Turning soil will thwart hornworms
Q. Last summer my tomatoes developed hornworms and I picked them off by hand to help the plants thrive. Unfortunately, I need to use the same beds this year for tomatoes. Is there a best way to treat the soil before planting to eliminate new hornworms from invading again this year? — M.E., Los Ranchos
A. My first hope is that you have been turning the garden soil periodically throughout the past dormant months.
By turning a bed that is laying dormant you can help eliminate a whole host of bugs and eggs, especially if the weather is really cold.
It’s the tomato hornworm moth that has started all your troubles. Here’s the life cycle of the hornworm. In June and July the moths emerge from soil borne pupae, that’s an encased youngster that is developing into an adult. The “skin” of the pupae splits, the adult moth crawls out of it, heads to the soil surface, dries out and expands its wings.
Once the outer “skeleton” has dried and taken on its adult color, it takes off, finds a mate and then lays this year’s crop of eggs on the underside of the tomato plant leaves. These eggs, usually laid in precision rows, are a bright orangeyyellow color and quickly hatch in a week.
The larva (hornworm caterpillar) feeds on your plants for about a month, then fall or crawl to the soil to pupate (I call it morphing) through the dormant months, waiting and growing into the pupae to become next year’s tomato hornworm moth adult.
The tomato hornworm is a remarkably beautiful creature too. About the size of a hummingbird, they have greyish-black brown patterned wings with a body that sports mauve-orange spots.
If you do notice a hummingbird-sized creature flitting about your plant from dusk on through the night, then be on guard and start faithfully inspecting the underneath side of the leaves for eggs.
If you find any eggs, pluck the leaf and dispose of them. DO NOT COMPOST these leaves or put them in the trash. If you’re brave, step on them and grind them up.
You asked for the best way to treat the soil now to have success this year. I know of no pesticide that would affect the pupae of the hornworm except turning the soil faithfully during the winter to get the pupae exposed enough to cause its demise.
If you do have a hornworm hatch, treat the plants with Bacillus thuringiensis var. kurstaki, or BTK for short.
The BTK is a bacterium that affects insects during the larval stage. You can find BTK in any well-stocked nursery’s pharmacy.
Also, while rereading about the hornworm, I learned that if you are going to start your tomatoes from seed, you should soak the seed in a 10% bleach solution for 10 minutes then rinse them in clean water before you plant. (That’s one teaspoon bleach to 9 teaspoons of water.) Evidently the soak and rinse reduces the chance of seed-borne diseases. Who knew?
I also read that you should add a cup of bonemeal to each hole if you’re planting already growing plants.
So get out there and give the space where you’re going to plant your tomatoes a good turn, keeping an eye out for any funky rust-brown cocoon scaly-looking things, and if found, dispose of them before you plant this year’s crop of tomatoes.
Happy Diggin’ In!