seems good results at less cost and less collateral damdages could be acheives with talc esp vs Squash vine bore??????????????????? Thanks
It is doubtful.
There is nothing that works very well on squash vine borer. I think talc would have zero effect on them.
Diatomaceous earth likely would have very little effect unless you can make it adhere to the plant. If the DE falls off onto the ground, it will have virtually no effect. The moth lays the eggs on the stems of the plant and they tunnel directly into the plant without traveling much distance on the outside of the stem. I haven't found DE to have much effect on anything except some crawling insects that have to crawl or walk through it on the ground where the sharp edges of the miniscule DE particles slice them up.
Kaolin clay is more effective on chewing insects that chew on the outside of plants, so it would have little effect on the borers who work on the inside of the plants. I have kaolin clay and use it to protect some plants from grasshoppers and it works at least as well on the hoppers as all-purpose flour, but is not as hard on the plants as flour is. I think that's because it is in such fine particles and when you mix it with water it doesn't form a thicker paste like flour does. The hope with kaolin clay is that it will keep the borers from tunneling into the stem to begin with, but in research studies, fields treated with kaolin clay did not show a significanct difference in SVB activity.
For Squash Vine Borers the most effective "controls" (and I use that word loosely because they are very hard--almost impossibly hard--to control) are to keep the plants very securely covered with floating row cover material. Then, when it is time for pollination, either uncover the plants briefly and hand-pollinate the flowers yourself, or you can uncover them and leave them uncovered, but that starts the SVB clock ticking because they'll find your uncovered plants very quickly. If using floating row cover it must be held tight to the ground around the entire perimeter of the covered area, and you have to plant in an area where you haven't grown squash previously because there might be overwintering cocoons in the ground that could hatch out and leave you with larvae trapped inside your covered row.
An alternate way to use floating row cover to protect squash is to cut it into long strips and wrap it around the plant stem to exclude the borer. I think this might succeed somewhat if you keep adding more row cover as the plant grows, but I bet the larvae would find their way inside a stem sooner or later.
Some people inject the stems of their plants with either Btk or beneficial nematodes, but I've never seen a scientific study that has examined this method for efficacy and I've heard mixed reports on whether this really works or not.
I have moderate to good success by using nylon hoisery to encase the stem of the plant. tTo make this work, I start seeds in small ( 2 or 3 oz.) paper cups with the bottom cut out but you could do it with purchased transplants. You might be able to use it with direct-seeded plants, although it would mean you'd have to dig down in the soil to pull the nylon down around the plant stem after the plant is up and growing. When I transplant the plants into the ground, I take a nylon knee-high with the foot portion cut out so I have just a long tube, and I pull that nylon tube down over the outside of the paper cup and then plant the cup. The top portion of the nylon tube is loosely bunched around the plant stem above ground and extends 2 or 3" below ground. As the plant grows, I pull the nylon tube up higher and higher to protect more of the rapidly enlarging and lengthening stem. In orger to prevent the SVBs from crawling under the nylon and penetrating the stem, I pull the loose nylon to one side of the stem and use a clothespin to hold it tight. (The stem is not in the clothespin--only the nylon is. I've done this with a zip tie, but then you have to cut and toss the zip tie each time you move the stocking up, so I have found a clothespin works better.) As the stem gets larger I readjust how much nylon is bunched up and pulled tight by the clothespin. Using this method I have been able to keep yellow summer squash and zucchini plants alive and producing into late July or early August. Here at our house, unprotected summer squash plants usually bite the dust in June or very early July.
With winter squash, I just plant C. moschata types that SVBs don't bother enough to kill if they bother them at all.