Foliage Damaged In Winter due to Windburn
A severe windburn may damage hypericum foliage during the winter, but these shrubs usually regenerate in the spring. Minimize damage by surrounding plants with protective material such as burlap or agricultural fleece. If this is an annual problem, move the plant to a more protected location.
Cottony Masses or Bumps on Twigs means Scale Insects
White, cottony masses or brownish bumps on hypericum stems clustered in crotches or close to buds are likely to be scale. These insects feed under protective shells. Female scale shells are gray and pear-shaped, and the male shells are smaller and narrower. The size of a pinhead, these pests sucks plant sap and secrete honeydew that, in turn, encourages sooty mold on the foliage and the branches. Scrape the pests off plant surfaces with a fingernail or a cotton swab dipped in rubbing alcohol. Spray severely infested plants with a mixture of rubbing alcohol and insecticidal soap every three days for two weeks. Add one-teaspoon alcohol to a pint of ready to use commercial soap spray. To control heavy infestations, cut and burn affected branches. In late March or early April spray plants that have chronic scale problems with "superior" dormant oil, before growth starts. This will smoother over wintering scale.
For more information see file on Controlling Scale.
Plants Look Sickly because of Root Knot Nematodes
Nematodes are whitish, translucent, wormlike creatures 1/125 to 1/20 inch long--barely visible to the naked eye. Hypericums infested with nematodes look sickly, wilted, or stunted, and show yellowed or bronzed foliage. They decline slowly and die. When they are pulled up from the soil their root systems look poorly developed, even partially decayed. Roots have knots, or galls, on them. The effects of nematode activity are most apparent in hot weather, when limp plants do not seem to revive after the heat of the day has passed. Control nematodes by adding lots of compost (especially leaf mold), if it is available, to the soil to encourage fungi that attack nematodes. Drench the soil near affected shrubs with dilute fish emulsion that is toxic, or repellant, to nematodes.
Powdery Spots on Leaf Undersides indicates Rust
A rust disease caused by a fungus causes pale areas to appear on upper hypericum leaf surfaces, with brownish powdery spots directly beneath. Remove infected leaves as soon as possible. Remove and destroy diseased plants and all nearby yard debris before growth starts in the spring. Treat the disease by spraying foliage periodically with wettable sulfur starting several weeks before the disease normally appears in the spring. Space plants widely apart for good ventilation, and avoid wetting foliage when watering.
For more information see file on Controlling Fungal Disease.
Leaves Covered With White Powder caused by Powdery Mildew
Powdery mildew caused by fungi attacks shrubs growing in shaded spots with little air circulation, especially in the southern states and the Pacific coast. Leaves are coated with a thin powdery deposit, later becoming discolored and dropping off. Spray foliage of affected shrubs thoroughly with wettable sulfur once or twice at weekly intervals starting as soon as the whitish fungus coating the leaves is visible. Collect and discard all aboveground yard and garden refuse in the fall to prevent contagion.
For more information see file on Controlling Fungal Disease.
Foliage Burned due to Dog Urine
Dog urine may discolor foliage and even kill branches of low growing plants along property borders. Spraying foliage with an anti transpirant gives some protection. Screen target plants or spray them with an aerosol pet repellant.
