Vol. 51—1997 - NorthEastern Weed Science Society

40
ECOL
ICAL ASPECfS OF CRABGRASS INFESTATION IN COOL-SEASON TURF
T. J. Kim' ,J. C. Neal 2 and F. S. Rossi'
ABSTRACf
s (Digitariaspp.) continue to be troublesome in turf management systems, but current
infonnatio on the ecological aspects of those infestations is limited. The development of more
efficient c ntrol strategies will require an improved understanding of seedling establishment,
growth an survival. The objectives of this study were to investigate how much open space (gap
size) is re uired for crabgrass seedling survival, how growth rate differs between gap sizes in
Cool-seas n turf and to identify potential causes for differences in crabgrass survival and growth
based on e vironmental monitoring.
Field periments were conducted in 1996 on a mature stand of turf-type tall fescue (Festuca
arundinace) with a history of heavy (site A) and no smooth crabgrass infestation (site B). Five
gap sizes f 2.5 to 20.0 em diameter were created by spot treatment with 2.0 % (v/v) Finale
(glufosina ) and arranged in a randomized complete block design. After the turf died, half of the
gaps were disturbed (dead grass and thatch removed and replaced with soil); the remaining gaps
were undi turbed. All plots were mowed bi-weekly at 2.5" height; clippings were removed, and
gap sizes ere maintained by clipping the encroaching grass blades once a week. Three grass weed
species, sooth crabgrass (D. ischaemum), large crabgrass (D. sanguinalis) and goosegrass
(Eleusine . a) were overseeded on 22 May in the gaps. Seedling emergence rate and tiller
developm nt were counted weekly from May to August. Throughout the month of August, weekly
seedhead ounts were recorded. Soil temperatures at 2.5 and 5 em depth were continuously
monitored from 24 May to 19 July at 30 minute intervals with in-ground thermocouples and a
Cambell RlOX data logger.
Mean aily temperatures were not substantially different for 2.5 and 5 em soil depth. However,
daily tern rature fluctuations were significantly different among the gap sizes, with higher and
lower te peratures recorded in the largest gap. Significantly more smooth crabgrass plants
emerged i gaps compared to no gap; but there were no differences in number of crabgrass plants
emerged ong the gap sizes. Therefore, gaps of any size could lead to smooth crabgrass
infestatio s. Following seedling emergence, tiller development was more rapid in larger than
smaller g ps. This suggests that the timing of postemergence herbicide treatments will be more
critical in pen turf (with larger gaps) than in a denser turf (smaller gaps) as plants will more
rapidly ac .eve the size that is more difficult to control in more open turf areas.
In ex riment B, goosegrass did not emerge when no gaps were created. While small numbers
of crabgr s seedlings were evident in no-gap areas, however, these seedlings did not survive.
Seedling mergence of threespecies were significantly influenced by thatch, however, there was
no thatch y gap size interaction. The emergence and survival of smooth crabgrass were similar to
what was observed in experiment A in gaps, while that of goosegrass was significantly lower,
especially in gaps with thatch. Seedhead production was not effected by gap sizes and was greater
for crab ss than goose grass.
In summary, the minimum gap size for crabgrass emergence and survival was between 0
and 2.5 c . In contrast, a gap size of 2.5 em was required for goosegrass emergence and 5.0 em
for surviv to seed production. These data confirm the paradigm that dense turf will exclude seedpropaga
weeds. However, it also illustrates that weed species differ in the minimum turf density
required t prevent weed infestations. This research suggest that both the prevention of weed seed
germinati n and inhibition of weed seedling growth and development are active components of this
competiti e relationship.
I Grad.
14853
s. Asst. and Asst. Professor, Dept. Om. & Hort., Cornell University, Ithaca, NY
2 Asst. fessor, Dept. Hort. Sci., NC State University, Raleigh, NC 27695-7609