# *Pennisetum clandestinum*

**Kikuyugrass**

**Poaceae**

*Pennisetum clandestinum* (kikuyugrass) is an extremely aggressive
perennial weed of turf (i.g., golf fairways, parks, and home lawns).
Originally from Africa, it was introduced to California in the 1920's
for erosion control on hillsides. It is adapted to warm, temperate
climates such as the coast and inland valleys of southern and central
California. Kikuyugrass reproduces by seed and asexually via vigorous
stolons and rhizomes (i.e., clonally). When kikuyugrass flowers, the
stigmas emerge 1 to 3 days before the stamens of the same flower, which
encourages outcrossing. Kikuyugrass is a tetraploid.

In a study investigating the diversity of genotypes at several locations
in California, Wilen et al (1995) concluded that populations of *P.
clandestinum* in turf environments tend to be less diverse because they
grow clonally, while populations that invade natural areas tend to
reproduce more by seed and have higher genetic diversity. However, they
noted that weediness of *P. clandestinum* is not necessarily associated
with high levels of genetic variation. Similarly, low levels of genetic
variation are not always correlated with similar levels of phenotypic
variation.

In a study of the rate of spread of *P. clandestinum*, Wilen et al
(1995) showed that the spreading strategy appears to be based on its
ability to expand from the main clonal patch and branch from its
numerous stolons at the periphery of the patch. Kikuyugrass can maintain
higher rates of photosynthesis at cooler temperatures than most C~4~
grasses; the large amount of leaf area it accumulates during warmer
intervals result in a plant that is likely to be more productive on a
whole-plant basis than other C~3~ or C~4~ grasses grown under similar
conditions (Wilen and Holt 1996a).

Cudney et al (1993) treated kikuyugrass-infested grasslands (*Lolium
perenne* and *Poa pratensis* sward) with monosodium salt of
methylarsonic acid (MSMA), triclopyr, and quinclorac over a 5-month
period at 4- to 5-week intervals. They found that this treatment reduced
cover of kikuyugrass from over 80% cover to less than 1% of the sward.
In a separate competition experiment, the same researchers found that
the same herbicide sequential application reduced competition in
kikuyugrass. They suggest that where reinvasion /reestablishment of cool
season species is desired, application of MSMA and triclopyr may dampen
kikuyugrass' competitive ability and allow the desired species to
reinvade. Some reseeding of cool season species may be necessary. Where
reestablishment of warm season species is desired, sequential
applications of MSMS should be used (triclopyr can injure warm season
species). Wilen et al (1995) warn that removal of the large main patch
of an invading weed may result in a worse weed problem due to numerous
small foci allowed to remain and grow around the perimeter of the
removed section. Since the spreading ability of kikuyugrass appears to
be based on its ability to branch from its stolons presumably due to
reallocation of resources, close mowing could slow the process of
invasion but is inadequate to control it, according to Wilen and Holt
(1996b).

Based on the results of their study, Elmore et al. (1997) suggest that
growing tall fescue (*Festuca arundinaceae*) next to stands of
kikuyugrass should slow or eliminate the penetration of kikuyugrass into
established turf swards. They found that perennial ryegrass (*Lolium
perenne*) was not capable of reducing the invasion of kikuyugrass
stolons as well as tall fescue.

An outbreak of the rust fungus Phakopsora apoda was initially observed
in South Africa in 1986. The rust appears only to decrease
photosynthetic capacity of infected leaves, but does not kill plants
(Adendorff and Rijkenberg, 1995).

**Literature Cited**:

Adendorff, R., and F. H. J. Rijkenberg. 1995. New report on rust on
kikuyu grass in South Africa caused by *Phakopsora apoda*. Plant Disease
79:1187.

Cudney, D. W., J. A. Downer, V. A. Gibeault, J. M. Henry, and J. S.
Reints. 1993. Kikuyugrass (*Pennisetum clandestinum*) management in
turf. Weed Technology 7:180-184.

Elmore, C. L., V. A. Gibeault, and D. W. Cudney. 1997. Invasion
resistance of tall fescue (*Festuca arundinaceae*) and perennial
ryegrass (*Lolium perenne*) to kikuyugrass (*Pennisetum clandestinum*).
Weed Technology 11:24-29.

Wilen, C. A., and J. S. Holt. 1996a. Physiological mechanisms for the
rapid growth of *Pennisetum clandestinum* in Mediterranean climates.
Weed Research 36:213-225.

Wilen, C. A. and J. S. Holt. 1996b. Spatial growth of Kikuyugrass
(*Pennisetum clandestinum*). Weed Science 44:323-330.

Wilen, C. A., J. S. Holt, N. C. Ellstrand, and R. G. Shaw. 1995.
Genotypic diversity of Kikuyugrass (*Pennisetum clandestinum*)
populations in California. Weed Science 43:209-214.