Two greenhouse experiments were conducted to study the influence of 12 soil-applied herbicides on the sprouting and mortality of yellow nutsedge (Cyperus esculentus L.) tubers. Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], butachlor [N-(butoxymethyl)-2-chloro-2′,6′-diethylacetanilide], cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), EPTC (S-ethyl dipropylthiocarbamate), napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide], and U-27267 (3,4,5-tribromo-N,N,α-trimethylpyrazole-1-acetamide) delayed sprouting of tubers and provided 6 to 12 weeks control, but failed to kill tubers. Tubers appeared to escape injury by failing to sprout until activity of the herbicides had substantially dissipated. Herbicides known to interfere with photosynthesis, atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], bromacil (5-bromo-3-sec-butyl-6-methyluracil), methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione], prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine], San-6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], and terbacil (3-tert-butyl-5-chloro-6-methyluracil) did not delay sprouting of tubers, but killed shoots after emergence. In addition to controlling vegetative growth, the photosynthetic inhibitors killed tubers by rapidly exhausting the food reserves of these storage organs.

Yellow nutsedge (Cyperus esculentus L.) was studied to determine the relationship between physical character of tubers and sprouting habits. All tuber lots studied, which averaged from 157 to 662 mg per tuber, sprouted and grew well under greenhouse conditions. Longevity (the time between initial planting and death) increased with tuber weight. Weight of the third and fourth sprouts equalled that of the first and second sprouts for heavy tubers, but sprout weight decreased for light tubers. Detaching the plants at 2-week intervals from the tubers which produced them allowed all buds present to sprout. However, when the plants were detached at 4-week intervals, a reduction in the number of sprouts and a decrease in longevity were observed. Allowing plants to grow for 8 weeks before detaching did not cause any further decrease. Number of buds, number of sprouts, number of multiple sprouts, the time interval between first planting and first sprout, and the time interval between successive sprouts did not vary with initial tuber weight. Prolonged refrigerated storage of tubers caused an increased number of multiple sprouts, a decreased initial and subsequent sprouting interval, and a short life.

Yellow nutsedge (Cyperus esculentus L.) tuber maturity was studied to determine its influence on accumulation of 14C from urea and NAA (naphthaleneacetic acid). Radioactive carbon from the above sources accumulated in tubers in decreasing amounts as tubers became more mature when the plants to which they were attached were treated. Tubers that were young at treatment accumulated the highest concentration of radioactivity and parent tubers (most mature) accumulated the least 14C. Tubers that were classified as mature, but not parents, accumulated insignificant amounts of radioactive carbon.

Nonradioactive and 14C-organic arsenical herbicides were applied to foliage of young cotton (Gossypium hirsutum L., var. Acala SJ-1) at various temperatures. An application of 3.36 kg/ha of monosodium methanearsonate (MSMA), with and without 0.5% surfactant, severely injured plants exposed at 13 C. Similar injury resulted when plants were exposed and treated at 20 C with MSMA containing 0.5% surfactant. Applications of MSMA did not injure plants exposed at 31 C. Disodium methanearsonate (DSMA) was less injurious to cotton than MSMA. Only slight to moderate injury resulted when plants were exposed and treated at 13 C with 3.36 kg/ha of DSMA containing 0.5% surfactant. Applications at higher temperatures did not injure cotton. Cotyledons absorbed 14C-methanearsonic acid (MAA) and 14C-MSMA more readily than 14C-DSMA. Contact injury from these herbicides was slight at 13 C but was pronounced at 20 and 29 C. Generally, translocation of herbicides into developing true leaves was slight. The exception resulted from applications of 14C-MSMA to plants at 13 C when contact injury was negligible.

