Problem Identifier / How to Get Rid of and Kill Caterpillars

What are Caterpillars?

Caterpillars are the larval stage of moths and butterflies. They can be fuzzy, spotted, bumpy or striped. They cannot reproduce but will eventually transform into either a butterfly or moth. Understanding whether or not caterpillars will cause damage to your garden or plants is based on correctly identifying the species.

Gloves should always be worn when handling an unknown species since many have stinging hairs or irritants. The majority of caterpillars responsible for damaging fall crops transform into moths. When eggs are laid by a moth on the leaves of a plant, there will eventually be caterpillars in the garden. It’s best to consider this fact when implementing an Integrated Pest Management (IPM) strategy. Caterpillars can be prevented with the proper IPM, and by applying Trifecta Crop Control as a preventative.

Identifying Garden Caterpillars

Tomato and tobacco hornworms are two of the most common and damaging types of caterpillars. You should always try to keep caterpillars out of your garden by applying  integrated pest management (IPM) because caterpillars cause a lot of destruction. Hornworms have a light green coloration, and often grow to a similar length and thickness as a human finger. Tobacco hornworms have seven white lines on a diagonal.

Tomato hornworms have eight lines in the shape of a V. The bodies of both have reddish dots, with pointy, curved rear horns. Tobacco hornworms have a red horn and  tomato hornworms have a black or blueish horn. These caterpillars will devour tomato, tobacco, potato and eggplant leaves.

When a leaf is turned over on a broccoli or cabbage plant during the summer, you will likely find small worms, called the inchworms. Inchworms are hard to see because their colors blend in with the leaf’s underside. Inchworms have white lines on both sides and their motion is loopy because there are no legs in between the hind legs and prolegs. Inchworms consume large quantities of cabbage crops. This includes collards, radish, cauliflower, kale, broccoli and turnips. When cabbage leaves are not available, inchworms will eat the leaves of almost every garden vegetable.

 

Asp caterpillars are most often found in the southern United States in shade trees. This pest can be identified by the furry body. The color can be rust, yellowish, tan or gray. Coming into direct contact with this caterpillar is dangerous because they have venomous spines capable of causing a lot of pain, neurological damage, and skin rashes. Asp caterpillars move slowly and are often found on the bark of trees.

Armyworms travel in extremely large groups. They are black, with yellow striping running the entire length of the body. Armyworms will devour almost anything including grass, beets, clover, flax, millet, corn and beans. The majority of caterpillar have different characteristics including coloration, size and stripes.

Identifying Caterpillars on Cannabis and Hemp Plants

Cannabis and hemp crops attract different species of caterpillars. Some of the most common are hemp borers, saltmarsh, cotton bollworms, beet armyworms, and silver Y.

Hemp borers do damage much like their name says: they bore into the stems and feast on the marrow within them which can result in necrosis. At an advanced stage, your plants can decompose. The holes made by hemp borers can also lead to fungi and attract other pests such as aphids or thrips.

 

Caterpillars are most likely to show up during the flowering stage, chowing down on your buds and destroying your crops right before you’re getting ready to harvest.  Caterpillars are not only hungry but they are nocturnal which means you probably won’t see much activity during the day. Inspecting your plants at night is the best way to catch caterpillars in the act but you may be able to catch them returning to or from their hiding place at dawn or dusk.

If you find holes in your leaves but do not see caterpillars, be sure to inspect your plants thoroughly, including the underside of the leaves and buds. If you find their excrement, it’s important to clean them off and rectify the issue or your plants could be susceptible to bud rot.

Caterpillar Life Cycle

In order to ensure caterpillars stay out of your garden or off your cannabis crops, you need to prevent moths from laying eggs on your plants! If there are no eggs on your plants, there will be no caterpillars hatched to cause damage. Also, learn how to identify their appearance during different life cycles. Caterpillars resemble worms, are usually hairy or brightly colored, and are the spiny larva of either a moth or a butterfly. Unless the species is correctly identified, it is impossible to determine if the caterpillar will transform into a butterfly or a moth.

The time required for pupation is dependent on the species. The majority of species are completely grown, with pupation occurring within a short period of time after hatching. Just four weeks are required for the Painted Lady butterfly. Some caterpillars become ready to complete growth during the winter. These species pupate during the next spring.

