Common Plant Diseases & Problems to Look For

These common plant diseases impact both indoor and outdoor plants, but you’ll need to be especially vigilant during seed starting season.

Pests and plant diseases that can plague your indoor plants

When you grow lettuce or start seedlings indoors in containers, on a window sill or under a grow light, generally you get by without the common plant diseases and pests that outdoor gardens face. However, indoor gardening is not without its nemeses.

Here are the telltale signs that you’ve got some of the most common plant diseases or pests, and how to treat it so that your plants can keep on growing.

1. Pest: White fly

Symptoms:

White flies are the bane of greenhouse growers. This garden pest lays their eggs on your plants, stunting their growth. When you approach the plants to water, the white flies will rise in a cloud. That might be your first indication that you have a problem.

Cause:

White flies are tiny flies that hide under the rim of planting pots, in the crevices of wood near your pots, and even under the pot itself. The pests are so tiny you may not notice them until there are dozens of them laying their eggs on the leaves of your plants.

Outdoors, there are often natural predators that consume both the flies and their larvae. Natural wind movement also prevents serious infestations outdoors. Indoors and in greenhouses though, white flies can devastate your plants by their sheer numbers.

Treatment:

You can vacuum up the adults when you see them, to control them. Dispose of the vacuum cleaner bag outside, away from your plants. Diatomaceous Earth (DE) sprinkled on the soil surface will take care of the larvae and stop their cycle. Replenish the DE once a month, or anytime you see adult white flies on your plants.

Commercial growers use fans set up to blow over bedding plants in the greenhouse, to discourage the flies from landing on tender seedlings.

Related: Natural Aphid Control in a Pesticide Free Garden

2. Common plant diseases: Damping-off

Symptoms:

Your plants will seem to be growing fine. Suddenly, the stems get very thin right at the soil surface. The plants break off and die.

Cause:

Damping-off disease comes from watering too frequently. A fungus grows under the soil surface, encouraged by the damp conditions. It consumes the stem of the plant right at the soil surface, separating the growing plant from its nutritional source. In severe cases it kills the emerging sprout before it has a chance to break the soil surface.

An ounce of prevention:

With damping-off disease, prevention is the best course of action. Begin with clean, sanitized pots. Damping off disease can linger in planting pots from one season to another. You can prevent it by watering from below the pot rather than over the soil surface.

Allow the surface of the soil to dry slightly before watering again. Your pots can be dry on the surface of the soil but still damp just under the soil. Time your watering so that the plants don’t dry completely but the soil surface has a chance to dry.

Other preventative measures include sprinkling the soil surface with powdered cinnamon. Cinnamon has anti-fungal and antibacterial properties. When you replace your spices each year, reserve you older cinnamon for this job. Sprinkle cinnamon on the soil surface at planting time. Reapply if you see any white mold beginning to form at the soil surface. Often this is the only preventative you need.

Using water that you’ve added hydrogen peroxide to also seems to help prevent the fungal disease. Use two teaspoons (10 ml) of hydrogen peroxide to one quart (1000 ml) of water.

Related: How to Eradicate Pocket Gophers

Related: 7 Organic Pest Control Methods

3. Garden pest: Get rid of spider mites

Symptoms:

You see fine webbing under the leaves and around the stems of your plants and planting pots. The leaves of your plants turn a bronzy color where the spider mites have burrowed into the leaves, sucking their juices. Untreated the leaves will shrivel and drop off, one leaf at a time. You need to get rid of spider mites.

Cause:

Spider mites lay their eggs on your plants. The larvae suck plant juices and cause the leaves to dry. You may not see the actual pest, but you’ll know you have them because of the fine threads of webbing around the leaves.

Treatment to get rid of spider mites:

If you see the webbing, wash off the leaves of your plants with a strong spray of water to dislodge any eggs or adult mites. Apply DE immediately to the soil surface. This works in the greenhouse, but to get rid of spider mites indoors, there are gentler approaches.

With my indoor plants I fill a sink with cool, soapy water and dip each plant upside down into the water, then rinse under a lightly flowing tap to get the soap off the leaves. Allow the plants to drain upright. Then apply DE to the soil surface.

Reapply the DE to the soil surface once a month to interrupt the life cycle of the mite and get rid of spider mites for good.

4. Common plant disease: Chlorosis

Symptoms:

Plant leaves turn pale with prominent green veining.

Cause:

You probably won’t see this in the first growth of your baby lettuce. However, while you are waiting for a second or third cutting the leaves may be paler. If there is also green veining on the pale leaves, your plants are lacking in magnesium.

Treatment:

Magnesium is necessary for the plants to produce chlorophyll through photosynthesis. You can correct this problem by watering with Epsom salts (magnesium sulphate).

Mix 1 teaspoon of Epsom salts in 1 quart of cool water. Mix until the Epsom salts dissolve fully.

Water your pots as usual. This mixture can also be used as a foliar spray. Plants seem to take up magnesium just as effectively through their leaves as they do through their root system.

Treat the problem early for best success rate

While this isn’t an exhaustive list of common plant diseases and pest problems, these are the ones you’ll most likely encounter when growing your plants indoors.

By understanding the symptoms and diagnosing the problem early, you’ll have a good chance of success with your indoor gardening projects. Click here for more on natural pest and disease control. 

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