Additive series experiments were conducted under greenhouse conditions to determine the effect of season-long interference of different initial population densities of purple nutsedge on the shoot dry weight and fruit yield of tomato and bell pepper. Purple nutsedge densities up to 200 plants/m2linearly reduced shoot dry weight at flowering and fruit yield of both crops as weed density increased. Both variables were directly correlated, and for each percentage unit of tomato shoot dry weight loss at flowering, fruit yield was reduced 1.24 units, whereas for bell pepper this relationship was 1 to 2.01. Total shoot and tuber biomass of purple nutsedge increased as density increased. The presence of either crop caused a decline in the total shoot dry weight accumulation of purple nutsedge, with tomato producing a higher degree of loss than bell pepper to the weed. Fruit yield losses due to purple nutsedge interference reached 44% for tomato and 32% for bell pepper.

Yellow nutsedge, a weed commonly present in Florida vegetable fields, may substantially reduce crop yields when not controlled. Soil fumigation with methyl bromide effectively controls nutsedges, but methyl bromide is being phased out of production and use in the United States. Therefore, nutsedge management in bell pepper is a cause for concern. An experiment was conducted during four seasons (spring and fall of 1999 and 2000) to determine the tolerance of bell pepper grown at two in-row spacings (23 and 31 cm) to interference resulting from planted yellow nutsedge tuber densities (0 to 120 tubers/m2). Relative to yields with no nutsedge, pepper fruit yields in each season were reduced 10% with fewer than 5 planted tubers/m2. Yield losses increased more rapidly with an increase in initial nutsedge density from 0 to 30 than from 30 to 120 tubers/m2. With 30 nutsedge tubers/m2, large fruit yield was reduced 54 to 74% compared to that with no nutsedge. Nutsedge shoots overtopped the pepper plants as early as 6 wk after treatment when, with 15 planted tubers/m2, nutsedge interference reduced pepper plant biomass by 10 to 47%. In the absence of methyl bromide, weed control strategies with high efficacy against yellow nutsedge will be needed for bell pepper production.

Twelve sweet corn (Zea mays L. var. rugosa Bonaf.) cultivars were tested for response to nicosulfuron at rates of 0, 18, 36, and 72 g a.i./ha. Weight of marketable ears indicated that five cultivars were intolerant to the herbicide. Three of the cultivars that were intolerant contained the shrunken-2 endosperm mutant (sh) and two contained the sugary enhancer endosperm mutant (se). Cultivars that were most tolerant of nicosulfuron contained the sh, gene. Incorporation of terbufos insecticide before planting led to decreased marketable yield when nicosulfuron was applied at 36 g·ha in all cultivars tested. Chlorpyrifos insecticide incorporated before planting did not affect tolerance to nicosulfuron. Neither soil-applied insecticide affected yield when nicosulfuron was not applied. Chemical names used: 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfony]-N,N-dimethyl-3-pyridinecarboxamide (nicosulfuron); S-[[(1,1-dimethylethyl)thio]methyl] O,O-diethylphosphorodithioate (terbufos); O,O-diethyl O-(3,5,6-trichloro-2-pyridyl)phosphorothioate (chlorpyrifos).

Replacement series experiments were conducted under greenhouse conditions to evaluate effects of population densities and proportions on the intraspecific and interspecific interference of either purple nutsedge or yellow nutsedge with tomato cv. Sunny, under nonlimiting conditions of water and nutrients. When grown with either nutsedge species for 40 d, tomato dry weight per plant increased and dry weight per plant of nutsedge decreased as their relative proportions decreased in mixture. Relative yield analysis indicated tomato is a stronger competitor than either nutsedge species. Both nutsedges appeared to be weak interspecific competitors but strong intraspecific competitors. Attenuated light on a purple nutsedge canopy showed that tomato additions can reduce light received by the weed compared to pure nutsedge stands.

Studies were conducted to determine the extent of full and partitioned interference of two nutsedge species with tomato. For full interference, the crop and the weed were transplanted in the same container. For belowground interference, tomato and either weed species were grown in the same container, but the canopies were separated. For aboveground interference, tomato and nutsedges were grown in separate containers placed adjacently, whereas for the no-interference treatment, tomato and nutsedge plants were grown in individual containers. Full interference by yellow nutsedge was more detrimental to tomato shoot dry weight accumulation (34% reduction) than was full interference by purple nutsedge (28% reduction). Belowground interference by purple nutsedge reduced tomato shoot dry weight (18%) more than did aboveground interference (9%). Yellow nutsedge interference above- or belowground reduced tomato shoot dry weight to a similar extent (19%). The belowground interference of both nutsedges with tomato resulted in deficient concentrations of nitrate in the sap of tomato (> 18% reduction). The growth of purple nutsedge was influenced more strongly by tomato shading than by belowground interference from the crop, whereas yellow nutsedge growth was equally affected by tomato above- and belowground. According to these results, shoot dry weight accumulation in tomato was affected to the same extent by belowground interference from purple and yellow nutsedge, and the higher effect of full interference by yellow nutsedge may be attributed to increased aboveground competition between tomato and yellow nutsedge.