Living-and succeeding-with kikuyugrass
No one plants it, but it gets into everything and seems to be everywhere. After it's established, you can't get rid of it-it's tough and it's strong. It seems as if you need a chainsaw to mow it. It grows so fast that you're afraid to leave a small child in it for too long. What is it? Kikuyugrass.
Kikuyugrass (Pennisetum clandestinum) is a warm-season grass that people brought to Southern California around 1920 for erosion protection and as a pasture grass, in a classic example of misdirected virtue. It grows along the California coast on slopes and in pastures, as well as on golf courses, in parks, on sports fields and in home lawns. It ranges as far north as the San Francisco Bay area, south to the Mexican border and east into the inland valleys.
Everywhere it grows, people are learning to live with kikuyugrass, whether they want to or not. Realizing this, we have conducted several studies at the University of California at Riverside (UCR) to better understand kikuyugrass ecology and, we hope, learn how to manage this species to obtain high quality turf. Here I'll discuss much of what we know about this challenging grass.
Invasion and control Kikuyugrass typically is coarse textured with a light-green color. While most people consider it a weedy species, it is becoming reluctantly accepted in the Mediterranean-type climates where it is adapted. Due to its sheer acreage-and the fact that you can't keep it out-it is becoming an important turfgrass by default. It is an aggressive invader, spreading by way of stolons, rhizomes and seed, with the help of mowers, golfers, football players and anything that is dragged, carried or rolled on the grass. In infested regions, low-maintenance turf facilities such as parks and home lawns eventually convert to kikuyugrass, regardless of the species in the original sward. Absent heroic measures, the same fate awaits high-maintenance turf.
Kikuyugrass is an exceptional plant-as a weed. It is aggressive, highly competitive, spreads easily by several means and tolerates drought, over-watering and poor soil. It is on both the California and the Federal noxious-weed lists. In other words, it is illegal to plant kikuyugrass deliberately. Chemical control is difficult with anything except methyl bromide fumigation, and even then some seeds or plant parts often appear to escape. Non-selective herbicides don't even work well on this pernicious species. However, UCR researchers found that they could significantly reduce the competitiveness of kikuyugrass, allowing desirable turf species to compete, with repeated applications of triclopyr (Turflon Ester, from DowElanco and Monterey Chemical) at 0.5 pound active ingredient (ai) per acre plus MSMA at 2.0 pounds ai per acre in cool-season turf. Quinclorac (Facet) at 0.65 pound ai per acre plus MSMA at 2.0 pounds ai per acre also provides suppression, but quinlcorac is still experimental and does not yet have full registration.
Considering how easily it spreads and how difficult it is to control, it is no wonder turf managers try to learn to live with kikuyugrass. Here's a summary of what we know about kikuyugrass management based on research and the practical experience of superintendents and other turf managers.
Kikuyugrass characteristics Golf balls sit up nicely on closely mowed kikuyugrass with minimal thatch. However, kikuyugrass prolifically produces thatch, giving mature turf a deep sponginess when thatch develops. Thatch changes the way the ball sits, and a lofted club can pass under a ball. When you allow kikuyugrass to grow taller, the ball sinks into it. Hitting a ball out of a kikuyugrass rough is a formidable task for golfers of any ability.
Older kikuyugrass playing fields, even those with adequate turf cover, have poor playability for just about any sport. The turf is slick, providing poor traction for tennis-shoe-clad players and causing them to slip and slide a great deal. However, it seems to reach out and grab the cleats on football and soccer shoes. The stolons are round and tough (see photo, page G 16) with long inter-nodes and grow 6 to 9 feet long. I know of one instance in a park where stolons grew in one door of a small building and out the other. Kikuyugrass turf has a great deal of lateral strength and is difficult to tear, which is not necessarily a desirable trait for football fields. Although it has better winter color than most bermudagrasses, kikuyugrass does not tolerate as much traffic and is slower to recover from injury.
Kikuyugrass produces flowers that are mostly enclosed by leaf sheaths low on the stem. However, the flowers produce long, white filaments that extend above the turf surface in considerable density. These are highly visible, giving the turf an unattractive silvery appearance (see photos, below and left).
Kikuyugrass ecology A UCR study found that over the range of 77 to 104oF-the temperature range in which it is most aggressive-kikuyugrass has a higher rate of photosynthesis than St. Augustinegrass and tall fescue, which is probably why it out-competes both of these turfgrasses. Plus, kikuyugrass tolerates cold better than most other warm-season turfgrasses, continuing to root at relatively low temperatures.
Spreading vegetatively by stolons and rhizomes is the most common means of kikuyugrass propagation on golf courses. Mowers, vertical mowers, aerators, sweepers and shoes spread the stolons. Trenching and any other digging spreads rhizomes present in the soil. Because the seeds are borne inside the turf canopy, they are less likely to be an important means of spreading. However, seeds can ride on wet shoes, equipment and in soil and may be able to become established in relatively open areas.
