Pictures to Help Identify Plant Disease

All gardeners know that identifying plant disease is an important task in the garden. In order to grow healthy flowers, vegetables, trees and shrubs, it's important to learn the basics skills for identifying plant disease. Pretend you're the Sherlock Holmes or Hercule Poirot of the garden. Begin your investigation by observation.

Being your sleuthing by taking a look at the entire plant. In this photo, the spaghetti squash nestled among the leaves looks healthy...but the plant's leaves show problems. They are turning yellow and some have turned brown and fallen off completely. These are important clues in identifying plant disease.

A closeup inspection of the squash leaves reveals the culprit: squash bugs. While technically not a diseases, part of identifying plant diseases is also ruling out insect damage. A careful inspection of the leaves reveals juvenile insects, such as the ones in the picture, and telltale brown eggs on the leaves. A few adult beetles could be seen on mature leaves too. The proper care for this is prevention using row covers or companion planting to repel insects. Fortunately, the squash appears to be recovering and is still producing fruits (squash).

Plant diseases follow a certain cycle very similar to diseases found in people. First, a pathogen such as a virus or bacteria arrives on the scene. It may touch the leaf, flower, or soil and travel through the roots and up into the plant. If the plant is strong and health, its own natural disease resistance may ward off the invader or keep it to a minimum. But if the plant lacks nutrients or has some other problem, the pathogen takes up residence where it completes its lifecycle - feeding off the plant, reproducing, and eventually weakening or killing its host. A neat garden keeps pathogens at bay by reducing places they can reproduce.

Fruits and vegetables yield many clues to identify pests and disease. If all your tomatoes or other fruiting vegetables are developing stains on the base that spread into big black circles like this, your plants are infected with a fungal disease called blossom end rot. It can strike tomatoes, peppers and nearly any vegetable. It is caused by a fungus. Plants are more susceptible if they receive inconsistent water and the soil lacks essential nutrients. Many fungal diseases create spots, splotches and odd marks on the fruit.

Trees, especially fruit trees, are susceptible to diseases. There are many diseases that attack fruit and fruit trees. This apple tree exhibits telltale brown spots on the leaves that may indicate rust, a fungal disease. Other signs of disease on foliage include a powdery white, gray or silver coating, which is powdery mildew. This may attack trees, shrubs, annuals or perennials, especially during very moist times of the year. Fungi love moisture and flourish during periods of rain or from improper watering. Many gardening experts recommend watering in the morning so that the sun can dry plant leaves.

Lastly, as you look at your plants, some clues signal insects more than pathogens. If you can actually see the insects on the plant, such as this swarm of Japanese beetles on the rose bush, you'll have an easier time determining which garden pest to contend with. Garden pests mimic disease by discoloring or damaging foliage. Chewed ends or holes in the center of leaves usually signal an insect problem rather than pathogens.

Some plants exhibit different symptoms at different times, but the symptoms all point to the same culprit. Iris borer, for example is an insect pest that tunnels through the leaves and crown of the iris. Depending on when you notice the problem, the iris may exhibit brown leaves or a mushy center. The leaves may die back. Brown leaves aren't always a sign of a fungal infection or a virus. In the case of a borer, it's an insect. Even the most skilled plant detective may need to consult an expert at the garden center or county extension for a full diagnosis, because so many plant diseases mimic others.

If you master the skills of identify plant disease and identifying garden pests, you can find a cure for your plants. Visit your local garden center or call your county cooperative extension office for advice. Keeping gardens clean and well maintained and feeding plants nourishing compost keeps them strong and healthy so they can produce wonderful fruits, vegetables and flowers.