Sooner or later, every grower faces the pest problem while growing marijuana. It is more difficult to control it in your outdoor garden, but even in more secure conditions, like a greenhouse or a growing room, it may happen as well.
Unfortunately, it is almost impossible to create the ideal conditions for growing cannabis, unless you are growing it in Holland, where you are simply obligated to provide as much security for your plants as it is possible including having a the detector of bacteria on your clothes. But real-life conditions for growing are much less strict and, therefore, much more comfortable for insects.
In fact, you do not need ideal sterile conditions for avoiding the pest problem. In most cases, it is enough to wash all the surfaces with soap and some bleach or chlorine to disinfect the room once in a while. Washing pots, buckets, and equipment after replanting plants is also a good idea. We would recommend you to disinfect all the reservoirs after every use, even if you are sure that there were no insects or other problems with the plant that was growing in there before. In this case, it is better to do some extra work than miss the problem because of negligence and then lose the whole crop.
If you have any carpets, you had better take them to another room: they create a perfect environment for both mold and pests. Cover your floor with plastic sheeting: it will make it easier to disinfect the surface and will not create a sanctuary for insects.
Another thing that can help you with the prevention of pests is filtering the air intake. This way you can block the majority of harmful pests and keep the growing room clean. It is also important to have proper air circulation in the room and not let the temperature and humidity rise above the norm.
Of course, the best way to avoid any problems with insects is through prevention. But even if you did get pests somehow, do not panic: if you can spot the problem on time and detect the pests, then you will be able to get rid of the stowaways and save your crop.
Adult fungus gnats may be not as dangerous as their maggots. However, it is almost impossible to spots maggots as they are tiny and transparent. The adult gnats are quite visible and resemble regular flies on disproportionately long legs. They usually sit on the surface of the leaves and stick to it so hard that it is almost impossible to remove them by force.
Female fungus gnats lay about 200 eggs every week on average and place them at the base of the plants. This way, fungus gnat maggots infest the upper roots and later spread throughout the whole root system. The best condition for them is a wet environment. They can live in wet soil, rockwool, and even in a hydroponic system.
First, they start damaging the tiny root hairs and then consume larger roots as well, making the plants weak and fading. Moreover, the adult species can also be dangerous for your plants as they may carry diseases like pythium, which can kill seedlings.
The presence of fungus gnats may also be a sign of a much more serious problem, such as rotting roots. For this reason, it may be useful to dry the soil and use less heavy substrates. If you do not notice the problem on time, the gnats infestation can lead to the formation of algae on the roots. If so, apart from drying the soil, apply an anti-algae product to the base of the plants. It will also significantly reduce the number of maggots.
To kill the population of gnats, use neem or insecticidal soap in 1-3 applications. You can also utilize sprays that have Bacillus thuringiensis var. israelensis as the main ingredient. However, you will get the best results if you combine spray and soil drenches together applying them every five days until the whole insect population is destroyed.
Yellow sticky traps placed close to the growing medium can also be very useful as they will catch the adult insects looking to spread.
There is no natural predator that can be effective against both adult and larvae fungus gnats, but you can apply several preventing measures if you know that infestation is possible.
Using diatomaceous earth to cover the soil in the pot is a great option. You can also use powdered cinnamon. But the best thing you can do is never overwater your garden and not let the humidity go too high. If you use a hydroponic system, do not forget to cover it to prevent the growth of green algae.
Growing cannabis in soil is the easiest and most common way of cultivation, but it can also bring some additional dangers to the whole process. The thing is, many insects use soil for incubation and hatching larvae. It is almost impossible to spot them, and therefore, the risk of using contaminated soil is quite high.
For this reason, you might want to choose sterilized or composted soil bought at the store. If you are going to use regular soil, it is important to sterilize it first, by, for instance, heating it in the oven for 10 minutes at the temperature of 390 ºF or keeping it in the microwave for 10-15 minutes.
You can also help your flower pots stay clean from pests by using diatomaceous earth also known as kieselgur. It is rock powder with sharp edges that serve as abrasive for insects' exoskeletons. If you put a 1-2 cm layer of kieselgur on top of the soil in the pots, it will act as a natural barrier for pests.
