Thomas A. Bewick

Above- and belowground interference of purple and yellow nutsedge (Cyperus spp.) with tomato

Abstract 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. Nomenclature: Purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES; tomato, Lycopersicon esculentum Mill. ‘Solimar’.

Effect of Age of Cocomposted MSW And Biosolids on Weed Seed Germination

The influence of municipal solid waste (MSW) and biosolids compost maturity on germination of several weed species seeds was evaluated. Ivyleaf morning glory (Ipomoea hederacea L.), barnyard grass (Echinochloa crus-galli L.), common purslane (Portulaca oleracea L.), and corn (Zea mays L.) were selected as plant indicators to determine the compost maturity stage with maximum germination inhibition. Extracts were prepared from immature (three day-old, four week-old, eight week-old), and mature (one year-old) composts. Extract from eight week-old compost decreased percentage germination, root growth, and germination index (a combination of germination percentage and root growth), and increased mean days to germination of each indicator specie. Extract from eight week-old compost was evaluated for effect on germination percentage of 14 economically important weed species. Extract from eight week-old compost inhibited germination of most weed species, except yellow nutsedge (Cyperus esculentus L.) for which tu...

Mechanisms of interference of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) on lettuce as influenced by phosphorus fertility

Abstract Greenhouse studies were conducted to assess the intensity of smooth pigweed and common purslane aboveground interference (AI) and belowground interference (BI) with lettuce and to determine primary mechanisms of interference of each species as affected by P fertility rates. Lettuce was transplanted in mixtures with either smooth pigweed or common purslane according to four partitioning regimes: no interference, full interference, BI, and AI. Soil used was low in P for optimum lettuce yields, therefore P was added at rates of 0, 0.4, and 0.8 grams of P per liter of soil. Shoot and root biomass and plant height were measured for each species, as well as P tissue content. The data obtained indicated that smooth pigweed interfered with lettuce primarily through light interception by its taller canopy. A secondary mechanism of interference was the absorption of P from the soil through luxury consumption, increasing the P tissue content without enhancing smooth pigweed biomass accumulation. In contrast, common purslane competed aggressively with lettuce for P. Because the weed grew taller than lettuce, light interception was a secondary interference factor. Nomenclature: Common purslane, Portulaca oleracea L. POROL; smooth pigweed, Amaranthus hybridus L. AMACH; lettuce, Lactuca sativa L.

Phosphorus absorption in lettuce, smooth pigweed (Amaranthus hybridus), and common purslane (Portulaca oleracea) mixtures

Abstract Greenhouse studies were conducted to determine the influence of phosphorus (P) concentrations on the growth of lettuce, smooth pigweed, and common purslane in monocultures and in mixtures and to determine the P-absorption rate of each species over time. For the P-competition studies, lettuce–smooth pigweed and lettuce–common purslane mixtures were established in P-less hydroponic solutions. Each lettuce–weed mixture was established separately. Concentrations of P were 10, 20, 40, 80, and 160 mg L−1. Lettuce to weed planting proportions were 2:0, 0:2, and 1:1. In the mixtures, biomass of common purslane increased sharply between 10 and 20 mg P L−1, depressing lettuce growth. No biomass changes were observed in smooth pigweed as P concentration increased. However, both weeds increased their P content within this range, depriving lettuce of this nutrient. Common purslane competed for P for its own growth, whereas smooth pigweed absorbed P luxuriously. For the P-absorption studies, roots of lettuce, smooth pigweed, and common purslane plants were submersed in a 20 mg P L−1 solution for 1, 2.5, 5, 10, 20, 40, 60, 90, 180, 360, 720, and 1,440 min. Common purslane was shown to be the most aggressive species for the nutrient, absorbing 50% of the content in 295 min, whereas lettuce and smooth pigweed needed 766 and 825 min to absorb 10 mg P L−1. Nomenclature: Common purslane, Portulaca oleracea L. POROL; smooth pigweed, Amaranthus hybridus L. AMACH; lettuce, Lactuca sativa L.

Effects of Repeat Annual Applications of Dichlobenil on Weed Populations and Yield Components of Cranberry1

To address grower concerns that repeated use of dichlobenil could negatively affect cranberry productivity, field studies were conducted at two commercial farms in either high weed density (HW) or low weed density (LW) areas. Data from 4 yr of repeat annual applications of 0, 1.8, and 4.5 kg ai/ha dichlobenil indicated minimal negative impact on cranberry vines. Herbicide application did not affect upright productivity, leaf biomass production, percent fruit set, or other yield parameters adversely; in addition, no improvement in these parameters was noted. Although the interaction of herbicide application with weed density on cranberry root length varied with sampling date, no consistent trend (adverse or positive) was seen. The presence of weeds, rather than herbicide application, was the important determinant of yield. Vines in LW areas produced more marketable fruit and had higher percentage of fruit set than vines growing in HW areas. Repeat annual applications of dichlobenil on commercial cranberry beds may be considered as part of a viable integrated weed management program with no adverse effect on crop growth or yield. Nomenclature: Dichlobenil; cranberry, Vaccinium macrocarpon Ait. Additional index words: Herbicides, root length, vegetation survey, weed community. Abbreviations: HW, high weed density; LW, low weed density.

Influence of method of phosphorus application on smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) interference in lettuce

Abstract Field trials were conducted to investigate the influence of P application method on the critical period of smooth pigweed and common purslane interference in lettuce. Studies were carried out in low-P histosols, where supplemental P fertilization is needed for lettuce production. Phosphorus was either broadcast or banded 5 cm beneath the lettuce rows at rates of 250 or 125 kg ha−1, respectively. Seedlings of either smooth pigweed or common purslane were transplanted at a density of 16 plants per 5.4 m2 (6-m row by 0.9 m wide). Weed interference duration was achieved by manual removal 2, 4, 6, or 8 wk after lettuce emergence and subsequently keeping the plot weed free until harvest. A weed-free control within each P regimen was also established. Marketable head number, head fresh yield, and head diameter were measured at harvest. Weed-free lettuce fresh yield was 20% higher with banded P than broadcast applications. In the weed–lettuce mixtures, the P regimen by weed removal interaction affected lettuce fresh yield and head diameter but not head number. Compared with broadcast P application, banded P extended the time needed to cause significant weed interference in lettuce by 10 d: from 24 to 34 d for smooth pigweed and from 37 to 47 d for common purslane. Nomenclature: Common purslane, Portulaca oleracea L. POROL; smooth pigweed, Amaranthus hybridus L. AMACH; lettuce, Lactuca sativa L.