Caterpillars

Caterpillars

In outdoor cultivation, caterpillars are one of the most voracious predators that attack cannabis plants. They can destroy them and render them unusable for consumption.

There are many types of caterpillars, but they all share some common characteristics: a segmented body, six legs, and five prolegs. Caterpillars are the larvae of insects in the Lepidoptera family, and after metamorphosis, they become butterflies.

Before finding a caterpillar on our cannabis plants, we'll see butterflies perched on the buds or leaves, usually in the highest parts where the largest and most inaccessible buds are located. The butterfly will typically lay its eggs before winter arrives. These eggs will hatch when ambient temperatures are most suitable, requiring the warmth of late summer, which coincides with the arrival of winter in about two months. It's quite possible, however, for butterflies to lay their eggs and for them not to hatch until the right conditions are met.
Caterpillars have long, segmented bodies with varied colors, generally adapted to camouflage themselves among vegetation to avoid being eaten by birds or other natural predators. They move using their six main legs along with ten prolegs distributed along their bodies, the position of which can vary depending on the type of caterpillar.

This chewing creature is one of the most feared marijuana pests among cannabis growers. Caterpillars are commonly known for their metamorphosis into colorful and beautiful butterflies. Their life cycle is simple: the butterflies lay their eggs on the plant, and when these hatch, the caterpillars emerge and feed relentlessly until they reach the right size and conditions to form the chrysalis in which they will become butterflies. During the first stage, when they are caterpillars, they can appear in a wide variety of colors, from greenish to a whole range of hues, although those that typically attack cannabis plants are green.

The adult form is a butterfly with a wingspan of 35 to 40 mm, with one pair of yellowish wings and the other pair brown. During the day, adults can be observed resting on the underside of leaves in sheltered locations.

As for the larvae or worms, their coloration is generally quite variable and depends on their diet. The early stages (small larvae) are usually brown, while the later stages are typically a bright green, like the plant they feed on.

detect caterpillars

Beware of butterflies: if you see them landing on your plants, try to shoo them away, as they may be laying eggs. If you've seen butterflies on your plants, you should start to suspect and look for caterpillars.
Inspect your plant: look for small yellow or translucent eggs on the undersides of the leaves; this is where the butterflies usually lay them. Also look for the small "droppings" left by the caterpillars—tiny black droppings that will indicate their presence.
Bite marks on the leaves: As mentioned earlier, this insect feeds on green matter, so if you find bite marks on your plants, especially on the leaves, it's very likely that your crop is being attacked by a caterpillar infestation. An infestation of this type can severely damage the plant's foliage, slowing its growth and metabolic functions, and in extreme cases, even causing the plant to die.
Dark spots or rot on the buds: the caterpillar also burrows inside the buds. Inspect them and look for bite marks or the presence of the caterpillars themselves. It's important that if you detect any of these symptoms, you act quickly because, apart from the fact that these insects have a voracious appetite and can quickly devour the largest marijuana buds in your harvest, the droppings they leave behind can promote the growth of fungi, usually botrytis.

We've explained that butterflies lay their eggs on plant leaves, but we haven't mentioned that these leaves will be the first vital food source for newly hatched caterpillars. It's worth noting that not all caterpillars prefer the same type of leaf, so we can find different varieties of caterpillars on cannabis plants, but they will almost always be the same type of caterpillar each year, belonging to the same species, if grown in the same geographical location.

First, we must carefully observe the leaves, looking at those leaves or buds located at the top of the plants, where butterflies lay their eggs. It's very difficult to see the eggs with the naked eye, but if we look closely, we can make them out as small clusters of dots that vary in color (white/yellow) and shape (round or oval) depending on the type of butterfly egg.

After this initial inspection, and once the flowering period has begun, we should examine the buds, starting from the top and gradually working our way down, looking for small black patches or darker bud areas showing signs of rot. The flowers that will be attacked first are those with a large but not overly compact bud, allowing the fungus to move through and devour the softer tissues, such as the small branches that form the base of the bud.

If we find a caterpillar, we should inspect the entire plant daily, especially during the hours when the sun is lower and the ambient humidity is higher, although it is very easy to find it the rest of the day eating non-stop, as its hunger is insatiable and voracious.

The first signs of the infestation are leaves that have been eaten, similar to how grasshoppers do it. Later, as the buds form, if we open them slightly we can see the caterpillars' droppings as tiny black pellets.

