A phone call during the onset of the spring season for a weed problem is the last thing a contractor wants to deal with.
But it doesn’t take a customer long to become unhappy with his or her lawn. That adds one extra visit to a property that a technician already doesn’t have time for and another application.
What if it were possible to apply a weed control product in the fall that would eliminate this spring problem? Some pesticide manufacturers and contractors believe this is the case.
POSITIVE PROGRAMMING. The successful turfgrass management program results from an integration of recommended cultural practices and a complete weed control program. In most landscape and turf care operations, knowledge of weed control is important. Maintaining a dense, healthy stand of turfgrass is one way to control many weeds, including annual grasses and broadleaf weeds. Proper mowing height and frequency, fertilization practices and irrigation scheduling are part of a cultural management program and should be practiced throughout the growing season.
Turfgrass managers should also be familiar with the following steps for a successful weed control program: (a) Knowing the specific weed problems (grassy weeds vs. broadleaf weeds) and life cycle of the weeds (annual vs. perennial), (b) Selection of the right herbicide, in relation to effective weed control and turfgrass tolerance.
Some of the commonly found annual grassy weeds include large crabgrass, small crabgrass, goosegrass, annual bluegrass, yellow foxtail, green foxtail, fall panicum and barnyardgrass.
| Putting It Down |
| During the winter months in the southern United States, bright green spots of annual bluegrass can be unsettling to lawn care customers who expect a brown lawn.
According to contractors, the use of a fall preemergent herbicide application is essential in keeping their customers in the warmer climates happy. As for the northern states, a fall preemergent herbicide application to control spring crabgrass can a contractor’s operational dream. “It means less customers in the spring, which means we have more time for new sales,” assured John Buechner, director of technical services, Lawn Doctor, Holmdel, New Jersey. “And there’s no pressure to beat the germination period.” A fall application, according to contractors, can be made from mid-August through October. But a fall application won’t last the whole year, stressed Phil Fogarty, who develops national accounts for Scotts Lawn Service in Cleveland, Ohio. “It only postpones the spring application until June.” The spring application becomes a “booster shot” to extend the residual of the fall application, said Dick Bare, owner and president of Arbor-Nomics, Norcross, Ga. The primary problem associated with fall preemergent applications, besides possibly putting grasses into dormancy prematurely, is with customers whose contracts expire Jan. 1. “After the fall application, there is no guarantee that the customer will renew their contract,” Buechner recognized. “You’re gambling with customer renewals.” Ergonomically, a fall application is the smart thing to do, but when relaying the idea to customers, it’s still experimental, Fogarty stated. “Customers think spring is the time to fertilize and take care of crabgrass and the late summer is for controlling weeds,” he said. “It takes a lot of communication and education to convince the customer fall is a good time for the preemergent application. They don’t think they have to worry about their lawn after Labor Day. The idea isn’t a fresh one, unless you’re talking to the customer. “This is not a new idea, but it’s new to them,” Fogarty assured. “It’ll take about two years to change the habits of lawn care customer buying.” - Nicole Wisniewski |
EMERGING PATTERNS. The preemergence weed control program has been a popular and very convenient program for lawn maintenance professionals and landscape operators. Some of the preemergence herbicides for grassy weed control in cool-season grasses that have been tested at the University of Massachusetts are prodiamine, bensulide, dithiopyr, pendimethalin, oxadiazon and siduron.
For some lawn care operators, preemergence application options include the application of such products in the fall for activity the following spring. Many turfgrass managers and lawn care operators need to cover numerous properties for preemergence applications and the time required to do this during the hectic and weather-vulnerable spring creates a major challenge for covering all of their clients’ properties.
Meanwhile, preemergence treatments can be applied in the fall as long as the soil is not frozen. The applied herbicides remain in the soil and provide control in the following spring based on their residual activity as well as the weather conditions. Some of the treatments applied in the fall have provided control of many weed species in the following spring or even throughout the year with the length of control the following year also being dependent upon the rates being used.
However, it is important to note based on the research we have conducted at the University of Massachusetts, fall-applied treatments have proven more effective in the cool-season turfgrass environments compared to other areas. This is most likely attributable to the increased rate at which the pesticide products will breakdown in warmer soils.
In general, one fall application of the recommended rates of some preemergents would provide weed control for the next season, and our data indicated that would be 90 to 100 percent control of many weed species during the year. Typically, a subsequent fall application would be required at the end of this first year for control to be achieved in the second year as well with any of these products.
Germination of annual grassy weeds is related to soil temperature. When the soil temperature reaches 65 F for a week, grasses begin germinating, although the peak germination period varies with the local soil type, rainfall and weather in the spring.
Therefore, timing the herbicide application accurately is very important. The key point is that preemergence herbicides need to be applied before grasses germinate in the spring. Treatments made too late will not control emerged grassy weeds. If the application’s timing does not coincide with the normal germination period of annual grassy weeds, control results may be erratic or poor. In general, preemergence herbicides should be applied one to two weeks prior to the expected weed seed germination period. Therefore, the application dates of preemergence herbicides will vary from one part of the country to another.
The most important product characteristic in the concept of fall preemergence applications is the increased residual properties exhibited by many of the newer products since herbicidal activity in controlling weeds is dependent upon the effectiveness of products still in the soil. Some herbicide may last only four to six weeks, while others may provide control 12 to 16 weeks from the time of application.
Based on the concept of long residual effects of several herbicides, we decided to examine the potential preemergence activity of various fall-applied herbicides in controlling weeds in the following spring. We initiated experiments in the fall of 1994, 1995, 1996 and 1997 at the Turfgrass Research Center, University of Massachusetts.
Experiments were conducted on established Kentucky bluegrass. Treatments were applied in the fall. All herbicides were formulated in granular form, including fertilizer base.
In our trial during 1994-95, several preemergence products applied in October 1994, resulted in excellent large crabgrass control on July 22 and Sept. 15, 1995. These dates correspond to 45 and 52 weeks after treatment (WAT). The weed control was best at the highest rate of each of these herbicides.
In other trials from 1994 to 1997, several preemergents, applied in the fall, were very effective in the control of crabgrass during the following spring. However, other products achieved effective control only when applied at the highest labeled rate.
The Kentucky bluegrass stand itself was generally not affected by most of the fall-applied treatments. However, some products, when applied at the highest labeled rate, did show potential to affect as much as 40 percent of the turfgrass.
OTHER CONSIDERATIONS. It is important to plan for fall-applied treatments since they also limit the effectiveness of programs such as reseeding. In general, preemergence herbicides persist in the soil for a length of time, allowing season-long weed control, so a reseeding interval would have to depend upon the herbicide and dosage used. However, contractors should not plan to use a fall application strategy if they plan to reseed a particular area in the spring.
In summary, a successful preemergence weed control program results from selecting the right herbicide and applying it uniformly at the proper time and appropriate dosage. The herbicide selection is dependent upon the weeds to be controlled and the turfgrass to be treated.
Choose the most effective herbicide offering maximum safety to the turfgrass. For crabgrass and other grassy weed control, lawn maintenance professionals should emphasize a preemergence herbicide program along with a good cultural program. The preemergence program would have the option of herbicide application either in the fall or in the spring.
The author is professor of weed science, the University of Massachusetts, Amherst.
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