Below is an article on caterpillar control relevant to all climate zones that I had in my gardening column in The St. Petersburg Times in 2004. My favorite brand of BT by FAR is the brand 'Dipel' made by Southern Ag, and sold to farmers in 4 lb. bags at feedstores. Look for a green bag and yellow label. Last year the cost was $5.50 at Shell's Feed in north Tampa, and since I keep the bag in my fridge to keep the bacteria alive, and since I rarely need to use it in the balanced ecology of my yard, I fully expect that bag will last me ten years.
ATTACK OF THE KILLER CATERPILLARS
Spring here can be like a scene from that corny 60’s Japanese sci-fi movie "Mothra", with giant caterpillars rampaging and wreaking havoc before transforming into winged beauties. St. Augustine lawns can be ravaged by sod webworms, mustard and broccoli stripped bare by caterpillars hatching from eggs laid by the beautiful Cabbage Looper butterfly, and I bet you have been grossed out by finding a tomato hornworm SO big you couldn’t stand to pick it off and step on it! Many of us have been painfully stung by those surrealistic looking spiky caterpillars whose acid-filled hairs stab an unsuspecting finger. And oleanders can look "furry" when heavily encrusted with those orange ones with long black hairs. Pretty scary!
Yup, spring is caterpillar time in central Florida. But before we declare war on them with insecticides, even natural ones, let’s remember that those crawling munching monsters mature into butterflies (or "flutterbyes" as they were called in Victorian times) and moths, many of them cherished for their beauty and grace in our gardens. So let’s control them only where they can render harm, likely the veggie garden and St. Augustine lawn. And let’s also feed our favorites like Monarch butterflies by planting butterfly weed, flat leaf parsley, fennel and dill in our flower gardens for the baby caterpillars to feed on.
Organic gardeners enjoy a lot of help from natural allies like birds and wasps who eat caterpillars and carry them off to their nests for their young to feed on…I have even seen wasps clutching caterpillars in their legs while in flight just like in the PBS specials! But since we don’t want our food crops and lawns ruined, we all need a specific tool to control caterpillars quickly. Luckily, this "silver bullet" has been around since the 1930’s and is available in many garden shops and feed stores that supply farmers, plus on-line.
It’s a natural bacteria called Bacillus thuringiensis var. kurstaki, or "BT" for short, sold under product names like ‘Dipel’, ‘Biotrol’. This plague of the caterpillar world isn’t genetically engineered and doesn’t hurt any other living things…honeybees, earthworms, flutterbyes, kids, pets, birds, in-laws, not a one. Just caterpillars who ingest it by biting a leaf sprinkled with BT…poor things, because just like in ‘Alien’, the organisms multiply inside their bodies, paralyzing their digestive track with sharp crystals of a protein toxic to them. As a result they quit feeding on your plants, often within 20 minutes of that first bite. Soon they die and their bodies split open, releasing billions more bacteria to further protect your lawn or garden.
That is why BT is the kiss of death for the butterfly garden so many of us have enjoyed creating and living with. Use it judiciously only where needed. And it has been my experience these 20 years of gardening here that just ONE application inoculates the organically maintained lawn or veggie permanently as the bacteria are soil dwelling and welcome the absence of fungicides and agricultural antibiotics. But to be sure you have enough of them living in your lawn or garden, consider reapplying BT each spring. Cheapest in 4 lb. bags at feed stores, it is also available in 1 pound canisters at many garden shops as a "tomato powder". I rarely use the liquid forms like Thuricide as the petroleum distillates they contain force the bacteria into the spore stage, delaying their becoming active in the garden. Just sprinkle the powder on the damp leaves or lawn so the moisture can bring the bacteria to life. Some folks prefer to mix the powder into bottled water (the chlorine in tap water can kill the bacteria) in their garden sprayer then spray it just where it is needed.
While none of us want "Mothra" pillaging our yards, flutterbyes and moths are essential aspects of the color and charm of Florida. And as more and more of us invite them in with butterfly gardens, perhaps fewer will become extinct due to habitat loss. But caterpillars on my broccoli? Ear worms in my corn? No thanks!