Bacillus Thuringiensis vs. Malacosoma disstria

To be clear, this is a battle not a comparison. A war between me and the tent caterpillars, the most destructive garden pest that is known to get into my fenced-in raised beds.  My weapon of choice is BT (Bacillus Thuringiensis), a microbial insecticide with caterpillar controlling capabilities. It is totally organic and doesn’t harm humans or any beneficial insects. Luke from the MIGardener channel mentions in this instructional video many other types of pests that are affected by this bacteria.

I am targeting Malacosoma disstria, or the Eastern Tent Caterpillar. These pictures are from last year, but I’m seeing the same thing all over again. They are prolific in my yard – and the whole county from what I can tell from seeing so many silk tents around. They damage the leaves of most of my plants including Brussels sprouts (especially), cabbage, broccoli, kale, chard, arugula – I’ve even seen holes on the beans and peppers. I’m not that bothered by the holes but the plants do get a little stressed.

This method worked well last year, but I can’t remember what ratio I used – hence the need for this blog! Today I’m mixing up a fresh batch with 2 tablespoons of concentrated BT to 1/2 gallon water. I don’t even need to fill my 1 gallon sprayer to cover my entire garden and the surrounding area. Last year I could actually see silk tents in our backyard. This year I am just finding the very hungry caterpillars crawling all around. I sprayed some of the surrounding trees for good measure.

I’ve learned a few important things to remember when spraying BT. First, rain and watering washes it off. So spray accordingly, and reapply. Second, sunlight weakens the impact, so it’s best to spray at sun down. And lastly, the shelf life is limited. A week or so ago, I sprayed the solution that was leftover in my sprayer from last year. It didn’t seem to help at all. When you apply BT properly, the results are noticeable on all new growth. If this application is ineffective, then I will know I need to purchase a new bottle of concentrate.

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