The Fox Moth stays in caterpillar form for 11 months, beginning in June, and ending in April. Other species, including the Goat Moth, stay in a tree trunk in the larval stage for a maximum of five years. Pupation is the life stage when all growth stops. The garden caterpillar then transforms into either a moth or a butterfly. The change takes place while the caterpillar is in a protective chrysalis or pupa casing.

This stage is often referred to as metamorphosis. Certain species of caterpillar moths spin an extra protective case called a cocoon. A spun silk mesh is formed using hair from the body. Most of these cocoons are extremely flimsy. The threads will stop specific parasites from penetrating the pupa but do not provide a lot of extra protection. Certain parasites will attempt to lay their eggs inside of the pupa.

 

Then there are cocoons constructed to be both impenetrable and solid. Enzymes that soften the cocoon enable the transformed moth or butterfly to make its way out of the cocoon. Most butterfly species and numerous moth species do not spin a cocoon.

The pupation stage takes place in a hairless pupal casing. The formation of the pupae can occur in a lot of different areas. This includes within the soil, throughout piles of leaves or leaf litter, on structures constructed by man such as the walls of homes, on tree trunks, and inside of plant stems. A pupa is frequently referred to as a chrysalis, with the word originating from Greek, and meaning gold. This is in reference to the golden-brown coloration of different types of pupae. The term chrysalis is most often used in reference to the pupation stage for a butterfly as opposed to a moth.

As the development of the butterfly or moth progresses, some of the pupae will begin to darken. The pupa is secured to a plant by the caterpillar, then well-disguised to blend in with the shapes and colors of its surroundings.

What Does Caterpillar Damage Look Like?

The damaged caused by caterpillars includes:

  • Ragged leaves
  • Deposits of fecal matter on the leaves
  • Leaves rolled together with silken threads
  • Leaves full of holes
  • Holes in the plant stems

The majority of caterpillars are large enough to see clearly with the human eye. A clear sign there are caterpillars are the raggedy appearance of the plants and leaves full of holes. When this type of damage is seen, there are most likely moth or caterpillar eggs underneath the leaves. If enough damage is done, young plants will most likely die.

Damage is usually caused when the caterpillars consume different sections of the plants, including flowers and foliage. Sometimes the mid-vein is left behind, or the entire leaf may be consumed. A good indication caterpillars are present is fecal matter on the leaves of the plant. Some species use silken threads for rolling the leaves together, and others create tunnels to enter the plant stems.

You should always take a preventative approach using Trifecta Crop Control to keep caterpillars out of your garden. Crop Control will repel moths and butterflies so they are unable to lay eggs on your plants in the first place. Once you have caterpillars, if it takes too much time to notice the damage, the quality of your plants will suffer or they will be completely destroyed. Some of the worst caterpillar damage is found in plants growing inside of a greenhouse. This is because the natural predators found outside are generally unable to eat the caterpillars.

How to Get Rid of or Kill Caterpillars Naturally

  • Bt (bacillus thuringiensis) and Trifecta Crop Control (in rotation)
  • Snipping off affected leaves
  • Regular and thorough examinations
  • Night time lighting
  • Removing weeds
  • Blacklight traps
  • Removing the caterpillars by hand

Bt is highly selective. It kills caterpillars and is not-toxic to their natural enemies. The bacterium is harmless to humans and animals and is considered environmentally safe. When used in conjunction with Trifecta Crop Control as part of your IPM, caterpillars should never become an issue. It is important to note that Crop Control will kill off and break down the Bt. The two products can be used in rotation to allow each to perform its function. Bt can be applied 2 days after Crop Control in a weekly application.

Cinnabar Moth Eggs
Cinnabar moth eggs on the underside of a leaf. PHOTO CREDIT Doug Doohan, Ohio State University/ OARDC, Bugwood.org

When eggs are suspected, the affected leaves can be snipped off, then disposed of correctly. The leaves should never be used for compost or the eggs will end up back in the garden. Fill a pail with soapy water before examining host plants. When a caterpillar is spotted, remove it from the plant, then put it into the bucket. This will kill the caterpillar.

Examining plants on a regular basis combined with removing the caterpillars will help keep the population to a minimum. There are a lot of caterpillars capable of stinging, especially furry puss caterpillars. For this reason, protective gloves should always be worn before picking any of them up. The sting of certain species is extremely painful.

