Insecticide resistance in cotton aphid Aphis gossypii (Glov.) in the Sudan Gezira

The resistance to insecticides of three Sudanese strains of A. gossypii (Glov.) collected from cotton fields in the Sudan Gezira Scheme over three seasons (1988, 1989, 1990) and that of two French strains was studied in the laboratory. When compared with a known susceptible strain, the aphids were found to be resistant-to the eight insecticides tested. Evolution of resistance in Sudanese strains during the three crop seasons was observed. Assay of aphid homogcnate for carboxytesterase activity towards the substrates α-naphthyl acetate and β-naphthyl acetate showed that there was no enhancement of this class of enzyme and thus it was not a cause of resistance in this species. A study of interaction between the acetylcholinesterase (AchE) and pirimicarb established the kinetics of the inhibition process. I₅₀ values were found to be much higher for the Sudanese strains than for the susceptible strain. First-order inhibition kinetics revealed that resistance towards pirimicarb in Sudanese-strains was caused by a modified AchE which had a reduced affinity (higher K_a value) and poor carbamylation ability (lower K₂ value) for pirimicarb. The resistance mechanisms for the other insecticides remain to be studied.     

Chemical Control of Weeds in Cotton in the Sudan Gezira

Abstract

Early work on chemical weed control in the fallow towards the end of the Second World War is reviewed briefly. Attempts to use contact residual herbicides as pre-emergence applications in the early 1950s are also described.

Pre-sowing applications of residual herbicides were found more phytotoxic to cotton than pre-emergence applications. The closer the time of pre-sowing application to cotton sowing, the more effective was suppression of weeds competing with cotton.

Mechanical cultivations and particularly disc ploughing and rotovation to a depth of more than 15 cm were found more effective in the control of Cynodon dactylon than pre-sowing herbicide applications.

Fluometuron, noruron and prometryne were found very effective as pre-emergence herbicides. Optimum rates of application were found to be only 25-50% of rates recommended for the USA and other countries. Resistant weeds included Cyperus rotundus, Cynodon dactylon, and Rhyncosia memnonia.

A large-scale trial with fluometuron, covering 125 feddans at Wad el Nairn showed that yields obtained were equal to those with normal weeding. Costs of herbicide treatments were also comparable to costs of hand-weeding in a year of exceptionally low hand-weeding costs.     

Factors influencing the weed flora in the Gezira Scheme, Sudan

Agriculture plays a major role in the economic and social development of Sudan. The most important agricultural area in Sudan is the irrigated Gezira Agricultural Scheme (GAS), which takes water from the Sennar Dam on the Blue Nile. This study investigated weed communities in relation to geographical location and crop rotation in 2000 and 2001. Five agricultural units were sampled from the central sector of the GAS; within each unit we surveyed weed communities in different phases of the crop rotation: cotton, groundnuts, sorghum, and a fallow. The distribution of weed species showed some similarities in the 2 years sampled, with most species being found in all agricultural units but their relative proportions differed. Broad-leaved weeds were dominant, suggesting that herbicides selected for weed control in the Gezira scheme need to be effective against this group of species. Agricultural unit and crop type affected weed communities in both years. The weed flora was largest in cotton, intermediate in groundnuts and sorghum, and smallest in the fallow. Although most weeds were found in all agricultural units; however, their relative abundances differed greatly, either as a result of differences in management between the units, or some other spatial effect. As such, weed control programmes need to be tailored at the agricultural unit scale.     

Insect Mobility and the Philosophy of Crop Protection with Reference to the Sudan Gezira

Abstract

Mobility results in movement of insects from their birth place (emigration) to another site (immigration). The scale, both in time and in space, on which such migration occurs may determine rates of increase or decrease in numbers in a fixed geographical area or plot. This is self evident in the case of mobile insects, such as locusts. Other documented examples include the spruce budworm in Canada and the Queensland fruit fly.

In the Sudan Gezira the distribution of the major insect pest of cotton, Heliothis armigera Hb., was found to conform to a common temporal pattern over probably some thousands of square kilometres, and other major pests, Empoasca libyca de Berg and Bemisia tabaci Gen., are considered to be similarly distributed, suggesting that their occurrence in damaging numbers may be dominated by transport and concentration by major windfields rather than by natality and mortality within a field or area. This posibility was investigated using a Pilatus Turbo-Porter aircraft fitted with Doppler Navigator equipment and an insect collecting net, and densities of flying insects monitored by a ground-based Marine-type Radar.