The optimum soil-temperature range for kikuyugrass germination is 65 to 85oF. However, the seed tolerates high temperatures and will germinate after 48 hours of exposure to 110oF. An Australian study found that seeds emerge readily from a planting depth of 1.25 inches and from as deep as 2.25 inches. Plus, seeds remain viable in soil for long periods. If you use a non-selective herbicide to kill existing kikuyugrass, you'll soon see seedlings emerging. In one recent study, researchers at UCR collected plants at golf courses in three locations representing the range of environmental conditions in which kikuyugrass grows in California. Analyses of several hundred plants identified 12 genotypes or genetic individuals. Yet 73 percent of the plants they examined represented only two genotypes, which occurred in all locations. If seeds were the primary mode of invasion and colonization, many more genotypes would exist at a given location. However, low genetic variability indicates the spread of kikuyugrass is predominantly by stolons and rhizomes.
Maintenance Kikuyugrass has received only grudging acknowledgment for low-maintenance uses. In contrast, a number of golf courses, including some upscale facilities, are successfully managing kikuyugrass as quality turf. Notable among them is Riviera Country Club in Pacific Palisades, Calif., site of the 1995 PGA Championship and annual host of the Los Angeles Open. Several golf-course superintendents and landscape managers have learned the vagaries of the grass and have been able to provide the intense management necessary. However, all are likely to agree that it is a challenge.
* Fertilization. It is a little frightening to consider fertilizing kikuyugrass. Its growth rate and aggressiveness don't seem to need much help. Applications of 1.0 pound nitrogen per 1,000 square feet in April, June and August produces high quality on well-trafficked kikuyugrass turf but also causes heavy thatch in the absence of traffic. Five applications of fertilizer per year at 0.5 pound nitrogen per 1,000 square feet in May, June, July, August and September produces good-quality turf under no- or low-traffic conditions. The main difference is that the three applications of nitrogen at a higher rate in the primary growing season produce a more traffic-tolerant turf.
Some turfgrass facilities are only able to apply fertilizer one time per season. However, at UCR we found that applying 2.0 pounds of nitrogen per 1,000 square feet in April actually will reduce turf quality compared to 1.0 pound of nitrogen at that time, indicating that you can push kikuyugrass, but not too much. Without traffic or vertical mowing, thatch accumulates more with increasing nitrogen.
* Vertical mowing. In kikuyugrass turf, biomass (mostly thatch) builds up fairly quickly. The spongy, deep mat is unwelcome on fairways, and the surface can even become too soft for field sports. On kikuyugrass with no or low traffic, you should perform vertical mowing three times per season, in May, July and August. You gain no advantage by vertical mowing more often than this. In our research at UCR, we discovered that traffic by itself also will reduce thatch. However, where traffic is insufficient to reduce thatch, vertical mowing is necessary. Some areas of turf on golf courses and sports fields get more traffic than others. Thus, it is likely that some parts of any kikuyugrass turf will need some vertical mowing if turf quality and playability are important.
* Mowing. Regular mowing produces selective pressure on kikuyugrass to favor plants with a prostrate growth habit. Plants that are prolific stolon and rhizome producers begin to dominate turf that is regularly mowed. Conversely, kikuyugrass grown without mowing, such as for erosion control or forage, does not have the selective pressure of mowing, and biotypes that are more upright may dominate the stand.
The acceptable mowing-height range for kikuyugrass is 0.5 to 2.0 inches, depending on use. You can maintain fairway-quality turf at 0.625 inch, though tournament play demands 0.5 inch. Mow sports fields at 0.625 inch or higher. Some superintendents maintain golf-course roughs at 2 inches or higher, which imposes a severe penalty on the wayward golf shot. As with any turfgrass, low and frequent mowing reduces root and top growth. Reducing mowing height helps control kikuyugrass by decreasing its overall biomass and rate of spread.
* Overseeding. You can overseed kikuyugrass relatively easily with cool-season grasses. Vertical mowing the kikuyugrass before over-seeding does not improve the stand of the overseeded turfgrass, although scalping does help stand uniformity. Tall fescue is the better choice for overseeding, because it competes better with kikuyugrass in the fall than perennial ryegrass. We have found that the optimum overseeding rate is around 10 pounds per 1,000 square feet.
Kikuyugrass is a weed-little debate exists about that. In addition, it is a pasture grass of some repute, particularly for goats. As we've seen, though, kikuyugrass also can be a turfgrass, albeit a "blue collar" turfgrass, and it can provide a decent cover for low-maintenance sites. However, as with most things, if someone really wants to spend the time to work with it, kikuyugrass can become a member of "high society." Superintendents on some fine golf courses have produced some excellent kikuyugrass turf.
Stephen Cockerham is superintendent of agricultural operations at the University of California-Riverside.
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