We’re all familiar with the excuse, “My dog ate my homework.” This year many people have been hearing what they suspect is the landscaper’s version of that, “Your lawn looks bad because of the weather.” Customers question the professionalism of their lawn care providers, assuming they are being fed a convenient excuse. The unfortunate truth is that this has been a nightmare of a season for lawn care, and it’s not over yet.
Up until last week, this year has seen a well-above average number of days with daytime temperatures over 80 degrees Fahrenheit with humidity above 75%, followed by nighttime temperatures above 70 degrees with humidity above 80%. These conditions, coupled with evening rainfall or lawn sprinkler activity, are a recipe for disease. From late spring through late summer this year, grass diseases have been rampant.
Although diseases do not always entirely kill the plant, they do weaken it. While it might seem obvious to apply fertilizer to your suffering lawn, unless you know what type of disease is afflicting your plants it is difficult to come up with a curative course of action. If the disease is caused by a fungus, a fungicide may help, but which one? Most lawn care companies can help you identify your lawn problems, but before you call Mr. Lawn Care Professional, let’s look at a few disease candidates.
Dollar Spot (Sclerotinea homeocarp) infection appears as tan or straw-colored spots ranging in size from that of a quarter to that of a silver dollar, which are sunken in the turf. These spots often coalesce into large patches. It is a fungus infection that can be spread by foot traffic from an infected area to an uninfected area, making dollar spot a serious problem if left untreated. This disease may be more serious than it first appears, because it kills the entire grass plant so that badly infected lawns may require reseeding. Fungicide is effective if applied before infection occurs, but a proactive approach is preferred. Correct watering programs, regular fertilizing with slow-release nitrogen, and mowing at the proper height will keep your grass healthy.
Pythium is a fungal blight which is especially damaging to bent grass, bluegrass and perennial rye grass. It spreads very quickly, affecting leaves and crowns, killing the plants, resulting in extensive loss of the turf area. Pythium occurs during the most uncomfortable days of summer, when the dew periods are long (greater than 14 hours) and evening temperatures average above 70 degrees Fahrenheit. During hot, humid weather, watch out for small, circular patches of collapsed, water-soaked leaves and stems on close-mown turf. White, cottony mycelium may show in the early morning hours. If not controlled promptly, large areas of turf may be killed in a matter of days.
Powdery mildew is easy to diagnose from a distance, as affected turf has a white or light gray appearance. It favors bluegrass and some fescues. It overwinters in either dormant turf or as specialized survival structures (cleistothecia) in turf grass litter. Powdery mildew occurs primarily on slow-growing turf species, usually in shaded areas. Pathogen activity is favored by cool, cloudy conditions that prevail in spring and fall. High humidity also favors development of the disease.
There are many other diseases and conditions that can damage lawns, but the three above are the primary problems we have encountered this year.
Once the culprit has been identified, can it be controlled? Unfortunately, the answer is yes and no – it really depends on the disease that has been identified. Dollar spot and powdery mildew may be controlled after they appear by application of an appropriate fungicide. It is virtually impossible to control an outbreak of Pythium, though spraying with a fungicide will give you a small amount of control by slowing down the spread, and provide some protection from further outbreaks.
The best approach to controlling any disease is a pro-active one. Formulate a regular spray program and stick to it. Pay close attention to temperature and relative humidity percentages. This is most important when dealing with Pythium as it favors high temperatures for longer than 14 hours and humidity well above 75% into the evening hours. Irrigating late in the day, so that grass does not dry off before nightfall, greatly aids development of disease. Irrigating late in the day is a hazard for grass. Time irrigation to allow several hours before evening so that the grass blades dry.
There are other best practices to reduce the incidence of disease in the lawn:
Mowing – Keep your mower blades sharp as shredded grass blades have a larger area of damage to recover from when cut. Mow in different directions each time you mow, rotating the direction by 90 degrees where possible.
Aeration – Regularly aerate the lawn during the year, using a solid tine (spike) aerator during the spring and summer months and a hollow core aerator (removes a plug), if needed, in the fall. A well-drained lawn may never require core aeration. Aerate in two directions, north to south, then east to west, collecting plugs if present before the second pass. Many people leave the plugs on the lawn and then run the mower over them to break them up. This is an unsound practice because the plugs will have dormant pathogens in them that will overwinter. If the plugs are to be replaced (a sound practice!) compost should be used as the heat created by the process of decomposition of the compost is high enough to kill any pathogens. Core aeration is especially useful for heavy soils, if the plugs are carefully removed and replaced with compost.
Thatching – Thatch is the accumulation of dead grass stems and leaf litter that has built up at the base of the grass plant. It is primarily a cellulose barrier which water, nutrients and free air cannot penetrate. In response to dense thatch, grasses will send their roots toward the surface to reach any moisture, exposing them to hot, variable temperatures, while the roots below the surface decline. Left with a weakened and depleted avenue for nutrition and water, the plant is subject to attack by opportunistic infections. Thatch removal is best done with a machine which can be rented at most equipment rental outlets. (When renting, make sure there are no missing blades on the machine and that the blades are not worn down too far.) When setting the depth of the blades, start off by setting the machine high, then gradually lower the depth until it reaches the thatch layer. For best results, make two passes, just as you would when aerating. Rake up the thatch from the first pass before making the second. You may have to thatch more than once during the year, especially if the thatch layer is greater than one-half inch thick. Determining how much thatch you have is easy – simply dig up a six-inch square patch of lawn and measure the depth of thatch on it. If the thatch is thicker than three-eighths inch, you will need to dethatch. Do not try to remove all the thatch in one operation, as you will undoubtedly cause irreparable damage. Remove thatch in repeated operations, about two weeks apart, until the thatch is removed. Bagging the mower clippings and then irrigating will hasten lawn recovery after dethatching. Ensure that the mower blades are sharp! Feeding the lawn about a week after dethatching will encourage the grass to grow and thicken, as long as irrigation is continued. Dethatching is best carried out during the spring and summer, when the grass is actively growing, so that recovery time is the shortest. Thatching in the fall is not recommended as soil temperatures and daytime air temperatures are declining, signaling the grass to slow its growth, leading to longer recovery time and leaving the lawn in a weakened state.
Lawn care products – fertilizers, insecticides, fungicides, ovicides, mowers, line trimmers, aeration machines, thatching machines, etc. – generate billions of dollars a year in sales. Lawn care requires dedication and constant vigilance, with occasional monetary investment. It is not an easy undertaking, but after all is said and done, you can justify putting out the sign “KEEP OFF THE GRASS!”