Have you ever grown a really beautiful squash plant that is perfectly healthy and then, all of a sudden, the entire plant wilts and dies? If so, you are familiar with the work of the Squash Vine Borer. Those of you who attended the Organic Gardening 101 class last weekend probably remember my talk about the Squash Vine Borer. This is one of the most difficult pests to control and, like clockwork, it has made its appearance in my home garden on June 1st.
The adult Borer looks like a wasp and flies like a wasp and is active during the day like a wasp. But the Squash Vine Borer is actually a moth. And even though I promptly delivered this colorful moth a powerful thump that sent him into an eternal dirt nap, the damage is likely to have already been done.
The Squash Vine Borer lays eggs at the base of plants and often chooses plants in the Squash family – and this one chose my pumpkin patch. Squash family plant stems are hollow. When the eggs hatch in about 7 days, the emerging grubs will bore little holes into the stem of the squash plant and begin feeding on the inside of the stems. Once the grubs have entered the stems, the only signs will be a small hole at the base and some saw dust-looking material protruding from their entry hole called “frass”. Within a few days, these grubs can completely destroy plant stems and ruin the entire squash crop.
What is an organic gardener to do?
Depending on the stage of the invasion, there are several options. Since I noticed the adult yesterday, I can only assume that the eggs have been laid. So I want to take care of the eggs before they hatch. For the first time this year, I am using beneficial garden nematodes. Beneficial nematodes are semi-microscopic organisms that feed off of the larvae of several types of damaging insects such as grubs and fleas. I made an application of nematodes last night and hopefully this will be enough to prevent the Vine Borer eggs from hatching and ever entering the squash stem.
As a secondary treatment, I will likely apply pyrethrins at the base of all of my squash plants in a few days so that the grubs will be killed before entering the plant stems. Pyrethrins are made from extracts of certain Chrysanthemum plants. The tricky part about applying pyrethrins is timing. Pyrethrins work best when they can make direct contact with pests. Hopefully the residual quality will prevent the borers from penetrating the plant stems.
Another pre-emptive option is to use a syringe and inject the hollow stem of the plant with a BT (Bacillus Thuricide) or the same nematodes that were mentioned earlier. As soon as the grubs enter the hollow plant stem they are greeted with a deadly desert that will end their plant pillage. If the nematodes prove ineffective in the soil application and the pyrethrins fail to stop the invasion, this will be my third option. I have lost this battle many times so I like to have plan A, B & C!
For plants that are already damaged by the borer, a last ditch effort can be made by using a razor blade to cut the plant stem and remove the pests. Dirt can then be mounded around the opened plant stem and roots will continue to grow. This technique can help lengthen the life of the squash but plants rarely fully recover.
So be on the lookout! Eliminate any adult Squash Vine Borers that you see and watch for any signs of borer grubs entering the stem of plants.