Weed competition in spring-planted raspberries

Spring-planted raspberries (Rubus idaeus L. cv. Malling Jewel) were exposed to competition from annual weeds for various lengths of time during the first growing season. Weeds germinating following crop planting in late March had no effect on numbers of new canes produced provided weed removal occurred by early June. The importance of preventing competition from these weeds during the critical period of cane emergence (June/July) was demonstrated. Dense weed cover reduced cane growth and, if weeds were left beyond late June, caused considerable mortality of planting material. Weed growth also frequently reduced cane height. In the second year, all plots were maintained free of weeds. Fruit yields showed effects of weeds similar to or greater than those indicated by total cane growth in the previous year. Height of new canes was unaffected by previous weeding treatments, but the numbers of new canes produced continued to show severe effects of initial competition from weeds. Allowing further weed growth to develop after initial weeding had no additional effect on crop survival or cane numbers in the first year. In one experiment, however, a reduction in cane height due to weeds germinating in June was followed in the second year by a reduction in the numbers of new canes produced.     

Weed competition and control in sugarcane

Losses of about 40% in cane yields due to natural stands of weeds were found in experiments conducted in sugarcane var. Co 527 in the year of planting at Guneid Sugarcane Research Station, Sudan. Weed competition lowered millable stalks per metre row by 32%, stalk height by 24%, stalk thickness by 15% and number of nodes per stalk by 14%. Tillering was the growth phase most affected by weed competition. Cane yields were increased as number of hand weedings increased, but four weedings were not markedly better than three. The average yield (67·04 t ha^?1) obtained from four weedings was not significantly (P= 0·05) better than that of three weedings carried out at 3, 6 and 9 weeks after cane planting. Juice analysis components were also affected by weeds and a 15% reduction in sucrose recovery was recorded. Reductions in the other components were only 4–7%. Atrazine and diuron (3·3 kg ha^?1), metribuzin (2·4 kg ha^?1) and metribuzin (1·3 kg ha^?1) in tank mixture with diuron (1·5 kg ha^?1) gave excellent residual weed control of the dominant weed species, Ipomoea cordofana Choisy., Brachiaria eruciformis (Sm.) Griseb., Corchorus fascicularis Lam., Ocimum basilicum L. and Dinebra retroflexa (Vahl) Panz., for most of the first growing season. Excellent control of weeds achieved by the herbicide treatments resulted in comparable yields to frequently-weeded cane. These herbicides were not phytotoxic to sugarcane var. Co 527.     

Weed competition in a cucumber crop

Abstract

Two field experiments were conducted on cucumber (var. Explorer) during 1979 in a randomised trial design with four replications on the red ferralitic soil of Havana province, Cuba. The effect on the crop of the following different treatments was established: weeded regularly for 20, 30 or 40 days after crop emergence and during the whole crop cycle; left unweeded for these same periods. The mean data of both experiments showed that the weed incidence for 20 or more days following crop emergence affects cucumber yields, causing losses of 100% if the weeds were not removed during the crop cycle. Good high yields, similar to those of the treatment weeded during the crop cycle, were obtained when the weeds were removed 30–40 days after crop emergence.     

Weed:spring barley competition for applied nitrogen in pig slurry

Summary The experiments were carried out in the two spring barley fields of the organic six-course cattle:crop rotation at Foulumgaard, Denmark. The weed density was 300 and 1800 plants m⁻² respectively. Pig slurry was applied by hand in microplots by four methods: broadcasting followed by incorporation, or injected in bands to depths of 5, 10 or 15 cm. Spring barley and weeds were sampled separately six times during the tillering and elongation phase of the spring barley. The effect of application method on dry-matter (d.m.) production, nitrogen uptake and recovery of applied nitrogen in the spring barley and the weeds is reported. Slurry banding halved the weed d.m. and weed N uptake compared with broadcasting, irrespective of weed density. Weeds recovered up to 12% of the applied nitrogen, which made them a significant competitor when the slurry was broadcast and incorporated. Banding by direct injection reduced the slurry:soil contact and the weed:crop competition balance for applied nitrogen moved in favour of the crop. Thus, the crop recovery of applied nitrogen at the end of the sampling period was increased from approximately 45% for broadcast and incorporated to approximately 50% for injected slurry, and coincidental weed recovery was reduced to a maximum of 5%. As the nitrogen supply normally affects plant d.m. production, banding of slurry might well improve crop competitiveness and its tolerance to mechanical weed control.     

