The Control Center: Getting a Grip on Goosegrass

It’s one tough weed to control, but it can be done, culturally and chemically

Goosegrass, silver crabgrass, flat grass … all names for one tough unwanted pest. In addition to these common names, the Latin name, Eleusine indica, is quite apt, as most golf course superintendents and agronomists consider it to be elusive and hard to control.

While difficulty in the endeavor of keeping it off the golf course is somewhat subjective, it can certainly require significant effort. Let’s put it this way: If five superintendents were on a team playing “The Family Feud,” and the question was to name a very difficult to control weed, it would be on the board as one of the most common answers in the survey. The only uncertainty would be whether the team chose to pass or play.

That’s goosegrass, all right

One of the few fortunate features of goosegrass is that it is relatively easy to identify. It has dark green leaves with stems that transition from green to white at the base. The blades are folded in the bud, fitting together in cross section to form a “V” rather than a “C” as they overlap.

Though rarely seen because of frequent mowing, they taper to a point at the ends. The ligule is membranous, toothed and divided at the midrib. A 10x hand lens is usually required to see these features.

The auricles of goosegrass are absent, while the sheath is light green above and becomes white near the base; it is flattened, with a few long hairs along the collar. The root system is shallow and fibrous, perhaps a bit more so than other warm-season annuals. The seed head is distinctive, divided into finger-like or zipper-like segments, thicker and more robust than crabgrass.

So much for mowing

The stems are thick and grow low to the ground, with several basal tillers radiating from a central common point. Fortunately for the plant, and unfortunately for the superintendent, the low growing habit allows it to persist and grow well under very low heights of cut, as the bulk of the leaf tissue remains after each mowing operation.

In general, one of the most effective control methods for weeds is mowing, which works quite well for weeds such as shepherd’s purse that have an upright growing habit, but not so well for goosegrass.

Favorable growing conditions

Like most other weeds, goosegrass favors thin, open turf stands. Due to the combination of wear from heavy foot traffic, compaction of the soil in the upper layers and divots, a tee tends to be the ideal growing environment for goosegrass.

Speculation abounds regarding the specific reason(s) for the proliferation in these locations, with the competitive advantage for growth in compacted soils because of a high tolerance for low oxygen levels being cited most often.

While evidence is scarce that goosegrass actually prefers compacted soils, the more sensible explanation for its ability to thrive is that because of the shallow fibrous root system, it simply outcompetes other plants (such as desirable turf species) when soil particles are excessively compressed.

Goosegrass germinates later than crabgrass, as it requires minimum soil temperatures between 60 and 70 degrees Fahrenheit. Once the soil temperature is consistently in this range, germination may continue all season until temperatures cool down in the fall. In addition to tees, low-cut fairways and in some cases greens are also susceptible to goosegrass invasion. Generally, to the extent that compaction and wear occur concurrently in trafficked areas, this elusive pest can be a problem.

Cultural control

With more easily controlled weeds such as dandelions, many integrated pest management (IPM) techniques are effective in eliminating, or at least lowering, weed populations. For example, mowing height is particularly impactful for reducing the invasion of crabgrass in fairways. This phenomenon tends to be most evident at fairway edges, where a higher height of cut produces a canopy of turf tissue that makes the soil surface less conducive for crabgrass germination by shading the soil.

While IPM techniques work quite well for these pests, they are not highly effective for controlling goosegrass. However, they are still worth considering, as they provide many ancillary benefits and produce a more competitive growing environment for desirable turf species. Generally, any turf management practice that reduces soil compaction and excessive soil moisture and promotes healthy turf is useful in minimizing goosegrass infestation.

As mentioned above, traffic is a compounding factor for goosegrass control. Diffusing and redirecting traffic, especially after a rain or irrigation event, can be helpful. Core aeration on a regular basis to alleviate compaction is also quite useful. These steps should be taken wherever goosegrass has been observed in the past, especially on tees and greens.

Because of its relatively shallow root system, goosegrass requires moisture in the upper inch of soil to germinate; as such, reductions in the frequency and amount of irrigation water can be a helpful limitation. Unfortunately, the root systems of desirable turfs are often also shallow, especially on tees.

If a strategy is put into place to dry out the soil in an attempt to limit germination of goosegrass, the vigorous growth of turf is also unsupported. As a balance between the two is reached, uniform irrigation is a worthy goal to avoid overly dry or wet sections of turf.

Another strategy to consider is encouragement of desirable turfs, such as bermuda and perennial ryegrass, as they normally respond favorably to increased fertilization. In most cases, 0.5 to 1 pound of nitrogen per 1,000 square feet helps to regrow turf areas that have been damaged by traffic and possibly outcompete goosegrass and other weeds.

The downside to increased fertilization is that the negative outcomes of increased susceptibility to foliar diseases and the production of succulent tissues can result. Again, balance is important for this approach.

Timing is important for most cultural practices on the golf course. Goosegrass control is no exception. Since there is a slight difference of preferred germination temperatures between goosegrass and cool-season turfs such as perennial ryegrass, a short window of time exists in spring to allow establishment before goosegrass is favored. However, as both species are encouraged by moist soils, this technique can be tricky to utilize. Seeding of cool-season turfs after soil temperatures rise into the low 60s should be avoided in areas with a history of goosegrass infestation.

Physical and mechanical removal are nice words for hand weeding, where roots are cut below the soil. With the large square footage involved on the golf course, this method is usually reserved for special occasions such as before tournaments.

Chemical control

As with all other turf pests, timing is critical to successful control. From a pre-emergence standpoint, applications should be made in midspring, when soil temperatures reach 60 degrees for 24 consecutive hours. When applying products after germination, recognition of newly emerged plants is important for efficacy, in that smaller weeds are more easily controlled than larger ones.

Many products are available for control including those that contain pendimethalin, oxadiazon, fenoxaprop-p-ethyl, prodiamine, bensulide, sulfentrazone, dithiopyr and quinclorac, as well as various combinations of these active ingredients. It is sometimes necessary to repeat postemergence applications for complete control. As with any pest control product, it is essential to read and follow all label directions.