Plant Health Problems
Diseases caused by Fungi:
Powdery mildew, Microsphaera euonymi and M. penicillata.
Powdery appearance of leaves indicates presence of one of these fungi. Infection is favored by hot humid weather.
Control of this disease is usually not necessary since symptoms develop late in the season.
Anthracnose, Colletotrichum gloeosporioides.
Brown to black lesions on the leaves are indicative of anthracnose. Lesions may occur on the stem, and portions of the plant distal to stem lesions frequently die back.
Management of this disease includes raking and removing fallen leaves and pruning to remove stem cankers. Control can also be achieved with the use of fungicides when applied before symptoms are severe. Among compounds registered for use in Connecticut are chlorothalonil and thiophanate-methyl. New research indicates that the fungus may become resistant to copper, so copper-containing compounds should be used on a limited basis, to prevent or delay development of resistance. Consult the label for dosage rates and safety precautions.
Diseases caused by Bacteria:
Crown gall, Agrobacterium tumefaciens.
Roots and running stems may show galls of considerable size. If infection is heavy, plants may be destroyed.
If there are only a few galls, affected stems may be removed. Pruning tools should be disinfected by dipping in dilute alcohol or dilute bleach (a solution of 10% bleach in water) between cuts. New varieties that are more resistant to crown gall are available and should be utilized.
Aphids, Aphis fabae.
The bean aphid occurs on euonymus. There are many generations each year. Eggs are laid in the autumn. They overwinter on various shrubs. For more detail and control measures, see the Aphid fact sheet.
Black vine weevil, Otiorhynchus sulcatus.
The larvae of this weevil often injure Euonymus plants, especially the wintercreeper varieties, in nurseries and ornamental plantings by feeding on the roots. The small grubs devour the small roots and progress to chewing the bark from the larger roots, often girdling them. The tops of girdled plants first turn yellow, then brown, and the severely injured plants die. Large landscape plants tolerate root grazing quite well, but leaf notching by adults can be unsightly. The 1/2" long adult weevil is black, with a beaded appearance to the thorax and scattered spots of yellow hairs on the wing covers. Only females are known, and the adults are flightless. They feed nocturnally, notching the margins of the foliage. The legless grub is white with a brown head and is curved like grubs of other weevils. Adults and large larvae overwinter, emerging from May - July. The adults have to feed for 3-4 weeks before being able to lay eggs. Treating the soil with insect pathogenic nematodes may control the larvae and should be the first line of defense for landscape plantings. Acephate and fluvalinate are among the compounds registered for control of this pest in Connecticut, and should be applied when there is adult feeding and before egg laying starts. The usual timing for these foliar sprays is during May, June and July at three week intervals. Insecticide resistance is very common; be aware that adults may appear to be dead following contact with fluvalinate, but may recover from poisoning within a few days. Consult the labels for dosage rates and safety precautions.
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.
Cottony maple scale, Pulvinaria innumerabilis. This scale infests euonymus. This is a brown, oval, soft scale on the stem in winter, but in June the large egg masses are formed, and their wax covering resembles a tuft of cotton. The young crawl in July and some of them live for a time on the leaves, but return to the twigs to pass the winter. Among the compounds registered for use against this pest in Connecticut are horticultural oil, imidacloprid and diazinon. The best means of control are a dormant horticultural oil spray applied in early spring or imidacloprid applied as a systemic to be taken up by the roots. Diazinon sprays in early July will control the young crawlers. Consult the labels for dosage rates and safety precautions.
Euonymus scale, Unaspis euonymi.
This is perhaps the most serious pest of euonymus, and it often kills entire branches. It also infests bittersweet and pachysandra. The female shells are gray and pear-shaped, and the male shells are smaller, narrower, and whiter. There are probably two generations each season, and the winter is passed in a nearly mature condition; eggs are formed during May and hatch later in the month. All badly infested and injured branches may be cut and burned. Among the compounds registered for control of this pest in Connecticut are horticultural oil, insecticidal soap and malathion. Spraying with ultrafine horticultural oil, either in mid-April for a dormant treatment or early June and again in mid-July, will control this scale while conserving the natural predators and parasites that might be present. Sprays of insecticidal soap and malathion applied in early June and again in mid-July will also control this scale. Consult the label for dosage rates and safety precautions.
San Jose scale, Quadraspidiotus perniciosus.
Large infestations of the San Jose scale can cause branch and even shrub death. Partially-grown scales overwinter under their circular gray covering or scale on the twigs and the branches of trees. They begin to feed as the sap starts to flow. When apple trees bloom, the males emerge from under their scales to mate with the immobile females. Females are circular and cone-shaped, and their circular scales are about 1/16" in diameter, with a raised center or nipple. The males are smaller and elongate, with the nipple not centered on the scale. Females give live birth to tiny bright yellow crawlers in June. The young crawlers quickly settle, insert their long mouthparts into the twigs, and then suck sap from branches. As they grow, the crawlers secrete a waxy filament that becomes their scale or covering. Overlapping generations are present from June through September. Scales may be controlled by applying horticultural oil at a dormant timing or in June when crawlers are active. Diazinon, which is among the compounds registered for control of this pest in Connecticut, may also be applied against the crawlers in June. Consult the labels for dosage rates and safety precautions. To detect the yellow crawlers, wrap black tape coated with Vaseline around small branches. Adult flights may be detected with pheromone traps.
Twospotted spider mite, Tetranychus urticae.
This pest infests the undersides of the leaves, especially of the burning bush varieties, 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 as 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 to 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. Abamectin is an effective restricted use product. Consult the labels for dosage rates and safety precautions. Avoid applying carbaryl or pyrethroids, which tend to be much more toxic to the predators than to the pest spider mites.