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Cannabis pests, molds and mildew


Below you will find some helpful information that will help spare your marijuana garden from the negative effects of fungi and insects. These are just a few of the negative effects that most marijuana gardens face, with others being viruses, diseases and bacteria that can harm or kill off your marijuana plants. Here are some of the most common issues and ways to hopefully prevent or fix them.

Marijuana bugs

Spider mites

Most marijuana growers will encounter spider mites on their marijuana plants, no matter if they are grown in an outdoor garden or an indoor grow-room. Spider mites use their whip-shaped mouths and damage the plant cells, allowing them to ingest the plant sap. When you notice a speckled appearance on the marijuana plant leaf, you will likely already have a serious infestation. With severe infestations, your marijuana plant leaves will show discoloration of either bronze or gray on the leaves. The worse the infestation becomes, the worse the problems will be, ultimately stressing out the plant prematurely or killing the plant.


Thrips appear longer and bigger than most mites with a body shape that is more linear. Their bites leave yellow or white marks behind in small clusters, leaving a more defined problem area behind than those that a mite would leave behind. You will likely notice feces left behind after thrips that appears black and clustered.


When you see little insects flying around your marijuana plants, you will likely have a whitefly infestation. This is especially easy to see when the plants get moved around by the grower or wind. Whiteflies are quite small, only growing to be about the size of pencil lead, and they are just white. They drink the juices from the plant, leaving residue behind on your marijuana plant that fungi love to eat.

Fungus gnats

Fungus gnats have many related species that can cause equal amounts of damage. These flying insects cause root and soil infections, making it much more difficult for marijuana plants to feed or get the necessary nutrients. Fungus gnats are quite dark, very small and easily mobile from plant to plant. Crane flies, a close relative, look like mosquitoes that fly around and damage your marijuana plants.


There are two things you will likely notice with budworms: they will rarely spin a web around a cluster of flowers (or buds), or more frequently, they will burrow their way right into ripe flower clusters. They enjoy eating flowers from the inside of the cluster, out. This leaves an opening for gray mold-a common and deadly fungal disease that marijuana plants come down with, also called botryis. Caterpillars are not as easy to spot as budworms are because they blend in with the leaves that they are eating. They usually manipulate the leaves before consumption so they can eat small portions of leaves between the veins or so they can get larger portions of the leaves right into their mouths.

Fungus [Fungi]

Almost all marijuana plants and leaves will show signs of good bacteria and fungi, but it is the bad fungi you need to worry about. Botryis is the deadliest form of fungi that marijuana plants regularly experience. This fungi is more commonly called gray mold. The ability to detect this fungus early on is almost non-existent, and it usually attacks the biggest and ripest buds of the marijuana plant from the inside of the bud, out. You will not see gray mold until you have marijuana flowers that are quite dense and very well developed because this is when this mold takes out the core of the bud and the stem of the flower. You will notice a gray-colored garbage on the bud that will quickly destroy the appearance and vigor of the bud. You can also be affected by gray mold when you have harvested marijuana, and even if you place your harvest in a freezer. This form of mold can cause problems anywhere that has humidity over 50% and a lack of proper aeration near the tops of the marijuana plants. Downy mildew should be considered nearly as deadly as gray mold is, but it does not cause quite as much damage and is typically more difficult to notice. You will usually see downy mildew begin with yellow or white spots across the tops of the leaves with little bumps that correspond on the underside of each leaf. Most leaves will begin to curl or mutate when the mildew begins to take hold of the plant. Another mold, known as powdery mildew, usually shows up as little bumps on top of each leaf with the leaves quickly looking as though they have a dusty grit covering them. Occasionally the powdery mildew will appear to look like resin glands of the plant, but that will quickly change. Molds that are called "damping off" molds will attack a marijuana seed at all forms of planting. Seedlings are also in danger from "damping off" molds if the mold allows the seedling to even sprout. Sometimes a "damping off" mold will rot the stem right out from a seedling at its base.

Viruses and Bacterias

Both people and plants are susceptible to viruses, especially the kinds that jump back and forth between people and plants. The deadliest marijuana viruses are considered to be "mosaic" and "streak" forms of viruses. Both of these cause a swirling of yellow and white on the marijuana plant leaves in an artistic fashion, but you will quickly notice wilted leaves falling off of your plants. Bacteria is also common among marijuana plant leaves, with most forms showing up as "blight" diseases. This will cause spots to show up on the leaves, followed by a wilting, rotting and decaying of the marijuana plants or even the harvested material.

Eliminating insects

Many marijuana plant growers use beneficial mites that prey on spider mites in their growing locations prior to the spider mites establishing themselves on their marijuana plants. These predatory mites help to defeat spider mites should they try and infest your marijuana plants because once you get an infestation of spider mites, you will likely have them for the rest of that crop. Sanitizing the growing location with all of the plants removed is your only realistic option once spider mites rear their heads. Organic sprays and soaps can sometimes also help kill spider mites, especially if the sprays contain garlic-cinnamide.

Toxic poison use on marijuana plants is dangerous and unethical, especially if used when the plant is flowering. Most bugs can be controlled between the use of a non-toxic spray or a predatory organism that will feed off of the harmful insects. Thrips are able to be killed with sprays that combine nicotinic acid, organic soap, pyrethrum and garlic-just make sure to coat the growing medium as well because this is where thrips reproduce. Whiteflies are attracted to yellow colored objects, so many marijuana growers use sticky strips that come in bright yellow to trap the bugs on the strips. Some growers prefer using wasps that feed on whiteflies, releasing them just before whiteflies can infest their growing location. Pyrethrum sprays and organic forms of gardening soap can also help destroy airborne whiteflies.

Always be sure to spray the top and bottom side of the leaves completely to make sure you get all of the pests off of the plant. Growing mediums harbor quite a few other pests, especially if there is heavy water and fertilizer use on the medium. If you happen to use organic fertilizers then you will likely end up with a gnat infestation. The best way to kill off gnats is by using one of the following methods: heating the soil, mixing up the soil, wasps that prey on gnats or a spray application of the following liquids-garlic, rotenone, neem and insecticide soap. Caterpillars and budworms can be knocked off of the marijuana plants by a thorough shaking daily. If your marijuana plants are growing vegetation, then you can spray insecticidal soaps or organic toxin sprays on them, but these should be avoided if your marijuana plants are beginning to flower. It is a much better option to simply remove the infected bud or section where the worm lives than to take a chance with a toxin on your buds that are ready to be harvested.

Controlling viruses, bacteria and molds

Most growing locations need to be cleared out of all plants if they become infected with any type of bacteria, virus, mold or fungi. If your crop is nearly ready to harvest, the only way to even partially salvage your crop may be by making water hash. Other than this, the remainder of your crop will need to be destroyed if it is infected, including sterilizing or destroying all of the clothing and tools that have contacted the infected plants.


Handling or smoking any marijuana that has been infected by mildew, mold or fungi can harm your health!

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