Critical periods of weed competition in cotton in Greece

Four experiments were conducted in central Greece during 1997 and 1998 to determine the late-season presence of weeds in cotton (Gossypium hirsutum L.) and the critical times for removing weeds. Experiments were conducted in natural, heavily infested cropland. The presence of weeds for more than 3 weeks after crop emergence caused significant reductions in crop growth and lint yields. However, weeds that emerged 11 weeks or more after crop emergence did not adversely impact yields. Total weed biomass increased with increasing time prior to weed removal. A weed-free period of 11 weeks after crop emergence was needed to prevent significant reductions in cotton height, biomass, number of squares, and yield. These results indicated that postemergence herbicides or other control measures should be initiated within 2 weeks after crop emergence to avoid significant yield reduction. For greater efficiency, soil-applied herbicides in cotton should provide effective weed control for at least 11 weeks. Curvilinear regression equations were derived to describe the relationship between critical periods of weed presence and cotton growth and fruit development.     

Critical period for weed control in sesame production

Planning effective weed control in cropping systems requires exact appraisal of the weed intensity and duration of their competition with the crops. This 2‐year study was carried out in order to determine the critical weed control period in sesame fields. Related and relative crop yields were monitored and analyzed using a four‐parametric log‐logistic model. We recorded data from weed‐free plots and compared these with data from different periods of weed interference. In both the study years, the longer period of weed interference decreased the relative yield of sesame, whereas the yield was increased with increasing duration of the weed‐free period. A 51–78.7% decline in sesame yield was noted if the weeds were allowed to compete with the crop from planting to harvest. In the first year, the duration of the critical period for weed control (CPWC) was 177–820 growing degree days (GDD), which corresponded to 14–64 days after crop emergence (DAE), and between 170 and 837 GDD (13–64 DAE) in the second year; this was based on a 5% acceptable yield loss. The results of this study clearly elaborated that maintaining weed‐free conditions is compulsory from as early as the second week after the emergence of sesame plants, and this should be maintained at least until the ninth week to avoid sesame yield losses by more than 5%. These findings show that growers can benefit from CPWC to improve weed control in sesame production, including the efficacy of a weed control program and its cost.     

Critical period of weed interference in chickpea

The critical period of weed interference in one variety of chickpea was determined in field experiments carried out at two sites, Tabriz 2002 and Kermanshah 2003, Iran. Chickpea culture was either kept free of weeds for 0, 12, 24, 36, 48 and 60 days after crop emergence (DAE) or weeds were allowed to grow for 0, 12, 24, 36, 48 and 60 DAE. In these experiments, chickpea yield increased with increasing duration of weed-free period and was reduced by increasing duration of weed-infested period. Unweeded conditions for the entire growing season caused 66.4% and 48.3% seed yield reduction when compared with the treatment that was weed-free throughout the growing season, at Tabriz 2002 and Kermanshah 2003, respectively. The results indicated that chickpea must be kept weed-free between the five-leaf and full flowering stages (24–48 DAE) and from the four-leaf to beginning of flowering stages (17–49 DAE) at the two sites, respectively, in order to prevent >10% seed yield loss. At both sites, reduction in seed yield, because of the increased weed interference period, was accompanied by simultaneous reduction in plant dry weight, number of branches, pods per plant and 100-seed weight. This was supported by significant and positive correlations between these traits and chickpea seed yield. There was no significant correlation between the number of seeds per pod and seed yield. A linear regression model was used to describe the relationship between weed dry weight and seed yield loss.     

Critical period for weed control in direct seeded red pepper (Capsicum annum L.)

Direct seeded red pepper is a cash crop in Kahramanmara? province of Turkey as well as some other nearby provinces. Weeds are a major constraint in red pepper production. Field studies were conducted to determine critical period for weed control (CPWC) in direct seeded spice pepper in Kahramanmara?, in 2008 and 2009. The CPWC in red pepper based on a 2.5%, 5% and 10% acceptable yield loss (AYL) was calculated by fitting logistic and Gompertz equations to relative yield data. The CPWC in red pepper was determined from 0 to 1087 growing degree days (GDD) in 2008 and from 109 to 796 GDD in 2009 for 10% AYL after crop emergence in red pepper. For 2.5–5% AYL, the CPWC starts with germination and lasts until harvest. Direct seeded red pepper is very vulnerable to weed competition and weed control programs for direct seeded spice pepper in Turkey should include pre‐emergence and residual herbicides.     

耕作方式对夏玉米地杂草关键无草期的影响

在河北省夏玉米地调查了免耕地和常规翻耕地条件下杂草出苗和发生的情况,比较了这两种耕作方式的关键无草期。免耕地杂草出苗较常规耕地略有延后,但很快便趋于一致,两种耕作方式下杂草结束出苗的时间没有区别。耕作方式对夏玉米地关键无草期没有影响,在免耕和翻耕两种耕作方式下,玉米相对产量(RY)和苗后无草期(T)的模型为:RY=98.93×exp[-0.1439×exp(-0.04031×T)],关键无草期均为玉米苗后31d。     

The use of fomesafen for pre-emergence weed control in cotton

The herbicide fomesafen was found to be selective in preplanting and pre-emergence treatments in cotton (Gossypium hirsutum L.). It was effective due to residual soil activity in controlling some of the most troublesome weeds in cotton fields,i.e., pigweed (Amaranthus spp.), black nightshade (Solarium nigrum L.), velvetleaf (Abutilon theophrasti Medik.) and cocklebur (Xanthium spp.). The best soil activity of fomesafen was achieved from pre-emergence or preplanting applications which were activated when the soil was wetted by rain or sprinkler irrigation, but the herbicide caused damage to the crop’s foliage if rain fell just after the cotton emergence. The most effective and safest method for applying fomesafen in cotton fields was preplanting followed by mechanical incorporation to a depth of 10 cm. Combinations of fomesafen with trifluralin were effective and completed the spectrum of controlled weeds in cotton, including annual grasses, common purslane (Portulaca oleracea L.) and field bindweed (Convolvulus arvensis L.).     

Critical periods for weed competition

Abstract

BIOCHEMICAL INSECT CONTROL: ITS IMPACT ON ECONOMY, ENVIRONMENT AND NATURAL SELECTION. M. Sayeed Quraishi. John Wiley and Sons, New York, 1977. ISBN 0 471 70275 7. Pp. viii + 280. Price £14.25, US $24.50.

DISEASES, PESTS AND WEEDS IN TROPICAL CROPS. Edited by Jürgen Kranz, Heinz Schmutter and Werner Koch. Verlag Paul Parey, Berlin and Hamburg, 1977. ISBN 3 489 67626 8. Pp. xv + 666, Colour plates 64. Price Dm. 68.

ENVIRONMENTAL TOXICOLOGY. A GUIDE TO INFORMATION SOURCES. Edited by R. L. Rudd. Gale Research Company, Detroit, 1977. ISBN 0 8103 13421. Pp. xii + 266. Price US $18.00

THE SAFETY OF THE HERBICIDES 2,4-D AND 2,4.5-T. D. J. Turner. Her Majesty's Stationery Office, London, 1977. ISBN 0 11 710149 4. Pp. 56. Price £1.20

PESTICIDE CHEMISTRY IN THE TWENTIETH CENTURY. Edited by J. R. Plimmer. ACS Symposium Series No. 37, American Chemical Society, Washington, USA, 1977. ISBN 0 8412 0364 4. Pp. 310. Price US $20.00

PESTICIDES IN AQUATIC ENVIRONMENTS. Edited by M. A. Q. Khan. Environmental Research Series, Volume 10. Plenum Press, New York and London, 1977. ISBN 0306 36310 0. Pp. xiii + 257. Price US $35.40, £18.75

THE FUTURE FOR INSECTICIDES. Edited by Robert L. Metcalf and John J. McKelvey Jr. John Wiley and Sons, New York, 1976. ISBN 0 471 59860 7. Pp. xiv + 524. Price £14.70, US $30.20

SYNTHETIC PYRETHROIDS. Edited by Michael Elliott. ACS Symposium Series No. 42, American Chemical Society, Washington, D.C., 1977. ISBN 0 84120368 7. Pp. xi + 229. Price £15.75

WEED CONTROL HANDBOOK. Volume 1, Principles, Edited by J. D. Fryer and R. J. Makepeace. Sixth Edition. Blackwell, London, 1977. ISBN 0632 00209 3. Pp. xvii + 510. Price £13.50

A PARTIAL BIBLIOGRAPHY OF WEED RESEARCH AND CONTROL: PUBLICATIONS FOR SOUTH AND CENTRAL AMERICA, THE CARIBBEAN AND MEXICO, 1942–1976. Second Edition. International Plant Protection Center, Oregon, USA, 1978. Pp. xiii + 241. Price US $5.00

MAJOR INSECT AND MITE PESTS OF AUSTRALIAN CROPS. E. Hassan, Ento Press, Queensland, Australia. ISBN 0 959 6962 88. Pp. 236.

THE BIOLOGY OF TRIBOLIUM, WITH SPECIAL EMPHASIS ON GENETIC ASPECTS, Volume 3. A. Sokoloff. Oxford University Press, Oxford, 1977. ISBN 0 19 857512 2. Pp. xix + 612. Price £25.00

TOOLS FOR AGRICULTURE. A buyer's guide to low-cost agricultural implements. Compiled by John Boyd. Intermediate Technology Publications Ltd., London, 1976. ISBN 0 903031 22 1. Pp. 173. Price £4.00

SEED PATHOLOGY. (Volumes I and II). Paul Neergaard. MacMillan Press Ltd., London, 1977. ISBN 0 333 19273 7. Pp. 1187. Price £50.00

CONTROL OF TROPICAL AQUATIC WEEDS. A. H. Pieterse. Bulletin 300, Department of Agricultural Research of the Royal Tropical Institute, Amsterdam, 1977. Pp. 20.     

黄河三角洲地区棉田杂草组成及其群落特征

采用倒置"W"九点取样法对黄河三角洲棉田杂草种类及其群落结构进行了调查,并进行物种多样性分析。结果表明:黄河三角洲棉田杂草有61种,隶属于19科、47属,其中菊科杂草最多,有13种;其次是禾本科,有9种。优势杂草有马唐、芦苇、马齿苋、牛筋草、鳢肠、打碗花、藜、稗、铁苋菜和白茅10种,区域性优势杂草有6种,常见杂草3种,一般杂草42种。从区域分布来看,垦利、广饶、河口等地杂草丰富度指数、香农指数、辛普森指数、均匀度指数普遍较高。从聚类分析结果来看,该地区棉田杂草群落变化与空间距离、地理环境、种植模式等因素有密切关系。东营和利津两区县聚类分析的欧氏距离最小,为10.5;黄河南岸的高青和黄河三角洲其他县区之间欧氏距离最大,为23.4。     

Site-specific weed control technologies

Site-specific weed control technologies are defined as machinery or equipment embedded with technologies that detect weeds growing in a crop and, taking into account predefined factors such as economics, take action to maximise the chances of successfully controlling them. In this study, we describe the basic parts of site-specific weed control technologies, comprising weed sensing systems, weed management models and precision weed control implements. A review of state-of-the-art technologies shows that several weed sensing systems and precision implements have been developed over the last two decades, although barriers prevent their breakthrough. Most important among these is the lack of a truly robust weed recognition method, owing to mutual shading among plants and limitations in the capacity of highly accurate spraying and weeding apparatus. Another barrier is the lack of knowledge about the economic and environmental potential for increasing the resolution of weed control. The integration of site-specific information on weed distribution, weed species composition and density and the effect on crop yield, is decisive for successful site-specific weed management.     

Barley seed vigour and mechanical weed control

Two field experiments investigated the influences of crop seed vigour on the effect of weed harrowing and crop:weed interactions in spring barley. Artificially reduced seed vigour, which was similar to the variation within commercial seed lots, caused a reduction in germination rate, delayed time of emergence and, consequently, caused reduced competitive ability against weeds. During both years, the reduced seed vigour increased the average weed biomass by 169% and 210%, and reduced the average crop yield by 16% and 21%. Without the influence of weeds, the yield reduction was estimated to be 8% and 10%. A three‐times harrowing strategy reduced the weed biomass by 75% and 72% on average. However, it also caused damage to the crop and reduced yield. There was no clear interaction between barley seed vigour and weed harrowing in the experiments but, in one year, reduced seed vigour tended to decrease the effect of weed harrowing and also increased crop damage. Results in both years, however, indicate potential possibilities for successful integrated weed control by adding the use of high seed quality to a weed harrowing strategy.     

铲除田埂杂草带对棉蚜防治效果的影响

通过对新和县1999、2002两年冬季铲除田埂杂草带棉田棉花卷叶率变化情况的观测,研究铲除田埂杂草对棉砾的防治效果。结果表明:苗期、蕾期防治效果可以达到70%～90%,棉花卷叶率下降3.35～16.83倍(P<0.05)。棉蚜越冬和早春迁飞与田埂上的杂草有关可能是这项技术有效的原因。     

Critical period of weed control in transplanted chilli pepper

Summary Field experiments were conducted from 1991 to 1993 to determine the critical period of weed control in chilli pepper. The maximum weed-infested period ranged between 0.7 and 3.2 weeks after transplanting (WAT) at a 5% yield loss level. To prevent losses in total and marketable yields, weeds should be removed 2.1 or 0.9 WAT respectively. The end of the critical period decreased as the predetermined yield loss level increased from 2.5% to 10%. The minimum weed-free period ranged between 6.7 and 15.3 WAT at a 5% yield loss level depending on crop yield category. The chilli pepper crop required an average of 12.2 weeks of weed-free maintenance to avoid losses above 5%. Using a 5% yield loss level, the duration of the critical period of weed control was 14 weeks in 1991 and 11.2 weeks in 1993, but was shortened to 5.1 weeks in 1992. The results suggest that weeds must be controlled during the first half of the crop's growing season in order to prevent yield losses.     

Herbicide options for weed control in papaya

This paper reviews the literature on weeds and weed control in papaya. There is limited research on this topic, and nearly all of the research focuses on herbicides. Effective use of paraquat and glyphosate in papaya is dependent on avoidance of spray contact to green bark and foliage. Pre-emergence herbicide tolerance is dependent on papaya age, size and maturity, and soil type. Only one herbicide, oryzalin is shown to be tolerated by papaya immediately after transplanting. Herbicides such as diuron and oxyfluorfen with a broader spectrum of weed control generally injure young papaya, however they can be effectively used if the initial application of these herbicides is delayed until papaya attains certain size or maturity indices. There is a need for further research on weeds and weed control to improve the efficiency of papaya production     

几种封闭除草剂两个时期用药效果对比及其交互作用分析

通过田间小区试验评价了前期筛选的几种适用“播喷同步”的封闭除草剂对水稻的安全性及对直播田杂草的防效, 明确了“播喷同步”技术与常规播后4 d封闭的差异, 以及施药时期×除草剂种类交互作用及对控草效果的影响, 优化水稻直播田杂草防控策略?试验结果表明, 播种当天(播喷同步)或播种后4 d(常规方法)喷施120 g/L噁草酮EC 360 g/hm2+10%苄嘧磺隆WP 30 g/hm2(有效剂量, 下同)?33%嗪吡嘧磺隆WG 74.25 g/hm2+300 g/L丙草胺EC 450 g/hm2?60%丁草胺EC 1 350 g/hm2+10%吡嘧磺隆WP 30 g/hm2?35%吡嘧·嘧草·丙OD 525 g/hm2?300 g/L丙草胺EC 450 g/hm2+10%苄嘧磺隆WP 30 g/hm2, 5组除草剂处理对直播稻均无可见药害, 各“播喷同步”处理的杂草防除效果不低于常规播后4 d用药; 同步喷施33%嗪吡嘧磺隆WG+300 g/L丙草胺EC防效最高, 药后35 d对禾本科?莎草科?阔叶草防效达到98.3%及以上; 水稻直播4 d后喷药, 水稻成苗率提高但 35 d 的禾本科杂草防效低, 33%嗪吡嘧磺隆WG+300 g/L丙草胺EC处理受喷药时间影响小; 复合双因子方差分析表明, 单一因子会对水稻安全性?杂草防效产生显著影响, 用药时期×除草剂种类交互对水稻安全性无显著影响, 对控草效果影响显著?因此, 直播田封闭除草剂宜尽早施药提高防治效果, 同时应选用安全高效的除草剂, 33%嗪吡嘧磺隆WG+300 g/L丙草胺EC处理, 可于播种当天到播种后4 d内用药, 保障直播田杂草防治效果的同时兼顾水稻安全?     

皖西南直播棉田杂草群落出苗模式

为明确皖西南直播棉田杂草群落出苗模式及其与气象因子的相关性,采用定点定时调查法,于2010—2012年对棉田杂草种类、数量及群落结构进行调查,分析物种多样性,并以灰色关联度法分析直播棉田杂草群落出苗数量与气象因子的相关性。结果表明,皖西南棉区直播棉田杂草种类有13科24种。棉田杂草出苗有2次高峰,分别在5—6月和8—9月。棉田杂草群落多样性指数年度间变化较一致,但物种丰富度变化较大。周积温、周最高积温和周最低积温是影响皖西南直播棉田杂草群落出苗数量季节变化的主要因素,另外还受降水量影响。5—6月的杂草出苗高峰期是棉田杂草重点防治时期;相对占优势的杂草有牛筋草、千金子、旱稗、通泉草和马齿苋,是棉田杂草重点防治对象。     

Advancing cover cropping in temperate integrated weed management

The effects of cover crops on weeds and the underlying mechanisms of competition, physical control and allelopathy are not fully understood. Current knowledge reveals great potential for using cover crops as a preventive method in integrated weed management. Cover crops are able to suppress 70–95% of weeds and volunteer crops in the fall‐to‐spring period between two main crops. In addition, cover crop residues can reduce weed emergence during early development of the following cash crop by presenting a physical barrier and releasing allelopathic compounds into the soil solution. Therefore, cover crops can partly replace the weed suppressive function of stubble‐tillage operations and non‐selective chemical weed control in the fall‐to‐spring season. This review describes methods to quantify the competitive and allelopathic effects of cover crops. Insight obtained through such analysis is useful for mixing competitive and allelopathic cover crop species with maximal total weed suppression ability. It seems that cover crops produce and release more allelochemicals when plants are exposed to stress or physical damage. Avena strigose, for example, showed stronger weed suppression under dry conditions than during a moist autumn. These findings raise the question of whether allelopathy can be induced artificially. © 2019 Society of Chemical Industry     

Some Preliminary Findings on the Value of Granular Nematocides for Improving Banana Production in the Windward Islands

Abstract

Granular applications of prophos 5 g a.i., phenamiphos 3 g a.i., carbofuran 2.5 g a.i. and oxamy! 6 g a.i. to bananas in the planting holes and subsequent surface applications at 2, 6, 10, 14 and 18 months after planting have given good nematode control as compared with a standard DBCP (dibromochloropropane) (75% e.c.) application of 11.23 l/ha (5.7 cc per plant) every six months and untreated plots. Although the differences in plant crop yields are not statistically significant the production cycle of the granular nematocide treatments was 23–30 days faster than that of control and DBCP treatments. Production data from the ratoon crop indicates a similar pattern.     

Agronomic practises for weed control in turmeric (Curcuma longa L.)

Weeds are the main problem with turmeric (Curcuma longa L.) cultivation where herbicides are not allowed. This is because herbicides cause water contamination, air pollution, soil microorganism hazards, health hazards, and food risks. Considering turmeric's medicinal value and the environmental problems caused by herbicides, various agronomic practises have been evaluated for non‐chemical weed control in turmeric. One additional weeding is required before turmeric emergence and weed infestation is much higher when turmeric is planted in February and March, as compared to April, May or June planting. A similarly higher yield of turmeric is achieved when it is planted in February, March, and April, compared to late plantings. Weed emergence and interference are not affected by planting depth, seed size, planting pattern, planting space, ridge spacing, and the row number of turmeric until 60 days after planting. This is because turmeric cannot develop a canopy structure until then. Thereafter, weed infestation reduces similarly and significantly when turmeric is planted at depths of 8, 12, and 16 cm, compared to shallower depths. The yield of turmeric at these depths is statistically the same, but the yield for the 16 cm depth is difficult to harvest and it tends to decrease. Turmeric grown from seed rhizomes (daughter rhizomes) weighing 30–40 g reduces weed infestation significantly and obtains a significantly higher yield compared to smaller seeds. The mother rhizome also can suppress weed infestation and increase the yield markedly. Around 9% weed control and 11% higher yield are achieved by planting turmeric in a triangular pattern compared to a quadrate pattern. The lowest weed infestation is found in turmeric grown in a 20 or 30 cm triangular pattern and the highest yield is obtained with the 30 cm triangular pattern. Turmeric gown on two‐row ridges spaced 75 cm apart shows excellent weed control efficiency and obtains the highest yield. This review concludes that turmeric seed rhizomes of 30–40 g and/or the mother rhizome could be planted in a 30 cm triangular pattern at the depth of 8–12 cm on two‐row ridges spaced 75–100 cm apart during March to April in order to reduce weed interference and obtain a higher yield. Mulching also suppresses weed growth and improves the yield. The above agronomic practises could not control weeds completely; biological weed management practises could be integrated in turmeric fields using rabbits, goats, sheep, ducks, cover crops or intercrops.     

Implications of delayed Echinochloa spp. germination and duration of competition for integrated weed management in water-seeded rice

Summary Co-ordinating herbicide applications with the suppressive ability of the crop has the potential to improve weed control and optimize herbicide use in water-seeded rice. However, the successful integration of herbicide applications and crop development depends on the timing and duration of competition between rice and weeds. The critical period of competition between rice and Echinochloa species was examined in field and glasshouse experiments from 1996 to 2000. In 1999 and 2000, Echinochloa species seeded 30 days after rice in field experiments did not survive and rice yields were not reduced when plots were kept weed-free for 30 days or longer. In a basin experiment conducted in 1998, E. phyllopogon seeded with the crop was unaffected by light competition alone but the relative importance of shading by the crop increased when E. phyllopogon was seeded after rice. Management strategies that delay the germination or growth of Echinochloa species might confer a competitive advantage to rice and reduce the need for herbicide applications. However, yields in the field experiments were reduced by at least 18% after only 30 days of competition in both years, suggesting that it may be difficult to integrate currently available herbicides with crop growth in water-seeded rice.