Weather Woes and Plant Diseases

Photo Credit: Michele Walfred
Hydrangea Frost Damage Photo Credit: Michele Walfred

Cloudy, wet, damp, cool and dreary are words that have been heard over and over recently, regarding the weather in Delaware. Cloudy and damp weather is conducive to plant pathogens that infect in the spring. Fungi and bacteria overwinter in twigs and buds of trees and shrubs. Spring rains and humidity will prompt new growth and spore production, and then winds and rains carry spores to newly emerging flowers and leaves. Recent weather has favored plant disease, but we have also had injury from freezing weather that occurred in April.  Hydrangea has been reported with browning and dieback, and samples have come into the Plant Diagnostic Clinic. New growth came out early due to warm weather, and growth of buds and leaves has been affected by the freezes that we had in the area April 5, 6, and 10th. Plants will put out new growth when the weather warms again. Affected growth could be pruned back, depending on the type of

Boxwood Frost Damage 2016 Image, N. Gregory
Boxwood Frost Damage 2016 Image, N. Gregory

hydrangea, and whether it blooms on new wood or old. Frost or freeze damage has also been observed on new growth of boxwood, and other shrubs. These plants should put out new growth when the weather warms. Fruit trees that were affected by frost and freeze will have fewer fruits this season. Keep up fruit tree sprays. Fungicide sprays should also be going on Douglas fir and spruce that are affected by needlecast fungi. Fungicide applications should be made when new needles are ¼ inch long, followed by a second application ten days later. Check annuals carefully for Botrytis blight or grey mold, and prune or discard plants. Sanitation is a big part of plant disease management.

N. Gregory 5/6/16