The results of this study will make it possible to determine the spatial extent of a threatening population and the time during which that population is present, so that control action may be taken on a commensurate scale. Such matching of scale of operations to insect mobility is of particular importance when repeated invasions occur during periods of rapid crop growth, because it enables non-persistent insecticides to be employed, thus providing potentially better utilisation of parasites and predators than can be achieved by maintaining the crop as an environment lethal to insects. These procedures, connoted ‘synoptic survey’ and ‘synchronous control’, require that the control is applied on a scale determined by pest mobility rather than by the boundaries of fields or other artificial constraints. Evidence is accumulating regarding the importance of insect mobility, in particular adaptive dispersal, in population dynamics and this may require re-assessment of farmer and government responsibilities in crop protection.     

Summary of cotton pest control practices in the Sudan

Abstract

This paper describes the treatment of plant material entering Australia through quarantine. The methods used for screening plants during post-entry quarantine are discussed and the plant-houses and equipment and techniques used for sterilising soil and controlling pests are described. A list of plants tested for the effects of fumigation with methyl bromide is given and recommendations for fungicide and pesticide are listed.     

Effect of environmental factors on herbicidal activity of diphenamid

Diphenamid (N,N-dimethyl-2,2-diphenylacetamide) in an aqueous solution in plastic bottles was partially detoxified when exposed to sunlight for 1 week. Varying spray volumes from 300 to 1,800 I/ha did not have an appreciable effect on the phytotoxicity of diphenamid, sprayed on a coarse or fine soil surface. The marked dissipation of diphenamid which occurred from the soil surface was attributed to photodecomposition and volatilization. Diphenamid phytotoxicity was greater when the first irrigation after spraying was applied in four increments of 100 m³/ha or two increments of 200 m¹/ha than when it was applied in a single 400 m¹/h watering; the latter caused more leaching of the herbicide. The diphenamid fraction leached out of a 4-cm soil layer increased as the organic matter content in the soil decreased, from 25% in peat (22.3% o.m.) to >88% in sandy loam (0.9% o.m.). The herbicidal activity remaining after leaching was lower in sandy loam and in peat than in soil with medium organic matter content (11.6% and 6.2%). Diphenamid degradation rate in soil at 50% field capacity moisture level, increased when temperature was increased from 10° to 30°C. After 4 months of incubation at 10°C, 40-50% of the original herbicide was detoxified, while at 20° and 30°C the loss exceeded 90%. Within the range of day-temperatures of 10° to 40°C in soil and of 10° to 35°C in nutrient solution, diphenamid phytotoxicity to tomato seedlings increased with temperature.     

Effect of δ-aminolevulinic acid on the herbicidal efficacy of foliar-applied MTB-951, a mycoherbicide to control Echinochloa crus-galli L.

The conidia of a plant pathogen ( Drechslera monoceras [Drechsler] Subram. et Jain [=  Exserohilum monoceras [Drechsler] Leonard et Suggs]), MTB-951, which was isolated from native Echinochloa species in Japan, were used as the herbicidal active ingredient. The effects of δ-aminolevulinic acid (ALA) on the efficacy of foliar-applied MTB-951 on Echinochloa crus-galli L. were examined. First, foliar-applied MTB-951 exhibited almost no efficacy when no dew period was provided. However, the efficacy increased depending on the length of the dew period. MTB-951 and ALA exhibited an additive effect on E. crus-galli under 3 day dew conditions, although they exhibited a significant synergistic effect under no-dew conditions. When the leaves of E. crus-galli were immersed in deionized water containing the conidia of MTB-951, cellular electrolyte leakage from the leaves was observed. The ALA increased the electrolyte leakage by MTB-951 synergistically. Also, ALA increased the number of lesions on the leaves of E. crus-galli caused by MTB-951 under light conditions but failed to increase the number under dark conditions. These results suggest that ALA promotes infection with MTB-951 for E. crus-galli through its photodynamic action.     

