Cannabis species are on the more tolerant and persistent side when it comes to handling pests and diseases among cultivated plants. However, although few, they too have enemies that can do them harm. By growing your plants indoors you significantly reduce exposure to potential pests, but they can nevertheless find their way around and infest your garden. Cannabis pests can significantly reduce yields and the quality of cannabis products (hemp, buds, seeds, etc.) and bring some unwanted tenants into your home. To get you one step ahead in the game, today we’ll talk about the most common cannabis pests and how to get rid of them in order to save your grow op from ultimate demise.
A Bit About Pest Control
Before we sink into the topic further, we need to say a word or two about pest control. The most common way of dealing with pests on most plants is to spray them with adequate pesticides. There is a wide variety of effective substances available on the market, and there are often multiple choices when it comes to active ingredients. However, when it comes to application of these substances on cannabis plants, we got to be extra careful. Pesticide residues in cannabis products is a very big and serious problem, especially with medical-grade products, as they are targeted at people with sensitive health.
When picking an insecticide for your cannabis plants, or any other pesticide, it is essential to look at the active ingredients. Certain active pesticide substances, or compounds they create after decomposing, can be persistent, toxic, and carcinogenic. Another problem is that the toxicity level of pesticide fumes and their effect on human lungs is not a part of standard testing for pesticide registration, so we don’t know which compounds are created in the burning process and how they interact with our tissues. This is why cherry-picking the safest pesticides and applying them in the right time frame is essential for avoiding contamination of the end product. In a nutshell – don’t use toxic substances and make sure to avoid applications near or during the harvest. If you are using commercial insecticides, it is essential to follow the instructions on the label to ensure proper and safe application.
If you see ants around your plants, stay vigilant. They are rarely bearers of good news. Aside from creating potential root damage, these insects might bring in other, more damaging pests, like aphids, whiteflies and mealybugs. Ants have complex relationships with other organisms, especially aphids. They use the aphids as livestock and protect them from potential enemies, perpetating the infestation. As with all pests, it is best to act early. As soon as you spot ants crawling around your plants, take steps to remove them and prevent their presence in the future.
If see only a few individuals moving around, remove them manually. Keep an eye on the grow area in the next couple of days, and continue removing the ants if you encounter them. If there is too many of them for simple manual removal, than it is best to use sprays and repellents.
Aphids are small, soft-bodied insects that feed on plant sap. They like to occupy leaf undersides, stems, buds and young growth, sucking plant juice and reproducing vigorously. Aside from live individuals, signs of aphid presence also include their whitish molts and traces of honeydew. By feeding on the plant sap, aphids ingest a lot of sugar, so they discard the excess in the form of honeydew. This sticky, sugar-rich substance attracts some unwanted visitors, like ants and sooty molds.
Although usually not lethal, aphid infesfations can severely affect the health of cannabis plants and the quality of their products. Aside from weakening the plants and inviting ants and fungi, aphids are also vectors of various plant viruses. Plant viruses are incurable and some strains can cause 100% yield loss, so it is best not to view aphid presence as nuisance, especially in indoor grow ops. When you see these pesky insects near or on your most favored greens, act immediately – but – don’t panic. There are multiple ways to get rid of them, and the key is persistence.
If there are too many individuals to remove manually, the easiest way to get rid of aphids is to spray the plants with insecticidal sprays and take action to prevent them from returning. There is a wide array of active substances and biologicals effective against aphids, and if you want an in-depth overview, check out our blog about aphid control.
Caterpillars are larvae of various moth and butterfly species of the Lepidoptera order. Their main task is to eat and grow bigger, so it is not a surprise that they are notorious for their insatiable hunger. These insects are common pests in outdoor grow setups and rarely create problems indoors. Nevertheless, stay vigilant. If you notice some irregularly-shaped holes on the leaves or stems, the chances are high that you have a some caterpillars in your cannabis garden. When present in small numbers, they are not lethal to plants, but they can reduce the plant’s photosynthetic surface area and eat away parts of stems enough to weaken the plant. Some species also like to take a bite of the cannabis stems and buds, creating a more serious problem. However, in greater numbers, caterpillars are devastating, eating away most of the plant mass.
Some of the most significant species include fall armyworm (Spodoptera frugiperda), yellow-striped armyworm (Spodoptera ornithogalli), beet armyworm (Spodoptera exigua), Eurasian hemp borer (Grapholita delineana), zebra caterpillar (Melanchra picta), beet webworm (Spoladea recurvalis) and variegated cutworm (Peridroma saucia).
