Houseplants are living organisms and get attacked by other living things that produce diseases. Here are some common symptoms and tips on how to treat the diseases they indicate.
Your houseplant may be covered with a powdery substance that is easily removed with the hand or a cloth. That’s a sign of powder mildew, a very common houseplant disease. The powder may be white or brown and is usually on the top of the leaves. The condition occurs most often when the plant has received too little light or the soil is kept too dry.
The condition can be treated simply, just by physically removing the mildew with a cloth. But for a more thorough treatment and longer term protection, use a mildewcide. Then place the plant where it can get more sun and be sure to water properly.
Brown spots on your leaves may be a sign of incorrect watering, which may produce leaf spot fungus. Find out how much water and when to apply it is appropriate for your particular size and species of plant. Give the plant a little more sun or move it under a lamp. There’s rarely any need to treat this with fungicide.
Spots may be concentric rings, in which case the most likely culprit is a fungus. Remove any dead leaves and allow for good air circulation around the plant. Ensure that water spots don’t remain on the leaves for long periods. That promotes the growth of fungi. Use a fungicide.
But leaf spots can also be caused by bacteria.
Bacterial leaf spots will often appear as a yellow halo and the spots will enlarge to the point they form a blob when the plant is kept wet. Dryer conditions produce brown spots and the leaves become speckled. Keep your plants warm enough for their species and give them plenty of room to spread out. Treat with a bacteriacide.
Another common watering-induced problem is stem rot. The outer leaves will not hold tightly to the plant and practically fall off in your hand. The outer edges will start to yellow. You can apply a fungicide for quick results, but the long-term solution is to find out how much and when to water your plant.
Root rot is another common problem produced by excess moisture in the soil. Bacteria that live there all the time grow to harmful levels and invade the roots, working their way up the plant. The leaves will be discolored. You can try easing off the water, but few plants will recover.
To minimize the odds of plants becoming infected by any disease, start with disease free plants. The best way to do that is buy from a reputable source. Use sterilized soil, not just any old dirt from around the yard. Treat early and often. Don’t let problems go unattended.