Degradation of oxadiazon in Kalyani alluvial soil

Residual fate and behaviour of the herbicide oxadiazon in Kalyani soil, paddy straw and grain were studied under subtropical conditions, in West Bengal following application @ 1 kg and 2 kg ha⁻¹. Dissipation of oxadiazon in soil followed first-order kinetics and DT₅₀ values ranged from 44 to 45 days. Residues at harvest in paddy grains and straw were also studied. Degradation of oxadiazon after 60 days of incubation at 28(± 1) °C in alluvial soil at water holding capacity yielded 10 metabolites of which four were characterised by spectroscopy. © 1999 Society of Chemical Industry     

The influence of soil moisture, simulated rainfall and time of application on the efficacy of glufosinate-ammonium

Laboratory experiments were conducted to determine the effects of soil moisture, simulated rainfall and time of day of spray application on the efficacy of glufosinate-ammonium in barley (Hordeum vulgare L. cv. ‘Samson’) and green foxtail (Setaria viridis (L.) Beauv.) plants. Environmental variables examined were three soil moisture levels (18% moisture, 50% moisture and saturated), three intensities of simulated rainfall following spray application [drizzle (4 mm), moderate (9 mm) and heavy (22 mm)] and two times of spray application (begin ning and end of a 16-h photoperiod). The efficacy of 100 g ha^?1 glufosinate-ammonium on barley was greatest at 18% soil moisture when measured by both ammonia and dry weight accumulation in the shoots. At the same dose green foxtail showed less ammonia accumula tion at 18% soil moisture than under other soil moisture levels, but showed no significant differences in dry weight accumulation 14 days after treatment (DAT). Simulated rainfall shortly after spraying reduced the efficacy of glufosinate-ammonium on both species. At the field dose of 800 g ha^?1, a rain-free period of 1–8 h was necessary for barley, while a period of less than 20 min was necessary for green foxtail to obtain herbicidal activity comparable with that of treated plants which received no rain. Based on dry weight accumulation, barley plants were equally sensitive and green foxtail plants were significantly more susceptible when glufosinate-ammonium was applied at the end compared to the beginning of the photoperiod. Both species accumulated significantly more ammonia in the shoots during the initial 24 h following application if sprayed at the end of the photoperiod. Of the environmental factors examined in this study, rainfall after spray application caused the greatest reduction of glufosinate-ammonium efficacy. Influence de I'humiditt du sol, de la pluie artificielle et de I'époque d'application sur I'effi cacité du glufosinate-ammonium Des essais de laboratoire ont été conduits pour déterminer les effets de Phumidité du sol, de la pluie et de I'époque d'application sur 1'efficacité de glufosinate-ammonium sur 1'orge (Hordeum vulgare L. c.v. ‘Samson’) et la sétaire (Setaria viridis (L.) Beauv.). Les variables environne mentales examinées étaient 3 taux d'humidité du sol (18%, 50% et saturation), 3 intensités de pluie artificielle suivant ('application (faible—4 mm; modéré 9 mm; et forte 22 mm) et 2 époques d'application (début et fin d'une photopériode de 16 h). L'efficacite de 100 g ha^?1 de glufosinate-ammonium sur orge était maximale a 18% d'humidité du sol, mesurée à la fois par I'accumulation d'azote et de matiére séche dans les tiges. A la même dose, la sétaire exprime une moins grande accumulation d'azote à 18% d'humidité du sol qu'aux autres taux d'humidité mais ne montre pas de différences dans I'accumulation de matière sèche 14 jours après le traitement (JAT). Une pluie artificielle suivant de près la pulvérisation réduit 1'eficacité du glufosinate-ammonium sur les deux espèces. A la dose d'utilisation de 800 g ha^?1, une période sans pluie de 1 à 8 heures est nécessaire pour l'orge, tandis que moins de 20 minutes sont nécessaires pour le sétaire pour obtenir une activité herbicide comparable à celle observée avec des plantes traitées sans pluie. En se fondant sur l'accumulation de matière sèche, les plantes d'orge étaient également sensibles, et les sétaires étaient significativement plus sensibles quand le glufosinate-ammonium était appliquéà la fin plutêt qu'au début de la photopériode. Les 2 espèces accumulent significativement plus d'azote dans les tiges pendant les 24 premières heures suivant l'application quand elle a lieu en fin de photopériode. Des facteurs environnementaux examinés dans cette étude, la pluie après la pulvérisation cause la plus grande réduction d'efficacité glufosinate-ammonium. Einfluβ von Bodenfeuchte, simuliertem Niederschlag und Applikationszeitpunkt auf die Wirksamkeit von Glufosinat-ammonium In Laborversuchen wurde der Einfluß von Bodenfeuchte, simuliertem Niederschlag und Applikationszeitpunkt auf die Wirksamkeit von Glufosinat-ammonium auf die Gersten-Sorte ‘Samson’ (Hordeum vulgäre L.) und Grüne Borstenhirse (Setaria viridis (L.) Beauv.) untersucht. Als Umweltvariablen wurden 3 Bodenfeuchtegrade (18%, 50% und gesättigt), 3 Niederschlagsintensitäten [Niesei (4 mm), mäßig (9 mm) und stark (22 mm)] nach der Behandlung und 2 Applikationszeitpunkte (Beginn und Ende einer 16-h-Photoperiode) eingesetzt. Die Wirkung von 100 g ha^?1 Glufosinat-ammonium auf die Gerste war bei 18% Bodenfeuchte sowohl hinsichtlich des Ammoniumgehalts als auch der Trockenmasse des Sprosses am größten. Bei derselben Dosis hatte die Grüne Borstenhirse einen geringeren Ammoniumgehalt bei 18% Bodenfeuchte als bei anderen Feuchtegraden, zeigte jedoch 14 Tage nach der Behandlung keine signifikanten Unterschiede in der Trockenmasse. Niederschlag kurz nach der Behandlung verminderte die Wirksamkeit bei beiden Arten. Bei der Felddosis von 800 g ha^?1 war eine niederschlagsfreie Periode von 8 Stunden notwendig, bei der Grünen Borstenhirse jedoch weniger als 20 Minuten, um dieselbe Wirkung zu erreichen wie bei Pflanzen, die ohne Regen geblieben waren. Hinsichtlich der Trockenmassebildung waren Gerstenpflanzen gleich empfindlich und Borstenhirsenpflanzen signifikant empfindlicher, wenn Glufosinat-ammonium am Ende statt am Beginn der Photoperiode appliziert wurde. Beide Arten hatten in den Sprossen während der ersten 24 Stunden nach der Behandlung am Ende der Photoperiode einen signifikant höheren Ammoniumgehalt. Von den hieruntersuchten Umweltfaktoren reduzierte der Niederschlag nach der Behandlung die Wirkung von Glufosinat-ammonium am meisten.     