Weed competition in willow coppice crops: the cause and extent of yield losses

Growth in 2-year-old willow Salix spp., grown in the short-rotation coppice (SRC) system on agricultural land, was compared in 30 weeded and 30 unweeded plots in each of 2 years after cutting. Non-destructive assessment methods of both crop and weed biomass were used. Coppice growth in year I was greater in the weeded plots than in the unweeded plots. In year II, coppice growth was not different between plots so that, over the 2-year study period, the coppice yield reductions with weeds reflected the losses in year I only. There was considerable variation in the amount of weeds in the unweeded plots. The relationship between the volume of weeds present and the extent of the coppice yield reduction over 1 and 2 years after cutting are described by linear models. Soil moisture and nutrient content, when measured in mid-summer, were not different between plots in either year. In year I, mid-summer coppice height was greater in the weedy plots, while stem numbers in both years and canopy density in year II were lower in the weedy plots. These results indicate that tall weeds competing for light and space in the first year of growth, rather than moisture or nutrient stress, caused fewer (and taller) stems to grow from the coppice stools, leading to the observed reductions in biomass.     

Dimethoate spray residues in strawberries

Strawberries were sprayed with solutions of 200, 300 and 500 mg dimethoate litre^?1 and analysed for dimethoate residues up to 21 days after the final spraying. The residues were found to be below the National Health and Medical Research Council limit of 2 mg kg^?1, 1, 2 and 4 days after spraying. Consequently, the withholding period of 7 days could be reduced to 3 days to allow uninterrupted picking of the ripe strawberry crop.     

Weed Problems and Weed Control in the Commonwealth Caribbean

Abstract

The effect of weeds on crops is discussed, with particular reference to the Commonwealth Caribbean. The most serious weeds in the region are Cyperus rotundas, Cynodon dactylon, Commelina spp., Parthenium hysterophorus, Portulaca oleracea, Cleome spp. and Amaranthus spp. Serious weeds include Eleusine indica, Echinochloa colonum, Euphorbia spp., Brachiaria mutica, Paspalum conjugatum, Sporobolus indicus and Ipomoea tiliaceae. Brief notes are given for these species and also for the locally serious weeds, Rottboellia exaltata, Digitaria sanguinalis, Mimosa pudica, Scleria reflexa, Cenchrus echinatus. Control measures include macheting, hand weeding, flooding, mulching and short-term fallows. Herbicides are used especially by larger vegetable growers and in sugarcane and citrus groves. Paraquat is the most widely used. Other chemicals used in specific situations are listed. Knapsack sprayers are the commonest application method but granular and c.d.a. application is likely to increase. Weed control research in the Commonwealth Caribbean is also briefly reviewed.     

