WATER RESOURCE CENTER
Can Seawater Be A Herbicide? March 16, 2015 By Brian Whitlark, agronomist, West Region

Although these greens appear perfectly healthy on the surface, rooting depth is shallow at only 2.5 inches. The top 2.5 inches of soil in this profile is high in organic matter and is not adequately diluted with sand.

Can seawater be used to remove bermudagrass and kikuyugrass from seashore paspalum?

While the weather continues to be a little nicer than normal in the Pacific Northwest, golf is making a comeback in Hawaii with a return to paradise on golf courses throughout the islands. However, a recent weather occurrence on the Big Island resulted in front-page photos and headlines. During the winter months, Hawaii can certainly receive a considerable amount of rain on each island, but when a blizzard occurs on Mauna Kea that is so powerful the locals can’t get up to enjoy the activities, it is rare. Furthermore, when snow covers at least 1,000 feet of the mountaintop, it is unheard of.

From an agronomic perspective, Tim Snelling, superintendent at the Mauna Lani Resort, noted a unique method to remove kikuyugrass and bermudagrass in seashore paspalum. Snelling noticed that despite two applications of Roundup®, kikuyugrass would come back via new seedlings on newly sprigged seashore paspalum. As an alternative, Snelling used a 300-gallon sprayer to apply a mixture of seawater and a surfactant at 100 gallons per acre on young seashore paspalum sprigs where kikuyugrass was resurging. In one day Snelling sprayed an area multiple times and achieved outstanding results without harming the salt-tolerant seashore paspalum. Snelling reported that six to seven applications of seawater and surfactant, made on the same day, killed the kikuyugrass and damaged the bermudagrass. While some of the bermudagrass returned, this strategy may offer a simple way to address warm-season weeds for those growing seashore paspalum. Snelling also mentioned that results were much better when applications were made on cloudless days during summer months. Snelling also is convinced that the surfactant made a difference as previous tests with just seawater were unsuccessful.

Unhappy with bentgrass rooting depth? Don’t blame compaction

As temperatures are ideal in the western portion of the country for cool-season turfgrass growth and root development, it is a great time to assess root health. Collect soil cores and evaluate at what depth the majority of root growth ceases. In many instances, there is a color and soil textural change where root growth stops. Although it is possible that roots stop growing due to a compacted layer resulting from continuous use of the same size aeration tines, more than likely roots are remaining in upper layers of the soil where moisture and nutrients are better retained. An inadequate sand topdressing program will result in organic matter and thatch development without dilution – which holds considerably more water and nutrients than the underlying soil. Therefore, roots generally will not extend growth into the underlying soil mixture when excessive, undiluted thatch layers are present. Work to resolve thatch problems through a combination of strategies including frequent “venting” using small-diameter solid tines, resume a regimented sand topdressing program, conduct aggressive aeration practices, and consider deep vertical mowing with sand injection to remove organic matter.

Spring has sprung in California

Beautiful spring weather throughout California makes for happy turf. Many courses are focused on completing core aeration, sand topdressing and broadleaf weed control. Although core aeration causes temporary disruption, the procedure introduces some much-needed oxygen back into the soil profile. Also, the mild temperatures allow turf to recover quickly.

As part of the core-aeration process, some superintendents are taking the opportunity to roll out surface imperfections on tees, collars, and approaches by using a putting green roller immediately after the cores are removed and before sand topdressing is applied.

Source: Pat Gross (pgross@usga.org), Brian Whitlark (bwhitlark@usga.org), Larry Gilhuly (lgilhuly@usga.org)

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