Four cropping systems were evaluated from 1975 to 1977 for the control of yellow nutsedge (Cyperus esculentus L.). Crops grown in 1975 and 1976 included alfalfa (Medicago sativa L. ‘Elcamino WL-600′), barley (Hordeum vulgare L. ‘CM-67′), corn (Zea mays L. ‘Dekalb T214′), and cotton (Gossypium hirsutum L. ‘Acala SJ-2′). Herbicides used included butylate (S-ethyl diisobutylthiocarbamate) in corn, EPTC (S-ethyl dipropylthiocarbamate) in alfalfa, glyphosate [N-(phosphonomethyl)glycine] in fallow plots, and MSMA (monosodium methanearsonate) in cotton. Cotton, which was grown continuously as one of the four cropping systems, was the only crop grown in 1977. Based on weed counts, crop yields, and the consistent decline in the number of tubers, all cropping systems provided substantial control of yellow nutsedge each year. Two years of either alfalfa treated with EPTC or double cropping barley with corn treated with butylate preceeding cotton reduced the number of viable yellow nutsedge tubers by 96%. Two years of chemically fallowing plots with glyphosate following barley and preceeding cotton was 98% effective in reducing viable tubers. Treating continuous cotton with MSMA, although somewhat inferior to the above systems, reduced the number of viable nutsedge tubers by 91% in 3 yr.

Studies were conducted on and in the vicinity of the U. S. Cotton Research Station at Shafter, California, to evaluate the prevalence of the insect Bactra verutana Zeller (Olethreutidae) and its potential for injury to yellow nutsedge (Cyperus esculentus L.). Field surveys during August 1966, and August and October 1967 revealed many infested yellow nutsedge plants. Other field studies indicated that the insect may significantly suppress the growth of yellow nutsedge, providing that the insect infestation is early, sufficiently severe, and present on both parent and subsequently emerging vegetative plants. Greenhouse studies further revealed that severely infested plants may survive to produce numerous vegetative plants and tubers. While Bactra verutana Zeller damaged yellow nutsedge plants late in the season, the absence of early infestation limited its usefulness as a biological control agent.

Nonradioactive and 14C-labeled arsenical herbicides were applied to foliage of purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (Cyperus esculentus L.) grown under greenhouse and growth chamber conditions. Disodium methanearsonate (DSMA) controlled purple nutsedge better at 20 and 29 C than at 13 C. Monosodium methanearsonate (MSMA) was as effective in controlling this weed at 13 C as at 20 and 29 C. DSMA and MSMA provided 80% or greater control of yellow nutsedge grown at the three temperatures. When plants were treated with 14C-DSMA and 14C-MSMA, greater radioactivity was detected in yellow nutsedge than in purple nutsedge. The apparent differential herbicide penetration of purple and yellow nutsedge leaves is believed to have contributed substantially to the control of nutsedge observed in this study.

We collected tubers from greenhouse-grown yellow nutsedge (Cyperus esculentus L.) control plants and plants foliarly-treated with 3.36 kg/ha of disodium methanearsonate (DSMA) or monosodium methanearsonate (MSMA). Where sufficient tubers were produced, they were separated into two classes, large and small. Some of the tubers were analyzed for elemental arsenic, and others were stored at 2 C and planted at various intervals. Vitality of tubers was noted in terms of sprouting and vegetative growth. Tubers collected from treated plants contained significantly more arsenic (4 to 33 ppm) than control tubers (1 ppm). Tubers collected from treated plants and planted without separation sprouted in significantly reduced numbers compared to control tubers. Small tubers contained a significantly higher concentration of arsenic (23 to 33 ppm) than large tubers (4 to 12 ppm). The treatments reduced the vitality of small tubers but had little or no effect on vitality of large tubers.

