
Monitor your conifers for the presence of spider mites. Mites have piercing mouth parts and their feeding results in a stippled appearance on the foliage. Beat test plants by tapping the plant over a white sheet of paper. Look for small green, black, tan, or red mites about the size of a speck of pepper. More than 20 mites per beat may indicate serious damage. You can remove the mites with a jet of water from the hose or treat plants with horticultural oil. You can also buy predatory mites and release them to feed on the pest mites.