EFFECTS OF SOIL-MOISTURE ON OBSERVED AND PREDICTED YELLOW NUTSEDGE (CYPERUS-ESCULENTUS L) EMERGENCE

Experiments were conducted to examine the effects of low soil moisture on yellow nutsedge emergence in relation to thermal and chronological time and test the ability of thermal models generated previously to p redict emergence under water stress, Unsprouted tubers from California and Arizona were planted in pots, buried at field sites in California and Arizona, and subjected to wet or dry treatments, Pots were monito red weekly to determine date of emergence and number of emerged shoots , The California genotype emerged 47 to 61 days after planting (DAP(3) ) in the dry treatment and 33 to 49 DAP in the wet treatment, dependin g on planting site, The range for the Arizona genotype was 51 to 76 DA P in the dry treatment and 43 to 61 DAP in the wet treatment, Days and degree-day intervals to first emergence differed between irrigation t reatments and planting sites but interactions were not significant, Al l models were accurate in predicting emergence dates for genotypes in the wet treatment at the California site, while emergence in Arizona w as underestimated by 9 d, Tubers subjected to the dry treatment needed a higher number of accumulated degree-day units before emergence occu rred and had fewer emerged shoots as compared to the wet treatment, De gree-day models generated for yellow nutsedge under optimal conditions lack sufficient robustness to be predictive under water stress condit ions.