Recovery of Pantoea ananatis, causal agent of center rot of onion, from weeds and crops in Georgia, USA

Center rot of onion, caused by Pantoea ananatis, has been a problem of sweet onions in Georgia since 1997. A polymerase chain reaction (PCR) protocol was developed to screen for populations of P. ananatis on plant surfaces. Plant samples producing a positive PCR reaction were targeted for further processing to culture the bacterium. In a survey of the Vidalia onion-growing region of Georgia, we detected and cultured P. ananatis from 25 asymptomatic weed species, which included commonly occurring weeds such as crabgrass (Digitaria sanguinalis), Florida beggarweed (Desmodium tortuosum), Florida pusley (Richardia scabra), sicklepod (Cassia obtusifolia), Texas Millet (Panicum texanum), tall verbena (Verbena bonariensis) and yellow nutsedge (Cyperus esculentus). In addition, the bacterium was recovered from crop plants such as Bermuda grass (Cynodon dactylon), cowpea (Vigna unguiculata) and soybean (Glycine max). Based on the field survey and tests with strains held in storage in the Coastal Plain Experiment Station culture collection, we concluded that P. ananatis was in Georgia prior to 1997, and was distributed widely on weeds and crops throughout southern Georgia.     

Response of weeds and soil microorganisms to imazaquin and pendimethalin in cowpea and soybean

Herbicides applied to combat weeds and increase crop yields may also have undesired effects on beneficial soil microorganisms. Field studies were conducted in 2005 and 2006 in Zaria, Nigeria, to evaluate the response of weeds and soil microorganisms to imazaquin applied at 0.05, 0.10, 0.20 and 0.40 kg a.i./ha and pendimethalin applied at 1.0, 2.0, 4.0, and 8.0 kg a.i./ha in cowpea and soybean. Hoe-weeded and unweeded (no herbicide) plots were controls. Both herbicides significantly reduced weed biomass in both crops, when compared to the unweeded control, which had the highest weed biomass at all sampling dates. Treatments with 0.40 kg a.i./ha of imazaquin, 2.0 and 4.0 kg a.i./ha of pendimethalin, and the hoe-weeded control, had the highest cowpea grain yield. The unweeded control had the lowest grain yield which was comparable to that in all other herbicide treatments. All treatments except 4.0 and 8.0 kg a.i./ha of pendimethalin had higher soybean grain yield than the unweeded control. Soybean yield was lowest in the unweeded control, and treatments that received 4.0 and 8.0 kg a.i./ha of pendimethalin. All rates of imazaquin gave similar soybean grain yields that were 29–41% higher than that from pendimethalin. The hoe-weeded control had the highest yield, which was 79% more than that in the unweeded control. Higher rates of imazaquin and pendimethalin reduced nodulation, nitrogen fixation, and vesicular arbuscular mycorrhizal (VAM) fungi colonisation in both crops. VAM fungi species diversity and species richness in cowpea rhizosphere soil and species diversity in soybean rhizosphere soil were reduced relative to the controls due to application of both herbicides with the rates of 0.10, 0.20, and 0.40 kg a.i./ha of imazaquin and 8.0 kg a.i./ha of pendimethalin being significantly effective.     

苏北垦区豆田杂草生长为害习性

苏北垦区豆田杂草分属15科,36属,41种,恶性杂草有稗,苍耳等9种。在大豆整个生育期间通常出现1～2个萌发高峰,主要集中在6月中旬～7月下旬。杂草种子于8～10月成熟。种子在土壤中的埋深及出苗期,直接影响杂草的出苗和繁殖。杂草与大豆的相互竞争,以在大豆播种一个月后最为剧烈。0～2cm和6～25cm耕层中贮葳的杂草种子最多。     

Evaluation of various methods of weed control for increasing rhubarb yields

Four herbicides, monthly handweeding and a 15 cm deep straw mulch were evaluated for weed control during 1982 to 1987 on rhubarb (Rheum rhabarbarum L. ≡ R. rhaponticum L. ‘Victoria Red’). The straw-mulched plots produced larger plants, provided higher yields and had fewer weeds than all other treatments during the five years of these field trials. Yields in 1987 were 29·42, 17·65 and 13·06 tonnes/hectare for straw, handweeded and herbicide treatments, respectively. Monthly handweeding produced large plants and high yields, but required much more hand labour than mulching, making straw mulch the most cost-effective treatment. The four herbicides evaluated (glyphosate, fluazifop, sethoxydim and propyzamide) provided weed control for up to 1 month and would require reapplication during the growing season.     

