In the southern Tohoku region of Japan, ceasing maintenance of creeping bentgrass leads to grass death and almost complete invasion by weeds. Manilagrass (Zoysia matrella) stays alive for at least 18 months with no maintenance, and has minimal weed invasion. Japanese lawngrass (Zoysia japonica) also stays alive, but has more weed invasion than seen on manilagrass.
What happens with manilagrass and other grasses like seashore paspalum (Paspalum vaginatum) and hybrid bermudagrass (Cynodon dactylon x C. transvaalensis) when maintenance is stopped in the tropical conditions of Thailand? And do observations of what happens when there is no maintenance have some implication on what the maintenance requirements may be for those grasses?
At the TT Tour in January 2008, we studied various grasses at the research facility. The grass immediately surrounding the paved area is manilagrass, and adjacent to the sala with the red tile roof is centipedegrass (Eremochloa ophiuroides).
In April 2009, irrigation was stopped at the research facility, and mowing was stopped from October 2009. So what happened to this manilagrass by November 2010, 19 months after the last irrigation, and 13 months after the last mowing? This is in Thailand, where the temperature is always warm, and the grass (and weeds) have the potential to grow all 12 months of the year.
The next photo shows the same area as the previous photo, but at a different angle; the paved area is now at left (and covered by weeds); the manilagrass that people are standing on in the above photo is in the center of the photo below.
How about bermudagrass and seashore paspalum?
The rainy season in this part of Thailand goes from late May until the end of October. The photo above was taken in mid-September 2009. Irrigation was stopped in April. Even though the grass was growing through the rainy season, the seashore paspalum in the foreground has almost all died without supplemental irrigation in only 5 months. The bermudagrass in the background remains alive, as does the surrounding manilagrass.
This next photo is taken from the same plot of mostly dead seashore paspalum, but turned to a different angle to show manilagrass in the background. The manilagrass, of course, remains alive with the natural rainfall and no supplemental irrigation.
Those photos showed the seashore paspalum after 5 months without irrigation. What happens after 19 months of no irrigation and 13 months with no mowing? In that case, the seashore paspalum has all died.
Seeing what happens when maintenance is withheld gives some indication of how much maintenance (irrigation, fertilizer, pesticides, mowing) are required when a species actually is maintained. Under the conditions of central Thailand, one can make some general observations based on this comparison of unmaintained grasses.
- manilagrass seems to require only mowing to persist as a turfgrass and is the most resistant to weed invasion
- seashore paspalum dies without supplemental irrigation
- bermudagrass does not die without supplemental irrigation but will eventually be invaded by weeds if not maintained intensively
These observations of manilagrass are very similar to what was seen in the photos from Japan. Also, these observations of dying seashore paspalum are similar to what was seen in a controlled experiment in southern China. Xie et al. found that seashore paspalum turf under low maintenance was naturally replaced by manilagrass within 2 to 3 years.