Another way of preventing pest contamination is covering the soil with a ½-inch layer of fine perlite. It will not damage the incests but will serve as a barrier as insect eggs do not usually grow in this medium.
The best way to prevent the appearance of soil-borne pests is to use hydroponic or aeroponic systems of growing cannabis.
An attack of thrips can become a real disaster for a marijuana garden. And unfortunately, these slender insects are some of the most common hitchhikers in indoor gardens. For some reason, they do not like to breed outdoors and prefer to sneak into any indoor growing room and reproduce there in large quantities.
There are more than 6,000 species of thrips, and most of them feed on plants (only a few are predators), destroying leaves like tiny lawnmowers. They consume chlorophyll, and that makes the leaves darker, more brittle, less vivid until they completely die.
Thrips can be pretty much any color, but you will easily recognize them by their distinctive oblong shape. They move very quickly; they can fly from one plant to another and use marijuana buds for nesting. All these facts make it almost impossible to get rid of thrips manually.
If you have already noticed the problem (the most obvious signs of thrip infestation are tiny black lines on the leaves that are actually the insects' feces), the best way to solve it is to apply pyrethrum or insecticidal soap. You should spray it 2-4 times every 5-10 days until all the pests are completely gone.
The treatment may take some time as the soap does not destroy eggs, and you should wait until the little insects hatch.
And of course, it is better to prevent thrip infestation than fight it. Keep your growing area clean and use powerful fans. A strong and constant air flow will not allow thrips to latch on to the plants or fly inside the room. Spraying cannabis with water can slow the reproduction of thrips and reduce their ability to damage the plants.
You can also use natural predators and buy a predatory mite colony: almost all insect predators use thrips as food. However, for better results, we would recommend combining spraying and introducing predators to the garden, as relying only on predatory mites can prolong the time of solving the problem.
If you have never seen spider mites before, it may be difficult for you to spot them with a naked eye. They live underneath the leaves. They can be whitish, red, or even brown, with two distinctive spots on their body. They have eight legs, and that is the reason why they are classified as spiders and not insects.
You can see these tiny creatures with the help of a magnifying power of 15x or more. If you can see the web, it usually means that mites have already bred, and there are at least two generations of them on your plants. Spider mites use chlorophyll cells as food, therefore they can significantly damage your flowers.
It is very important to remove all the mites as soon as possible, as female mites can lay about 100 eggs every five days, and once they become fertilized, they remain so for life. Even a few days of delay in solving this problem can kill your crop completely.
The best way is, as always, preventing the appearance of the pests. Keep your growing room clean, disinfect all the equipment and all the pots, and carefully check all the clones you bring into your growing room.
Once you spot the problem, the best option is to kill them with a special spray. It can be neem oil (it is considered to be the most effective), horticultural oil, pyrethrum, or insecticidal soap. Spray your plants according to the instructions. Usually, in 5-10 days, the whole mite population should be destroyed.
These sprays are not really effective against spider mite eggs; that is why you need to be absolutely sure that you kill all the generations. The eggs usually hatch after 5-10 days, so if you need to spray a few times more, do not hesitate. In most cases, three spray sessions are enough.
If the infestation returns, you had better change the chemical so that you can be sure that mites do not develop a resistance to the spray you use. Be careful and not use miticides that have DDT or other components that are toxic for humans.
To make sure that the mites do not breed in between the spraying sessions, decrease the temperature in the room to 60 ºF/16 ºC and leave the humidity at 50% or lower. It will make the mites feel uncomfortable and significantly slow their reproduction rates. It is also recommended to avoid spraying water on leaves during these days as it may blast larger colonies.
If you grow organic cannabis, you may want to avoid any chemicals. In this situation, apart from the natural oils, you can also use natural predators of spider mites: Mesoseiulus longipes and Neoseiulus californicus. They use spider mites as food and can kill up to 5 adult mites or 20 eggs a day. Once they destroy the whole colony, they will die as well.