How to Identify Indoor Garden Pests & Diseases

By Susan Eitel
Published: December 27, 2016 | Last updated: April 23, 2021 03:01:43
Key Takeaways

If you need a little help addressing a pest or disease problem in your growroom, look no further than Susan Eitel’s handy guide to identifying common pests and diseases, all of which have been known to compromise the quality of indoor gardens everywhere.

After working in the indoor gardening industry for many years, I have discovered the most common pest insects you’ll find in the growroom include aphids, spider mites, thrips, fungus gnats and whiteflies. And if it's not pests attacking your garden, often diseases like downy or powdery mildew, gray or white mold, or root rot are making an appearance. Here are some simple practices you can embrace to help combat these common plant pests and diseases.





Aphids, also known as plant lice, come in different colors like gray, black and green. Regardless of their color, aphids weaken plants by sucking the juices out of their leaves and turning them yellow. They can be found anywhere on the plant, but often congregate along its stems.

Spider Mites

Spider mites, at less than 1-mm long, are tiny arachnids with eight legs and oval bodies. Their mouth parts pierce and suck, causing damage by puncturing plant cells, resulting in fluid loss that eventually kills plants. Spider mites look much like grains of sand and are found mostly on the undersides of leaves. The type you’ll see most often is the two-spotted spider mite, which has a dark spot on either side of its body. An adult female can lay up to 20 eggs per day, causing infestations quickly. Eggs are round and clear and become a creamy color just before hatching. If you see webbing, you most likely have an infestation.



Thrips are hard to see at a mere 5-mm long. They leave fecal droppings on plants that appear as black spots. Females bore holes in leaves where they lay their eggs. If your garden is infested with thrips, leaves will eventually look dry—not wilted—and have yellowish spots.


Fungus Gnats

Adult fungus gnats are small and black with thread-like antennae, long slender legs and clear wings. Their larvae feed on plant roots, causing weak, slow-growing plants. The larvae can be clear or cream-colored with shiny black heads that look like small black specks to the naked eye and grow about a ¼-in. long. The flying adults do not cause damage to the plant, but they lay eggs in the growing media. The larvae feed on the roots, making the plant weak and slow-growing, potentially leading to plant death.


Whiteflies resemble small, white moths and are about 1-mm long. An adult’s mouth parts pierce and suck juices from plant leaves, causing white spots and yellowing. Females lay their eggs on the undersides of leaves. Another downside to whiteflies is that they secrete a sticky substance called honeydew, which is a breeding ground for sooty mold.


Downy Mildew

Downy mildew is caused by the fungus Plasmopora viticola. Early signs of a downy mildew infection are pale-yellow mottling on the tops of leaves. If left alone, the later signs of downy mildew show a patchwork of abrasions that are red, yellow and brown, also on the upper sides of the leaves. The fuzzy, white downy mildew appears mainly on the undersides of leaves.

Powdery Mildew

Powdery mildew is caused by a fungus related to downy mildew called Cleistothecia. If it looks like white powder has been sprinkled on the stems and leaves of your plants, powdery mildew could be the culprit. Other symptoms include stunted plant growth, leaf drop and chlorosis (the yellowing of plant tissues).

Gray Mold

Gray mold is caused by the fungus Botrytis sp. It starts out as spots on the leaves, which lead to fuzzy, gray abrasions that eventually become brown and mushy.

White Mold

White mold is caused by the fungus Sclerotinia sclerotiorum. An infestation looks like wet baking soda clinging to the plant. Plants wilt and leaves appear tattered and bleached. In later stages, the white mold becomes hard and black.

Root Rot

Root rot is caused by too much water and soil-borne pathogens. Plant growth will become stunted, and then plants will wilt and turn yellow. Roots may become mushy, but not always.


Cleanliness is key to keeping garden pests and diseases at bay. It is imperative you keep floors, growing surfaces, substrates, tools and clothing clean and disinfected. Here are some more things to keep in mind when it comes to preventing pest infestations:

Disinfect Tools: A separate set of tools for the growroom is essential. Disinfecting tools with isopropyl alcohol and handwashing before moving from one plant to another will prevent pests and diseases from being transported via you and your tools.

Wear Clean Clothes: Pests can also be transported into the growroom on your clothes and your pets. Changing into clean clothes and footwear before entering the growroom and keeping pets out will make a big difference.

Choose Strong Plants: Whenever possible, choose plants that were bred to be resistant to pests and diseases, and keep up with their recommended fertilization requirements.

Monitor the pH: pH is a numeric scale used to identify acidity or alkalinity, where 0-6 is acidic, 7 is neutral and 8-14 is alkaline. Most plants do well in a slightly acidic environment that has a pH of 6-6.5.

Remove Pests: Vacuum plants with a shop vac. This can be done during both the vegetative and the flowering stages. You can also spray plants with water, making sure you get the undersides of leaves. This procedure is not recommended if you are dealing with a mold or mildew problem.

Increase Air Circulation: Keep the air in your growroom well-circulated and the humidity around 50%, with daytime temperatures around 75°F and nighttime temperatures between 60 and 65°F, depending on what you’re growing.

Prune Plants: Give plants enough room to grow by pruning out dead or diseased leaves and branches. Remove any fallen leaves or other debris from the pots and the growroom floor.

Don’t Overwater: Make sure your growing media can adequately drain. If you’re growing using hydroponics, the water needs to be heavily aerated. Roots should never be kept soggy or sitting in stagnant water.



To monitor pest populations in the growroom, hang sticky cards around the room to trap flying pests, which will make for easy identification. Blue sticky cards attract thrips, while yellow ones attract fungus gnats and whiteflies. Make sure you place some of the cards at soil level, which is where fungus gnats tend to hang out. A powerful magnifying glass will also help with identification. Once you know what pests you’re dealing with, you can take appropriate action.


There are a few ways to go about treating a pest infestation, including using beneficial bugs, which is known as integrated pest management (IPM). Beneficial bugs are basically good bugs that eat bad bugs. You can purchase specific predators for a specific pest or general predators that will pretty much eat anything. As a general rule, specific predators are more costly than general predators, but the specific predators usually do a better job, especially if there is already an infestation.

Chemical and organic sprays are another way to treat pest and disease infestations. These sprays are toxic to beneficial bugs, so these two methods cannot be used together. There are also insecticidal sprays designed for use on edible plants. Sprays of insecticidal soap, neem oil, habanero pepper and pyrethrum are some examples of common non-toxic sprays, many of which work only if they come in contact with the pests. Sprayers help by creating a fine mist to help get under the leaves and into cracks and crevices. For safety’s sake—both yours and your plants—I suggest visiting your local hydroponics or indoor garden specialists for correct application methods and rates if you’re unsure.

When it comes to pest and disease control in the indoor garden, remember these three key factors: identify, prevent and control. I hope this article gives you a solid base to build on so you can enjoy many pest- and disease-free yields.


Share This Article

  • Facebook
  • LinkedIn
  • Twitter

Written by Susan Eitel

Profile Picture of Susan Eitel
Susan Eitel has a degree in landscape horticulture from Humber College in Toronto, Ontario. She has worked in the hydroponics industry for more than 25 years. Susan has always been interested in beneficial insects and integrated pest management. She lives in the Niagara area with her beloved husband and dog.

Related Articles

Go back to top
Maximum Yield Logo

You must be 19 years of age or older to enter this site.

Please confirm your date of birth:

This feature requires cookies to be enabled