Caterpillars are quite big and create visible symptoms quickly, so it is easy to notice them during regular checkups. If only a few individuals are present, they can be taken care of manually, with physical removal. In case of a more severe infestation, it is most efficient to spray the plants with adequate insecticides. Sprays based on Bacillus thuringiensis bacterium are very effective, as well as the ones based on neem oil. These are both of 100% natural origin and leave no harmful residues. However, be careful not to apply Bt sprays near harvest time.
Do you see some tiny flies flying near the soil of your cannabis plants? If the answer is yes, then you might have a problem with fungus gnats. Adult fungus gnats that you see flying around do not harm your plants, but their larvae are a whole different story. Juvenile fungus gnats live in the soil, where they feed on fungi and organic matter, but oftentimes also take a bite of plant seedlings, roots, and root hairs. The damage they create hinders the roots’ ability to absorb water and nutrients, leading to slowed or stumped growth of the plants. The aerial parts of the plant become wilted and undernourished, and if the infestation is severe, it can decrease yields, as well as the quality of the product.
Fungus gnats thrive in moist conditions, so it is really important to be careful not to overwater. Soggy soil is one of the primary causes of a fungus gnat infestation. Other causes include infested soil and poor soil structure. Make sure to use “clean” substrates that come from trusted producers, and have a well-balanced structure with adequate drainage.
Prevention is one thing, but what to do when you already have a problem on your hands? There are multiple ways to deal with these tiny pests, depending on whether you grow your plants outdoors or indoors, and on the severity of the infestation. Since fungus gnat larvae roam in the soil, it is not as easy to get to them compared to pests that affect aerial parts of the plant. However, you can use yellow sticky traps to capture the adults to prevent their reproduction, as well as ensure that soil moisture levels are not as favorable for the larvae.
There is a number of synthetic insecticides that work against fungus gnat larvae, but they are not allowed in cannabis production. However, there are some options on the biological side – Bacillus thuringiensis subsp. israelensis is a bacterium that acts as an insecticide and can help curb fungus gnat numbers.
Mealybugs are small, fluffy, white insects with flat, oval bodies, that feed by sucking the sap from plant tissues. They are common pests in outdoor cannabis grow, and are significantly less of a threat for indoor growers. You can usually see them hanging around the nervature of the leaves, as well as leaf and branch nodes. They are easily recognized by their characteristic bodies covered in a white, waxy substance. Similar to aphids, mealybugs produce honeydew that can attract other pests and diseases. They too have a high reproductive potential, and can take over the garden if the conditions are favorable. The characteristic sign of their presence, besides live individuals, is the threads of waxy, clumpy substance on leaf undersides.
Initially, mealybugs don’t cause any visible symptoms on plants and don’t affect their health as much. However, the power of mealybugs lies in their numbers, and once they establish a sizable population, you may have trouble on your hands.
The key to successful mealybug control is acting early, since they can get more difficult to get rid of if their numbers go rampant. Remove the individuals as soon as you see them manually, or spray them off the plants with a water hose. Mealybugs are not very mobile creatures, so the chances that they’ll return are quite slim. If you want to be extra-cautious, sprinkle some diatomaceous earth on your plants. Make sure you don’t get it on your buds, though. Attracting or adding mealybug predators and natural enemies can also be very useful and efficiently keep their numbers in check.
If you got a larger infestation that must be dealt with right away, you might want to apply adequate insecticides. Insecticidal soaps, mixture of water and rubbing alcohol, as well as neem oil can work well and leave no harmful residues. However, it is important to note that neem oil spray can cause burns on plant tissue if applied in intensive lighting conditions. It also leaves a sticky coating on the plant, so avoid applying it on the buds.
Rodents are probably some of the most damaging pests out there, causing problems in a wide variety of human activities. Aside from their most notorious role as disease vectors, they create considerable material damage by chewing on cables, building materials, and cultivated plants, as well as contaminating stored goods with their droppings. Most rodents are herbivores, with the exception of mice and rodents, which are omnivores. They feed on a wide variety of plants, cannabis included.
Don’t fall into the trap of thinking that rodents are only a threat to outdoor grow ops. Some species, like moles and rabbits, can only be found in outdoor settings, but mice and rats are far more adaptable. They can slip through small openings and gaps, as well as create holes in the building material with their hard teeth. If you see one, be sure that there are others nearby. These mammals are social creatures that enjoy the company of other individuals of their species.
Considering that a single mouse or a rat can wreak havoc in the garden, an infestation is the last thing you want to have on your hands. Rats and mice reproduce at staggering rates, so prevention and timely control are essential. These pests are very stealthy, so the chances that you’ll catch them in the act are slim. However, their presence has visible signs – chewed stalks, piles of droppings, bite marks. You also might hear them moving in the walls or the attic during the night.
