Preparing your turf for winter
1 Sep, 2007 By: Kathy Kalmowitz Ph.D. LM Direct!Turfgrass stressed from poor cultural or pest management practices in the summer can cause problems that will linger into the following growing season. Fall is the optimum time for lawn care and grounds professionals to make a successful spring transition.
The first step to ensure healthy turf growth in the spring is to take stock of fertility rates and nutrient loads going into the winter.
Stimulate cool-season grasses
High temperatures, heat stress and draughty conditions cause cool-season grass stands to thin during summer months. Turf professionals should stimulate active growth of these grasses with a complete fertilizer from August through September and pay special attention in charging the nitrogen rates. As evening temperatures begin to cool below 70? F,nitrogen increase nitrogen rates from below 5% to greater than 16%.
Deliver half the nitrogen source in a slow-release form, such as sulfur-coated or urea-based nitrogen. Fertilizers based solely on ammonia nitrate nitrogen will release too quickly, making them unable to spread the turfgrass fertility needs through the winter. If you experience excess rainfall, periodic liquid fertilization that includes an iron source may be helpful.
Before purchasing fertilizers, check the label to determine if both the source of nitrogen (ammoniacal nitrogen, urea or sulfur-coated urea) and percentage (16%, 19%, 22%, 34%, etc.) satisfies the cool-season turfgrass needs for the fall.
If you’re reseeding thinned turfgrass stands in late August through October, consider delaying complete fertilization until the new stand has grown-in and you’ve mowed several times. This will help avoid disease problems that can occur while daytime temperatures are still high. In this situation, consider a liquid foliar starter fertilizer lower in nitrogen and higher in phosphorus and potassium to encourage root growth.
Winterize warm-season grasses
In areas where warm-season turfgrasses go dormant or are susceptible to periodic low winter temperatures, begin to slow the turfgrass growth and prepare to ‘winterize’ in August. Reduce but do not eliminate nitrogen rates. This helps maintain but not push excessive new top growth. A balanced fertilizer should be in the range of 5-10-20 or 5-10-31 where phosphorus (i.e., 10) or the potassium source (i.e., 20 -31) are a ratio of elements that promote strong roots for the fall and winter months.
Mechanical & cultural controls
— Aerification: Core removal through aerification promotes air circulation in the soil’s root zone. Aerification reduces the amount of thatch while follow-up verticutting removes the thatchy material, providing an even surface. Complete aerification by early August; in warm-season turf as growth slows adequate recovery must occur before dormancy. An increase in weed growth may also follow due to the increased light penetration to the soil. Raising mowing heights will help reduce weed-seed germination.
— Overseeding. In warm-season grasses, a lawn care operator or sports turf manager needs to determine if an active, green-growing surface is desired through the winter months. If so, overseeding with a cool-season grass should take place from August through October, typically the best month to overseed in most regions.
Overseeding in warm-season turf can be more stressful and problematic as the practice will affect both fertilizer forms and the timing of a pre-emergent herbicide application. Carefully select the amount and type of nitrogen levels in starter fertilizers to avoid stimulating late-season growth of the warm-season turfgrass.
For cool-season turf, seeding re-establishes the turfgrass stand after it has thinned during hot summer months. When well timed, the reseeded stand establishes good root growth and a dense canopy prior to the onset of limiting, cooler nighttime temperatures.
Chemical controls
If you’ve chosen not to overseed warm-season turfgrass, it is recommended to apply a pre-emergent herbicide to prevent winter annual broadleaf weeds and grasses including annual bluegrass, also known as Poa annua. Although Poa can germinate over several months, the greatest flush has been documented in early fall. In non-overseeded bermudagrass, a pre-emergent should be applied from August to October. Pre-emergent herbicides such as the dinitoranilines (DNA), dithiopyr, or the pre-post product pronamide should be applied two to four months prior to, or two to four months after, if overseeding. Always consult specific product labels for herbicide restrictions, rates and use sites.
Several post-emergent herbicides are available for use on bermudagrass for control of Poa annua and include: rimsulfuron, foramsulfuron, atrazine, simazine and sulfentrazone.
When a dense stand of cool-season grass is established in a timely manner and appropriately fed, winter weed control may not be necessary. As the months progress, broadleaf weeds may develop and are easily controlled with a number of liquid post-emergent herbicides. A ‘weed and feed’ post herbicide plus fertilizer can be applied in the spring if a granular product is favored.
Whether you’re maintaining warm-season or cool-season turfgrass, develop a preventative plan. If you don’t have healthy turfgrass during the active growing months, you’ll have to deal with replacing turf and even greater pest management control when spring arrives. Begin with establishing fertility to promote a healthy stand of turf and follow-up with the appropriate cultural and chemical controls to keep healthy turfgrass through the winter.
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