MASTER GARDENERS STUDY PLANT DISEASE
Sheila McBride, Diagnostician at Texas A&M Research Laboratory, recently addressed a Limestone County Master Gardener class about plant diseases. McBride stated that pathogens cause disease, and pathogens can be either biotic (living) or abiotic (non-living). Evidence of plant disease caused by both often look similar which makes diagnosis hard to determine.
Examples of "biotic" causes for disease include fungi, nematodes, mites, bacteria, viruses and animals. "Abiotic" causes for disease would be non-living factors such as drift from chemicals; injury from wind, heat and freezing; nutrient deficiency; periods of extreme drought and flooding; compacted soil; and improper amounts of light.
According to McBride, plants store carbohydrates as food reserves to help them grow, ward off disease and repair injuries. Plants that experience prolonged stress may deplete their stored carbohydrates and are then susceptible to disease and possibly death.
For example, parts of Texas experienced drought in 2011 and then an overabundance of rain in 2016. Many trees are now showing the effects from those stressful events. Ms. McBride helped investigate recent complaints of why so many post oaks are dying in Texas. The cause was a soil-borne pathogen, not oak wilt as many thought. The extreme stress oaks have experienced in recent years from droughts and floods has led to disease susceptibility. Oaks don't like "wet feet".
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