Problems With Wine & Rose Shrubs

Woody ornamental shrubs that produce deep burgundy foliage and rosy pink flowers, 'Wine & Roses' weigela are popular with gardeners and landscapers alike. Hardy in USDA Hardiness Zones 4 through 8, the attractive shrubs grows 5 to 6 feet tall and equally wide. Each easy-to-grow shrub attracts butterflies and takes well to pruning. Although largely pest- and disease-resistant, 'Wine & Roses' weigela are susceptible to minor problems that affect their health and growth.

Although disease-resistant for the most part, improper pruning and overcrowding make this weigela susceptible to crown gall. Each gall or swelling appears on the part of the shrub closest to the soil, usually the area where the roots and stems that protrude from the soil join.

Caused by the bacterium Agrobacterium tumefaciens, the disease is similar to a tumor that spreads throughout the plant, and causes death in extreme cases. The bacterium enters the shrub through wounds in the soil, irrigated water or unclean tools. To control the vulnerability of the shrub to the disease, use sterilized pruning equipment and make small cuts when you trim the shrub.

Cut back infected parts if the disease is mild, or remove the entire plant if the extent of damage is severe.

A fungal disease, leaf spot causes the attractive foliage of the shrub to turn yellow or light brown. Infected leaves also feature thick black spots that are actually fruiting bodies of the disease. Shrubs weakened by improper cultural practices are most susceptible to leaf spot.

To reduce the susceptibility to leaf spot, prune the canes near the center of the shrub to increase air circulation. Enrich the soil with organic matter to provide essential nutrients to the plant, and ensure that the soil drains well. If the plant has been infected, snip off and destroy affected leaves to prevent spread, and spray foliage with a copper-containing spray in early spring to prevent the disease.

'Wine & Roses' weigela is most susceptible to damage by scale--tiny, rounded, black, white or yellow insects with waxy bodies. These insects resemble tiny blisters on bumps on the shrubs leaves and canes. Symptoms include discoloration or paling of the upper surface of leaves, leaf drop, stunted growth and even death in extreme cases. Some species of scale secrete a honeydew-like substance that attracts sooty mold.

Over or under watering or over-fertilizing makes the shrub susceptible to the insects. Spray infected parts with neem oil or horticultural oil designed to tackle scale insects.

The four-lined plant bug (Poecilocapsus lineatus) damages the leaves of the shrub. Each one-third-inch-long bug features a yellow body and wings distinctly marked with four black and three green stripes. Females lay eggs on stems that hatch in May. The young ones suck the sap from the foliage, causing infected parts to appear sunken and turn into holes with time. Control the bugs with regular applications of insecticidal soap or horticultural oil.

Japanese beetle adults and grubs damage ornamental shrubs including weigela, causing large holes in the leaves. The metallic-green, one-half-inch-long body of an adult features two bronze wings. Inspect the shrubs frequently and handpick adults to control their numbers, since pesticides are ineffective against large populations. Use pesticides to control grubs in the soil.