Phage sensitivity in relation to pathogenicity and virulence of the cotton bacterial blight pathogen of Sudan

At least two pathotypes of Xanthomonas campestris pv. malvacearum are now known to exist in Sudan. The pre-Barakat (race 1) and post-Barakat (race 2) pathogens have been shown to exhibit different host specificity. The former is pathogenic and highly aggressive on only cultivars with no resistance genes or with the B₂ and/or B₃ resistance factors, while the latter can infect the B₆ cultivars also. Race 2 in Sudan, which was previously reported to infect all the standard differentials, produced milder angular leaf spot symptoms and occasionally restricted vein infection. Moreover, it exhibited reduced growth in planta compared with race 1.
Bacteriophage studies revealed that the two races are quite distinct in their phage sensitivity. Race 1 can be lysed by only three, or rarely four, of the six phages used for typing, while race 2 is sensitive to all of them. The present study suggests that phage 7 may be the type-determining phage for race 2. Race 2 strain mutants resistant to phage 3 or 4 were found to be sensitive to phage 7 and pathogenic to both Acala and Barakat, although showing marked attenuation of virulence. However, mutants resistant to phage 2 or 7 were insensitive to all the phages and although they retained their pathogenicity to Acala, they either lost the ability to infect Barakat or produced a hypersensitive reaction. The resistance of all mutants was found to be due to failure to adsorb the homologous phage, indicating a change in the cell wall. The association of this with the attenuation of virulence suggests that bacterial wall components may function as virulence determinants in Xanthomonas campestris pv. malvacearum.     

Effects of herbicidal carbamates on mitochondria and chloroplasts

At concentrations near 2 × 10^?4M, barban, chlorpropham, and phenmedipham are inhibitors of the electron transfer in potato and mung bean mitochondria. The inhibition seems to be localized in the flavoprotein region. It affects preferentially the exogenous NADH dehydrogenation, in potato mitochondria (I₅₀, 10^?4M). Succinate dehydrogenation is less inhibited. At noninhibiting concentrations, the studied carbamates cannot uncouple the oxidative phosphorylations. Photosynthesis is completely inhibited by 2.10^?7M phenmedipham, 5 × 10^?5M barban, and 2 × 10^?4M chlorpropham. The inhibition takes place at the PS II level. Moreover, barban and chlorpropham are uncouplers of the photophosphorylations for concentrations between 5 × 10^?5 and 5 × 10^?4M. The effects observed on mitochondrial respiration can also be found on respiration of Acer cultured cells. The effects on isolated chloroplast photosynthesis are also observed for slightly higher concentrations on cultured Chlorella and on pea and oat leaf fragments.     

紫花苜蓿药剂灭茬试验初报

北京市大面积种植紫花苜蓿已进入第5个年头,随着群体的衰弱和产量的逐渐下降,苜蓿已进入了轮换倒茬期。由于苜蓿抗药性较强,常规药剂和剂量杀灭效果差。又因苜蓿生命力强,机械翻耕后还可恢复生长,对倒茬后新播作物的正常生长会造成影响。为控制其对换茬作物的危害,确保新播作物     

Effects of bifenox and oxadiazon on isolated chloroplasts,plant mitochondria and leaf pieces

The effects of bifenox (methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate) and oxadiazon (5-tert-butyl-3-(2,4-dichloro-5-isopropoxyphenyl)-1,3,4-oxadiazol-2(3H)-one on photosynthetic activity were investigated in isolated chloroplasts, and on respiratory activity in isolated mitochondria. The global effects of these chemicals were also investigated on cucumber cotyledon pieces. It was found that, in vitro, bifenox and oxadiazon acted on cotyledon pieces as typical diphenyl ether herbicides, causing complete pigment bleaching, even at low concentrations. In addition, bifenox and oxadiazon were shown to inhibit the photosynthesis process at the chloroplast level. At concentrations of up to 40-50 μM, oxadiazon and bifenox were observed to inhibit fully the light-dependent oxygen evolution of spinach class A chloroplasts, oxadiazon acting preferentially on electron transfer at the PS II level whereas bifenox acted on the photophosphorylation process. Comparison of the amounts of herbicide needed to inhibit photosynthesis and to cause bleaching of cucumber pieces leads to the conclusion that photosynthesis inhibition by bifenox and oxadiazon is only a secondary effect.     

Influence of application volume on the efficacy of clodinafop-propargyl and fenoxaprop-P-ethyl on oats

The influence of application volume on the efficacy of clodinafop‐propargyl and fenoxaprop‐P‐ethyl on cultivated oats (Avena sativa) was studied in the glasshouse. Both herbicides were more efficacious when applied in 75 L ha^?1 than in 300 L ha^?1, with 11002 and 11006 nozzles respectively. However, when the same two volume rates were created by varying the speed of a 11003 nozzle, clodinafop‐propargyl efficacy was not affected by application volume, whereas fenoxaprop‐P‐ethyl remained more efficacious at 75 L ha^?1. This suggests that in the first experiment, fenoxaprop‐P‐ethyl efficacy was affected by changes in both spray quality and concentration, whereas only the former influenced clodinafop‐propargyl efficacy. The hypothesis that the fenoxaprop‐P‐ethyl formulation was more influenced by concentration than clodinafop‐propargyl was supported by dynamic surface tension studies and measures of active ingredient retention by oat plants. Within the practically relevant concentration range considered, surface activity of clodinafop‐propargyl remained low, with little influence on herbicide retention. In contrast, depending on the concentration, surface activity of fenoxaprop‐P‐ethyl was below or above levels that were critical for its retention. Although these differences may not be as apparent in the field as in the glasshouse, our study certainly indicates that both clodinafop‐propargyl and fenoxaprop‐P‐ethyl are herbicides favoured by low application volumes.     

