Increased purple nutsedge (Cyperus rotundus) tuber sprouting with diurnally fluctuating temperatures.

Authors: WALLACE, REBEKAH - University Of Georgia; GREY, TIMOTHY - University Of Georgia; Webster, Theodore; VENCILL, WILLIAM - University Of Georgia

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2012
Publication Date: 1/2/2013
Citation: Wallace, R.D., Grey, T.L., Webster, T.M., Vencill, W.K. 2013. Increased purple nutsedge (Cyperus rotundus) tuber sprouting with diurnally fluctuating temperatures. Weed Science. 61:126-130.

Interpretive Summary: Suspected to be a weed by 1st century A.D., purple nutsedge continues to be an economic threat to vegetable crop production around the world, including the Southeast US. Purple nutsedge is a perennial that can reproduce sexually from seed and asexually from tubers, but tubers are the primary method of reproduction. Until recently, high-value vegetable production in the Southeast US used methyl bromide to control a multitude of pests, including plant pathogens, soil borne insects, nematodes, and weeds. However, use of methyl bromide has been eliminated as a fumigant for vegetable production due to concerns that it is an ozone-depleting substance, with exception to critical use exemptions that are granted by the Methyl Bromide Technical Options Committee of the United Nations. As growers transition from methyl bromide to alternative fumigants, purple nutsedge has become a more common weed in Georgia vegetables. This weed shift necessitates a greater understanding of the biology and physiology of purple nutsedge to improve management tactics. Purple nutsedge is among the most troublesome weeds of vegetables in the Southeast US and a substantial impediment in the search for methyl bromide alternatives. Greater understanding of the environmental cues that regulate tuber sprouting may assist in improved nutsedge management. Experiments were conducted to evaluate the effect of diurnal temperature variation on sprouting of purple nutsedge tubers. When average temperature was 28 C, cumulative tuber sprouting ranged from 88 to 92%, with no detectable differences among diurnal fluctuations. The high average temperature in the first study may have negated any type of enforced sprouting suppression. However, when average temperature was lowered to 16 C (simulating early spring diurnal fluctuations under polyethylene mulch), there was a positive linear correlation between maximum tuber sprouting and temperature variation. With an average temperature of 16 C, the absence of temperature variation resulted in 52% purple nutsedge sprouting, while 87% sprouting occurred when daily temperature varied 18.5 C at the same average temperature. The use of various types of mulching material can affect average soil temperatures and diurnal variations, potentially shifting nutsedge emergence. Further studies are needed to determine if these data on tuber sprouting in response to alternating temperatures can facilitate more efficient weed management.

Technical Abstract: Purple nutsedge is among the most troublesome weeds of vegetables in the Southeast US and a substantial impediment in the search for methyl bromide alternatives. Greater understanding of the environmental cues that regulate tuber sprouting may assist in improved nutsedge management. Experiments were conducted to evaluate the effect of diurnal temperature variation on sprouting of purple nutsedge tubers. Two temperature regimes were evaluated: the first averaged 28 C, with daily fluctuations ranging from 0 to 19.5 C; the second temperature regime averaged 16 C, with daily fluctuations ranging from 0 to 18.5 C. When average temperature was 28 C, cumulative tuber sprouting ranged from 88 to 92%, with no detectable differences among diurnal fluctuations. The high average temperature in the first study may have negated any type of enforced sprouting suppression. However, when average temperature was lowered to 16 C (simulating early spring diurnal fluctuations under polyethylene mulch), there was a positive linear correlation between maximum tuber sprouting and temperature variation. With an average temperature of 16 C, the absence of temperature variation resulted in 52% purple nutsedge sprouting, while 87% sprouting occurred when daily temperature varied 18.5 C at the same average temperature. The use of various types of mulching material can affect average soil temperatures and diurnal variations, potentially shifting nutsedge emergence. Further studies are needed to determine if these data on tuber sprouting in response to alternating temperatures can facilitate more efficient weed management.