Plant Health Problems
Diseases caused by Fungi:
Root rot, Phytophthora spp.
Above-ground symptoms are non-specific and include a general decline and lack of vigor. Needles appear chlorotic and often drop, growth may be stunted, twigs and branches show symptoms of dieback, roots and crown tissues are discolored, and in extreme cases, whole shrubs may die.
Disease management includes practices that minimize wet soil such as selection of an appropriate planting site and use of proper planting practices and cultural practices that maintain plant vigor and stimulate growth. It is also helpful to prune dead or dying tissues to minimize secondary invaders and opportunistic pests. Once a plant is infected, recovery is unlikely. However, efforts to protect surrounding plants include fungicide sprays or drenches which are applied on a preventative basis. Among the compounds registered for use in Connecticut are metalaxyl and fosetyl-Al. Consult the label for dosage rates and safety precautions.
Diseases caused by Physiological/Environmental Factors:
Root rot or Wet feet, excess soil moisture.
Roots in flooded or water-logged soils are damaged and die from oxygen deficiency. Damage can be sudden or gradual, depending upon the flooding conditions. Entire plants can die if flooded for only a few days during the growing season. Visible symptoms are often not evident until considerably after and appear as chlorosis or yellowing of the foliage, edema, reduced and stunted growth, twig dieback, needle drop, root death, and in extreme cases, whole plant death.
Strategies for minimizing wet soil problems include selection of an appropriate site and use of proper planting practices and cultural practices that maintain plant vigor and stimulate growth. It is also helpful to prune dead or dying tissues to minimize secondary invaders and opportunistic pests. For more information, see the fact sheet on Excess Water Problems on Woody Ornamentals.
Black vine weevil, Otiorhynchus sulcatus.
The larvae of this weevil often injure Taxus 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. Adults are flightless and feed nocturnally. 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 may 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.
Mealybugs, Phenacoccus citri, P. gossypii, P. longispinus.
Yews and other plants in greenhouses, homes and landscapes are commonly infested with mealybugs. White cottony masses appear on leaf surfaces and in leaf axils. These insects damage plants by sucking sap. Sprays of insecticidal soap, ultrafine horticultural oil or resmethrin, which are among the compounds registered for control of this pest in Connecticut, are most effective against crawlers. The spray needs to contact the insect so direct it downward into growing tips and leaf axils as well as upward to contact mealybugs feeding on the undersides of needles. Mealybugs can also be controlled with imidacloprid applied as a systemic to be taken up by the roots. Read and follow all label directions for any insecticide used.
Soft scale, Parthenolecanium fletcheri.
This is a small brown hemispherical scale occurring on arborvitae and yew. A dormant application of ultrafine horticultural oil can be applied to control overwintering nymphs. If needed, malathion, applied in late April, early July and early September should give good control. Imidacloprid, a restricted use insecticide applied as a soil drench by a licensed pesticide applicator, will provide season-long systemic control. Consult the labels for dosage rates and safety precautions.