High Temperatures and Infestations tend to go hand in hand when it comes to summer crops, and a lot of people tend to grow indoors in the middle of summer. Doing this without any sort of air conditioning is practically impossible, you’d end up with a crop that has a temperature of 30ºC and 60% humidity, although the humidity might be less or more depending on where you’re growing. When you grow cannabis you have to respect a certain set of temperatures to make sure that your end product is of acceptable quality. Also, keep in mind that high temperatures can cause important essential oils and terpenes to evaporate, as well as inviting unwanted guests to come and invade your crop.
We’ll begin by talking about the least likely infestation to happen in indoor crops; caterpillars. It really is rare, but it can actually happen so it’s always best to be prepared.
Caterpillars are forms of moths or butterflies, and there are 10000 different types. Sometimes it’s even funny to see them sitting on your plant leaves, looking like little inoffensive bugs, but trust us; they’re offensive. As soon as those babies lay their eggs, you’ll end up with an infestation of caterpillars coming up from underneath the leaves, between the branches, eating your plants as they go along. This wouldn’t be as annoying if it weren’t for the fact that they literally don’t stop eating, and they leave their feces all over the plant and on the buds, completely taking over your plants and wherever they decide to take a bite out of you should be prepared to deal with mildew like botrytis inside your buds. They prefer temperatures between 22º and 28º, although they can deal with brusque changes in temperature and sometimes put up with “extreme” temperatures; they need around 40% humidity to really get going. Indoors, like we’ve said, it’s extremely rare and hard to end up with this infestation, but if you somehow manage it then we recommend products like Bacillus Thuringiensis, a biological product that doesn’t require you to stop using it before harvesting.
Apart from caterpillars, there are much more common infestations like thrips; the 70 subspecies of this insect leave silver-looking bit marks which can easily be confused with white flies, although plants infected with thrips won’t have that annoying white web fluttering about them. Thrips thrive in temperatures between 25º and 30º with a medium to low humidity level, and these conditions are usually the exact conditions you’d want in an indoor crop, so you’ll need to prevent thrips from appearing by using potassic soap or neem oil. Pyrethrin is also a decent preventive measure and used to get rid of pests when they’ve already infected your crop. Another good idea is to lower the temperature to 24º so it doesn’t affect your plants, and raise humidity up to 60%; this won’t get rid of the insects but it will interfere with their life cycle and they’ll stop growing. A thrip can live for up to 12 months! When it comes to fighting fire with fire, you can always consider getting some Amblyseius Swirskii, a type of mite that actually feeds on thrip, red and white spider eggs. It works the best in temperatures between 18ºC and 24ºC, with humidity higher than 60%.
It’s also rather particular how at around 35º, thrips’ life cycle stops completely, and between 30º and 32º for three days straight, the nymphs die off completely.
Another infestation that’s extremely common indoors with these temperatures and is usually brought in from outside without realizing is the white fly, a plague that can live in a wide range of temperatures; between 16º and 34º, and they die off at less than 9º and more than 40º, although you’d lose your crop too if you were to try and get rid of them in that manner. White flies can complete their life cycle in just a month between 22º and 25º. Males can live for 15 days in 28º heats, while females can live twice as much under just 2º more. White flies have quite a curious reproduction process; fecundated eggs create females, whereas those which aren’t fecundated create males. Females can lay between 2 and 7 eggs per day, which take just 7 days to hatch. Encarsia Formosa is an amazing ally for these pests; it’s a parasitic wasp that renders the flies eggs useless, killing the flies as they give birth. Swirskii can also help against larvae in this case. We recommend using about 10 wasps per square meter.
Red spiders are every grower’s nightmare due to how difficult it is to get rid of them once they’ve popped up. Obviously, to prevent them you’ll need to keep your space clean, tidy, and avoid the conditions that they flourish in; a temperature between 28º and 34º and a humidity level somewhere between 35% and 55%. Once these pests appear they’re incredibly difficult to get rid of; you’ll need to lower the temperature to around 22-25º, as well as raising humidity to somewhere between 60-70%. Another good method is to use Phytoseiulus Permisilis, a mite that preys on red spiders as well as being cannibalistic, meaning that they’ll eat each other once they’ve finished with the red spiders, making for a more ecologic or at least biologic way of treating your plants.
There’s also a type of fungus that can be incredibly useful for getting rid of red spiders and white flies. This fungus is called Verticillium Lecanii, a strain that has a large spore version and a small spore version; the small spores are ideal for controlling white flies, although getting the flies to be contaminated with this fungus is a bit difficult. This specific fungus doesn’t affect mammals, reptiles, birds of fish; just white flies and other aphids, like red spiders and the like.
So, it’s quite obvious that during the summer, without a decent air conditioner, you’ll have to grow outdoors or wait for temperatures to let up a bit, or else you’ll probably end up with your own little zoo indoors rather than a crop in decent conditions.
Author: Fabio Inga
Translation: Ciara Murphy