Hydrangea With Blight

Blight Symptoms

• Botrytis blight, also called gray mold, often grows on a hydrangea during long stretches of cool and overly wet weather. Caused by the fungal pathogen Botrytis cinerea, this disease triggers a range of symptoms, including blossom and shoot blight as well as crown and stem rot. Symptoms usually start out as small, water-soaked spots before turning into large, soft and watery splotches that cause the plant part to wilt and collapse. High humidity levels encourage the growth of fuzzy, brown to gray fungal threads on the infected tissue. Flower buds often rot and fail to open, while opened blossoms develop discolored spots. Stems and leaves wilt and decay before falling from the plant. The fungal spores spread easily through splashed water or wind gusts, and can germinate and infect new plants within hours.

Cultural Control

• Following proper sanitation procedures is an essential part of blight control. Prune out and discard all dead or blighted hydrangea flowers and foliage. Only prune during dry weather or you risk spreading the fungal spores along with the water you'll inevitably splash. Rake up and dispose of fallen plant material around the hydrangea bush because the blight fungus thrives on plant litter. Increase air circulation around your hydrangea by pruning out crowded interior branches. The air flow helps reduce humidity levels, which inhibits the growth of gray mold.

  Don't mist your hydrangea or water it from above. Water the shrub at its roots while keeping the flowers and leaves dry. Water your plant early in the morning so the leaves have plenty of time to dry off before the evening.

Chemical Control

• Spraying hydrangea shrubs with a chlorothalonil-based fungicide can help protect them from Botrytis blight infections if used in conjunction with proper cultural practices. You must start treating your shrubs before blight symptoms appear, so begin when the forecast for your area predicts prolonged cool and damp weather.

  Following the instructions on your specific product's label, mix about 2 1/4 teaspoons of fungicide per 1 gallon of water. Spray your hydrangea thoroughly, making sure you cover the stems, flowers, buds and the undersides and tops of leaves. Repeat applications every seven to 14 days until the weather conditions no longer favor blight.

Growing Hydrangeas

• Taking proper care of your hydrangea can help keep it healthy and vigorous enough to withstand blight. Hydrangeas prefer rich, well-draining soil and morning sun and some afternoon shade. These shrubs appreciate some supplemental water during long dry spells, especially the bigleaf hydrangea because its large leaves can quickly lose moisture and wilt. Prevent drought stress by giving your shrub 1 inch of water every week when it hasn't rained. Applying a 2- to 3- inch layer of organic mulch around your hydrangea can help retain soil moisture while keeping the root zone cool. Don't place the mulching material up against the plant's stems.