Leaf wetness and excess fertilizer effects on lawn diseases (04-01-13)

Many Southern lawns have their greatest incidence of turf disease pressure during spring transition. This pressure is often enhanced by fertilization and leaf wetness. If your lawn has a history of spring turf diseases, particularly large patch, then be careful not to overly fertilize your lawn during the next few weeks.

Fertilizers with readily available water soluble nitrogen sources that stimulate excessive lush growth tend to create the greatest potential for lawn diseases. Therefore, it would be a better choice to select a fertilizer that has at least some of the nitrogen source in a water insoluble (WIN form).

Leaf wetness, along with the lush growth from the fertilizer, is an invitation for turf disease flare-ups. We can’t prevent leaf wetness caused by Mother Nature, but we can manage our watering regimes to limit the length of time the grass foliage remains wet from irrigation.

When is the best time of day to water the lawn? Early morning between 3:00 and 10:00 is considered the ideal time. The reason being that the less time the foliage is wet the lower the incidence of disease. Generally by 3:00 a.m. the foliage is wet from dew or exudates from the leaves anyway. Generally it takes until about mid-morning for this to dry.

The worst time to water is just before nightfall, as this will prolong leaf wetness for the entire night. I don’t expect many of us to get up at 3:00 a.m. to water our lawns, but hopefully we can find some time early enough in the day to allow the leaves of the grass to dry before nightfall. It is also better to water thoroughly only once or twice a week than to apply small amounts daily.

Get a free copy of Extension publication #1322 Establish and Manage Your Home Lawn from your local Extension office or this Web site for information on other turfgrass management issues.

Published April 1, 2013

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu