Learn to avoid and eliminate caterpillars and other creepy crawlies that can threaten your cannabis grow

Protecting your cannabis plants from the attack of voracious caterpillars is essential to reach harvest time with healthy and productive plants. Caterpillars, as well as slugs and snails, are common pests in marijuana grows. In this post we explain how to prevent, identify and combat these creatures so they don’t feast on your precious harvest of aromatic buds.

Although there are many different types of caterpillars that can invade your outdoor cannabis grow, the species that most often attack marijuana plants are Helicoverpa armigera or ‘cotton bollworm’ (also known as ‘corn earworm’ or ‘Old World bollworm’) and Spodoptera exigua, aka ‘beet armyworm’. These Lepidoptera are medium-sized and have a bright green body, often with lighter longitudinal stripes on their backs. They are extremely voracious pests that feed on the tissue of different types of plants (especially cannabis, which they absolutely love).

There are other types of caterpillars known as ‘borers’ (for instance Grapholita delineana, also known as ‘hemp moth’ when it reaches adulthood) which are more attracted to the stems of the plants. They tunnel into these and feed on the tissue within them, leading to the formation of necrosis.

Caterpillars are a dangerous pest for marijuana grows because they can cause serious damage to the plants in very little time, resulting in a significant decrease in the quantity and quality of the crop.

How to prevent caterpillars in marijuana cultivation

In the case of caterpillars, and as with any other pest, prevention is always the key to avoiding any future issues.

• To ensure that your cannabis plants remain caterpillar-free, it is important to inspect them regularly, checking to see if butterflies or moths have laid their eggs on them; or even looking for the presence of young caterpillars, which are their larvae.
• Using insect nets or protective netting is a good strategy to keep these butterflies from laying their eggs. You can also introduce natural predators like parasitic wasps or ladybirds, which are voracious allies. Another common tactic consists of installing nesting boxes for birds whose diets include caterpillars, such as goldfinches, sparrows or robins.
• In other cases, you can create protective barriers by planting other species for which these creatures feel a special predilection; for example, cabbage or soy. This will keep them entertained at a safe distance and stop them from looking for nourishment from your marijuana plants.
• Keeping your grow clean is also essential to prevent the appearance of caterpillars. Get rid of weeds so they don’t have as many spaces to hide or reproduce.

How to identify caterpillars in marijuana plants

The signs that caterpillars have settled in your cannabis grow are usually obvious, as these hungry insects leave marks which are visible to the human eye:

• Bites on the leaves: Caterpillars feed on plant matter, leaving highly visible damage behind. Check for round or tear-shaped marks on the leaves of your cannabis plants.
• Check your plants at night: Some types of caterpillars that attack cannabis plants are hard to identify because they mimic the colour of the canopy. You’ll find it easier to spot them at night with a torch as they tend to be more active at that time, and the reflection of artificial light makes it easier to tell their bodies apart from the leaves.
• Pay attention to butterflies: If you notice butterflies either hovering around or perching on your cannabis plants, it is very likely that they are laying their eggs. Therefore, you must chase them away and check your plants immediately.
• Look for small black and brown droppings on your cannabis plants. This is another sign that caterpillars have settled in your grow.
• Damaged buds: Caterpillars also feed on marijuana buds during the flowering period, which can turn out to be something even more dramatic because their bites and droppings are the gateway for fungi like botrytis.

Don’t underestimate the importance of early detection to protect your plants from these hungry intruders!

How to eliminate caterpillars from your marijuana plants

Once this pest has settled in your grow, it is imperative to eliminate it as soon as possible so it doesn’t cause irreversible damage.

If you detect caterpillars while your marijuana plants are in their growth phase, you can apply these remedies to get rid of them:

• Spray neem, pyrethrum, or rotenone oil, which is an insecticide of plant origin extracted from three tropical species from the legume family.
• It is important to combine the spraying with the manual removal of both eggs and adult caterpillars.

If your cannabis plants are already in the flowering phase, you need to be more careful to protect your buds.

• Therefore, you can selectively apply biological insecticides, preventing them from coming into contact with the cannabis flowers.
• You can use insecticides based on Bacillus thuringiensis, a bacteria that produces toxic proteins for certain insects and other organisms but is considered a safe biological product for humans. Having said that, it’s best to avoid spraying the plants during the last 15 days of flowering to allow for a sufficient safety period.
• Focus your energy on inspection and the frequent removal of caterpillars and eggs. This is the most effective way to prevent your buds from being affected and avoid any damage during the flowering period.

Slug and snail control in marijuana growing

Aside from caterpillars, other crawling species like slugs and snails also enjoy feasting on cannabis plants. These pests tend to appear under wet conditions, so you must keep an eye out after it’s been raining, or during the arrival of the bad autumn weather.

If they’re not stopped in time, these small gastropod molluscs can cause serious damage to your marijuana plants. These are the steps that you should take to prevent this:

• Keep your cannabis grow nice and clean: Hygiene is key to keep slugs and snails at bay. Remove leaves and traces of organic matter that may have fallen on the ground and started decomposing ― they’re the ideal refuge for these creatures.
• Build barriers around your plants: Place ash or diatomaceous earth around the perimeter of your marijuana grow. Diatomaceous powder has a microscopic abrasive structure that can damage the cuticle of these molluscs, penetrating their bodies and tearing and dehydrating their exoskeleton.
• Water first thing in the morning so the soil dries during the day, and avoid watering in excess.

How to identify slugs and snails in your cannabis plants

To identify these invertebrates in your grow, you must look for the following signs:

• Visible traces of the shiny mucus that they leave behind when they move.
• Bites on the leaves, especially on the edges.
• Check your cannabis plants at night, which is when these invaders are more active.

How to eliminate slugs and snails from your outdoor marijuana grow

If you detect their presence amongst your plants, you need to act fast:

• Place beer-filled containers around your plants, buried at ground level. These molluscs are attracted by the smell of beer and will fall into the liquid and drown.
• They’re quite easy to detect, so you can get rid of them manually. But keep in mind that some slug species can be carriers of parasites or diseases, so it’s best to avoid direct contact, or make sure you wash your hands thoroughly after handling them.

And always remember that prevention is vital in the fight against caterpillars, slugs, snails, or any other creeping organisms that dare to threaten your plants. Keeping your growing space clean and inspecting it regularly will definitely be key to a successful harvest.