Chemical weed control in irrigated direct-seeded rice in the Sudan Gezira

Unrestricted weed growth resulted in serious yield losses (60–75%) in rice (Oryza saliva L.). Hand-weeding once at 2 weeks after crop emergence was ineffective, but weeding at 2 and 2 weeks after crop emergence brought yield losses down to 20%. Pre-emergence application of bifenox and oxadiazon (12 l) and post-emergence application of molinate + propanil gave crop yields comparable to that of the clean weeded control (91–129%). Grain yields obtained with pre-emergence application of oxadiazon (25 EC) and post-emergence applications of propanil, bentazone + propanil, and bifenox alone or as a tank mix with propanil or bentazone were considerably less than those obtained from the clean weeded plots. Bifenox, oxadiazon (12 l) and propanil + molinate gave adequate and persistent weed control (72–97%), and did not damage rice. Oxadiazon (25 EC) gave good weed control but resulted in a serious stand reduction. Post-emergence application of propanil, propanil + bentazone bifenox alone or as a tank mix with propanil or bentazone had no adverse effect on crop stand, but gave poor control of grasses (0–40%).     

Response of onion (Allium cepa L.) plants to fertilizers, weed competition duration, and planting times in the central Jordan Valley

The competitive ability of onion with weeds and the effects of weeds on onion crop growth and yield were investigated in three field experiments carried out in the central Jordan Valley during the 1997–1998 growing season. Fertilizer application to the onion plants in the presence of weeds significantly lowered the onion yield and reduced the bulb diameter, compared to the unfertilized, weed-infested onion crop. Weed competition and onion yield reduction increased with an increase in the fertilizer rate. All weed-free treatments with or without fertilizer gave a significantly higher onion yield than any of the fertilized, weedy plots. The highest yield of onion was obtained from the weed-free plots with a moderate application of fertilizer. Weed competition reduced the growth, bulb yield, and size of onion in the plots established from bulbs, seedlings, and seeds when compared to the relevant weed-free controls. The effect increased with competition duration and was more pronounced in direct-seeded onion than in the other two types of planting material. However, onion grown from bulbs or seedlings gave better growth, bulb weight, and number and was more competitive than the direct-seeded onion. The results showed that the minimum number of days of weed competition needed for a significant reduction in onion growth was 42 days when propagated from bulbs or seedlings and 21 days after direct-seeding. Onion grown from bulbs tolerated weed competition better and produced a higher bulb yield than that obtained from direct-seeded or transplanted onion, irrespective of the planting dates. December was found to be the best planting time for onion that was grown from bulbs and seedlings, while November was the best planting time for direct-seeded onion, provided the plots were weed-free throughout the growing season.     

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.     

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.     

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.     

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.     

Tolerance of onions (Allium cepa L.) to the pink root disease caused byPyrenochaeta terrestris

The response of 11 onion cultivars (Allium cepa, L.) grown in flats containing soil infested withPyrenochaeta terrestris, the causal agent of pink root disease, was studied. In addition, four cultivars were tested in field trials. Pink roots were found on all the cultivars, including those considered to be resistant. The cultivars ‘Golden’ and ‘Yellow Creole’ were highly susceptible to pink root, whereas cvs. ‘Dessex’, ‘Granex’, ‘Laredo’, ‘Grano 502’ and ‘Grano’ (local) managed to grow and produce reasonable yields, despite having infected roots. Following infection, the growth period of early and intermediate maturing cultivars was shortened by 4–14 days, and that of late maturing cultivars by 18–45 days. A large percentage of small bulbs was produced by most of the susceptible cultivars, but no consistent results were obtained with the resistant cvs. ‘Granex’, ‘Dessex’, and ‘Laredo’. The resistant cultivars maintained an, extensive and viable root system which enabled them to tolerate the disease when grown in infested soils.     

