Common Garden Plant Diseases

Common Garden Plant Diseases

By Michael Jenkins

Gardening is innately a seasonal affair, and as we move through the year we find ourselves facing different chores, problems, and challenges in our garden spaces. For many of us, July is the peak of summer, and we’re dealing with some of the joys and issues that brings. Among the joys of July are lush ripe tomatoes, crisp peppers, tasty garden cucumbers, and other produce. The problems come in the form of unpredictable weather and garden diseases. Like people, your plants can get sick too, and it’s important for home gardeners to know the signs of common garden diseases and how to treat them.  In this blog we’ll address some of the most common illnesses that can strike your garden plants, how to recognize them, and what to do about them.

Rust is a common problem for a wide variety of both ornamental and vegetable plants. Manifesting as discolored, rusty-looking spots on leaves, rust is fungal disease that may occur at any time during the plant’s growing year. However, it is especially common in the summer so we’ll address it now. While rust itself is unlikely to kill a plant, it may result in lost leaves, which can weaken a plant. This may make your plant less productive and more prone to other diseases or to be overwhelmed by weeds.

If you see the signs of rust on your plant, ensure that you have healthy soil and that you’re regularly feeding your plants with good fertilizer. The rust fungus can overwinter in the garden, so remove all infected parts of the plant and throw them away in the trash, not the compost heap. Likewise, rust fungus can spread on garden tools, so make sure to clean and disinfect them after working with rust-infected plants—don’t forget to wash your hands! Rust likes moist, dark conditions, so avoid over-watering and overcrowding your garden space.

Powdery mildew is another fungal disease, and like rust may affect both ornamental and vegetable plants. Powdery mildew is most common during warm, dry weather, and manifests as a white powdery coating on the surface of leaves and stems.  As it is a fungal disease, prevention and treatment are similar to those for rust: ensure healthy well-fed soil, promote good air circulation around your plants, and take care to disinfect your tools and safely dispose of waste. A garden-safe fungicide is a good idea for treating powdery mildew; spray it around the base of your plants and the upper side of the leaves for best results.

Bacterial wilt is a particularly pernicious plant disease. As the name suggests it is caused by a bacteria that attacks the plant’s vascular system and causes wilting. This makes it especially difficult to diagnose, as wilting can be caused by many things including heat, under-watering, and transplant stress. Bacterial wilt is especially common in squash, cucumbers, tomatoes, peppers, and eggplant, though it may occur in other plants as well. In addition to being spread by infected garden tools (sterilize your equipment if you think bacterial wilt is a problem) the disease may also by spread by cucumber beetles and squash beetle. Thus, preventing them from taking up residence in your garden via proactive spraying of a plant-friendly insecticide is an important preventative step.  There is no cure or treatment for bacterial wilt, so if you think you may have it in your garden remove the infected plants immediately. Dispose of them in the trash, not the compost heap, and do not save seeds from infected plants.

Cucumber Mosaic Virus is another tricky garden problem that may arise during the warmer months—though it can occur at any time during the growing season. A viral disease, it is most famous for affecting cucumbers but in reality it has a wide swath of victims. Cucumber mosaic virus can appear in many garden plants; in fact it has the widest range of hosts of any known plant virus! The primary sign of cucumber mosaic virus is a mottled pattern on the leaves, a mosaic of dark green, light green, and brown/yellow areas. Eventually this will lead to leaves dying off, which can kill the plant. Unfortunately, there’s no known treatment for cucumber mosaic virus, so it’s important to follow steps for prevention. Clear away weeds, feed and water appropriately, ensure good air circulation, and disinfect tools. If you spot signs of the virus, remove the affected plant immediately and dispose of it in the trash away from other plants or compost.

There’s a lot more to talk about—we’ve already discussed tomato issues in two other blogs—but we hope this guide gets you started in understanding and dealing with common garden disease. The main lesson is that prevention is the key, rather than cure, so take the steps you need to keep your garden healthy!

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