Horticulture & Chemicals

Not turf's best friend What can I do about dog-urine spots in my client's lawn?-Minnesota

This problem is sometimes called "female-dog-spot disease." The problem stems from the fact that females, unlike male dogs, tend to urinate all at once and in one spot, not from any difference in urine composition.

The burn results from excess nitrogen. Ironically, well-tended lawns often suffer more than neglected lawns. Soil-nitrogen levels are relatively high on lawns that have received fertilizer, so it takes less urine to elevate concentrations to levels that produce burn.

With enough water, it's not difficult to reduce nitrogen levels to non-phytotoxic levels, but turf will need to be re-established in dead areas. The best solution is for the owner to train the dog to use an out-of-the-way section of the yard.

Almost universally, homeowners equate "burn" with "acidity." Thus, liming is a recommendation you'll hear frequently. However, pH has little or no part in the burning that urine causes (as reported by Dr. A.W. Allard, a Colorado veterinarian). Therefore, liming, as well as the numerous dietary supplements designed to alter urine pH, will have little or no value in this situation. (Always consult a veterinarian before using supplements or altering a dog's diet.)

One solution that works for some pet owners is installing motion-activated sprinklers that turn on whenever the dog enters the protected area. A drawback is that birds, squirrels or other wildlife may trigger the sprinklers frequently, resulting in over-watered turf and high water bills. Aside from this, all that you-the turf manager-can do is continue to repair the burned spots (obviously, sod plugs are quicker than seed).

Stubborn trees My customers want their yards cleared of leaves by Thanksgiving, but many trees don't drop them until December. Is there any way to make trees drop their leaves earlier?-New Jersey

There's no denying that extended periods of leaf drop can be frustrating. However, attempting to promote early leaf drop would be an inappropriate imposition of human timetables on nature. Trees drop their leaves at different times according to their age, species, climate and weather, and other factors, and do so when the time is right for them. To expect all trees to be bare by Thanksgiving is unreasonable. I realize that you simply are reacting to your customers' wants, so consider this an opportunity to educate them.

According to Dr. Kim Coder, an arborist with the University of Georgia (Athens, Ga.), conceivable treatments that might cause early leaf drop are unjustifiably stressful to trees. However, Coder notes that blowers or long poles are possible mechanical methods of prompting leaves to drop once they've begun to turn color. One factor of which you should be aware is excessive fall nitrogen, which, Coder explains, can cause trees to delay leaf drop. Trees growing in lawns often experience relatively high nitrogen levels from fall turf fertilization, so consider reducing or eliminating fall nitrogen on turf surrounding trees with persistent leaves.

Little specific information is available regarding germination timing of the annual biotype of annual bluegrass (Poa annua ssp. annua). This is surprising considering the serious problems this weed causes on golf courses. To better understand the germination timing of annual bluegrass, Dr. Peter Dernoeden, a University of Maryland researcher, undertook a study using various rates and timing of prodiamine, a pre-emergence herbicide.

Using three rates of the herbicide, Dernoeden made applications on three dates (mid-August, -September and -October) in 1995. Subsequently, he evaluated percent cover of annual bluegrass in the study plots. The August and September applications provided much better control than the October treatment. This was consistent with preliminary observations that germination begins in mid-September in Maryland.

Dernoeden repeated the test in 1996, but with applications in late August, mid-September and late September. The late-September application provided poor control relative to the other two application dates. Again, this was consistent with a mid-September germination.

Dernoeden also found that applications close to the onset of germination reduced the rate necessary for good control. As little as 0.32 pounds per acre (0.12 ounces per 1,000 square feet) of active ingredient-less than one-fourth the labeled annual maximum rate for annual-bluegrass control in Kentucky bluegrass-provided control of more than 95 percent.

Dernoeden notes that other geographic regions can expect different germination times. For example, a Michigan researcher found that three pre-emergent treatments were necessary annually to control annual bluegrass (which germinated heavily there in both spring and fall). In Tennessee, by contrast, mid-November to early January is the germination window.

Dernoeden stresses that these results are specific not only to the mid-Atlantic region, but also to the study's specific conditions-non-core-aerated Kentucky-bluegrass turf mowed above 2 inches. However, this research illustrates the importance of application timing for good annual-bluegrass control and the need for region-specific annual-bluegrass germination data.

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