Prevention & Control: Insecticides should only be used if infestations are heavy. Horticultural oil applied at the summer rate of 1 – 2% (2-1/2 to 5 tablespoons oil per gallon of water) will kill eggs and adult mites. As with all pesticides, read and follow all label instructions and precautions. Boxwood mites prefer feeding on young leaves, but damage is most obvious on second- and third-year leaves. Adults also feed on boxwood, but are less damaging than the nymphs. The annual removal and destruction of all leaves that have lodged in crotches is recommended. Ty. Prune dead branches well below cankered areas. Nematode-tolerant shrubs such as yaupon holly and Burford holly can be used to replace boxwoods, which were killed by nematodes. Insecticides & Fungicides for Boxwood Diseases & Insect Pests. Why do we need this? Prevention & Control: Use of insecticides against boxwood leafminer is not recommended unless damage is intolerable. Macrophoma candollei can cause leaf blight, but it usually acts as a weak pathogen following root diseases or environmental stresses. Prevention & Treatment: A thorough diagnosis of the associated factors is important before corrective action is taken. Under wet conditions, white fungal growth is observed on the leaves and twig lesions. Photo by Kelly Ivors, Plant Pathologist, California Polytechnic State University, San Luis Obispo, CA. Root Rot: Root rot is caused by the fungi Phytophthora nicotianae and P. cinnamomi. The goal is to keep the population low enough to prevent damaging symptoms that weaken the plant. All stages of boxwood mite feed on both leaf surfaces. Mites can be removed with a strong spray of water, if applied on a regular basis. Stems become infected and form dark brown to black lesions or cankers. Photo by Meg Williamson, ©2016 Clemson Plant and Pest Diagnostic Clinic. Prevention & Control: Naturally occurring enemies of mites include various predator mites, ladybird beetles (ladybugs) and other insects. But if Phytophthora root rot is confirmed, the site should be avoided for future boxwood plantings. (Although I suspect that if we had a better picture we'd see that the plant in question isn't boxwood at all but instead, Boxleaf Euonymus) Informational table showing disease name, symptoms, pathogen/cause, and management of Boxwood diseases. Wood under the sunken canker is blackened. They produce a white, waxy material that often covers their bodies. Initial leaf spot symptom of boxwood blight pathogen. A heavy infestation can cause serious loss of leaves and result in death of the boxwood. Nymphs hatch from eggs in the spring. Join our mailing list to receive the latest updates from HGIC. The pathogen can survive for at least five years on blighted and fallen foliage, as well as on the stem lesions on the dying or dead plants. Clemson University Cooperative Extension Service offers its programs to people of all ages, regardless of race, color, gender, religion, national origin, disability, political beliefs, sexual orientation, gender identity, marital or family status and is an equal opportunity employer. This is especially important in upstate areas where the soil can freeze and remain frozen on sunny days. Plants, grass, trees and shrubs are all in danger of contracting powdery mildew, and the disease can potentially destroy the whole plant. Straw-yellow leaves are dotted with small, black fungal fruiting structures. They pierce the plants and suck the juices. Horticultural oil may be sprayed when temperatures are between 45 and 85 degrees. The leafminer is the larva (immature form) of a small, orangish mosquito-like fly. Symptoms consist of leaf bronzing, stunted growth and general decline of boxwood. Nematodes: Boxwoods are susceptible to several parasitic nematodes (microscopic round worms), including the Southern root-knot nematode (Meloidogyne incognita), the ring nematode (Mesocriconema), the lesion nematode (Pratylenchus), and the stunt nematode (Tylenchorhynchus). Initial infections are smaller white … Protect shrubs from drought and drying winds in the autumn and winter. The soil around infected plants may be treated with the appropriate fungicide according to the directions on the label. Dinotefuran may move into shrubs more quickly than imidacloprid for faster control. Kelly Ivors, Plant Pathologist, California Polytechnic State University, San Luis Obispo, CA. Disinfect pruning shears frequently in household bleach diluted 1:9 with water or rubbing (isopropyl) alcohol for 10 seconds. We're used to tree leaves changing color throughout the year, but dusty white usually isn't in their color palette. Infested leaves typically turn yellow or brown in splotches, are smaller and drop sooner than healthy leaves. Leaves often have pink eruptions of spores on black fruiting bodies. If the soil is heavy clay, mix it with a porous material such as bark. Boxwood psyllids are small insects that cause new leaves to cup as the nymphs extract sap from the tender foliage. We thought we were going to … After further development during the spring, adults are formed. Since insecticide use kills predators as well as mites, insecticides should be avoided unless absolutely necessary. However, Paecilomyces buxi has been consistently associated with roots of English boxwood exhibiting the syndrome of boxwood decline, and decline often follows periods of drought stress. Apply a fungicide to protect new growth in the spring and in the fall. LEARN HOW TO STOP THE INVASIVE SPOTTED LANTERNFLY, Coronavirus: Information and resources for the Extension Community, Prepared by Gary W. Moorman, Professor of Plant Pathology. Since mites are so small and early symptoms are not distinctive, it is easy to overlook the problem until a heavy infestation occurs and greater damage has occurred. “Boxwood blight has been detected in South Carolina and was recently introduced into the state by shipments of asymptomatic plants to instate nurseries.” Boxwood blight is caused by the fungal pathogen Calonectria pseudonaviculata (synonym Cylindrocladium pseudonaviculatum), which causes leaf spots, stem cankers, defoliation, and death of boxwoods.