Soil-applied herbicide use in wide- and narrow-row glyphosate-resistant soybean (Glycine max)

A field study was conducted in 2001 and 2002 at Blackville, SC, to compare the effectiveness of soil-applied herbicide programmes followed by glyphosate with sequential glyphosate applications in 19- and 97-cm row soybean. Treatments included pre-emergence applications of flumetsulam, chlorimuron plus sulfentrazone, metribuzin, or flumioxazin all applied with S-metolachlor with a subsequent application of glyphosate applied 5 wk after soybean planting (WAP). Additional treatments included sequential applications of glyphosate at 3 and 5 WAP and a non-treated control. Weed control was comparable in wide and narrow rows, and soil-applied herbicides were similar to sequential glyphosate applications in either row width. Amaranthus palmeri S. Wats., Digitaria sanguinalis (L.) Scop., and Cyperus rotundus L. control with all herbicides was 98–100%. All herbicide programmes provided at least 92% Ipomoea hederacea var. integriuscula Gray and I. lacunosa L. control. S-metolachlor plus flumetsulam followed by glyphosate provided 99% Senna obtusifolia (L.) Irwin and Barneby control, which was superior to the 88% and 90% obtained with chlorimuron plus sulfentrazone and metribuzin programmes, respectively. Flumioxazin and sulfentrazone caused up to 12% soybean injury. In 2001, soybean yields and gross profit margins were similar for soil-applied programmes followed by glyphosate and sequential glyphosate applications in wide and narrow rows. Conversely, soybean yields and profit margins in 2002 averaged across soil-applied programs were 380 kg/ha and $50/ha superior to sequential glyphosate applications in wide rows, but were similar in narrow rows. This research indicates a highly efficacious soil-applied herbicide program followed by glyphosate provides similar weed control to sequential glyphosate applications in wide- and narrow-row soybean; however, a soil-applied herbicide programme followed by glyphosate may improve yields and returns of wide-row soybean over sequential glyphosate applications alone.     

Genetically-modified herbicide-resistant (GMHR) crops a two-edged sword? An Americas perspective on development and effect on weed management

GMHR crops have been cultivated in the Americas for nearly 20 years. Prior to release, regulators asked the question, “will herbicide selection pressure for evolution of HR weeds increase significantly as a result of GMHR crop cultivation?” In hindsight, they could not have imagined the rapid, widespread adoption of glyphosate-resistant (GR) crops and subsequent chain of events: surge in glyphosate usage at the expense of other herbicides, sharp drop in investment in herbicide discovery, unrelenting rise of GR and multiple-HR weed populations, and increasing herbicide use in GMHR cropping systems. In this brief review, we outline grower adoption of GMHR soybean, maize, cotton, and oilseed rape (canola) in the Americas, and their impact on herbicide-use practices for weed management. Cultivars with stacked-HR traits (e.g., glyphosate + glufosinate + dicamba or 2,4-D) will provide a short-term respite from HR weeds, but will perpetuate the chemical treadmill and selection of multiple-HR weeds. The only sustainable solution is for government or end-users of commodities to set herbicide-use reduction targets in our major field crops similar to European Union member states, and include financial incentives or penalties in agricultural programs to support this policy. Concomitantly, industry incentives must expand to improve grower adoption of best management practices for HR weeds. New or emerging technologies will provide additional tools for reactive HR weed management in the future, but their time of arrival is uncertain.     

Chemical control of weeds in transplanted tomatoes in Saudi Arabia

The herbicides metobromuron, diphenamid and dinitramine were tested either singly or in combination with dalapon for the control of weed species in transplanted tomato crops in Saudi Arabia, during 1979 and 1980. All herbicides were effective in controlling Chenopodium murale L., the primary broad-leaved weed in the area. However, they were less effective against other broad-leaved weed species and, even in combination with dalapon, failed to reduce populations of grass weeds. Tomato seedlings showed various degrees of injury: dinitramine was the most phytotoxic herbicide, followed by metobromuron and diphenamid. No toxicity was observed for dalapon. Diphenamid was the most promising herbicide for controlling weeds and producing significantly higher yields of tomatoes.     

Gum and protein enrichment from sicklepod (Cassia obtusifolia) seed by fine grinding and sieving

Sicklepod (Cassia obtusifolia) is a weed species that has contaminated soybean and other crops. Although sicklepod continues to be a problem weed, the advent of herbicide-resistant soybeans has reduced the problem somewhat in the last few years. Sicklepod seed contains a gum of commercial interest in addition to protein and fat. An inexpensive process to enrich gum and protein contents of sicklepod seed is desirable for increased utilization and further processing. This study was conducted to determine whether fine grinding and sieving of sicklepod seed into separate fractions according to particle size could enrich gum and protein. Sicklepod seed was finely ground in a pin mill at different speed, and the resulting ground seed was separated into various fractions according to particle size. Gum content increased with particle size, and protein content decreased with particle size. Fine grinding and sieving of sicklepod seed can enrich gum in the fraction with largest particle size and can enrich protein in the fraction with smallest particle size. Fine grinding and sieving of sicklepod seed can make further processing more economical.     

阿特拉津对不同种子大小品种大豆的危害

玉米和大豆轮作是我国东北地区应用广泛的种植方式,但玉米田除草剂阿特拉津常引起下茬大豆药害。选用东北地区推广应用的45个不同种子大小的大豆品种（粒重范围81～302 mg/seed）进行温室盆栽试验,探讨大豆地上冠部和地下根系对阿特拉津危害的响应。结果表明,阿特拉津在土壤中有效成分用量为500g/hm2的条件下,大豆地上部干物质生产随种子重量增加而增加,呈显著正相关（P＜0.05）,而根系干物质生产与种子大小未呈显著正相关（P＞0.05）。这说明大粒品种大豆对阿特拉津耐药性强,小粒品种则敏感,因此,种植大粒品种大豆或品种中大粒种子,可使阿特拉津对大豆危害降到最低。 

     

农威豆田防除杂草的安全性试验研究

５％农威ＥＣ是一种低毒、高效、广谱，具有选择性内吸传导型，苗后茎叶处理的豆田除草剂。防除禾本科杂草防效达９５％以上，对阔叶杂草及莎草科杂草防效一般大于８５％，一次性施药，麦茬免耕种植夏大豆，省工省时。按每公顷剂量６７５ｍｌ于傍晚施药，其轻微药害７天后即可恢复，不伤害大豆植株，并增产５－１０％，不污染环境，药效期４０天左右，不影响下茬作物，安全性高，使用方便，在当前农业生产上属少有新品种。     

氯氟吡氧乙酸与顶尖或骠马混用对小麦田间杂草的防除效果

为了研究除草剂混配对小麦田间杂革的防效,测定了15%顶尖WP或6.9%骠马EW与20%氯氟吡氧乙酸EC混配对小麦田杂草的防效、田间透光率、杂草对水肥的吸收量和小麦产量.结果表明,除草剂混配对小走田间杂草的综合密度防效和综合鲜重防效分别达到98.21%～100.00%和99.46%～100.00%,显著优于单剂的防效.除草剂混配能有效抑制杂革的株高,顶尖WP与最低剂量的氯氟吡氧乙酸混配,野燕麦即被全部防除,大巢莱和猪殃殃的株高亦显著降低.除草剂混配使用能显著提高小麦田间不同部位的透光率,小麦顶部透光率比时照增加54.08%～57.20%;离地50 cm的透光率比对照增加47.21%～52.73%;离地10 cm的透光率比对照增加22.84%～27.44%.除草剂混配使用降低了杂草对水肥的吸收,高剂量的组合中,杂草的水肥含量均降为零.除草剂混配喷施后增产效果显著,增产率达到124.63%～172.88%.     

Water-nutrient-herbicide management of potatoes with trickle irrigation

A study was designed to test the effectiveness of nitrogen and herbicide applications through soil moisture-controlled, trickle-irrigation systems, and to test the effectiveness of automatic irrigation via soil moisture control to minimize the water requirement and N-losses for high-frequency, trickle-irrigation systems. Results indicated that single or multiple applications of herbicide at recommended rates can be used effectively with trickle irrigation to control weeds in the potato row where cultivation is not possible. Nitrogen can be efficiently applied through a trickle system that features automatic soil moisture control through the use of a high-frequency irrigation schedule.     

大豆田除草剂混用技术及药害

为了指导大豆田杂草防除技术,介绍了大豆田杂草发生的主要种类与特点,除草剂混用品种的选择,除草剂药害的分类,除草剂药害调查分级与除草剂混用性能比较等,以及大豆田杂草防除技术和施用除草剂混剂不当造成的药害.     

Multi-Year Evaluation of Model-Based Weed Control Under Variable Crop and Tillage Conditions

Abstract

Selecting effective weed management options requires biological, ecological, and economic information. This study compared model-based to standard-herbicide weed control in a corn (Zea mays L.)/soybean [Glycine max (L.) Merr.] rotation that had a long-term history of different tillage and weed management practices. The model integrates weed population dynamics, herbicide efficacies, and economic information to evaluate preplant incorporated (PPI) or preemergence (PRE) weed control options based on weed seed bank size and postem-ergence (POST) strategies based on weed seedling densities. There were fewer weeds in standard-herbicide compared with model-based treatments. No-tillage had the greatest numbers of weeds 3 out of 4 years. Soybean yield was reduced the first year of the study in several treatments receiving model-based weed control and the third year in all model-based treatments. Corn yields were greatest in reduced tillage. Resuits of using model recommendations to control weeds were mixed, with PRE recommendations being insensitive to a common cocklebur (Xan-thium strumarium L.) infestation. Our conclusions agree with those of others that the nature of the weed pressure may be a prevailing influence on the outcome of using weed control recommendations of bioeconomic models.     

绥化市大豆田主要杂草发生及防除对策研究

采用路线踏查与定点观察相结合方法对绥化市大豆田主要杂草种类及发生规律进行调查,并在此基础上对杂草的防除技术进行研究,结果显示:绥化市大豆田杂草共有15科24种,并且杂草发生期集中,高峰期的出草量占总出草量的85%左右.化学防除技术研究显示土壤封闭、茎叶处理所用不同除草剂单混效果不同.并对化学除草的注意事项进行说明,应根据气候条件、土壤墒情、大豆发育进度、杂草大小等灵活运用防除对策.     

Effect of herbicide application on weed flora under conservation agriculture in Zimbabwe

Increased challenges of weed control in the smallholder farming sector of southern Africa have often resulted in small yields. The objective of this study was to evaluate the effects of different weed control strategies on weed flora and composition under conservation agriculture (CA) systems in Zimbabwe. This study was conducted at three on-station trial sites namely Domboshawa Training Centre (DTC), University of Zimbabwe farm (UZ farm) and Henderson Research Station (HRS) in a maize–soybean rotation for four seasons from 2009–2010 to 2012–2013 seasons. Hand weeding was done whenever weeds were 10 cm tall or 10 cm in circumference for weeds with a stoloniferous growth habit. Weed identification was done up to the weed species level, and the Shannon–Weiner diversity and evenness index was used to determine the response of weed flora to herbicides. Results showed that there were more weeds in the early years which decreased gradually until the final season. Weed species diversity was not affected by herbicide application and the results indicated that weed species diversity was small in CA systems. Annual weed species constituted a greater proportion of species, and species richness decreased with the duration of the study. Richardia scabra L. and Galinsoga parviflora Cav. were the most common dominant weed species at all sites and in all seasons. Moreover, herbicide application had no effect on the evenness of weeds in the plots but site characteristics had a significant effect on the distribution of weed species (weed species evenness). The results presented in this study suggest that herbicide application facilitates a depletion of weed seed bank/number of weeds over time. Thus, herbicide application in CA has potential to reduce weed density, species richness and species diversity in the long term which may lead to more labour savings and larger yields.     

Glyphosate management strategies,weed diversity and soybean yield in Argentina

From their introduction in 1996, glyphosate resistant (GR) soybean cultivars have been rapidly adopted by farmers in Argentina and in other countries in the world. The high rate of adoption of this technology seems to be based on the simplicity of use provided by a single herbicide (glyphosate), its high efficacy to control many weeds and, the low costs of the technology relative to that used in conventional crops. During 2001–2002, 2002–2003 and 2003–2004 soybean growing seasons, field surveys and field experiments were performed with the aim of studying the effect of different glyphosate management strategies on the diversity of soybean weed communities, weed control, individual survival, fecundity and crop yield. In addition, the emergence pattern of three important weeds, Digitaria sanguinalis, Cyperus rotundus and Anoda cristata, was also studied. Both field surveys and field experiments were carried out on no-till soybean crops sown immediately after wheat or barley harvest (double cropped system). Experiments were set up in commercial soybean crops and consisted of different times of a single glyphosate application, two glyphosate applications and also the application of glyphosate plus a residual herbicide imazethapyr. A. cristata, D. sanguinalis, Stellaria media, Chenopodium album and Cyperus sp. were the most prevalent weeds recorded at pre-harvest of the soybean crops, showing regional constancy higher than 80% in both years. In three out of four field experiments, crop yield was not increased when glyphosate was applied twice compared with a single application of the herbicide. In addition there was a lower negative effect on weed species richness when glyphosate was applied once during the crop cycle than with two applications of glyphosate or glyphosate plus imazethapyr. D. sanguinalis escaped the glyphosate early treatment because of the long weed emergence period, while A. cristata and C. rotundus survived treatments due to their high individual tolerance. The results suggest that it is possible to manage glyphosate application to get high crop yield with a low impact on weed diversity, depending on the weed species and their abundance.     

Broadleaved weed control in wide-row soybean (Glycine max) using conventional and glyphosate herbicide programmes

A field study was conducted in 2001 and 2002 at Blackville, SC, to evaluate broadleaved weed control and economics of conventional and glyphosate-containing herbicide programmes in glyphosate-resistant soybean planted in 97-cm-wide rows. Treatments included chlorimuron plus sulfentrazone or chlorimuron plus metribuzin applied pre-emergence followed by post-emergence applications of lactofen or glyphosate 4 wk after soybean emergence (WAE). Other treatments were glyphosate applied 4 WAE, sequential applications of low dose glyphosate applied 2 and 4 WAE, and a non-treated control. Pre-emergence herbicides followed by glyphosate, controlled Ipomoea lacunosa L. 8 WAE. I. hederacea var. integriuscula Gray control with pre-emergence herbicides followed by glyphosate was 100% with similar control from chlorimuron plus sulfentrazone followed by lactofen, whereas control following the single glyphosate application was 84%. Amaranthus palmeri S. Wats. control 9 WAE was 100% following single or sequential glyphosate applications, while control ranged from 76% to 96% with pre-emergence herbicides followed by lactofen. However, early season weed interference when a single application of glyphosate was delayed until 4 WAE reduced soybean yields an average of 389 kg/ha compared to pre-emergence herbicides followed by glyphosate. Based on mean contrasts, pre-emergence herbicides followed by glyphosate had greater gross profit margins than a single glyphosate application alone, but were similar to sequential glyphosate applications. Gross profit margins from pre-emergence herbicides followed by lactofen were not different from glyphosate alone.     

行距对大豆竞争有限资源的影响

不同行距引起大豆生长竞争.当某一因子的直接供应不能满足群体生长的需要而成为限制因子时,竞争便开始.本文主要从基因型、光、水、养分和杂草等5方面综述过去40年行距变化对大豆竞争资源的影响.研究表明,不同品种对行距变化的反映不同,其依赖于季节降雨和灌溉.有限结荚习性类型可获得较高产量,抗倒伏的大豆品种适于窄行种植.无限结荚习性大豆在一定的行距条件下也可获得最佳产量.与宽行大豆种植相比,窄行大豆栽培增加光截获(LI),其原因在于LAI、消光系数的增加及分枝类型品种的选择.水分利用效率和蒸发蒸腾作用不受行距影响,但在灌溉条件下产量增加.行距变化对养分吸收影响较大,随着行距的减小,植株产量和N、P、K的吸收均增加,且增加幅度受施肥水平制约.行距不影响N素的固定.行距不影响杂草密度、萌发高峰及持续时期,但在窄行栽培条件下可减少杂草的数量及干重,再配以适量的除草剂可获得良好的除草效果.不同行距条件下的大豆生理反应、养分和水分的吸收及转运,不同冠层的光能利用以及土壤环境的变化仍需进一步深入研究.     

Weed problems of the next decade in Britain

The potential changes in weed problems in British agriculture and horticulture over the next decade are reviewed. The attributes which confer survival and success to weed species are considered, of which the most important for arable weeds is seed behaviour. These attributes are then discussed in relation to the changes which are deemed likely to occur in various cropping systems. In arable land, the main factors influencing weed population composition are method of straw disposal, level of cultivation, season of drilling, crop grown, fertilizer regime, herbicide usage and herbicide resistance. Few major changes in agriculture are foreseen, but there will be a trend towards increasing specialization in many areas. The predominance of winter cereals and oilseed rape will continue, which will favour autumn-generating weeds such as Galium aparine and Alopecurus myosuroides. It is postulated that most weed problems over the next decade will arise from existing weeds or from native plants common in field margins from which they could invade fields through changes in management. A few new aliens, especially grasses, may well appear, e.g. Phalaris paradoxa. Weeds could also arise from recently introduced crop plants, e.g. Bromus willdenowii and B.carinatus, which may present problems in the future, just as cereal volunteers are often a problem at present.