Will Sulfur Deter Squash Borers?

Squash Vine Borer Basics

• After spending the winter in cocoons in the ground, adult borers emerge in late spring or early summer and lay eggs at the bases of susceptible plants. Adult borers, wasp-like in appearance, are about 1/2 inch long with metallic-green wings and orange abdomens with black spots. They fly during the day, making a buzzing sound. A week after they lay their eggs, their larvae hatch and burrow into the bottom 12 inches of squash stems, leaving holes where they extrude a yellow granular frass that looks like sawdust. Injured vines become wet and shiny and often rot, sometimes killing the plant. One plant usually hosts one larva, although up to 100 larvae have been found on one plant with multiple stems.

Cultural Controls

• Fill yellow bowls or pans with water and place them in your garden in late spring. Adult borers are attracted to yellow and will land in the water and drown. You can also monitor the pests' appearance by using pheromone sticky traps sold by most garden supply centers. You’ll hear a buzzing sound when they're flying. When you spot the first adult, place floating row covers over your vines and leave them there for two weeks -- but not when the flowers are blooming, because that will block pollinating bees. You can also cover the lower 3 feet of the stems with nylon stockings or cheese cloth to prevent the moths from laying eggs. The adults are easy to catch in the late evening or early morning when they rest on the bottoms of the leaves. If your plants are already infected, use a sharp knife to slit the vine and stab the larva with a wire to kill it, or remove it with tweezers. After you deal with the larva, press the the wound together and cover it with soil so it can heal.

Chemical Insecticides

• The key to using insecticides is to apply them when the borer eggs are hatching. Apply insecticides within a week after you detect adults in your garden, and then reapply them every seven to 10 days for two to five weeks. Insecticides registered for controlling squash vine borers include those with the active ingredients carbaryl, bifenthrin, esfenvalerate, permethrin and malathion. Regulations and restrictions for using these insecticides vary from state to state, so check with your county extension agent before using them. Always wear protective clothing when applying insecticides, and make sure children and pets are away from the area.

Sulfur Use

• Sulfur is one of the oldest natural fungicides used to control powdery mildew and other fungal diseases that typically develop in wet, damp weather. Sprayed or dusted as a powder, sulfur prevents fungal spores from germinating. Do not apply it to your squash if the temperature is over 80 degrees Fahrenheit. Recommendations for its use on squash are mixed. University of Florida horticulturalists say sulfur provides only a moderate amount of control of powdery mildew on squash. Purdue University horticulturalists say you should not apply sulfur on curcurbits because it can cause them to burn.