Powdery mildew on my trumpet vine.


I live in north Toronto and have a 10 year old trumpet vine Growing on my iron fence, so it gets plenty airflow. Sun in the morning until 1:00PM, then shade. What can I do to avoid the spread? Is there an organic treatment (spray).


Thank you for contacting the Toronto Master Gardeners concerning your trumpet vine.

Powdery mildew fungi develop when daytime temperatures are warm and nights are cool and humid. The fungi can overwinter on infected fallen leaves and tissue, which can cause reinfection. Leaf spot fungal pathogens favor free moisture on leaf surfaces, high humidity and poor air circulation. Infection occurs in mid spring to early summer during rainy conditions.

We receive numerous questions on how to control powdery mildew on plants. The following information is from one of our earlier posts:

Powdery mildew is an air-borne fungi, and is one of a large group of the most common fungi that cause harm to garden plants. Powdery mildew appears as opaque and powdery grayish-white spots. According to the book, What’s Wrong With My Plant (And How Do I Fix It?) by plant pathologist David Deardorff, PhD, and naturalist Kathryn Wadsworth, the best approach is prevention by removing infected plant material (and putting it in the garbage, not the compost), mulching to prevent water from splashing around and spreading the fungal spores, providing air movement around the individual plant, and choosing resistant cultivars.

When you water your garden make sure to water only the roots of the plant, keeping the foliage dry and water early in the day so that the water has a chance to evaporate. If the infection is severe you might consider purchasing a fungicide from your local nursery. As always, remember to follow directions on the bottle. This article gives additional information on powdery mildew treatment.”

Good garden practices can also help to prevent the spread of this disease. During hot weather, powdery mildew attacks many herbaceous plants especially plants that are stressed due to drought. To help control it give your plants good air circulation and water well during hot spells.  A good layer of mulch can help to keep plants from drying out.  Remove and dispose of any diseased leaves in the garbage. Do not compost them as the spores will remain viable.