Leaves Curled and Distorted means Aphids
Aphids, also called "plant lice," are soft-bodied, pear-shaped sucking insects about the size of the head of a pin. They sometimes cluster on leaves and tender buds. Their feeding retards plant growth. Periwinkle leaves may turn yellow or brown. They wilt under bright sunlight, or sometimes curl and pucker. Spray the insects with insecticidal soap every 3 to 5 days. If that doesn't work, try spraying both aphids and foliage surfaces with Neem 2 or 3 times at ten-day intervals.
For more information see file on Dealing with Aphids.
Leaves Discolored, Distorted due to Aster Leafhoppers
Aster leafhoppers, or six-spotted leafhoppers, are 1/8 inch long, greenish-yellow with six black spots. Immature insects (nymphs) are grayish. If periwinkle leaves are finely mottled with white or yellow spots and they eventually shrivel and drop off, suspect these pests. Because this leafhopper prefers open spaces, plants grown near a house or next to walls suffer less damage. The pests spread aster yellows disease, which they pick up in spring when feeding on infected wild plants. Cover early spring plants with an agricultural fleece barrier, and spray a preventive spray of insecticidal soap on the foliage of vulnerable plants during their first month of growth. Later, spray with insecticidal soap laced with rubbing alcohol to control serious attacks.
Plants Grow Poorly indicates Mealybugs
Mealybugs are 1/5 to 1/3 inch long, oval, flattened, covered with white waxy powder and adorned with short, soft spines around their edges. Mealybug infested plants look unsightly and do not grow well. Plants may die if severely infested. The insects gather in cottony white masses on roots, stems and leaves, sucking sap and reducing plant vigor. Honeydew secretions from their feeding encourage mold growth on the foliage and attract ants and fungi. Control mealybugs by spraying them and plant foliage with Neem 2 or 3 times at ten-day intervals to catch the pests in all their lifecycle stages.
Small Bumps On Leaves And Stems caused by Scale Insects
Scale insects form groups of small bumps or blister-like outgrowths on stems and leaves. These are waxy shells that protect the tiny sap-sucking insect feeding beneath. The shells may be white, yellow, or brown to black, and are about 1/10 to 2/5 inch in diameter. The first sign of a scale attack is often discoloration of the upper leaf surface, followed by leaf drop, reduced growth, and stunted plants. Heavy infestations kill plants. Some species excrete honeydew, which coats foliage and encourages ants and sooty mold growth. 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. Spray affected periwinkle stems and foliage with light ("superior") oil which will smother the scale.
For more information see file on Dealing with Scale.
Shoots Blacken and Die Back to Ground because of Canker and Dieback
A fungus causes canker and dieback. The tips of periwinkle vines turn dark brown or black, wilt and die back to the soil. The disease is most troublesome during rainy weather. Remove and destroy infected plants or plant parts as soon as you notice them. A spray of Bordeaux mixture may give some control, possibly reducing the spread of the disease to adjacent plants.
For more information see file on Dealing with Fungal Disease.
Leaves Spotted or Blotched means Fungal Leaf Spot
Fungal leaf spot diseases thrive on moist leaf surfaces and cause transparent, brown or black spots that disfigure periwinkle leaves. Flecks or black dots, the spore-bearing fruiting bodies surround some fungal spots. Often spots come together to form larger patches of dead tissue. Dig up and discard seriously infected plants together with the soil surrounding their roots. If leaf spot is a problem, water periwinkle with a drip irrigation system to avoid wetting the foliage. Spray at weekly to 10 day intervals with a flowable sulfur spray.
For more information see file on Dealing with Fungal Disease.
Foliage Burned due to Dog Urine
Dog urine is a problem with groundcovers. It may discolor and kill foliage. Spraying the foliage of endangered periwinkle with an anti-transpirant gives some protection. Try an aerosol pet repellent.
