When to Put Sulphur Dust on Yellow Squash

Sulphur dust, or powdered sulphur, can be used as an insecticide to ward off mites and insects or as a fungicide to control mildew in the home garden. Sulphur can be used on yellow squash, which is susceptible to mildew.

Function of Sulphur Dust

• Sulphur dust is only effective as a preventative measure against powdery mildew and should be applied before symptoms of mildew appear. It does not eliminate established disease on squash plants, but can protect new leaves on the plant from the development of mildew.

Symptoms of Powdery Mildew

• When powdery mildew first develops, it looks like spots of white powder on the leaves of the squash plant. These spots can spread and grow larger over time. Mildew does not typically spread to the squash itself, although it can cause the leaves to drop off the plant, resulting in sunburned squash due to the lack of protection from the leaves.

Precautions

• While sulphur dust is not toxic, it is an irritant to the skin and eyes. Transferring sulphur dust from its original container to a different container should be avoided and those using sulphur dust in the garden should carefully wash their hands after use. Sulphur dust is not suitable for use in temperatures above 90 degrees or within two weeks of using an oil-based fungicide, as it may damage the squash.