Chemical weed control in rainfed cowpea (Vigna unguiculata (L.) Walp) in the Guinea savanna zone of Nigeria

In a field trial in 1978 at Mokwa, southern Guinea savanna zone of Nigeria, metolachlor at 1.5 and 3.0, prometryne at 2.0 and norflurazon and diuron at 1.6 kg/ha combined good weed control with high grain yield of cowpeas. The grain yields with these herbicides were comparable to those of the hoe-weeded and significantly higher than the weedy controls. In 1979, under wetter conditions, crop injury was observed with prometryne and linuron at 2.0 kg/ha. However, the grain yields obtained with alachlor, metolachlor, chloramben, pendimethalin and norflurazon and their mixtures with prometryne, linuron, diuron or metobromuron were comparable to that of the hoe-weeded treatment. In 1979 at Samaru, northern Guinea savanna, pendimethalin at 1.5, metolachlor at 3.0 and chlorbromuron and linuron at 1.0 kg/ha gave selective weed control. Prometryne at 2.0 kg/ha was the only herbicide that gave a significantly lower broad-leaved weed weight than the weedy check but it reduced the crop stand. At 1.0 kg/ha it was tolerated by the crop but failed to control grasses. Metolachlor at 1.5 kg/ha had a significantly higher broad-leaved weed weight than the weedy check. All theherbicides, except pendimethalin at 3.0 kg/ha, controlled the annual sedges at Samaru.     

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.     

Spoilage of stored onion (Allium cepa L. var Cepa) by Pseudomonas aeruginosa (Schroeter) Migula in Lowland Papua New Guinea

Abstract

Biochemical and pathogenicity studies of bacterial isolates from onions with discoloured internal tissues indicated the fluorescent pseudomonad Pseudomonas aeruginosa (Schroeter, 1872) Migula, 1900 to be the causal agent and that a site of injury was necessary for infection to take place. It is postulated that in the field a likely mode of infection would be through the necks of onion bulbs which are damaged during or after harvest.     

Evaluation of cultural practices (surface burning,deep ploughing,organic amendments) for management of rice root-knot nematode in rice - onion cropping system and their effect on onion (Allium cepa L.) yield

Rice hull burning (RHB) is a traditional cultural practice of many onion growers in San Jose City, Nueva Ecija, Philippines, mainly for weed control and increased yield. The resulting carbonized rice hull (ash) is incorporated into the soil during land preparation before transplanting of onion. Studies to evaluate the effect of RHB on the population of the rice root-knotnematode, Meloidogyne graminicola, and onion yield were conducted in a farmer's field naturally infested with the pathogen. Burning of 15-cm-deep rice hulls significantly reduced the nematode populations in the soil and increased onion yield. Increasing the thickness of rice hulls burned to 30 cm deep resulted in a yield increase of 44.2% over no RHB and 11.9% over 15-cm-deep rice hulls, while the yield increase with 15-cm-thick hulls was 28.8% over no RHB. Plots that received rice hulls 30 cm deep also produced 37.7% more large bulbs for export than those plots that received 15-cm-deep hulls, and 151.7% more than those plots with no RHB. Deep ploughing did not significantly affect nematode populations compared with standard ploughing. Organic amendment did not contribute to an increase in onion yield and has no effect on the population of rice root-knot nematode.     

Pathology and taxonomy of Cladosporium leaf blotch of onion (Allium cepa) and leek (A. porrum)

Cross-inoculations to leek and onion plants using isolates of Cladosporium from leaf blotches on leeks or onions showed that no cross-infection occurred between isolates and their respective hosts. The species causing leaf blotch on leeks was morphologically distinct from that causing a similar disease on onions and the differences, augmented by the results obtained from the cross-pathogenicity tests, indicate that two taxa should be recognized at the rank of species. Following an examination of type or authentic material it was concluded that the name C. allii (Ell. & G. W. Martin) P. M. Kirk & Crompton comb. nov. should apply to the species causing leaf blotch on leeks and C. allii–cepae (Ranojevi) M. B. Ellis to that on onions.     

