Bribe hornworms with other nightshades to keep tomatoes safe

Dear readers: Not long ago, I was asked how to grow healthy tomato plants and keep tomato hornworms at bay without harming them. I suggested having a sacrificial tomato plant that could be grown as a relocation spot for any hornworms found on the main crop. I also suggested searching for and capturing any hornworms that were found on the beloved tomato plants and relocating them.

I reached out to readers for additional suggestions about keeping the main tomato crop from attack, and did receive several responses. Many offered guidance on the eradication of the hornworms, which wasn’t the goal D.J. is aiming for. She wants to save her tomato plants, yet allow the hornworms to live.

One letter from reader S.S. went along with me as to moving any hornworms to the sacrificial planting, then treating the main crop with the insecticide — Bacillus thuringiensis (Bt for short) — to offer the wanted protection for the balance of the tomato crop. Unfortunately, the use of an insecticide is counterproductive to D.J.’s aim.

My suggestion of a relocation of captured hornworms anywhere there was a collection of weeds was met with some disdain. A reader reminded me that you would need to be sure that there are plants that the hornworm will be able to feed off of before depositing them willy-nilly in the weeds. So on that note, I was reminded that tomatoes are in the nightshade family in the plant kingdom. Since several plants in that nightshade family grow really well here, finding host plants shouldn’t be too much trouble.

The two most common plants I know of will be considered by most folks to be weeds. First is one called silverleaf nightshade. The silverleaf grows everywhere here. A relatively tall plant, upwards to two feet tall, that sports pretty light purple star-shaped blooms on a rather spiny stemmed plant. The whole plant, leaves and stems are a pale gray/silver color. After flowering, the silverleaf sets seed pod clusters that can range in color from orange-yellow to black. Reader P.G. says she actually allows the silverleaf to grow near her garden as a relocation plant for any interloping hornworms she finds. She said that after placing a hornworm near the silverleaf, the hornworm strips the silverleaf and goes on about their business, leaving the tomatoes safer. I will suggest that if you do keep any of the perennial silverleaf as a decoy plant, you get in the habit of cutting the seed clusters off so they don’t become too much of a challenge in your gardens.

Next, reader W.B. says that growing a truly remarkable plant — sacred datura — makes a great host for tomato hornworms. I had the pleasure of knowing a sacred datura plant, that each year, would grow to a width of ten feet and stand easily 3½ feet tall. The spread of this plant was so eye-catching. Fairly large gray-green foliage covers this plant that is all too often thought of as a weed. It certainly isn’t good fodder for grazing animals but in my opinion a lovely plant. The blooms offered by the sacred datura are large, brilliant white, softly scented trumpet-shaped blooms that bees, bumbles and hummingbirds appreciate all blooming season long. After the datura finishes blooming, it sets spiny pods that are in their own right very pretty.

My reference book “Weeds of the West” lists twelve different weeds in the nightshade family that could be grown as decoy hosts for an overwhelming influx of tomato hornworm. If you do choose to maintain any other plants in the nightshade family as sacrificial plants, do aim to keep them controlled so they don’t try to take over the world. They do that really well on their own.

Reader P.N. also wrote in to share that there are many weeds that serve as alternate hosts, including horsenettle, jimsonweed and most all in the nightshade family.

So do a bit of poking around to see if you can or do have an alternative plant that you can offer the hornworm so you can grow a crop of tomatoes. It can be very challenging to garden here, but with help from Mother Nature, you can find other plants to bribe the hornworms. That way you can continue the circle of life where we get to see those amazing, hummingbird sized moths each year.

Happy Diggin’ In and thank you to all who offered information on tomato hornworms! I appreciate that you took the time to write.

Tracey Fitzgibbon is a certified nurseryman. Send garden-related questions to Digging In, Albuquerque Journal, 7777 Jefferson NE, Albuquerque, NM 87109, or to features@abqjournal.com