5 Most Common Houseplant Diseases: Prevention and Treatment

Anthracnose can sometimes be confused with other plant diseases and often a laboratory analysis is needed to confirm its presence. Anthracnose in houseplants typically begins with yellowing around the leaf margins and tips. The tips will darken to brown before slowly extending up and around the whole leaf. Eventually the leaves will shrivel, die, and fall from the plant.

Preventing anthracnose in houseplants involves a few key practices. First, ensure plants are in well-drained soil and a container with drainage at the bottom. Avoid overhead watering, as excess moisture can promote fungal growth and spores can be spread easily via splashing water.

Maximize air circulation around your plants by spacing them adequately and pruning any overcrowded foliage. Keep your houseplant display tidy by disposing of fallen leaves and debris, which can help reduce the risk of anthracnose. Regularly inspect your plants for early signs of infection, such as small, dark spots on leaves.

To manage anthracnose, first prune off and destroy any infected leaves to prevent the disease from spreading. Be sure to disinfect pruners thoroughly after pruning each plant to avoid spreading fungal spores.

After removing the infected plant material, apply a foliar spray on the remaining leaves. Neem oil has been shown to be effective in reducing the severity of anthracnose. While it does not truly cure any diseases, neem oil prevents the germination of spores and keeps spores from penetrating leaf tissue. If neem oil doesn’t work, try a liquid copper fungicide, which can be applied directly to the remaining leaves.

Bacterial leaf spot presents as dark brown leaf blotches or lesions. The lesions usually have a yellow ring or edge around them. These symptoms are usually seen on leaves, but occasionally are found on the plant stems as well. The blotches will grow and merge together over time, especially in very humid conditions.

Purchase houseplants and seeds from a reputable grower. Infected seeds or plant cuttings are a major vector of bacterial leaf spot. Local spread can occur by water splashing between plants and soil, so avoid misting or drenching the leaves when watering.

Remove all infected leaves, and dispose of them with the trash headed for the landfill. If a plant is heavily infected, it may be best to toss the entire plant and start fresh. Do not try to compost infected plant material. Sanitize all pruners and pots associated with the infected plant.

There is no way to completely cure a plant with bacterial leaf spot, but some treatments can be used to slow and limit its spread. After the infected plant material has been removed, apply a liquid copper soap to the remaining leaves, or consider trying a biocontrol treatment. Biocontrol treatments rely on a beneficial bacterium, usually Bacillus amyloliquefaciens, to trigger a plant’s immune response to fight off impending pathogens. However, the efficacy of fungicides and biocontrol is still under study.

Botrytis can infect a huge range of plants, from edibles like berry bushes and tomato plants, to ornamentals like dahlias, impatiens, hyacinth, and of course, lilies. It can also affect common houseplants like African violets, orchids, and cyclamen.

You may first notice irregular flecks and brown spots on buds and flowers, with older blooms rotting rapidly. After a while, soft brown spots can appear on leaves, stems, and flowers. These soft areas will eventually be covered in the characteristic fuzzy, gray growth.

The key to preventing botrytis lies in reducing the humidity and ramping up the air circulation. This can be tricky in a home, where you probably want to keep your windows closed at times, but stagnant, humid conditions are perfect for fungal growth.

Try to vent rooms as much as possible, move houseplants outside to protected porches when the weather is mild, and set up a fan to keep the indoor air moving. A regular application of neem oil to plant leaves will also prevent botrytis, and other fungal diseases, from moving in. However, use caution as some plants are sensitive to regular applications of any solution.

Fungal diseases, botrytis included, can be very difficult to eradicate completely. Treatment usually focuses on limiting the spread of this aggressive disease. Remove and dispose of all infected plant material, taking care to disinfect pruners and pots immediately afterwards.

Apply a liquid copper fungicide to the remaining plant leaves. However, don’t rely solely on foliar spraying. To keep your soil and plants healthy and well-protected, enrich the soil with beneficial mycorrhizal fungi and bacteria.

These organisms not only help prevent diseases but also enhance your plant’s nutrient uptake. For preventing botrytis, the most effective biocontrols are the beneficial Trichoderma and Cladosporium. Ensure that any product you use contains these two types, as they are effective and often gentler than chemical fungicides.

As its name implies, powdery mildew appears as a dusty, pale gray coating that can extend over leaves, stems, and buds. If allowed to spread throughout the plant, powdery mildew can actually impair photosynthesis and lead to slow, stunted growth.

Powdery mildew spreads rapidly in humid conditions. Avoid overhead watering, as spores can be spread easily via splashing water. Maximize air circulation around your plants by spacing them adequately and pruning any overcrowded foliage. Fungi survive in dead and decaying plant material, so be sure to keep debris and leaves from collecting on the soil surface. This prevents proliferation in the soil.

As with other houseplant diseases listed here, the first course of action is to remove the diseased plant material. Severely infected plants should be discarded. Gardeners have had moderate success treating powdery mildew with baking soda.

Baking soda appears to slow the spread of spores but doesn’t eradicate the fungus completely. It’s also important to note that prolonged use of baking soda can alter salt levels in the soil as well as change the pH; this could be just as damaging to some houseplants. Applying a liquid copper fungicide is recommended, but not for long as some strains of this disease can build resistance to fungicides.

Gardeners may first notice that their plant is wilting heavily, even though it has been well-watered. In addition to wilting stems and leaves, plants impacted by root rot will have girdled stems that appear weakened near the soil level. There may be a black or brown ring of decaying tissue at the soil level as well. Healthy roots that are normally firm and pale in color, may be dark brown, mushy, and even a bit funky-smelling.

Hands down, the most effective way to prevent root rot is to ensure houseplants are potted in a well-drained, high-quality potting mix. Do not use random soil from your backyard, as it is likely far too heavy and full of clay. Root rot fungi thrive in waterlogged soil. Make sure the container your plant is in has drainage holes at the bottom, and allow the container to drain and dry out thoroughly before watering again.

If the entire root ball is infected, you will likely need to dispose of the entire plant. Where symptoms are infecting some but not all the roots, cut out the infected roots, then repot the plant in fresh potting mix and a sterile pot.

Remember, healthy roots will be firm and light in color. It may be tempting to hit your houseplant with a dose of concentrated nutrients after being repotted, but hold the fertilizer. Your stressed plant will need time to establish new roots before putting energy into leaves and buds.