Larvae in stage three or higher cause the most damage, both because of their size and their preference for the buds. If these infestations coincide with periods of rain, botrytis often appears quite rapidly, making the pest doubly damaging.

prevention and control

If the caterpillar has already infested your cannabis crop, it's important to act as soon as possible, so take note because here are a series of biological remedies you can use:

Manual removal: With patience and some plastic gloves, you can remove the caterpillars you find on your plants.
Spraying: You can combine manual removal with homemade insecticides such as an infusion of pepper and garlic. Pyrethrum and rotenone also work very well.
Use Bacillus thuringiensis: we recommend this biological insecticide as the most effective for treating caterpillar infestations. This insecticide works by contact; that is, when a caterpillar is sprayed with Bacillus, it becomes infected and dies. Keep in mind that although it is a biological product, it is advisable to allow a safety period and not apply it during the last 15 days of the caterpillar's life cycle. Furthermore, it is recommended to combine spraying this product with manual removal.
Introduce predatory species: Trichogramma wasps and Podisus maculiventris can be a great help

No matter what measures you've taken against the caterpillar infestation, some may have escaped the purge and remain hidden on your plants. At harvest time, it's important to hang the plants upside down and keep a close eye on them. If any caterpillars remain on your harvest, as soon as the cannabis plants begin to dry, these unwanted companions will pack their bags and leave in search of greener pastures, since your plants will no longer provide them with sustenance. You must be vigilant because if they manage to escape undetected, they can complete their life cycle by forming pupae in the most unexpected corners of your home, and thus the cycle begins again, becoming a never-ending story.

After conducting a thorough search of our plants, if we have detected a caterpillar or observed chewed buds on the plants, we should apply a product that repels or kills butterfly eggs and larvae.

These products are generally made with a gram-positive bacillus, such as Bio Thur, which is naturally found in soil and plants. They are specifically designed to treat lepidopteran larvae infestations, with varying degrees of effectiveness depending on the type of larva, but consistently delivering excellent results.

We can also treat the plants with broad-spectrum products to control not only the caterpillars but also other potential pests that may be present at the same time. In this case, Mittel Concentrate could be applied at a dosage of 1 ml/l. When the butterfly larvae eat the plant material treated with the product, they will be poisoned and die, leaving the plant free of intruders.

Another product we can use to treat caterpillars and other types of sap-sucking insects is the insecticide Prireprot. Its active ingredient is pyrethrins, which work on contact, eliminating insects from cannabis plants. In this case, the caterpillars would be removed from the plants, leaving them clean and ready to continue flowering without problems.

It is worth noting that all the products mentioned are biodegradable and biological, so they can be used multiple times as needed, either as a preventative measure or to eradicate caterpillar infestations. The safety period is relatively short, but it is recommended and important not to apply the product during the last 15 days before harvesting cannabis plants to allow time for the treatment to eliminate any traces of the product in the buds.

If the infestation appears in the last 15 days, we must carry out a thorough daily monitoring, observing the plants and buds, opening the buds to see if the caterpillars are hiding among the flowers.

If we do not proceed in this way, it is very likely that the plants will be harvested with the largest buds clearly damaged or even have to be thrown away because they are rendered unusable by the bites of the caterpillars and their droppings that cause the appearance of fungi such as botrytis.

If your plants are affected by botrytis, you can treat them as long as it's not within the last 15 days before harvest. If it's at the end of flowering, it's best to check the trichomes; if they are sufficiently mature, you can harvest the plants.

Once harvested, we must immediately remove the infected part from the healthy rest. If we don't separate the fungal parts, the fungus will spread and eventually rot the entire bud, even during drying, since it takes a few days to lose much of the moisture it contains during its metabolism.

In extensive crops and greenhouses, sex pheromone traps are used to track flight patterns and determine the optimal time for treatments. As long as no insects are captured, there is no risk to the crop.

However, pheromone traps wouldn't make much sense for outdoor cannabis cultivation, as the number of plants is usually small. The most sensible approach is to carry out preventative treatments starting in the second week of July.

The recommended product for combating this pest is Bacillus thuringiensis, marketed as Cordalene, by TRABE. It is a product that is completely safe for beneficial insects and only kills the larvae of the budworm.

Bacillus thuringiensis var. kurstakii, better known as BT, is a bacterium that, when it reproduces as spores, synthesizes proteins that are toxic only to the larvae of this species. If we apply it to our plants, they become colonized with BT, and the caterpillar larvae will die after feeding on the leaves and buds.

It is very important to begin treatment before bud formation; otherwise, the larvae can enter and begin feeding without being affected by the BT treatment. It is best to apply the treatment every two weeks, from mid-July to early September.

Most natural insecticides that act as repellents for other insects also work against the budworm, so sprays with products like Tec-fort are also highly recommended.

One solution for growing potted plants is to bring them indoors or into storage overnight. Since the moth that lays the bud caterpillar eggs is nocturnal, it won't find any plants on which to lay them.

As a last resort, though not recommended for the squeamish, you can manually inspect the buds and locate the worms by looking for their droppings. Once found, the best thing to do is eliminate them permanently by crushing them.

With this final tip, we'll say goodbye until the next post. As always, we invite you to leave your questions and comments, and to participate in the Cactus Martorell cultivation guide.