Dollar spot initially was a major concern on bent grass where it forms spots the size of silver dollars, hence the name “dollar spot.” However, on Kentucky bluegrass lawns the fungi may infect large areas in just a few days. Infected areas four inches or larger may run together, causing large patches. Irregular patches up to twelve feet wide are not uncommon on bluegrass lawns.
Quick Reference:
- Dollar spot is making a comeback as rain and humidity have finally returned to the front range.
- Dollar Spot is often confused with Ascochyta leaf blight.
- Lawns under stress are more susceptible to infection.
- Proper lawn management, such as aeration, proper watering and fertilization, will reduce dollar spot problems.
In Colorado, this disease can also be a problem on annual bluegrass, Bermuda grass, fine-leaf fescues, perennial rye grass and zoysia grass.
Dollar spot fungi may be spread by mowers and other maintenance equipment. Maintaining clean equipment will help in preventing spreading.
Strains of dollar spot fungi grow within a wide range of temperatures, but tend to favor warm temperatures with higher humidity. However, most problems occur when temperatures are moderately warm and change rapidly, as with warm days and cool nights. Because this disease is serious for lawns during warmer weather, many misdiagnose this disease as lack of water. This can lead to overwatering in an attempt to correct the problem. When this happens, it can make the disease much worse.
Identification:
At first, affected leaves show yellow-green blotches or bands. These lesions gradually bleach the blades of grass to a white or straw color. On finer-textured grasses, individual lesions on the leaves often span the width of the grass blade, producing a constricted area resembling an hourglass. On coarser grasses, the spots caused by dollar spot may not span the blade. Unlike Ascochyta, the leaf damage is in the middle of the blades, not the tips.
Individual leaf blades may have a single lesion or many small lesions or be entirely blighted. Infected blades usually have a distinctive tan to purplish streak between the white and green portions of the blade. These white-banded blades are most evident between dead areas and green turf.
The tip of the leaf blade may show the characteristic lesion, or the lesion may be in the middle of the blade, leaving the leaf tip green. When grass is wet from early morning dew, a fine, white cobweb-like mycelial growth (strands of fungus) may be visible on diseased leaves. As the grass dries, the mycelium disappears. These can easily be confused with spider webs or the downy seed tufts of cottonwood trees.
Stress Factors
Grass under stress is more susceptible to dollar spot than is properly maintained turf. Low nitrogen fertilizer, improper mowing (frequency and height), excessive soluble salt (alkali) levels, and improper watering all make turf more susceptible to disease. Newly sodded or seeded lawns that receive heavy watering also are frequently attacked.
Infestations of chinch bugs, white grubs, billbug grubs and other soil-inhabiting insects may stress grass by eating plant roots. Dollar-spot infected areas may mask the more serious insect problem. Always check infected lawns and treat for insect pests.
Long periods of high humidity or free moisture within the foliar canopy of the grass may cause severe outbreaks. Watering turf at the wrong time may extend this susceptible period and increase the incidence of disease.
Heavy thatch layers may promote dollar spot because water, air and nutrients cannot penetrate to the underlying soil and grass roots. This results in shallow and poorly developed roots that are quite susceptible to drought stress. Thatch also ties up and reduces the effectiveness of pesticides. Two aerations per year are recommended for yards with history of lawn diseases for this reason.
Resistant Grasses
Seeding or sodding with two or more varieties of bluegrass may reduce the chance of losing the lawn to dollar spot. Bluegrass varieties demonstrate varying degrees of resistance.
Disease Management
Watering in the early morning, before 7AM, can often time wash the dew off the grass and reduce the spread of the fungi.
If you want to water later in the morning, allow grass to dry for at least one hour before watering it. When watering late in the day, allow time for grass blades to dry before nightfall.
In some cases, the over seeding of resistant varieties of the same type of grass into existing turf can reduce continued flair-ups. As disease kills susceptible varieties, resistant varieties fill in dead spots.
Fungicides & Treatment
If nitrogen fertilizer levels are properly managed, and other cultural stresses are reduced, the use of fungicides for dollar spot control in residential lawns is normally not required. View our Denver lawn fertilization services »
Dollar spot fungi have varying degrees of tolerance to common fungicides used to control them. Some fungicide-resistant strains of dollar spot have developed. A particular fungicide, therefore, may be effective at one time but not another. Also, fungicides may increase future insect and disease problems due to their effect on beneficial soil organisms (earthworms, microbes, etc.). Without these organisms, thatch does not decompose and the efficiency of pesticides is significantly reduced. Earthworms and other beneficial soil organisms, which help aerate soil and improve grass health, may be negatively affected by fungicides. In other words it is recommended to use fungicides only as a last resort where there is an established history of recurrent disease.
Contact us today and we’ll send over a lawn technician to take a look at your lawn for signs of Dollar Spot or any other turf issues, and provide a plan for how to keep your lawn healthy and green.