In deep

Aquatic weeds present numerous problems for superintendents. They dirty ponds and lakes, and clog mechanical pumping systems. If you have a problem with aquatic weeds, your first instinct might be to use the most powerful chemical on the market. But when weed-infested ponds are also used to irrigate fairways and greens, the process for managing weeds often becomes more difficult. To prevent unwanted chemicals from getting into an irrigation system, it’s important to know which chemicals to use, how much to use and when to use them.

There is often a difference in how you manage irrigation ponds versus non-irrigation ponds, says Dr. Rob Richardson, assistant professor of crop science at North Carolina State University. “Some of the herbicides that are available are going to say not to irrigate that growing season or wait up to 120 days,” he says. “Obviously if you have to irrigate, then you can’t do that, and you have to look at other management options.”

Duckweed is a problem for Crystal River Golf Club’s eight acres of non-irrigated ponds, which rest in an 80 percent flood zone, says Rich Herber, superintendent of the Homosassa, Fla., club.
“We have an aquatic guy coming in and spraying the ponds,” Herber says. “We have for probably about eight years.”

The technician makes monthly visits to the year-round club to control the duckweed, which obstructs views of the ponds, Herber says.

SePRO’s SonarOne systemic herbicide controls duckweed, says Scott Shuler, invasive weeds management portfolio leader at SePRO. For non-irrigated ponds, the granular product, which comes in a 20-pound pail, is best applied in the early spring.

“SonarOne, or one of the other formulations of Sonar, is hands down the best duckweed product out there,” Shuler says. “It provides very long-term control, very complete control. In irrigation ponds, it gets tricky because the rate that you need for duckweed control is above the irrigation limit.”

For courses that have an off-season for irrigation, crew members should wait until the fall to apply SonarOne, which is slow-acting but should provide control at least through the following season. Depending on the severity of the weed problem, crew members should apply somewhere between six and 10 pounds per acre, he says. For courses with year-round irrigation, SePRO’s Komeen Crystal Aquatic Herbicide, which has no irrigation restrictions, could be a better alternative, he says.

In Florida, where aquatic weed problems are abundant and irrigation ponds operate year-round, there are several restrictions on aquatic operations, says Steve Kammerer, director of the USGA Green Section Southeast Region. Florida requires a specific applicators license, which is why many superintendents in the state are contracting out the work, he says.

SePRO has 17 technical reps around the U.S., Shuler says. “Their contact information is readily available via our website and they can tailor a specific treatment to a specific pond anywhere,” he says.

Gary Roush, longtime superintendent of Riverside Golf Club in Mason W.Va., says this year he plans to treat the duckweed in his non-irrigation ponds with Sonar. “Any aquatic weeds that floats, is what Sonar will take care of,” he says.

Roush doesn’t use Sonar or other chemicals in Riverside’s single irrigation pond. Weeds have not been an issue in it due to another proven solution. “We have a fountain that normally keeps it aerified and takes care of it,” he says.

When looking to identify issues with clogged irrigation pumps and screens, filamentous algae and submersed weeds like pondweed, watermilfoil and hydrilla, are often more likely to be the culprit than duckweed, Richardson says.

Most of these issues can be treated with herbicides, but it’s important to take precautions, Richardson says. “The intent of an herbicide is to kill a specific plant, but if it has herbicidal activity you need to be really cautious about where that water goes after it’s been treated,” he says.

For most aquatic weeds in irrigation ponds, Shuler recommends Komeen Crystal. “It’s going to burn back the biomass that’s present in the pond at that time,” he says. “But it is a contact herbicide, so the plants can regrow relatively quickly and depending on the climate you’re in, you may have to retreat every six to eight weeks through the growing season.”

The copper-based Komeen Crystal comes in in 20-pound bags. Superintendents or their workers should use between 40 and 60 pounds per acre of weeds, Shuler says.

“It’s a granular, so you would spread it out over the weed bed with a belly grinder or a granular blower, or even hand-tossing with the appropriate PPE or safety gloves, throw it out over the weed beds, either by shore or by boat,” he says.

Superintendents with irrigated ponds should keep in mind that whatever they put into their water, or in some cases what municipal facilities might bring in, could influence the health of their greens and fairways, Kammerer says.

“If they’re just treating ponds that are retention ponds on the golf course, that’s one issue," he says. "If they’re treating ponds that they’re depending on for irrigation, that’s very different.”

Patrick Williams is a GCI contributing editor. He can be reached at gwilliams@gie.net.