Summertime is when our beautiful native plants, majestic trees and shrubs, and yes, even our soils teem with living organisms. Parasitoids, beneficial nematodes and fungi, along with insect predators, are just a few of these organisms that help keep the bad pest populations at bay. These are the good guys. However, as the Fourth of July approaches, be on the lookout for some of the following damaging insects and diseases that may need your attention.
Boxwood Blight – Boxwood blight is a relatively new and threatening boxwood disease caused by the fungus Calonectria pseudonaviculata. Boxwood Blight results in severe leaf drop and decline of susceptible boxwoods. Symptoms include: dark or light brown circular leaf spots, often with darker margins; straw to bronze colored blighted foliage; dark cankers or black streaks on stems; and leaf drop. Disease development of leaf blighting and defoliation can occur swiftly with complete leaf loss under warm (64 to 80°F), humid and shady conditions. Oftentimes, when boxwood blight is in advanced stages, symptoms can be confused with damage caused by other pests such as nematodes, Volutella blight or the root rot disease Phytophthora cinnamoni. If you suspect you have boxwood blight contact your Extension Center at 586-4009.
Fire Blight – Fruit trees such as pears, apples and crabapples are potentially susceptible to this bacterial disease. The bacterium is often introduced by pollinating insects e.g., bees. Affected shoots will first appear water-soaked, followed by wilting. Eventually the leaves turn brown or black and remain on the stem. The bacterium continues to grow down the stem and will kill the trees if not removed. For control measures prune at least a foot below any sign of injury. Make sure to sterilize pruners with a solution of one-part household bleach to nine parts water between cuts. Continue to monitor the plant for further signs of disease and prune as needed. There is no product that can cure these infected stems, which will get worse if left unattended. The following spring, spray with agricultural streptomycin (Agrimycin) in sprays (8 oz/100 gal or 1 teaspoon/gal) applied at five-day intervals beginning when 5-10 percent of the blossoms are open and continuing until petal fall.
Leaf Galls: Leaf galls found on azaleas or camellias consist of thick fleshy tissue that is pale compared to normal leaves. These galls are more alarming than damaging. In spring, leaves become thickened, curled, fleshy and pale green/white. Handpick the leaves and destroy them. Do not touch other parts of the plant unnecessarily, and wash hands to avoid spreading the fungus further. In later stages, leaves are covered with a white powdery substance. Leaf gall seldom does enough damage to justify spraying, especially if you keep galls picked off. Pruning and removing infected stems is generally the most effective control strategy.
Fruit Rots: Generally, warm, rainy or damp conditions are very conducive for the development of fruit tree diseases. Often these fungi are transferred to the new fruit from infected flowers or from cankers on the tree. The fruit is infected soon after formation, but the rot is not obvious until much later in the summer. The most effective way to avoid these rotting pathogens involves a complete IPM (integrated pest management) strategy that includes site selection (full sun, good air movement), pruning (to enhance light penetration and air movement) and fungicide sprays. Fungicides will not cure the problem but will be part of your IPM toolbox for the following year.
Lacebugs: Lacebugs can be found throughout the year and are particularly keen on azaleas and rhododendrons. As the flowers fade and new growth emerges, lacebug eggs hatch and begin migrating to the tender young foliage for feeding. By inserting their piercing mouth parts into the plant tissue, juveniles feed and make the plants look “washed out.” Once the damage is done, the leaves are aesthetically ruined, so it’s a good idea to scout. If you observe older unhealthy leaves, look underneath. If you find dark spots of excrement (about pinhead size), it’s safe to assume lacebugs have been feeding. If the damage looks severe, pruning may help reduce the numbers of insects. In addition, you will need to treat the lower surface of all leaves with insecticidal soap. Make sure to get complete coverage on the lower sides of leaves and repeat in about two weeks. Follow up with a plant inspection on a monthly basis.
For more information on these pest problems contact your County Extension office at 586-4009.
Christine Bredenkamp is NCSU horticulture extension agent for Jackson and Swain counties.