Plant Health Problems
Diseases caused by Fungi:
Leaf spots, Mycosphaerella cercidicola, Phyllosticta.
Symptoms appear as spots which are at first rusty brown with a raised border, but later develop a gray appearance on the upper surface while tissues remain brown on the underside of the leaf.
Rake and dispose of fallen leaves to reduce the chance of infection in the following season. Fertilize trees in the spring and water during dry weather to maintain tree vigor. Since this disease is usually not a serious problem for the health of the trees, chemical controls are usually not necessary.
Canker and dieback, Botryosphaeria berengeriana (Dothiorella).
Cankers begin as small sunken areas in the bark, which gradually increase in size to become sunken, elongated cankers with black, cracked centers. The leaves wilt as branches or trunks are girdled, and everything beyond the canker dies. Some of the cultivars are not hardy in Connecticut, and winter injury can lead to predisposition to this disease.
Pruning infected material well back of any discoloration in the wood may prevent further spread. Fertilize trees in the spring and water during dry weather to maintain tree vigor. Avoid insect and mechanical injuries to reduce chances of infection.
Asiatic oak weevil, Cyrtepistomus castaneus.
These 1/4" weevils are dark brown, with whitish scales on the body and yellowish brown legs. The snout is very short. Adults are the most damaging stage, feeding on the edges and thereby scalloping the leaves of many plants. The adults then lay their eggs in the soil, where the small legless larvae develop on roots. In high populations, adults are attracted to lights, where they may become a nuisance inside houses.
European fruit lecanium, Parthenolecanium corni.
These convex soft scales are considerably larger than San Jose or Forbes scales. They are rare in Connecticut and control usually is not required.
Green fruitworm, Lithophane antennata.
Green and other fruitworms eat foliage in May and June. The cutworm-like caterpillars are green with longitudinal white stripes. Fruitworms, which have one generation per year, can be controlled when larvae are small with spinosad or Bacillus thuringiensis var Kurstaki, which are among the compounds registered for use against this pest in Connecticut. Consult the labels for dosage rates and safety precautions.
Terrapin scale, Mesolecanium nigrofasciatum.
This small, reddish, oval, convex scale occurs on the small twigs of redbud, often killing them. It varies from 1/16 - 1/8" long and is usually reddish-brown mottled with black. Eggs are deposited in June under the old shells and there is one generation each year. Among the compounds registered for control of this pest in Connecticut are horticultural oil, malathion and imidacloprid. Spray horticultural oil in early spring, or spray malathion in April when crawlers are active. To determine exactly when crawlers are active, wrap black tape around infested limbs and coat the tape with Vaseline. The light-colored crawlers are easily seen on the tape. Alternatively, imidacloprid may be applied as a systemic to be taken up by the roots. Consult the labels for dosage rates and safety precautions.
Twomarked treehopper, Enchenopa binotata.
This grotesque little insect has a curious projection on the thorax that makes it resemble, in profile, a bird. When several individuals walk along the stem one behind another, they resemble a flock of geese marching single file. The eggs are laid in white frothy masses on the twigs. Immatures and adults are present in July and August. The adults are dark brown with two narrow white spots on the ridge of the back.
Ordinarily, control measures are not needed, but the immatures may be managed with sprays of malathion, which is among the compounds registered for control of this pest in Connecticut. Imidacloprid applied as a systemic to be taken up by the roots will also provide season-long control. Consult the label for dosage rates and safety precautions.
Twospotted spider mite, Tetranychus urticae.
This pest infests the undersides of the leaves, which become light yellow in color, and the plants have a generally unhealthy appearance. Sometimes the mites form webs, which more or less enclose the upper as well the lower leaf surface. Among the compounds registered for control of this pest in Connecticut are insecticidal soap and ultrafine horticultural oil. Spraying with insecticidal soap will give sufficient 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. Special care should be taken with soap or oil to obtain thorough spray coverage, because they only work on contact. Commercial growers may consider using hexythiazox or abamectin (a restricted use product) to control spider mites. Consult the label for dosage rates and safety precautions. Avoid applying carbaryl, spinosad or pyrethroids, which tend to be much more toxic to the predators than to the pest spider mites.
Whitemarked tussock moth, Hemerocampa leucostigma.
This insect has two generations each year, and spends the winter in frothy white egg masses on the trees. Eggs hatch in late May and the caterpillars mature about July 1. They make their gray cocoons on the trees. Two weeks later, the moths emerge and females usually lay egg masses on the old cocoons. The second-generation larvae hatch in July and mature in August. The caterpillars reach a length of about 1 1/2". They are striped lengthwise with brown and yellow, and are hairy, with four upright white tufts on the front half, two long black hairs near the head, and a similar one on the tail. There is a bright red spot just behind the head. The female is ash-gray without wings. The male has prominent feathered antennae and ash-gray wings with darker gray markings. It has a wingspread of about 1 1/4". This caterpillar can be controlled by sprays of malathion, carbaryl, spinosad, or Bacillus thuringiensis var. kurstaki, which are among the compounds registered for use against this pest in Connecticut. Consult the label for dosage rates and safety precautions.
White prunicola scale.