Plant Health Problems
Diseases caused by Physiological/Environmental Factors:
Purple spot or Spine spot.
Mechanical injury to holly leaves causes a purplish discoloration immediately surrounding the injured area. Wind-whipping in winter may drive the leaf points into other leaves. The problem may be reduced by planting holly in a sheltered area, out of severe winter winds. A similar injury may be produced by the holly leafminer.
Cottony Camellia or Taxus Scale, Pulvinaria floccifera.
This soft scale attacks Euonymus, holly, Hydrangea, maple, Taxus and many other plants. The scale overwinters as a second instar mostly on twigs. Brown, oval females produce long white cottony egg masses on the undersides of host leaves in late spring. Crawler treatments should be applied after the eggs have hatched around mid-June, between 800 and 1400 degree days. Crawlers will disperse to new areas, insert their mouthparts, and begin to feed. Once settled, the young scales never move again. There is one generation per year. Black sooty mold grows on the honeydew that scales excrete as they feed. Horticultural oil can be applied during the dormant season. A summer rate of horticultural oil, along with deltamethrin, carbaryl or malathion, which are among the compounds registered for use against this insect in Connecticut, can be applied to foliage in late June against crawlers. Restricted-use imidacloprid can be applied by a licensed pesticide applicator in spring for season-long control, but should not be applied to plants, such as holly or certain cultivars of hydrangea, that are highly attractive to pollinators. An alternative systemic product containing acetamiprid may be considered for managing cottony scales on bee-attractive plants.
Holly leaf miner, Phytomyza ilicis. The adult is a small, black fly about 1/16" long. It emerges in late May or during June. Eggs are deposited in the underside of the leaves. Larvae make mines that broaden as the insects develop. There is one generation a year. Remove and destroy affected leaves in April. Spinosad may be sprayed to control larvae in leaves. Imidacloprid, which is among the compounds registered for control of this pest in Connecticut, applied as a soil drench in mid-May will provide season-long, systemic control. Consult the labels for dosage rates and safety precautions.
Southern red mites, Oligonychus ilicis. Southern red mite can be a problem on several species of holly. This mite overwinters as reddish eggs on the under-surface of leaves. Adults and nymphs feed on both the lower and upper leaf surfaces. The oval-shaped adults are normally red, but can be green with lighter colored legs. Multiple generations occur each season. If not controlled in the spring, populations will rise again in the fall. Some damaged leaves drop. Among the compounds registered for control of this pest in Connecticut are insecticidal soap and ultrafine horticultural oil. Spraying with insecticidal soap will give good control if applied at least twice at 7-10 day intervals. The predatory mite, Neoseiulus fallacis, is most commonly found feeding where there are mite infestations. A single application of ultrafine horticultural oil (1/2 - 1% dilution) can be effective if predatory mites are present. Consult the labels for dosage rates and safety precautions. Special care should be taken with soap or oil to obtain thorough spray coverage, because they only work on contact. Hexythiazox or abamectin are effective restricted use products. Avoid applying carbaryl or pyrethroids, which tend to be much more toxic to beneficial predatory mites than to the pest mites.