Landscape & Irrigation

January/February 2014

Landscape and Irrigation is read by decision makers throughout the landscape and irrigation markets — including contractors, landscape architects, professional grounds managers, and irrigation and water mgmt companies and reaches the entire spetrum.

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www.landscapeirrigation.com Landscape and Irrigation 19 LI applied at a certain rate and a different material could have an eight- week residual. The cost of the materials and the longevity could be deciding factors. Conversely, the amount of labor to make more than one application of any material may top the list of deciding factors. These issues must be adjusted to accommodate each turf manager's specific requirements. Figure 4 represents the application of preemergence materials and the expected length of time crabgrass will be controlled. This graph shows how things are supposed to work. The X axis represents time and the Y axis represents the concentration of preemergence herbicide in the soil where the crabgrass seed will be germinating. For example in the Mid-Atlantic re- gion, typically crabgrass germination starts some- time in late April and continues until about mid-July. This is about 3 months (or 12 weeks or 90 days). The preemer- gence material must have adequate concen- tration in the soil profile in order to prevent the crabgrass seed from germinating. This is represented by the yellow line on the graph. Any level of concentration of preemergence material above the yellow line will prevent germination, and any level below will not. The red line on the graph represents the concentration level of a preemergence material applied once. The blue lines represent "split applications" (two applications) of materials. As indicated on the graph, when time passes, the concentration of preemergence material de- creases in the soil profile but in both cases have lasted 90 days or more. This should control the majority of crabgrass germination. Product labels will have information about the residual (longevity) of the product and application rates. If the preemergence control of crabgrass has not been attainable, reevaluate your strategy. Review the following questions: Has the correct rate of product been applied at the correct time of the year? When was the last time you calibrated you application equipment? Does the product have enough residual to last for the season using the single application methodology? Should split applications of product be incorporated into the program? Was the product watered in per the label instructions? These are some of the key questions to consider. Remember, you can make a plan — but plan to change it frequently to adapt to nature. Jeffrey Borger is an instructor, Turfgrass Weed Management, in the College of Ag Sciences at Penn State's main campus in University Park, Pa. Figure 4. A visual representation of the preemergence herbicide concentrations in the top 1/4 inch of the soil profile following an application in the spring of the year. Now you can access all the latest news and events anywhere, anytime. Simply visit www.landscapeirrigation.com/mobile to stay connected. has gone mobile!

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