Introduction to Plant Diseases

What are Plant Diseases?

When we think about disease in humans and animals, we think about the immune system–is it strong enough to be effective and keep us in good health and safe from the harmful effects of whatever microbe is challenging our immune system.

Plants do not have immune systems (obviously) but they do actively engage strategies in an attempt  to minimize damage from microbes and harmful environmental conditions. My goal as a gardener is to keep plants that successfully grow and develop despite microbes and environment. I prefer organic gardening with minimal chemicals. There are, however, times when chemicals are used to stop the destruction of plants that normally have no problem. For example, my roses came under invasion from bag worms about 2 years ago — the bag worms thrived when we were in strong drought conditions.

Some conditions are worth treating, others are not. After considerable stress, the roses began dropping leaves and were nearly defoliated— so I used a bagworm-specific pesticide to spray the roses once a week until they began adding leaves that were not immediately consumed by the bagworms. In another case, I had two pear trees that produced large volumes of wonderful pears each Fall. Unfortunately, the pears had “fire blight” — so named because the new leaves die rapidly (too fast for the tree to defoliate) and produce an overall appearance that the leaves were burned (pictures in later posts). The cause of fireblight is bacterial—the only way to treat it is with antibiotics. Without immune systems, however, antibiotics must be repeatedly injected into the sap of the tree each spring — that can be very expensive and time consuming. So, we decided to give up growing pears. The trees lived and produced fruit for an additional 3 years or so.

Plants can also be challenged by insects that consume leaves or other plant parts. I’m not a bug expert, but there are some differences in symptoms generated from bugs versus microbes. As I find cases, I’ll include them in my “diseases” category posts. Stay tuned for more about pests in future posts.

Happy Gardening!