PLANT DISEASES AND DROUGHT

by Edward A. Brown, Extension Leader-Plant Pathology

Plant disease-causing fungi are usually inhibited during periods of drought. Most fungi require water to infect and develop. Although drought factors tend to reduce disease incidence there are some disease situations that are enhanced.

GRASS PASTURES

Leaf spotting fungi in the Helminthosporium complex are more severe when the potassium levels are low. The lack of soil moisture due to droughts can affect the availability of these nutrients although there may be adequate levels in the soil. During dew periods and other sporadic moisture periods, nutrient deficient plants can become infected and disease can develop. These leaf-spotting disease fungi can reduce hay quality.

WOODY ORNAMENTALS AND TREES

Trees and shrubs have a relatively shallow root system and are subject to losses of roots during droughts. The damage is many times not realized immediately but may take four to six months before symptoms occur. This stress and drought damage may make the plant more susceptible to dieback diseases caused by a number of fungi. Botryosphaeria sp. is the most common fungus associated with dieback. Chemical control is limited and back to the basics management is recommended. Provide adequate irrigation for the plant. Prune properly to remove damaged limbs if dieback occurs.

Slime flux is common following periods of drought. In most cases the flux is noticed the spring following the drought. Damage is caused by the drought stress and bacteria and yeast infect the cambium feeding on the carbohydrates in the sap. High pressures develop as in fermentation and the result is the exuding of these plant juices from damaged areas in the bark. Provide the best possible growing conditions for the plant during the drought and after. Once the problem is identified there are no pesticides that will provide controls.

Producers of commercial agricultural crops should use data of environmental conditions to formulate disease control practices.