Manduca quinquemaculata is a large, green caterpillar that gives the impression it is a worm, when referred to by its better known name – the tomato hornworm. These are very hungry bugs with a huge appetite that will strip your plant bare, leaves, green tomatoes and all. The first sign of invasion, will be small nibbles missing from the fruit and small sections from the leaves but be warned, the more they eat the bigger they grown and then more food they will require, regularly grow up to 4 inches. If you are meticulous in checking your plants daily, picking them off by hand may be sufficient to get them under control. However spotting them can be difficult, even the really big ones as they are gifted at camouflage so watch out for the signs if you cant see the worms themselves. The nibble marks are a giveaway as is frass on leaves – bug poop in other words – which resembles a cross between brown unripened blackberries and rabbit droppings.
There are also some organic methods to control the spread of the worms.
Bacillus thuringiensis or BT as it is commonly known is a natural bacteria used for centuries to control many species of moths and caterpillars. It has the added bonus of being safe for plants, animals and fish and can be purchased commercially as Dipel or Thuricide.
Pyrethrin is found in many commercial sprays and is an organic insecticide which comes from the seed pod of a flower by the same name, also known as the Dalmation chrysanthemum. In small doses it is harmful although large amounts can be toxic to both animals and humans however many commercial pest spray products contain some of this. A mixture of this and a good insecticidal soap also helps with aphids and small flies as well as the tomato hornworm.
There is a type of small wasp that only grows to around 1/4 of an inch and you can purchase their eggs at the start of the growing season. These wasps make cocoons on the worm’s backs when they hatch; those resemble tiny grains of rice and slowly eat the worm for food as they grow. This type of wasp is very common and can be found around the country so it’s possible you may be fortunate enough to have some already. If you spot a hornworm with white things attached to it, pick it off and stick it in a jar. Don’t kill it, just throw in some leaves and the pupae will turn into more wasps that will be hungry for a big juicy tomato hornworm. It is always advisable to clip the entire leaf off if you notice any damage then it is easier to tell if you are looking at a new attack or the existing one. If you keep on top of it and catch them early you’ll still have a bumper crop at summer’s end.