To prevent rodents from entering your indoor garden and home, make sure that the area is clean and there are no holes they can get through. Take a good look at all nooks and crannies in your indoor garden to check for possible entry points and seal them. Another way to prevent rodents from establishing is getting a cat.
If it is too late for prevention and you are seeking for a way to get rid of them, there are a couple of approaches:
- Repellents – A variety of commercially-available rodent repellents are available in stores for only a few bucks. Make sure to pick the one that is suitable for indoor application. Growers that are looking for a natural alternative can apply strong-smelling repelling agents like peppermint oil, black pepper, cayenne pepper, cloves, and vinegar.
- Traps – There are many types of mice and rat traps available in stores. However, they can get messy and some of them are quite inhumane, so it is better to turn to other removal methods if possible.
- Dry ice – A non-toxic and efficient way to get rid of rodents is to place chunks of dry ice in their burrows and seal them. Carbon dioxide from the dry ice will put the rodents to sleep and suffocate them. It may sound harsh, but it is some of the most effective and painless ways to exterminate unwanted rodents.
- Professional removal – If the infestation is too great or persistent, it is best to ask for professional help.
Spider mites are tiny arachnids, relatives of spiders, that live on plants and feed on their juices. They are probably the most common indoor cannabis pests, due to their proclivity to consistently warm and dry environments. Spider mites usually occupy the leaf undersides, where they weave their tiny webs and feed on the epidermal cells of leaf tissues. Only a few individuals can turn into a large colony in a matter of few weeks in favorable conditions. Their feeding activities leave blemishes on leaves and weaken the plant. A severe infestation can destroy the entire growing operation, so it is very important to stay alert and to inspect plants regularly. If you see webbing on leaf undersides, take a magnifying glass and give them a thorough inspection. Spider mites are one of those pests that can be notoriously hard to get rid of, so act preventively and promptly.
The first step to efficient spider mite control is to ensure that the conditions are not favorable for their establishment and spread. This means that the soil needs to be moist, and that air humidity is above 60%. Good air circulation is also beneficial, as well as keeping an eye on the thermometer.
When it comes to foliar sprays that can be used for spider mite control, the most effective ones include insecticidal soaps, diluted alcohol, neem oil, spinosad, and horticultural oils. Make sure to avoid applying these substances on buds and during harvest, as they can negatively affect the end product and reduce quality. The addition of predatory species like Phytoseiulus persimilis and pirate bugs (Orius spp.) is also beneficial.
Thrips are tiny insects notorious among many growers due to the damage they cause in plant production, especially in greenhouses and other indoor environments. Their life cycle is short and efficient, so they can develop multiple generations within the same season and reproduce vigorously. Thrips don’t do great damage to adult plants, but having them in great numbers during early phases of plant development can have very serious consequences. Thrips like to feed on the buds, so they can severely affect their development and quality.
Since thrips lay their eggs in soil, the most common way of introduction is through contaminated substrates, so the first step towards successful control is to use quality substrate from a reliable source. Spraying the plants with insecticidal soaps, diluted alcohol, neem oil and diatomaceous earth can help curb thrips numbers, but it is best to remove the substrate of infested plants and replace it with new, healthy substrate. The introduction of predatory species like Amblyseius mites and pirate bugs (Orius spp.) can also help keep them in check.
Whiteflies are tiny, moth-like insects that feed on the plants by sucking on their juicy, nutritive tissues, leaving yellow spots and causing die-off. Similar to aphids, they excrete honeydew, attracting other harmful organisms. Whiteflies are usually found on leaf undersides, with adults hanging out in the upper parts of the plant, and egges and nymphs on the lower parts. They reproduce quickly and have a short life span, so they can develop multiple generations within a single season and severely jeopardize the yields. The speed of their development is highly dependent on temperature – the higher the temperature the faster it is.
Whiteflies are successfully controlled with the help of spice sprays, and neem oil, but if you don’t want to spray your plants, yellow sticky traps are also a good option. Another one is the inclusion of biological control agents like parasitic wasp Encarsia formosa, lagybugs, and predatory mites.
Some growers like to apply mechanical methods of removal against whiteflies – they vacuum the plants in the early morning, when the little pests are slow and lethargic. This method also works well in removing other pests, like aphids and thrips.
Neem oil spray recipe
- 1 tablespoon of cold-pressed, concentrated neem oil
- 1 liter of warm water
- 1 drop of liquid soap
Shake the mixture well before spraying the plants. Repeat the application every 7-10 days during critical phases of plant and pest development. It is effective against aphids, mealybugs, spider mites, thrips and whiteflies.
Diluted alcohol recipe
- 1 part 70% rubbing alcohol
- 9 parts water
Apply the mixture once or twice a week to get rid of aphids, mealybugs, spider mites, thrips, and whiteflies.
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