We have focused over the last few weeks on lawn care and how to keep a lawn healthy. Keeping the lawn healthy is the best defense against any diseases that potentially can damage the turf. Thankfully, diseases of the lawn are the exception and not the rule, but it’s good to have a basic understanding of how disease can possibly develop and affect the turf grass.
Lawns can have spots or patches that are discolored, but that does not necessarily mean there is a disease. Injuries can occur to the lawn such as drought, mowing the grass too short, or damage from excessive herbicide. Those injuries can look like disease, but there are no pathogens (disease causing organisms) involved. But, an injured turf may be weakened so that is becomes susceptible to pathogens.
There are 3 factors that must exist in order for a disease to develop:
- A susceptible plant
- A disease producing organism or pathogen
- An environment favorable to the growth of the disease
Every lawn has some susceptible grasses and dormant pathogens (usually fungi). Diseases do not begin to develop until the environmental conditions begin to favor the population of pathogens or increase the susceptibility of grasses. Environmental conditions can include the weather such as temperatures and drought or excessive moisture as well a changes in maintenance.
There are potential turf grass diseases for nearly every environmental condition. There are diseases that occur in the cold of winter under snow, and there are other diseases that occur during the heat and humidity of summer. Wet soils and high rates of fertilizer can trigger diseases just as dry soils and poor fertility can bring on disease.
So, the emphasis for you, the average home owner, needs to be on the care of grass to prevent disease. Controlling the weather or overall environment is impossible, but there are practices you can keep that will change the local environment and that do not promote disease development.
- Mowing – cutting grass below optimum height causes the grass to be stressed; mower blades need to be sharp so that they cut the grass instead of tearing it; mow frequently enough so that no more than 1/3 of the leaf is cut at one time; avoid mowing wet grass.
- Watering – time irrigation to the early morning hours; irrigate only when drought stress is observed and then apply enough water to saturate the root zone; irrigating every day for a short duration does not provide ample water to the root zone, but it is beneficial to the turf grass pathogens.
- Nutrition – many diseases are directly affected by the nutrition of the grass, especially nitrogen; both excessive nitrogen and low nitrogen contribute to disease, so it is best to apply the minimal amount of nitrogen that is required by the turf grass; potassium is important in the prevention of disease; damaged grass benefits for the application of liquid fertilizers that can be absorbed both through the leaf tissues and the roots.
- Thatch – a thatch build up of more than 1 inch can lead to increased stress and disease; remove excess thatch.
- Soil – aerate soil to improve the ability for air, water and nutrients to be able to flow into the root zone; monitor the pH of the soil.
What do you do when despite your best efforts a disease occurs? There is nothing easy when it comes to lawn diseases. Assistance from university extension agencies and lawn care professionals is very helpful. Turf grass professionals are able to identify the disease, identify the environmental factors that have promoted the disease, and they are able to recommend management practices that will decrease the stress on the grass and make it less susceptible.
Lawn care professionals may treat the disease with a fungicide. Fungicides are pesticides that kill fungi, and they can be a part of the disease-control program, but first the disease must be identified before fungicides are used. Even though fungicides are available in many retail stores, without direction from extension agencies or professionals, the use is discouraged as it requires knowing which fungicide to use and the correct timing of the application(s).
Every maintenance practice that you do for your lawn has an impact on the health of the grass, and normally with good lawn care methods, you can keep the grass healthy, less stressed and less susceptible to disease.
Question of the week: Have you ever experienced a lawn disease?
By Kimberly Bell
Disease diagram from: