Mature Weed Research Articles

The opportunities and challenges for harvest weed seed control (HWSC) in India: An opinion

Weeds which are escaped during the control measures are one of the source of soil weed seedbank. At the time of crop harvest, several weed species retain a considerable quantity of their seed. These weed seeds are evenly spread across the crop field through various weed seed dispersal mechanisms. By knowing the weed seed retention character of every weed species, their effective weed control can be achieved by the collection and/or destruction of weed seeds during crop harvest using harvest weed seed control (HWSC) methods. Narrow windrow burning, chaff tramlining, chaff carts, chaff lining, the Harrington seed destructor (HSD) and the bale direct system are common HWSC procedures. The crop harvest is a primary contributor to the transmission of weed seeds over the crop fields and with HWSC, we can now skip this process and prevent weed seed spread. This strategy is useful to target weed species that retain a large part of their seed after maturity and was found highly effective in controlling the spread of herbicide resistant weed seeds. HWSC aims to prevent the mature weeds seed from entering the seedbank. Through HWSC, we can prevent the enrichment of soil weed seedbanks and deplete existing soil weed seedbanks in long run. In India, the scope for HWSC is high in organic farming, direct-seeded rice, zero-till wheat, herbicide tolerant rice and high intensive irrigated agriculture while its scope is much limited in rainfed agriculture. However, the efforts on using HWSC are yet to begin in India and should be initiated.

Managing cool‐season turfgrass without herbicides: Optimizing maintenance practices to control weeds

AbstractBans on the use of synthetic herbicides require innovative management approaches to maintain the attractiveness and usability of turfgrass swards. Such measures should include the use of locally adapted cultivars that germinate and establish quickly, resulting in the densest possible stands. Additionally, a number of turfgrasses have been reported to produce allelopathic substances that inhibit common turfgrass weeds. Mowing heights should be set to achieve maximum weed suppression while still providing acceptable quality for desired use. Sustainable turfgrass management programs have led to a reduction in fertilizer inputs; however, without the availability of herbicides, fertilization regimes need to be re‐examined. The literature suggests that broadleaf weeds are reduced but never fully controlled when more N is applied; therefore, finding a balance between what is needed and what is environmentally safe and sustainable is critical. Organic herbicides include plant pathogens from the fungus Phoma and strains of the bacterium Pseudomonas fluorescens. Both can be used to control several weeds common to turfgrasses. Acetic acid has also been shown to have herbicidal activity; however, it has limited residual activity, and its efficacy remains questionable on mature weeds. Thermal weed control can be used to sterilize a seedbank or spot treat existing weeds. Future turfgrass breeding programs could focus on understanding and enhancing the allelopathic potential of turfgrasses to outcompete weeds more effectively. Furthermore, more research should be directed at assessing the competitiveness of certain turfgrasses against weeds within the limitations of producing turfgrass areas of acceptable aesthetics and playing quality.

Biology of Galerucella placida Baly (Coleoptera: Chrysomelidae) on the Rice-Field Weed Polygonum orientale L. (Polygonaceae)

Galerucella placida Baly (Coleoptera: Chrysomelidae) is a promising biocontrol agent of the rice-field weed Polygonum orientale L. (Polygonaceae) in India and Bangladesh. The longevity of G. placida adults was related with nutrients and antinutrients of young, mature and senescent leaves of P. orientale. Mature leaves of P. orientale had higher level of nutrients (carbohydrates, proteins, lipids, nitrogen and amino acids) and lower level of antinutrients (phenols and flavonols) compared to young and senescent leaves. Higher level of carbohydrates, proteins, lipids, nitrogen, amino acids including water content, and lower phenol and flavonol content of mature leaves had influenced higher survival of G. placida. Total larval developmental and pupal periods were 26.27 ± 0.45 SE and 7.06 ± 0.17 SE days on mature weed leaves, respectively; whilst adult males and females lived for 52.15 ± 0.33 SE and 58.0 ± 0.38 SE days on mature leaves, respectively. Fecundity of individual G. placida was 133.3 ± 3.2 SE eggs during life time. The net reproductive rate, generation time, intrinsic rate of increase, finite rate of increase and doubling time were 66.675, 27.5376, 0.1525, 1.2502 and 4.5452 days, respectively, under laboratory conditions (27 ± 0.5 °C, 12L:12D photoperiod, 65 ± 5% RH).

Seed bank dynamics and emergence pattern of weeds as affected by tillage systems in dry direct-seeded rice

The vertical weed seed distribution in the soil and the emergence pattern of weeds have implications for weed management in different cropping systems. Various agronomic practices have been reported to influence these factors, and tillage has a great role to play in weed management strategies. The effect of conventional tillage (CONT) and zero tillage (ZT) on the distribution of weed seeds in the soil, and the emergence pattern of different weed species was evaluated in dry direct-seeded rice in the summer (kharif) seasons of 2012 and 2013. The ZT system resulted in a higher proportion of weed seeds in 0–2 cm of the soil layer at the time of crop sowing, with 48–52% of broadleaved and 45–55% of grassy weed seeds; whereas, CONT had weed seeds buried in deeper layers, with 47–48% of broadleaved and 50–55% of grassy weed seeds in the lowermost layer (5–10 cm). At crop harvest, both tillage systems showed higher proportions of weed seeds in the upper 2 cm of the soil layer; however, this was due to seed shedding of mature weeds on the soil surface. The maximum emergence of Cyperus rotundus and Echinochloa colona was 33–42% and 20–26% higher in ZT than CONT. In 2012, Cyperus compressus emergence in ZT exceeded CONT by 65%, whereas Echinochloa crus-galli and Dactyloctenium aegyptium emerged 22% and 52% more in the CONT system than ZT. The emergence pattern of Digitaria ciliaris was not influenced by tillage systems. The information from this study will facilitate better decision making in weed management through the integration of tillage systems and other weed control measures in dry direct-seeded rice.

High Seed Retention at Maturity of Annual Weeds Infesting Crop Fields Highlights the Potential for Harvest Weed Seed Control

Seed production of annual weeds persisting through cropping phases replenishes/establishes viable seed banks from which these weeds will continue to interfere with crop production. Harvest weed seed control (HWSC) systems are now viewed as an effective means of interrupting this process by targeting mature weed seed, preventing seed bank inputs. However, the efficacy of these systems is directly related to the proportion of total seed production that the targeted weed species retains (seed retention) at crop maturity. This study determined the seed retention of the four dominant annual weeds of Australian cropping systems - annual ryegrass, wild radish, brome grass, and wild oat. Beginning at the first opportunity for wheat harvest and on a weekly basis for 28 d afterwards the proportion of total seed production retained above a 15 cm harvest cutting height was determined for these weed species present in wheat crops at nine locations across the Western Australian (WA) wheat-belt. Very high proportions of total seed production were retained at wheat crop maturity for annual ryegrass (85%), wild radish (99%), brome grass (77%), and wild oat (84%). Importantly, seed retention remained high for annual ryegrass and wild radish throughout the 28 d harvest period. At the end of this period, 63 and 79% of total seed production for annual ryegrass and wild radish respectively, was retained above harvest cutting height. However, seed retention for brome grass (41%) and wild oat (39%) was substantially lower after 28 d. High seed retention at crop maturity, as identified here, clearly indicates the potential for HWSC systems to reduce seed bank replenishment and diminish subsequent crop interference by the four most problematic species of Australian crops.

Weed Control in Sugarbeet

Weeds left in beet crops can make harvesting more difficult and costly, interfere with clamping and affect processing if taken into the factory. Mature weeds shed seed to add to the soil bank and germinate in subsequent crops. Most importantly, severe yield penalties can result from a failure to control weeds. In the last three decades, herbicide and weed control developments have made a significant contribution to the increase of average sugar beet yields. In the 1990s, the reduced use of herbicides has become a necessity in order to limit environmental pollution and to safeguard human health. As a consequence, in the last years, the general trend of the crop is to achieve a gradual reduction in doses applied in pre and post-emergence by using several blends of products to valorize their synergy effects. The reduction of the use of herbicides can be obtained replacing herbicide treatments with revaluation of agronomic techniques and minimizing the dose rate of herbicides. In this way weed control involve chemical and non-chemical strategies in the integrated weed management. This system offers the potential to reduce but not to replace the use of herbicides in sugar beets on larger scale basis.

Site-specific herbicide applications based on weed maps provide effective control

More-effective weed control in agricultural fields can be achieved by utilizing information about the spatial distribution of the previous year's mature weeds. In our study, variable-rate herbicide applications based on weed infestation maps developed just before the previous year's harvest provided effective weed control. The results showed that when information about the spatial distribution of the previous year's weed seedlings or mature weeds was used, weed control was comparable to uniform, one-rate, herbicide applications, while the total amount of herbicide applied decreased. Herbicide use was reduced an estimated 39% for the seedling map and 24% for the mature map approach. However, incorporating the weed-seed redistribution from harvest to application time into the treatment maps could further improve weed control.

Controle químico de Brachiaria decumbens em pastagem de Cynodon dactylon híbridos Coast-cross e Tifton 85

Aiming at the control of the Brachiaria decumbens in degraded pastures of the Coast-Cross and Tifton 85 hybrids (Cynodon dactylon), two experiments were carried out, each one for each forage, where increasing doses of the commercial mixture diuron/ MSMA and one dose of MSMA were applied. The randomized block experimental design was used with seven treatments and four replicates. The plots were 6m long and 4m wide. The treatments were applied on the total area and on mature weeds. The diuron / MSMA mixture at the dose of 1120 + 2880 g/ha, respectively, provided efficient control (90%) of B. decumbens at 42 DAA. MSMA at the dose of 2880 g/ha was not effective in controlling B. decumbens over the appraised period, since its control was lower than 70% from 14 to 42 DAA. Diuron / MSMA at the dose of 1120 + 2880 g/ha and MSMA at the dose of 2880 g/ha provided light injuries in C. dactylon hybrids from 7 to 14 DAA, that disappeared at 30 DAA and not affected the development of the forages, so making possible a fast reestablishment of the pasture.

Infestation and spatial dependence of weed seedling and mature weed populations in corn

Abstract Knowing the distribution of weed seedlings in farmer-managed fields could help researchers develop reliable distribution maps for site-specific weed management. With a knowledge of the spatial arrangement of a weed population, cost effective sampling programs and management strategies can be designed, so inputs can be selected and applied to specific field areas where management is warranted. In 1997 and 1998, weeds were sampled at 612 to 682 sites in two center pivot irrigated corn fields (71 and 53 ha) in eastern Colorado. Weeds were enumerated when corn reached the two-leaf, four-leaf, and physiological maturity stages in a 76.2- by 76.2-m grid, a random-directed grid where sites were established at intervals of 76.2 m, and a star configuration based on a 7.62- by 7.62-m grid within three 23,225 m2 areas. Directional correlograms were calculated for 0, 30, 60, 90, 120, and 150° from the crop row. Fifteen weed species were observed across fields. Spatial dependence occurred in 7 of the 93 sampl...

Host Preferences and Reproduction of Four Cereal Aphids (Hemiptera: Aphididae) on Some Common Weed Grasses of the Northern Plains1

We tested preferences and reproduction of the greenbug, Schizaphis graminum (Rondani), English grain aphid, Macrosiphum (Sitobion) avenae (F.), Rhopalosiphun padi (L.), and the com leaf aphid, R. maidis (Fitch) on the seedling and mature stages of the following weed grasses under controlled conditions in environmental chambers: Japanese chess, Sromas japonieus Thunb.; downy brome, B. feeforum L.; Kentucky bluegrass, Poa prafensis L.; stinkgrass, Eragrostis cilianensis (All.) Lutati; quackgrass, Agropyron repens (L.) Beauv.; wild oats, Avenafaluu L.; timothy, Phleum pratense L.; crabgrass, digitaria sanguinalis Scop.; barnyard grass, Echinoehloa crasgalli (L.) Beauv.; yellow foxtail, Setaria latescens (Weigel) Hubb.; green foxtail, S. viridis (L.) Beauv.; foxtail barley, Hordeum jubatum L.; needle and thread, Stipa comatu Trin. and Rupr.; green needlegrass, S. viridula Trin.; and witchgrass, Panieum capillare L. In the preference tests, three to five species of the grasses were as attractive (P < 0.05) to alighting aphids as the control, Hordeum vulgare L. Cereal aphid reproduction was generally higher on seedling than mature grasses. Rhopalosipham padi at least doubled its numbers in I week on II seedling and 13 mature weed grasses, whereas R. muidis did so on four seedling and three mature grasses; the other aphid species ranged between these extremes in their adaptability. Correlation coefficients showed that aphid preferences for particular grasses and their reproductive success when confined on them were often closely related.