The influence of artificial shading (0, 30, 47, 70, 80, and 94% shade) on growth of yellow nutsedge (Cyperus esculentus L.) and the time required for developing canopies of several crops to intercept a given amount of light were investigated in field studies to estimate the potential of crops to compete with yellow nutsedge for light. Average number of shoots and tubers and total dry matter production of yellow nutsedge increased in direct proportion to increased amounts of light (correlation coefficient (r ≥.98). Compared to no shade, flower production was substantially reduced by 30 and 47% shade and was essentially absent under more dense treatments. Photosynthetically active radiation (PAR) measured at weekly intervals indicated that light interception occurred first within the drill row of crops, then on shoulders of planting beds, and finally in furrows. The most rapidly developing canopies studied [corn (Zea mays L.), potatoes (Solanum tuberosum L.), and safflower (Carthamus tinctorius L.)] intercepted 90% or greater PAR, including illumination in furrows, within 8 to 9 weeks after planting. About 12, 12, and 16 weeks were required for 80% interception for cowpeas [Vigna unguiculata (L.) Walp.], milo [Sorghum bicolor (L.) Moench.], and cotton (Gossypium hirsutum L.), respectively. Fall-planted barley (Hordeum vulgare L.) intercepted about 90% PAR by March 12. Alfalfa (Medicago sativa L.) intercepted about 90% PAR within 2 to 3 weeks after individual cuttings. Although onions (Allium cepa L.) planted in December intercepted 95% of the PAR in each of the two drill rows per bed about 26 weeks after planting, only 20 to 30% interception occurred in furrows and row middles.

Six cropping/weed control systems were evaluated from 1978 to 1980 for the control of yellow nutsedge (Cyperus esculentus L.). Supplementing cultivation of cotton (Gossypium hirsutum L. ‘Acala SJ-2′) with either preplant applications of fluridone {1 - methyl - 3 - phenyl - 5 - [3 - (trifluoromethyl)phenyl] -4(1H-pyridinone} or two hoeings for 2 yr preceding cotton treated with DSMA (disodium methanearsonate) and MSMA (monosodium methanearsonate) reduced populations of viable yellow nutsedge tubers 98 to 99% within 3 yr. Dry- or wet - fallowing plus tillage after barley (Hordeum vulgare L. ‘Kombyne’), and double cropping potatoes (Solanum tuberosum L. ‘White Rose’) treated with EPTC (S-ethyl dipropylthiocarbamate) with soybeans [Glycine max (L.) Merr. ‘Williams’] treated with alachlor [2-chloro - 2′, 6’ - diethyl - N - (methoxymethyl)acetanilide] for 2 yr preceding cotton, reduced populations of tubers 98 to 99% within 3 yr. A similar reduction of tubers (97%) was obtained by double cropping potatoes with milo [Sorghum bicolor (L.) Moench. ‘NK- 265′] for 2 yr preceding cotton.

The following herbicides were evaluated for relative phytotoxicity to cotton (Gossypium hirsutum L. ‘Acala SJ-1′), purple nutsedge (Cyperus rotundus L.), and yellow nutsedge (Cyperus esculentus L.) under greenhouse conditions: 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl)acetanilide (CP-53619); 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (VCS-438); 4-chloro-5-(dimethylamino)-2-α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone (San-6706); 2-(α naphthoxy)-N,N-diethyl-propionamide (R-7465); and S-isopropyl 5-ethyl-2-methyl-piperidine-1-carbiothioate (R-12001). Herbicides were incorporated 6.35 cm deep, at rates of 1.12, 2.24, and 4.48 kg/ha, into a fine sandy loam prior to planting. All treatments except the low rate of alachlor and VCS-438 controlled yellow nutsedge for 8 weeks. R-7465 and R-12001 at 1.12 kg/ha and San-6706 at 2.24 kg/ha controlled purple nutsedge for 8 weeks. Alachlor and CP-53619 were somewhat less effective against purple nutsedge than yellow nutsedge, but their intermediate rates suppressed purple nutsedge for 4 weeks. Even the high rate of VCS-438 was ineffective against purple nutsedge. Cotton, in terms of fresh shoot weight, exhibited considerable tolerance to 1.12 and 2.24 kg/ha of VCS-438 and CP-53619 and 1.12 kg/ha of R-7465. Applications of 2.24 kg/ha of CP-53619 and 1.12 kg/ha of R-7465, however, suppressed the development of lateral roots of cotton. Other rates of these herbicides and all rates of alachlor, R-12001, and San-6706 moderately to severely injured cotton in most of the experiments.