Turning on lights at night will attract moths around both gardens and greenhouses. When a light is required, the lowest intensity bulb should be used. There are also lights designed to help prevent the collection of moths. Bright lights will not only attract females, but the chances of eggs appearing will be high.

Managing weeds both outside and inside of greenhouses is important. Adult females will lay eggs in weeds. All plant debris needs to be removed to eliminate any pupae left during the winter months. Outdoor blacklight traps are effective for detecting the activity of adult moths. When the adults are in flight, plants should be inspected on a regular basis. Look closely at any plants close to an opening including doors, vents and sidewalls.

These are the openings adults use to gain entry. Do not use lights at night for vegetable gardens containing soybean or corn unless absolutely necessary. Caterpillars can also be removed from plants by hand provided you are wearing protective gloves.

How to Prevent Caterpillars Naturally

The following options are effective to prevent caterpillars naturally:

  • Using Trifecta Crop Control to repel moths, thus preventing egg laying and caterpillars hatching
  • Do not leave lights on in gardens or greenhouses overnight
  • Examine plants regularly
  • Keep plants covered using porous netting
  • Plants herbs with a strong smell
  • Rotate crops
  • Attract birds with birdbaths, nesting houses and feeders
  • Allow chickens or ducks occasional access to the garden

Moths are repelled by herbs such as rosemary, mint, thyme and cloves – all ingredients in Trifecta Crop Control. By applying Trifecta Crop Control as a preventative, you can feel confident that you will prevent caterpillars naturally. Apply as follows or click here to view and/or download our Application Guidelines.

  • .5oz per gallon applied once per week during veg
  • 1oz per gallon applied once per week during flower up to 2 weeks before harvest

Do not leave lights on in the garden overnight or moths will be attracted. Plants should be examined at least a couple times each week to look for little green caterpillars and moth eggs. These should be removed immediately. Porous netting can be used for covering the plants. Pests will be kept out, but sunlight and air will still reach the plants.

Caterpillars are discouraged by planting herbs with strong smells including lavender, sage, peppermint and mugwort. Crops need to be rotated. The same plants should not be planted in the same areas over and over again because both caterpillars and moths will become established.

A portion of the garden can be used to intentionally attract butterflies by planting milk weed, varieties of the lantana plant, thistle, red clover and verbena. This should keep them from laying eggs on your plants.

Birdbaths, nesting boxes and feeders can be used to attract birds to eat the caterpillars. Toads, box turtles and lizards are easily attracted by offering hiding places with logs or broken clay pots. These predators will remain if there is water in shallow dishes placed on the ground, and flat rocks ideal for sunning. If there are chickens or ducks, letting them loose in the garden occasionally will substantially decrease both pests and eggs.

Caterpillar Management in Greenhouses Using Biocontrols

Trichogramma spp.

Trichogramma Wasp
Trichogramma Wasp

Trichogramma is an egg parasitoid effective and popular for controlling caterpillars. The parasitoid wasps are tiny with a length of just 0.9 millimeters. These predators lay eggs on numerous caterpillars. The lifecycle of the wasp is completed in the parasitized egg. After killing the egg, a new wasp emerges. Before you use this wasp for biocontrol, your crops need to be inspected for eggs.

This is because Trichogramma will only attack this life stage. They are shipped as parasitized grain moth eggs and are either in capsules of 500 pupae or glued to small cards. Put the cards all over your crops to enable the wasps to emerge and look for caterpillar eggs on your plants. Protect the cards from ants or they will consume the eggs. While in the capsules, Trichogramma are protected from ants, then will emerge through holes placed in the top. You need to release four predators for each square foot.

Tips for Trichogramma use include:

  • You must control ants to prevent them from eating Trichogramma eggs
  • These predators should only be released when there are host eggs available
  • If you are unable to control the ants, the predators must be left in the shipping bags until the emergence of the first adults.

Check the bags every day, then hang the cards when adults appear. You can then shake the wasps out of the bag.

Other IPM Techniques

Biorational Pesticides

There are several strains of (Bt) Bacillus thuringiensis available for caterpillars not causing any harm to other pests or biocontrols. The Bt insecticides most often used are Dipel and Monterey. Both products are only toxic to moth and butterfly larvae. Bt is only lethal when ingested by the targeted pest. This will result in some feeding damage. The mortality rate varies according to the dose consumed, targeted species and the size of the larval.

Defeat Pests, Mold and Mildew… NATURALLY!

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