Effect of soil water content at the time of application on herbicide content in soil solution extracted in a pressure membrane apparatus

Wettable powder formulations of simazine, metribuzin and linuron and a suspension concentrate of simazine were sprayed on to soil particles which were either at a water content equivalent to pF 2·5 or air dry. Air dry samples were then wetted to pF 2·5 immediately or after 24 h. Soil solutions were removed using a pressure membrane apparatus at intervals up to 96 h after wetting. In each case the concentration in soil solutions expressed after 96 h following application to wet soil, or dry soil wetted immediately, were close to those predicted on the basis of Freundlich adsorption isotherm data obtained in slurry equilibrium conditions. There were, however, some differences after shorter periods. Concentrations were always lower in solutions obtained from air dry soil that was not wetted for 24 h. After 96 h simazine and metribuzin concentrations were about 50% of those obtained following application to wet soil, while that of linuron was about 25%. Differences of this size may be large enough to affect mass transfer phenomena and phytotoxicity. It seems likely that suspension of these herbicides sprayed in formulations on to wet soil dissolved in soil water at least as fast as would be predicted theoretically.     

Chemical catalysis of the isomerisation of peroxidising herbicidal thiadiazolidines

Model reactions with various -SH, -OH and -NH nucleophiles in an aprotic solvent were used to characterise the nature of the enzymatic conversion of thiadiazolidines to triazolidines. This conversion results in greater inhibition of protoporphrinogen oxidase (protox). It is inferred that GST-isoforms probably promote formation of one of the intermediates.     

Effect of temperature on herbicidal properties of MTB-951, a mycoherbicide to control Echinochloa crus-galli L.

MTB-951 is a potential mycoherbicide using a fungal plant pathogen ( Drechslera monoceras ) isolated from native Echinochloa species in Japan. Conidia of this pathogen were used as the active ingredient and the effect of temperature on its properties was examined in a laboratory. The optimum temperature for conidium germination was broad between 15 and 35°C and no difference in the germination ratio existed within this temperature range. Mycelial growth was the fastest at 25°C but was slower outside of the range 15–35°C. When leaves of Echinochloa crus-galli L. were immersed in deionized water containing the conidia, cellular electrolyte leakage from the leaves was observed. However, no electrolyte leakage occurred from leaves of rice ( Oryza sativa L.) under the same conditions. The occurrence of electrolyte leakage from E. crus-galli was dependent on the temperature and was the highest at 25°C. Herbicidal activity of MTB-951 against E. crus-galli was high between 25°C and 30°C, but decreased at 35°C in a glass vessel. In the present study, it was revealed that the physiological and herbicidal properties of MTB-951 depended on the temperature.     

坡柳种子提取物的除草作用初报

以小麦、高粱、稗草3种植物种子为供试对象,用小杯法测定了坡柳种子石油醚、氯仿、乙酸乙酯和乙醇提取物的除草作用.结果表明,坡柳提取物对幼根的抑制程度比幼芽大,乙醇提取物的除草活性明显高于其他提取物,其对高粱幼根的IC如为4.10 mg/L,对小麦幼芽的IC50为2 189.53 mg/L.石油醚提取物的活性最弱,低浓度有促进植物生长的作用.     

尿素除草活性的培养箱实验

以8种杂草为对象,通过培养箱试验研究不同浓度的尿素溶液对供试杂草萌发及根茎生长的影响。供试草种分别为鬼针草(Bidens bipinnata)、杂三叶(Trifolium hybridum)、马蹄金(Dichondra repens)、一点红(Emiliasonchifolia)、水蜈蚣(Kyllinga brevifolia)、狗尾草(Setariae Viridis)、高羊茅(Festuca arundinacea)、多年生黑麦草(Lolium perenne)。结果表明,尿素除对狗尾草的萌发无明显抑制作用外,对其他杂草的萌发、根长、茎长均有明显的抑制作用,并随着尿素溶液浓度的增高抑制作用增强,且以对根长的抑制作用最为明显。尿素对供试草种的萌发和根茎生长的抑制作用存在明显的种间差异,对尿素胁迫最敏感的是三叶草和水蜈蚣,然后分别是鬼针草、一点红、高羊茅、马蹄金、多年生黑麦草,最不敏感的是狗尾草,较低浓度的尿素处理反而促进了狗尾草的萌发。