Residues and efficacy of fluazifop-butyl in strawberries

Residues of fluazifop-butyl were determined in strawberries from New Brunswick and Nova Scotia, Canada and North Carolina, U.S.A. using a High Performance Liquid Chromatography (HPLC) system. Strawberries harvested within 28 days of treatment (pre-harvest interval= PHI) had detectable residues of fluazifop, ranging from 0.05 ppmw with a split application of 0.25 kg ha-¹ and a 18-day PHI to 3.24 ppmw with a split application of 0.5 kg ha^?1 and a 12-day PHI. Fluazifop was not detected in samples treated 287 days or more before harvest (prior growing season) at 0.25–1.65 kg ha^?1 (three applications of 0.55 kg ha^?1). Fluazifop-butyl did not provide acceptable control (50% with two applications of 0.25 kg ha^?1) of Elymus repens (L.) Gould in a commercial planting in New Brunswick. Control of Digitaria sanguinalis (L.) Scop. was better than 90% with two applications of 0.30 kg ha^?1 in North Carolina. Fluazifop-butyl did not injure strawberries at any of the rates or sites tested. Résidus et efficacité du fluazifop-butyle en culture de fraises Les résidus du fluazifop-butyle dans des fraises provenant de New Brunswick et Nova Scotia au Canada et de North Carolina aux Etats-Unis ont été déterminés en utilisant un système de chromatographie liquide à haute performance (HPLC). Des fraises récoltées avant 28 jours après le traitement (PHI 28) contenaient des résidus de fluazifop décelables, allant de 0.05 ppmw après un apport fractionné de 0,25 kg ha^?1 et PHI 18 à 3,24 ppmw après un apport fractionné de 0,5 kg ha^?1 et PHI 12. Nulle trace de fluazifop n'a été décelée dans des échantillons traités au moins 287 jours avant la récolte, c'est-à-dire pendant la saison précédente, aux doses de 0,25 à 1,65 kg ha^?1 (trois pulvérisations à 0,55 kg ha^?1). Le fluazifop-butyle n'a pas permis une destruction convenable d'Elymus repens (L.) Gould dans une exploitation commerciale au New Brunswick (50% suivant deux pulvérisations à 0,25 kg ha^?1). La destruction de Digitaria sanguinalis (L.) Scop. avec deux pulvérisations à 0,30 kg ha^?1 en North Carolina dépassait 90%. Le fluazifop-butyle n'a provoqué de dégâts dans les fraises à aucune des doses testées ni à aucune localité. Rückstände und Wirkung von Fluazifop-Butyl in Erdbeeren Erdbeeren von Neu-Braunschweig, Neu-Schott-land (Kanada) und Nord-Karolina (U.S.A.) wurden mittels Hochleistungs-Flüssigkeits-Chromatographie (HPLC) auf Rückstande von Fluazifop-Butyl untersucht. Innert 28 Tagen nach der Behandlung (Intervall vor der Ernte = PHI) geerntete Erdbeeren enthielten messbare Rückstande von Fluazifop; sie betrugen zwischen 0,05 ppmw nach einer Split-Applikation von 0,25 kg ha^?1 und einem PHI von 18 Tagen und 3,24 ppmw nach Split-Applikation von 0,5 kg ha^?1 und 12 Tagen PHI. Es wurden keine Rückstände in Proben gefunden, die 287 oder mehr Tage vor der Ernte mit 0,5–1,65 kg ha^?1 (drei Applikationen von je 0,55 kg ha^?1) behandelt worden waren (vor der Wachstumsperiode). Fluazifop-Butyl erzielte keine genügende Kontrolle von Elymus repens (L.) Gould (50% Erfolg nach zwei Behandlungen mit 0,25 kg ha^?1) in einer Produktionspflanzung in Neu-Braunschweig. Der Erfolg gegen Digitaria sanguinalis (L.) Scop. war in Nord-Karolina nach zwei Applikationen von 0,30 kg ha^?1 höher als 98%. Fluazifop-Butyl schädigte die Erdbeeren an keinem der Standorte und mit keiner Dosierung.     

Weed Control in Nigeria

Abstract

Chemical weed control is playing an increasing role in Nigerian agriculture due to the increasing cost and widespread unavailability of the labour required to carry out traditional practices. Nigeria's drive towards increased food production must involve a systematic approach to weed control based on a good understanding of weed biology and ecology. The objectives of such an approach must be the development of effective control methods which are efficient in the use of available resources and within the reach of the farmers. This paper reviews the major weed problems, the status of weed science research, and some constraints to herbicide use in Nigeria.     

Weed competition in irrigated cotton (Gossypium barbadense L.) and groundnut (Arachis hypogaea L.) in the Sudan Gezira

Losses of crop yield due to weed competition in unweeded plots averaged nearly 60% of weed-free yields in cotton and 70% in groundnuts. Weed competition was not directly related to weed groundcover but was dependent on the seasonal growing conditions. The critical period of weed competition in both crops was the 6 weeks between 4 and 10 weeks after crop emergence. During this period cotton could tolerate up to 25% weed groundcover without appreciable loss in crop yield. Groundnuts could tolerate not more than 10% weed cover before yield loss occurred. A main factor in achieving standards of weed control within these limits was preventing the early growth of monocotyledonous weed species: pre-sowing application of trifluralin and benfiuralin provided this over a wide range of growing conditions.     

Weed Control

Abstract

The white powdery scale Cribrolecanium andersoni (Newstead), which occurs on citrus in South Africa and Swaziland, is of economic importance. The scale secretes honeydew on which sooty mould develops. Parasitoid sampling entailed the collection of C. andersoni‐infested leaves at seven different localities. Female and male Euxanthellus philippiae Silvestri (Aphelinidae), the female Coccophagus pulvinariae Compere (Aphelinidae), Metaphycus spp. (Encyrtidae), an unidentified encyrtid (probably a new genus), Tetrastichus sp. (Eulophidae) and a male Coccophagus sp. were found to be parasitoids of C. andersoni. E. philippiae and the unidentified encyrtid appeared to be the most common parasitoids of C. andersoni. No parasitoids were collected from first‐instar C. andersoni. The number of parasitized C. andersoni was the lowest during October to December.     