In field plots, Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Link) W. F. Wight] competed strongly with yellow nutsedge (Cyperus esculentus L.), reducing its dry weight and the number of plants and tubers with no loss of dry weight to the millet. Because Japanese millet did not shade the nutsedge for more than half the day, the main competition was thought to be ‘root’ competition (nutrient and water) with light competition as a minor factor. The greenhouse studies verified that roots were the primary area of competition. However, light competition between the two species was stronger in the greenhouse than in field plots. Also, when confined to limited light and soil volumes with a 1-month growing period, Japanese millet was reduced in dry weight by nutsedge competition.

Seed of johnsongrass [Sorghum halepense (L.) Pers.] were planted during 1976 and 1977 at monthly intervals from March through October to study the growth and reproductive habits of this weed at Shafter, California. Plants were grown for 12 weeks and harvested at 3-week intervals. Emergence and development of plants increased with temperature. April through August plantings yielded 10-to 20-fold as much total fresh weight as March and September plantings. After planting, rhizome production normally began in 3 to 6 weeks and seed production in 6 to 9 weeks. From the April through August plantings, rhizomes accounted for averages of 13, 25, and 40% of the total fresh weight of plants 6, 9, and 12 weeks after planting, respectively. This compared, respectively, with 16, 9, and 6% for roots and 70, 66, and 54% for shoots. Seedlings emerging in March produced rhizomes in early June and viable seed in late June. Seedlings emerging as late as September produced rhizomes and some viable seed before killing frosts in November.

Ten herbicides were each applied at two rates to Panache loam for 5 or 6 yr as soil-incorporated broadcast sprays directed to the base of cotton (Gossypium hirsutum L. ‘Acala SJ-1’) at last cultivation. Chemical determinations 6 months after annual treatment showed that trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], benefin (N-butyl-N-ethyl-a,a,a-trifluoro-2,6-dinitro-p-toluidine), DCPA (dimethyl tetrachloroterephthalate), and prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] residues were essentially confined to the tilled zone of soil; whereas, bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercapteothyl)benzenesulfonamide], fluometuron [1,1-dimethyl-3-(a,a,a,-trifluoro-m-tolyl)urea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] residues were found below the tilled zone. At time of retreatment, annual residue determinations from the upper 15 cm of soil showed that nitralin and prometryn had dissipated completely and residues of the other herbicides and were notably reduced as compared to levels at cotton harvest. One year after final treatment herbicide residues below the tilled zone were essentially nondetectable, except for diuron, linuron, and fluometuron. There was no evidence of herbicide accumulation in soil with repeated applications.

In five field experiments conducted during 1972 and 1973, yellow nutsedge (Cyperus esculentus L.) was either undisturbed or removed from planting beds by hoeing 0, 2, 4, 6, and 8 weeks after cotton (Gossypium hirsutum L. ‘Acala SJ-1’) emergence. Yellow nutsedge undisturbed in beds increased from 23 plants/m of row at cotton emergence to 100 plants/m at harvest. Nutsedge competing with cotton for more than 4 weeks reduced yield of seed cotton. Nutsedge that competed all season reduced yields 34%, as compared with 20% when it competed for 6 and 8 weeks. Nutsedge that competed with cotton for more than 4 weeks reduced height and number of cotton plants and delayed maturity. Although nutsedge competition reduced yields and delayed maturity, it generally did not alter fiber properties. When nutsedge was removed at cotton emergence and was followed by 14 weekly hoeings, the final tuber population was reduced to 24% of the beginning population. When nutsedge removal was delayed for 6 weeks and was followed by nine weekly hoeings, a fourfold increase in tubers resulted. A further tenfold increase resulted when nutsedge was not removed.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], and benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) were applied at two rates for five consecutive years (1966 through 1970) as soil-incorporated treatments to cotton (Gossypium hirsutum L. ‘Acala SJ-1’) before the preplanting irrigation. Repeated applications did not significantly affect stand or yield of cotton. Soil samples taken to depth of 120 cm showed that herbicide residues were confined to the tilled zone of soil (upper 30 cm), and about 80% of the residue was in the upper 15 cm of soil. The amount of herbicide residue found annually in the upper 15 cm of soil varied with herbicide and with season. Residues 15 months after final application had been reduced markedly, but were still sufficient to injure sensitive crops. Residues at 30 months had been reduced to innocuous amounts.

