Pests and Diseases

Bugs would love to move into your room and destroy your crop as quickly as they can. Disease spores are always present in the air (we breathe in millions a day), and would be very happy in a humid, neglected garden. The best way to control these potentially devastating problems is through prevention.

If you have ever heard someone say things like “spider mites are always around; you just have to make sure they don’t get the upper hand,” then they are idiots, and lazy ones at that. Cleanliness, cleanliness, cleanliness – this will keep problems from occurring so you don’t have to treat for them. Every time you have to spray or bomb, your plants experience stress combined with the stress of insect or disease damage.

Wash your hands. Change your clothes. Don’t allow visitors. Don’t smoke in your room; the tobacco mosaic virus is virulent. Any new plants should be isolated until proven safe to introduce into your room. A free clone can cause the ruin of an entire crop. Sterilize your tools frequently. Sweep up any mess of the floor, and wash down your walls between crops. Do not reuse soil. Keep plants healthy and provide good air circulation. In other words, treat your grow room like a surgery.

Laziness is the number one cause of disease and pests. Plants are never lazy; the grower is.


Spider mites are the worst offenders in the indoor garden. These tiny nasties hitch rides on you, your dog, your friends, and other plants. Evergreens, especially the arborvitae, are the natural home to these bugs. If you have a lot of decorative evergreens around your home, take extra precaution. Personally, I yank out the outdoor plants and replace with deciduous (leaf-dropper in the fall) perennials.

Spider mites first establish a home base on a weak susceptible plant, usually located closest to the door (after all, you brought them in.) From there, they spread out, munching and laying eggs. They are found on the undersides of leaves sucking away the life-giving fluids in your plants. Nearly invisible, they are hard to spot, but stippling (tiny yellowish spots) will be visible on the tops of leaves. Get and use a microscope or loupe to find these things. Once webbing occurs, usually in your flowers, you have a serious, if not fatal, infestation.

Spidermite females, 75% of the total population, only require one breeding to be fertile for life. Each female lays about 100 eggs, which hatch and become adults within two weeks. Females can lay eggs every five days.

Spider mites thrive in a dry, 70-80 degree room. Lower the temperature, raise the humidity and get to work. Neem oil, especially the highly pure Einstein Oil, is a good insecticide. Mix according to directions and spray just before the light go out. You can also use pyrethrum sprays, or bombs if you are not in flower.

Insecticidal soaps are very gentle, and work by softening the protective shells on the insect and degrading the eggs.

Never use a toxic bug spray found in regular stores to treat any pest. Do not use a systemic poison, often used in outdoor ornamentals, on any plant that will be consumed in any way.

Specialty oils, such as garlic, rosemary, citrus and liquid seaweed can be moderately, but safely effective.

Another product that can be used during flowering is Mighty Wash. This product is electrostatically charged water, and kills by physically zapping the insect. The bugs cannot build up a tolerance to this method.

Any product used needs to be repeated at 3 – 5 day intervals. It is a good idea to use different insecticides to prevent immunity in the bugs.

Fungus gnats are another common indoor pest. These annoying flying bugs can be quickly trapped with yellow sticky traps. The flying adults do no harm except for laying about 200 eggs in your soil or growing medium every week. The damage comes from the larvae. These tiny things have a black head and a transparent, wormlike body. They eat fine root hairs and scar larger roots, causing plants to lose vigor and turn pale.

Fungus gnats thrive when green algae, such as that which grows easily on Rockwool, appears. Cover the exposed surface with cube caps, squares of black and white poly, or foil. Use Gnatrol or Azatrol as a root drench to kill the larvae.

Aphids, leafhoppers, and mealybugs are usually less common, but can be treated the same way as spider mites. Aphids are about the size of a pinhead and normally gray to black. Aphids give birth to live aphids without mating, and can produce 40 – 100 offspring that begin reproducing soon after birth. Yellow sticky traps placed at the base of each plant are a good way to monitor these invaders. When they begin to feed, they cannot move, so manual removal of a few is easy. Insecticidal soap should be your first attack.

Leafhoppers are small wedge-shaped insects, usually green or yellow. Their wings peak like roof rafters when not in use. They suck plant juices, resulting in stippling. They exude a sticky substance that is fertile ground for molds. Pyrethrum or rotenone are the best controls.

Mealybugs are oblong, waxy-white insects that move slowly, mature slowly, and live in colonies usually at the stem joints. They excrete honeydew which encourages mold. Soaps, pyrethrum, and neem oil are good controls.


Cloth curtains, clothes, and carpet are all prime fields for fungus spores. Cover carpet with plastic, cover the window with plastic and wear a minimum of clean clothing to work in your room.

Gray Mold (Botrytis) is the most common fungus that attacks indoor plants. It flourishes in warm, humid (above 50%) environments. It begins in the flower buds and is hard to see at the start – it is grayish-white or bluish-green. It looks hair-like and a lot like laundry lint. The foliage will turn sort of slimy. Dry to the touch, gray mold infected material often crumbles if rubbed.

Look out for single leaves that mysteriously dry out. Constant observation, especially in the two weeks leading up to harvest, is vital. Gray mold can wipe out an entire crop in just a week. Flowers are reduced to slime or a dry powder.

Minimize gray mold by reducing humidity to below 50%, provide ample air movement and circulation, and keep the room temperature above 70 degrees. Elimination is drastic: use alcohol dipped pruners to remove infected flowers at least 1 inch below the infected area. 2- 4 inches ensures elimination. Do not let the infected part touch anything! Place the bad bits into a thick zip lock bag and destroy far away from your room. After being around the gray mold, shower and wash your clothes ASAP. Increase the temperature of your room to 80 degrees.

The spores are always present in the air, so prevention is vital.

Pythium is the worst of the fungi. This causes the damping-off of new seedlings, it prevents newly sprouted seeds from emerging, and will even attack clones and older plants at the soil line, bringing irreversible death. Pythium is also a root problem in a hydro system. Wherever you find it, it is always the result of a lack of oxygen, since it is an anaerobic fungus. Overwatering of soil, or inadequate oxygenation of res solution are the primary causes. Beneficial fungi and bacteria can help this at the root level, and Serenade works well on the plant itself.

Mildew is another group of fungal infections. Downy mildew appears on young, succulent foliage as whitish-yellow spots on the top of leaves. Grayish spawn is on the undersides of the leaves, opposite the spots. It spreads quickly.

Remove and destroy infected plants, not just the leaves. Do not crowd the plants, and provide good air circulation. Keep temperature above 75 degrees and humidity no higher than 50%. Serenade is a reasonable treatment, but ditch the infected plants.

Powdery mildew appears as small spots on tops of the leaves, spreading quickly to a fine, pale powdery coating on shoots, leaves, and stems. Use Serenade, and remove all foliage more than 50% infected.