For years now I have done battle with the tomato hornworm. You know him: big, green brute with a spiky horn on his butt. Sort of a cross between a backward rhinoceros and The Hulk. He can get to be 4 inches long and will decimate a tomato plant overnight.
In the past I've used a number of methods to try to keep this marauder at bay.
• Sevin Powder: works pretty well but is a chemical insecticide.
• Neem oil: works pretty well and is a natural repellent, but has to be reapplied after every rainfall.
• Hand picking: It is harder than one might think to spot these well-camouflaged beasties. Even as big as they get, they can be hard to see in amongst the leaves. I look mostly for the leaf damage and poo-pellets they leave, then go hunting in that region.
• Braconid Wasp: a natural control in that these iridescent blue wasps lay their eggs on the hornworm and when the eggs hatch, they feed on the form and kill it. When I find a worm packing a load of eggs on its back I move that one to a sacrificial plant where it can live out its life and help proliferate the Braconids. I've never been stung by a Braconid despite having them nest in my barn eaves. I consider them good fellows and welcome them.
• Bacillus thuringiensis: a naturally occurring bacterium that attacks the digestive systems of numerous leaf-feeders, including hornworms. It is available in spray or powder form under the trade names of Dipel and Thuricide.
This year I tried a new weapon: Borage. Also known as Starflower, Borage makes a great companion plant for tomatoes and squash.
The L.A. Times – The Global Garden says:
“As a seedling, borage doesn’t reveal its potential. The leaves are rough and fat, and as they get older, covered in fur. Only when the sparkling lavender star-shaped flowers appear in spring-summer does borage, also known as starflower, show its potential: Bees and pest-killing wasps love the blooms.
"Borage is more than an easy-growing ornamental that brings in pollinators and pest predators. The younger leaves and flowers can be used in salads. The flowers are particularly tasty added to iced water or tea, used fresh or frozen into ice cubes. The flower and leaves have a slight cucumber taste but with a splash of honey (though it's worth noting that pregnant and nursing women are advised not to consume borage because of health risks to them and their children).
"Borage flowers were made into candies in the Middle Ages in Europe, where the plant grows wild around the Mediterranean. They are still used as decorations on pastries or desserts. A tea of borage was considered as a mood enhancer, leading to its reputation as a sedative.”
I planted Borage seed between my tomato plants. They turned out to be bigger than I expected, leading to some over-crowding, but they don't seem to be interfering with the tomatoes or contributing to problems resulting from staying wet.
I have not tried eating the leaves or flowers yet, but I can attest that I have not found a single hornworm in my tomatoes this year, and I've used no other repellent! I've also noted that I have not had problems with leaf blight or blossom rot despite it being a wet summer, but cannot officially attribute that to the Borage. Whatever the reason, I am happy to report that we are poised for a tremendous tomato crop this year.