Four field experiments conducted over 3 yr indicated that cultivation alone failed to prevent johnsongrass [Sorghum halepense (L.) Pers.] from reaching densities that severely reduced yields of cotton (Gossypium hirsutum L. ‘Acala SJ-2’). Density of johnsongrass in plots cultivated four times and hoed weekly for 8 weeks after emergence was reduced to 1 shoot/m2 at harvest compared to 74 shoots/m2 for plots that were only cultivated. In addition to a 60% average yield loss of seed cotton, yield losses ranging from 40 to 76%, ginning losses were also greater from cultivated than from hand-weeded plots. Compared to cultivated plots, supplementing cultivation with two postemergence applications of 3.0 kg/ha of DSMA (disodium methanearsonate) increased the average yield of cotton by 20% and reduced perennial johnsongrass densities by 64% at harvest. Although yields were improved by applying DSMA, they averaged 40% less than those of hand-weeded plots. The temporary weed control obtained with DSMA was profitable in terms of the additional lint and seed obtained, but insufficient cotton was produced to pay expenses for producing the crop by any of the methods of weed control. High labor costs for hoeing prevented this treatment from being profitable.

Seven herbicides were evaluated for the control of yellow nutsedge (Cyperus esculentus L.) in cotton (Gossypium hirsutum L. ‘Acala SJ-1’) in three field experiments during 1970 and 1971. The herbicides, 2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide (alachlor); 2-chloro-2′,6′-diethyl-N-(butoxymethyl) acetanilide (CP-53619); 2,4-bis(isopropylamino)-6-methylthio)-s-triazine (prometryne); 2-(α-naphthoxy)-N, N-diethylpropionamide (R-7465); S-isopropyl 5-ethyl-2-methylpiperidine-1-carbothioate (R-12001); 4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3-(2H)-pyridazinone (San-6706); and 2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione (methazole), were applied broadcast and incorporated 10 cm deep into the soil before the preplanting irrigation. All herbicides controlled nutsedge for at least 1 month in two or more experiments. Cotton was most tolerant to applications of 2.24 and 4.48 kg/ha of CP-53619, 3.36 and 6.72 kg/ha of prometryne, 1.12 kg/ha of San-6706, and 2.24 kg/ha of methazole. Higher rates of San-6706 and methazole and all rates of alachlor, R-7465, and R-12001 reduced the yield of cotton in one or more experiments.

Yellow nutsedge (Cyperus esculentus L.) produced an average of 1227 and 6685 flowers per inflorescence from eight California fields sampled during 1974, 1975, and 1976. Up to 17% of the flowers produced seeds and up to 78% of the seed germinated. There was a linear relationship between seed weight and germination percentage. Purple nutsedge (C. rotundus L.) averaged between 186 and 1354 flowers per inflorescence from three California fields sampled in 1974 and 1976. Only 43 purple nutsedge seed were collected and none germinated. Yellow nutsedge produced viable seed about 2 weeks after anthesis. A day/night temperature of 38/32 C was best for seed germination, especially when accompanied by a light period. Yellow nutsedge has potential to reproduce by seed, but probability of purple nutsedge reproducing by seed is low.