Leaves Curled, Discolored and Distorted means Aphid
Aphids, also called "plant lice," attack tender branches and flower clusters. The pests are spindly-legged, pear-shaped insects little bigger than the head of a pin. They suck sap from leaves and stems, causing the foliage to curl, pucker, and turn yellow, while reducing the plant's vigor. Ants, attracted by the aphids' honeydew secretions, wander over the plants and protect the aphids from natural predators. Check leaf undersides for small groups of aphids. For light infestations, spray leaf undersides vigorously with water three times, once every other day, in the early morning. Eliminate nearby ant nests if possible. Use insecticidal soap every two to three days for heavier infestations. As a last resort, use pyrethrum spray. For more information see file on Controlling Aphids.
Silvery, Webbed Leaves because of Spider Mite
Spider mites turn leaves silvery or yellow, giving them a parched appearance. The leaves may curl and become covered with fine webbing, especially on undersides, and fruit is deformed. Adult mites are reddish brown or pale tan and 1/150 to 1/50 inch long. They are more easily visible through a hand lens. Mites lay their eggs on leaves and buds or at the base of plants. You may control mites, which favor hot, dry locations, by spraying plants in early morning with a forceful jet of cold water. Repeat the water spray daily for three days. If that doesn't do the job, spray with insecticidal soap every three to five days for two weeks. Dormant oil spray will destroy many over wintering mites. Spray with 1 part flowable sulfur fungicide in 10 parts of "superior" type dormant oil before growth begins in spring. For more information see file on Controlling Mites.
Foliage Turns Pale or Mottled due to Hawthorn Lace Bug
Lace bugs suck sap from the undersides of leaves, causing the foliage to turn pale or mottled. The adults are small square-shaped bugs, 3/16 inch long or less, with elaborately reticulated wings that resemble lacework. This sucking insect appears in late June and in the summer on the undersides of the leaves. For small infestations, you can crush the bugs by drawing the leaves between your thumb and forefinger. Control larger infestations by spraying the leaf undersides with insecticidal soap, a nicotine spray, or a pyrethrum spray. Make three applications at 3 to 5 day intervals. For more information see the file Dealing With Lacebugs
Leaves Turn Yellow, Become Sticky means Scale
Leaves turn yellow and may drop. A shiny or sticky material (honeydew) may cover the leaves, especially on the undersides. Scale insects appear as clusters of somewhat flattened, waxy reddish gray or brown bumps a bit bigger than the head of pin. The bumps are protective shells, under which the pests insert thread-like sucking mouthparts into the plant and suck the sap. They often cover plants with white cottony, cushion-like masses. Scale outbreaks can be triggered by pesticides used against other pests or by environmental stresses such as too much or too little water. Overuse of nitrogen fertilizer can encourage the growth of scale populations. Avoid this by using a slow-release nitrogen fertilizer. If caught early on, scale can be scraped off plant surfaces with a fingernail or a cotton swab dipped in rubbing alcohol. Spray infested plants with a mixture of alcohol and insecticidal soap every three days for two weeks. The mixture includes 1 cup of isopropyl alcohol and 1 tablespoon of commercial insecticidal soap concentrate in 1-quart water. If you have soap already mixed with water, add 1 tablespoon of alcohol to a pint of mixed soap spray. For more information see file on Controlling Scale.
Webbing Holds Leaves and Twigs Together indicates Cotoneaster Webworm
The cotoneaster webworm caterpillar is yellow to dark brown, and is nearly ½-inches long when full grown. It weaves together leaves and twigs with webbing, forming a nest within which it feeds. This webbing usually starts after midsummer, and the nests remain on the bushes during the winter. Some of the nests of webworm can be handpicked and destroyed. To more effectively control webworm, spray BT (Bacillus thuringiensis) on the foliage as soon as you spot small worms starting to feed. Making three applications over a three-week period so that all emerging caterpillars eat it. They will sicken and die in a matter of days. If that doesn't work try a spray or dust of pyrethrum.
Red to brown blister underside leaves because of Pear Leaf Blister Mites
The Pear Leaf Blister Mite is common to cotoneaster plants. The mites are microscopic pinkish or white in color. Serious infections may nearly cover the underside of leaves with reddish or brownish blisters. The upper surface of the leaves is brown or blackish. Adults winter over in the bud scales. A Volck oil spray in spring should handle the problem.
Spots On Leaves; Twig Dieback and Blackening due to Fireblight
Fireblight causes dark spots on or "shot holes" in leaves, death of flowers and twigs and girdling of main stems and branches. Infected twigs wilt from the tip and turn black. Cankers form on the bark, becoming sunken and cracked. Fruit shrivels and turns black. Sticky ooze may appear on any infected part. Fireblight is a bacterium that over winters on cankers and on large branches of apples and pears, and is spread from plant to plant by insects and splashing raindrops. To control this disease, prune all blighted plant parts 4 inches below visible cankers and burn them. Disinfest pruners in between cuts with a bleach or sodium hypochlorite solution. Also keep rapid growth in check by fertilizing only moderately and avoiding high-nitrogen applications. Dormant sprays of copper sulfate or Bordeaux mixture may offer some additional protection when used in combination with other control measures.
Leaf Spot means Canker
Fungi and bacteria cause cankers on cotoneaster stems. These are localized, swollen and discolored dead areas resulting from infection of the soft tissue just under the stem's surface. They commonly split open, exposing underlying tissues, and sometimes bleed a gummy exudate. The germs and spores that cause them are spread by rain splashes, handling of plants, or contaminated tools. Infection usually occurs as a result of wound injury, or is hastened by some other problem that weakens plants, such as nutrient deficiency, severe winter conditions, or nematodes and insect pests. Remove and destroy infected plants or plant parts as soon as you notice the symptoms. Cut affected stems back several inches below the cankers. Prompt pruning of infected plants is the best control. Disinfect clippers and other tools after using them on cankered plants. In the fall gather and destroy all infected parts above ground to reduce chances of the fungus over wintering. A spray with Bordeaux mixture may give some control, and possibly reduce the spread of the disease to adjacent plants. For more information see file on Controlling Fungal Disease.
Foliage Burned due to Dog Urine
Urination by dogs may discolor foliage and even kill branches. Spraying foliage with an anti-transpirant gives some protection. Screen the plants or spray with an aerosol pet repellant. For more information see file on Dogs and Cats
Bark of Stems and Roots Gnawed because of Rodents
Small rodents gnaw bark off main stem, causing injury that allows disease organisms to invade. Rake mulch away from plant bases during the winter; keep the area clear of weeds and grass; and wrap the base of the plant with a guard of 1/4-inch hardware cloth.
For more information see files on Dealing With Mice, Dealing With Rabbits and Dealing With Voles.