Getting Ahead of the Weeds: Preemergent Control

Obviously, lawn care operators, even those in the more northern climates, keep busy month after month taking care of customers’ lawns and battling the weeds that want to inhabit those lawns.

Preemergence weed control products represent just one of the weapons available to the lawn care professionals in this war, but the effective use of that one weapon can often mean the difference between victory and defeat.

"I spend thousands of dollars on preemergence herbicides every year, and I wish I didn’t have to put them down. But I just can’t see a lawn care program without these products," remarked Rick Wolfe, president, Spring Green Lawn & Tree Care, Niles, Mich.

"The preemergent application is an important aspect of the lawn care program because the density of the turf hasn’t developed early in the spring," agreed Kyle Miller, senior technical specialist, American Cyanamid, Parsippany, N.J.

When a healthy, dense stand of turf is present, lawn care operators have less to worry about in terms of weed establishment because the competition for space and nutrients from the turf minimizes weed development, explained Miller. Early in the spring, however, many lawns lack that complete turf coverage in a yard and even the tiniest gaps in turf present opportunities for weeds and a summer full of headaches.

WHEN THE TIME IS RIGHT. A contractor can buy the right product and make a text-book application, but everything will be wasted if the application isn’t timed correctly.

"Timing depends on the weeds the applicator is trying to control," pointed out Dom Riego, area technical development manager, Monsanto, Indianapolis, Ind. "Most of the weeds that LCOs are trying to control from a preemergence standpoint are crabgrass, which typically germinates when soil temperatures get to around 60 degrees Fahrenheit. Miss that mark and the crabgrass will germinate and the product won’t work.

"For other weeds, like goosegrass, the application can be made a little bit later because goosegrass germinates at warmer soil temperatures," Riego added.

"Applicators don’t want to miss the window by delaying the application, but, fortunately, the preemergence products we have today have longer residuals," explained Dr. Jamie Breuninger, technical leader, Dow AgroSciences turf and ornamental research group, Indianapolis, Ind.

"I think one of the issues we’re always encountering with lawn care operators is that sometimes they have to make some preemergence applications a little too early in order to get to all of their accounts in the limited window of opportunity they have," added Miller. "As a result, some lawns get applications early in the season and the product might not deliver as much control or control for as long as the applicator wants, and that may call for an additional application of postemergence products or create control problems in the summer."

Miller also noted that early applications can create more challenges if they end up being followed by a difficult summer, such as the summer of 1999.

"A lack of rain means the turf will be less competitive and LCOs are likely to see more weed breakthrough," he explained. "That’s the time when you really want your preemergence product to still be working for you."

Breuninger also recommended that lawn care operators be sensitive to the areas of a property that tend to be most susceptible to crabgrass problems.

"Crabgrass often shows up along the edges of turf and sidewalks or driveways because these areas are likely to heat up because of the sunlight on the hard surface," Breuninger explained. "This extra heat can lead to thinner turf in these areas and let more sunlight get down to the soil layer and breakdown the preemergence product, which makes it easier for weeds to develop."

The answer to this problem is not necessarily to apply extra preemergence product, however, Breuninger cautioned. "Applying a 3x rate or something above the labeled rate will just damage the turf and help the weeds develop," he said.

DOING THE SPLITS. The practice of making split applications (multiple applications of preemergence product during the year) has become increasingly popular.

"There is no doubt the southern part of the United States is almost entirely split applications because of the length of the weed germination season," observed Miller. "Some southern companies even do three or four preemergence applications during the year.

"Some companies within the transition zone and northern states are doing split applications to make sure they don’t have any callbacks," Miller continued, explaining that the split applications in these areas generally consist of an initial application based on the product’s standard rate and a later, second application at the full or a reduced rate to get through the summer.

"The benefit of the split application is protecting yourself against a really bad summer," he added. "If the weather is bad in the summer, a lot of applicators may end up wishing they had made that second application. The applicators who are making split applications part of their regular program are just making sure they’ll have enough product down for a tough season."

Riego also observed that some LCOs have taken to reducing the rate in their round one when planning to apply the preemergent in a split application.

"For example, if the product is labeled for 3 pounds to be applied, the contractor might split that into an application of 2 pounds and an application of 1 pound or two applications of 1½ pounds," he explained. "Doing this helps the contractor distribute his or her costs for the product and, if there hasn’t been any weed pressure when the time arrives for the second application, the contractor may decide that second application isn’t necessary and avoid putting unnecessary product in the ground."

FALL GUYS. One idea that has stirred up some debate among lawn care contractors in the last few years is the notion of a fall application of preemergence herbicide. The reasoning behind the idea is that the product won’t break down much during the cool winter months and each application made during the fall is one less application that has to be made during the hectic spring.

"Making fall applications does provide a wider window to work in and lets contractors service more customers," recognized Riego. "The disadvantages of fall applications are that the compounds to be used to last through the winter can be more expensive and if the weather doesn’t cooperate the product can end up breaking down during the fall, thereby wasting the application."

Contractors are also reluctant to make applications of a product that they might not get paid for, as can be case when a customer cancels a service during the winter after a fall preemergence application has been made.

"Fall applications for crabgrass control are not particularly common but tend to be a little more common in situations where the applicator knows he or she will still be caring for the property the next spring, like on golf courses or municipalities," noted Miller, adding that even then applicators have to be concerned about re-seeding options if they have extensive winter kill of the turf.

TAKING FORM. Another issue for contractors to consider is the best formulation to use – liquid or granular?

The general consensus is that contractors are fairly evenly divided between the two formulations with factors such as geographic location and application timing weighing heavily on the formulation decision.

"I use granular products because sometimes I can start applications in February because of warm weather instead of our regular March application dates," noted Wolfe. "I don’t want to apply liquid product that could freeze if the weather changes.

"But then we switch to liquid formulations once I don’t have to worry about the weather," Wolfe added, saying he believes liquid formulations are more effective so long as they are applied correctly. "We do a double overlap spray with liquid formulations to make sure we have complete coverage."

One advantage of using the granular products, however, is that technicians can see where the granular product goes when it hits the ground.

"Liquid products hit the ground and disappear into the turf and the soil," related Riego. "Granular products may also be easier to apply because the spreaders are easier to calibrate correctly than a lot of the spray systems are."