This week at Wellfield, I encountered my old nemesis, the moth species Melitta curcubitae, or squash vine borer (SVB for short). It has hit our trellised Hubbard squash with a vengeance. I have had little problem dealing with this insect species in the past when growing cucurbits on the ground. I merely wait until I see the classic indicators, perform a little surgery to remove the larvae and bury the stem. The vine merely reroots and continues along its happy way. However, how to deal with this problem when the vines are trellised and I cannot bury the stem? Good question, Josh!
Squash vine borer adult moths emerge from underground cocoons in late June or July. They then lay eggs along the stems of their chosen host plants. The larvae then hatch, find a nice spot and bore into the hollow stem to feast on internal stem tissue, cutting off the vascular system along that stretch of vine. Thus, one of the first symptoms is a wilting section vine, when all else looks peachy. Close examination will reveal little holes and yellow green frass piles, where the borer has done its business.
There are many suggested solutions, many of which I am too late to implement at this point. Since I had such a large number of larvae going all Old Country Buffet on me, I decided to experiment. Using my pruner blade, I made a careful slice of the stem, opening up the interior to look for the off white, grub-looking larvae. Then, I pulled the larvae out of the stem to remove the threat. The trick now is, how to prevent the exposed vine from desiccating. I am experimenting using floral wrap to tape up the cuts. I do not hold out much hope, but experimentation is the spice of gardening.
Peruse any number of gardening forums, and you will run across all kinds of experimental treatments for SVB. Then, come on by the gardens and see the results.
Josh Steffen, Horticulture and Facilities Manager