南京市小麦田杂草调查及其防除对策

通过对南京市各县区麦田杂草的系统调查,探讨本地小麦田杂草群落结构及发生规律,调查发现目前南京市小麦田间常见杂草有11科26种,主要杂草有猪殃殃、播娘蒿、看麦娘、荠菜、大巢菜、牛繁缕、婆婆纳、麦家公、野燕麦、泽漆等。并对已有小麦田杂草农业防除配套技术进行了充实和完善。     

Weed Control

Abstract

Research into weed control in Iraq is largely the responsibility of the Ministry of Agriculture. The recommendations which the Department of Weed Control have made on the basis of this research are presented. The principal weed species of Iraq are listed with some indication of their occurrence and importance. Both research and control of weeds in Iraq are limited at present.     

Weed Problems in Chotanagpur Agriculture

Abstract

Micron Sprayers Ltd have produced a sprayer, the Herbi, designed to produce uniform atomisation with both oil- and water-based formulations. Three different nozzle sizes give low, medium and high flow rates. In performance tests wetting agents were found to be necessary to produce uniform droplets. The volume distribution across the swath showed four peaks and for the flow rate, liquid and atomiser height examined the two major peaks were at 50 and 60 cms either side of the line of the sprayer, indicating a peak to peak width of 110 cm. Of the collected spray, 75% settled within a central band of 120 cm, 99% within 180 cm and 100% within 195 cm. To prevent superimposition of peaks leading to high overdose, a swath width of 150–160 cm is suggested, such that overlap occurs at the outer position of half peak height. To avoid excessive spray drift it is recommended that the sprayer is not used in any but very light wind. The authors conclude that this machine should prove very useful for very low volume application between rows in bush and tree crops, and for treating larger areas.     

Eupatorium Weed Species in Australia

Abstract

High temperature together with high rainfall favour infection and development of Erwinia stalk rot of maize (Erwinia chrysanthemi pv. zeae Victoria, Arboleda and Munoz). An attempt was made to correlate temperature, relative humidity, total rainfall and duration of bright sunshine with disease incidence in six maize cultivars during six crop seasons. Temperature and relative humidity did not fluctuate much during the flowering period at the time of disease appearance. Significant differences in total rainfall and duration of bright sunshine were observed. Longer duration of bright sunshine (8.2 h/day) along with moderate rainfall (81.7 mm) were recorded in high disease incidence years. Using these weather conditions a linear equation was derived to predict disease incidence.     

Weed size hierarchies in Denmark

In 962 field trials in different crops, the size of a number of weed species was investigated. The weeds were ranked according to their size on a single occasion. The ranks of the species were examined relative to two weed species, Viola arvensis and Matricaria inodora. The ranking was, however, independent of which of the two species were used as standard. The correlation between the rankings with Viola arvensis as standard, and the rankings with Matricaria inodora as standard were r= 0-93 for spring sown crops, and r= 0.84 for autumn sown crops. Sinapis arvensis was the largest weed species in spring sown crops, with a weight of 14.5 times that of Viola arvensis, followed by Brassica napus, Galeopsis spp., Thlaspi arvense and Amsinckia spp. Viola arvensis. Veronica spp. and Lamium spp. were the smallest weed species in spring sown crops. Galium aparine was the largest species in autumn sown crops, whereas spring germinating species such as Polygonum spp. were among the smallest. The ranks of Viola arvensis, Myosotis arvensis, Lapsana communis, Matricaria inodora and Lamium spp. were almost identical in spring sown crops and in autumn sown crops.     

Residues of methomyl in strawberries,tomatoes and cucumbers

An accurate and rapid high performance liquid chromatography method was developed to monitor residues of methomyl in plant extracts. The rate of disappearance of foliage-applied methomyl from strawberries, tomatoes and cucumbers was studied. Residues reached levels of 0.55, 0.2 and 0.6 mg kg^?1 seven days after methomyl had been applied to strawberries, tomatoes and cucumbers, respectively. Results also showed that rinsing treated fruits with tap water removed considerable amounts of methomyl. Samples of strawberries, tomatoes and cucumbers were collected from local markets at Ismailia, and checked for methomyl residues. Residues in 12.5% of tomato and 25% of strawberry samples were above 0.2 mg kg^?1.