From powdery mildew to anthracnose, severity and types of plant disease symptoms may range from unusual, mild discoloration of leaves to rotten, unusable fruit. Fortunately, you can take some measures to contain the contagion-and maybe even prevent disease from taking hold in the first place. Of course, before you know how to treat diseased plants you need to know what's making them sick. Here are a few possibilities to consider.
Powdery mildew isn't picky; the fungal disease will attack almost any plant, but you are most likely to notice it on bee balm, phlox, lilac bushes, roses, zinnias, begonias, and other ornamentals. Leaves of affected plants look like they've been dusted with a whitish-grey powder, and, as the disease progresses, photosynthesis slows and the plant is substantially weakened. Powdery mildew thrives in conditions where relative humidity is high and temperatures are cool.
Downy mildew exhibits some symptoms similar to those of powdery mildew. Vegetables such as cucumbers, peas, and spinach are fairly susceptible to downy mildew which causes yellow spots on the tops of leaves and covers leaf undersides with a white, blue, or grey powder.
You can keep mildews in check by making sure plants have adequate air circulation. Have they grown too close to one another? Prune regularly with disinfected tools to help increase air circulation around your plants. Also, remove any lower leaves that might touch the ground to further reduce contact with harmful fungal spores. Plants in areas which are too shady may be more susceptible to mildew, too, so make sure they are getting plenty of sunlight.
Black spot doesn't leave much to the imagination. As the name suggests, this fungal disease causes black spots to appear on plant leaves. Areas around the black spots then turn yellow, and eventually, the whole leaf will fall off. Black spot prefers wet conditions and is most likely to attack your roses. For plants showing signs of black spot, remove diseased leaves and stems with clean pruning shears and dispose of them. Also, keep the centers of rose bushes and other affected plants pruned to improve air circulation. Finally, because water evaporates less quickly at night, water plants in the morning rather than the evening to help prevent future outbreaks.
Tobacco mosaic virus most commonly affects tomatoes but it can also attack peppers, eggplants, and petunias to name a few. Plants battling tobacco mosaic virus exhibit mottled foliage and distorted leaves. Overall, plants are stunted and may not bear fruit. Interestingly, this virus can be spread to plants from close proximity to ornamental tobacco plants and even by smoking while handling tomato plants. The best way to prevent tobacco mosaic is to keep hands and garden equipment disinfected, and, if you have had a tobacco mosaic outbreak, you'll want to sterilize the soil in that area before planting new crops.
Anthracnose, likewise, can overwinter on diseased plant debris so keeping the growing area clean is essential. The fungal disease will cause sunken, rotten spots on your tomatoes and can make entire fruits unusable. Unfortunately, anthracnose is easily spread to healthy plants because it travels via airborne spores.
You really can avoid serious problems by keeping an eye on the garden and keeping your garden tools clean. Look at your plants closely every day for signs of disease, and act swiftly at the first signs of trouble. Remove all diseased leaves and stems from affected plants and, to disinfect contaminated garden tools, simply rinse them with a ten percent bleach solution. For more serious outbreaks you might choose to apply a sulfur-based fungicide, but read labels carefully to make sure the product you use is right for your particular problem.