Since my last article on heat stress, I have received questions from sports field managers about what role wetting agents might play in soil moisture management during the summer months when cool-season grasses are heat and drought stressed.
Let’s start by looking at what wetting agents are and how they work. Wetting agents are chemical substances that increase the spreading and penetrating properties of water by lowering its surface tension. Water is a polar molecule, so it has a positive end and a negative end, much like magnets do. Water molecules are attracted to each other, and it is these forces that cause water droplets to form (hence the term “surface tension”). Surfactants are a class of compounds that reduces this surface tension, which can either be between two liquids or between a liquid and a solid. There are different kinds of surfactants, including detergents, wetting agents, and emulsifiers. So, a wetting agent is a surfactant, but not all surfactants are wetting agents. Wetting agents used in turfgrass management are a class of surfactants that reduce the surface tension of liquids, helping them to disperse, penetrate and percolate into soil.
There are many different types of wetting agents available. Unlike pesticides, they are not regulated by the EPA, so manufacturers don’t necessarily have to divulge the ingredients. Many of the products are also mixed with other ingredients. Anionic (negatively charged) wetting agents are used to move water uniformly through the soil, but they can be phytotoxic to turf plants, and could also disperse clay particles, affecting the soil structure in a rootzone containing fine soils. Nonionic (no net charge) wetting agents are more common. Some of the older chemistries could also cause some phytotoxicity to turfgrass, but the newer formulations typically do not.
Application rates and timing will depend upon the purpose of the application, time of year, and severity of soil repellency issues. Some wetting agents can be applied as little as once per year, and some are applied every two to four weeks. A rule of thumb with localized dry spot (LDS) is to apply a wetting agent preemptively before it becomes a problem. Many of the wetting agents can also be tank mixed with other products, such as fertilizer, pesticides and plant growth regulators, to maximize return on investment. Work with your local rep to determine what wetting agent works best. Your local turfgrass Extension program can also be helpful.
Wetting agents are typically applied to the turf surface as a liquid or granular product, then watered in. The efficacy of any particular product depends upon many factors, such as levels of organic matter. If thatch is greater than ½” or soil organic matter is greater than 3.5%, it’s a good idea to core aerate to make sure the wetting agent does not bind to the organic material, preventing its infiltration into the rootzone.
According to the Golf Course Superintendents Association of America, 98% of golf course superintendents use wetting agents. I do not know what percentage of sports field managers use them, but I suspect it’s much lower. Their use in golf is predominantly linked to issues such as LDS, which is a phenomenon that affects low-cut (i.e., less than 1”) turf on sand rootzones where the top inch of soil becomes hydrophobic and extends deeper into the soil profile. The substances that cause development of hydrophobic dry spots (water-repelling root exudates, fungi, decomposing organic matter) are non-polar. When water comes in contact with a non-polar hydrophobic substance, it tends to bead rather than penetrating into the substance, making it very difficult to get water down into the soil profile. Wetting agents are used to break the surface tension between the water and the hydrophobic soil particles. While all soils have a certain level of water repellency, LDS occurs mainly on low-cut sand-based sports surfaces such as those used for tennis, cricket, soccer, and field hockey. LDS is not common on native soils or high-cut turf.
Other sports field uses include providing consistent soil moisture and irrigation efficacy across the entire field; high-traffic areas under water stress; on baseball/softball skins to reduce dust and maintain a firm, moist surface; new sod installations during post-harvest; and new artificial turf installations if the surface is hydrophobic. Wetting agent granules can also be added to divot mixes.
If blanket applications are too much for the budget, consider using them for situations that require a little extra help.