Many organisms are associated with Cannabis crops, some of them are beneficial and some are harmful to the plant. Those organisms considered harmful to the plant are also called pests. Spider mites, thrips, fungus gnats, and aphids are some of the most common insect and arachnid “bug” pests in indoor marijuana crops.
In this article, you’ll learn how to identify bugs that are considered pests and how to get rid of them to have a healthy crop. There’s a list of the environmental conditions (temperature and humidity levels) in which these pests appear and breed most rapidly so you can take preventive measures.
Spider Mites are one of the most common pests on cannabis crops. Spider mites are not insects but small arachnids and there are around 1200 species of them. Spider mites are very small so a magnifying glass or 10X hand lens is very helpful to spot them. They are less than 1 mm (0.04 in) in size and may be red, brown, or green. Spider mites live on the underside of plant leaves, where they feed on the plant’s tissue and produce protective silk fabrics.
Early signs of spider mites include small spots or bites on the leaves and small dots on the underside of the leaves and branches. The plant infested with spider mites starts to show white spots and discoloring of the leaves. When the colony grows, spider mites start growing their silky “spider” webs on the underside of the leaves and then on the buds.
It’s very difficult to recover a plant at this stage so act as soon as you spot the first signals. If the pest progresses, leaves might turn yellow, flabby, and eventually die completely. A large spider mite infestation can have a negative effect on a cannabis plant and reduce yield significantly.
Spider mites breed and multiply quickly with hot temperatures around 27°C/80°F and low humidity levels (below 60%).
Thrips are small sap-sucking insects that live in cannabis plants and feed on them. Thrips have elongated bodies, most of them from 0.6 to 3 mm (0.02 to 0.12 inches) so they can look like small dots moving on a leaf. Use a 10x hand lens to spot adult thrips and larvae on the top and the underside of the leaves.
Early signs of a thrip infestation are white, silvery, and shiny spots on the leaves’ surface. After a few days, the leaves show small white dots similar to “rice grains” (larvae) on them and sometimes small black dots (thrips feces). Adult thrips reproduce very fast and can hibernate in the soil mix during the cold months.
Thrips are not the most harmful pest but they breed very rapidly and they can be damaging in great numbers. Leaves start wilting when thrip damage advances and show lots of white and silvery spots, where thrips had eaten the leaf tissue.
Thrips reproduce very fast with high temperatures (25°C to 27°C / 77°F to 80°F) and high humidity levels (60% to 85%) so be careful, especially during the summer months.
Aphids are very small insects but still visible to the naked eye. They may be yellow, brown, or black, the adults have wings and the young don’t. Aphids live on the back of leaves and stems and create large colonies, so check your plant frequently.
Aphids can appear in both indoor and outdoor crops and they multiply very rapidly (sexually and asexually).
Aphids suck the leaves’ tissue and then secrete a thick, sticky, sugary liquid that attracts ants. The aphid’s secretion may grow mold fungus on the leaves too. Aphids can also carry diseases, such as viruses, inject toxins into the plant and make leaves curl. Stressed plants are more vulnerable to aphids and take longer to recover.
Most aphid species multiply faster at temperatures from 20°C to 28°C/ 68°F to 82°F and relative humidity from 50 to 80%.
Fungus gnats are small insects with wings. They are visible to the naked eye and they look like small flies. Fungus gnats are attracted to crops with high humidity levels and breed on the soil, filling it with white and very small larvae.
Fungus gnats do not eat the plant, they eat decaying matter and fungi, but their larvae may eat some of the root hairs. Plants infected with fungus gnats show yellow leaves and a general wilting of the entire plant.
Fungus gnats thrive in warm and wet conditions with high humidity levels, so do not overwater your plants. Leaving trays with runoff water for a long time in the tent attracts fungus gnats.
Cannabis plants are intended for human consumption so consider safety in pest management to avoid health issues associated with pesticides. Read all labels carefully and follow the instructions. Always wear protective gloves and face masks to apply any of the mentioned products.
The best way to avoid pests and bugs in a grow tent is by prevention because once they appear, fighting them can be a difficult task. Creating an efficient pest management system is key before pests had already been established.
Sometimes you first spot signs of the presence of insects and bugs before seeing the actual insects, because they are too small or they hide from the naked eye. Check leaves on both sides and look for white spots, dark spots, fuzzy patches, and anything not “normal”. Pest control during flowering is key for a good harvest. Check for bugs and pests before changing the photoperiod to 12/12 as it’s easier to apply product during the vegetative stage.
When finding any sign of pests, act as soon as possible and get rid of them. After that, monitor your plants and environments for the following weeks.
There are many commercial chemical pesticides and products for almost every pest but they get quickly resistant. Also, some of these pesticides have negative environmental and health effects so we give some safer options for treating your plants.
Insecticidal soap has no residual effect against bugs after it has dried, this means it will only kill pests on contact. Apply potassium soap solutions repeatedly to control high populations of pests. On the other hand, neem oil acts as prevention because it has a residual effect, so there’s no need to spray the plant so often.
Reminder: Do not apply these products to the buds during the late flowering stage, always aim at the leaves.
If some of your plants are already infected, isolate them if possible, taking them away from your crop until you deal with the pest. As a means of prevention treat all the plants living in the grow room or tent.
Read the following article for 10 tips to prevent pests indoors.
Log all your pest management actions in the Grow with Jane app for cannabis growing. Set reminders to apply products and monitor for results, add photos and comments.
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Tell us in the comments, which pests are the most common in your area and how do you manage them?
Nice info on pest bugs. Ive been annoyed by this problem from a long time, Keep up the good work mate!!! Love your blog
Hi Crystalcloud9! Thanks for reading and for your kind words! Stay tuned as some new articles on this subject and new guides are coming soon! Happy growing!