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.     

Chemical weed control in rainfed peanuts

Field studies at Bangalore, India, demonstrated that benfiuralin, fluchloralin and profluralin were effective for the selective control of many weed species in field experiments with peanuts (Arachis hypogaea L.‘BH-8-18′). Trifluralin and dinitramine were effective against many weed species but reduced crop stand by about 10%. These two herbicides also reduced the incidence of leaf spot disease (Cercospora arachidicola) and peanut pod yields were similar to clean weeded treatments. Bentazon was ineffective on most weed species and metribuzin was lethal to the crop. Alachlor, nitrofen and chloramben were only partially effective and would require supplemental hand weeding or mechanical tillage to obtain satisfactory weed control.     

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.     

Evaluation of the allelopathic potential of Kava (Piper methysticum L.) for weed control in rice

Kava is a perennial pepper plant from the Oceanic region, which is commonly used as a drink by natives and for pharmacological purposes. Results of this study concluded that Kava has allelopathic potential and suppressed germination and growth of lettuce ( Lactuca sativa L), barnyardgrass ( E. crus-galli Beauv var. formosensis Ohwi.), and duck-tongue weed ( M. vaginalis Presl var. plantaginea Solms-Laub.) Moreover, Kava inhibited emergence of weeds in paddy soils. The inhibition of Kava became stronger as the applied concentration increased. In a greenhouse experiment, Kava had the greatest inhibition on emergence and weed growth in paddy soils when a dose of 1 ton ha⁻¹ of Kava was divided and applied at 3, 16, and 23 days after watering. Inhibition by Kava varied among weed species. Results from this study suggest that Kava might be useful for weed control in rice or reduce dependence on herbicide.     

Chemical and cultural control of bulrush (Scirpus maritimus L.) and annual weeds in lowland rice (Oryza sativa L.)

Chemical and non-chemical or cultural approaches for the control of Scirpus maritimus L. (bulrush) and of annual weeds in lowland rice were examined in the field. Herbicides such as bentazon [3-isopropyl-1H-H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and 2,4-D [2,4-dichlorophenoxy)acetic acid] effectively controlled S. maritimus but not the annual grasses [Echinochloa glabrescens Munro ex Hook. f. and Echinochloa crus-galli ssp. hispidula [(Retz.) Honda] when applied at the six- to eight-leaf stage 20–28 days after transplanting or seeding rice). S. maritimus was not adequately controlled when the herbicides were applied pre- or early post-emergence. A granular formulation of bensulfuron-methyl [(methy1–2-[[(4,6-dimethoxypirimidin-2-yl)aminosulfonylmethyl]benzoate)] applied 6 or 8 days after transplanting or seeding (two- to four-leaf stage of the weed) effectively controlled S. maritimus and the annuals E. glabrescens, E. crus-galli ssp. hispidula, and Monochoria vaginalis, Presl. (Burm. f.) S. maritimus stand was drastically reduced by shifting land preparation back and forth from wet to dry. Neither tillage intensity nor use of intermediate-statured modern rice cultivars affected the weed stand. La lutte chimique et culturelle contre le scirpe (Scirpus maritimus L.) et les mauvaises herbes annuelles en culture de riz (Oryza sativa L.) Des possibilitiés chimiques et culturelles dans la lutte contre Scirpus maritimus L. (le scirpe) et les mauvaises herbes annuelles en culture de riz ont fait l'objet d'une étude sur le terrain. Appliqués au stade 6- à 8-feuilles des graminées annuelles, Echinochloa glabrescens Munro ex Hook. f. et Echinochloa crus-galli ssp. hispidula [(Retz) Honda] (20 à 28 jours après le repiquage ou le semis du riz), les herbicides, tel le bentazone [isopropyl-3 1H 3H-benzothiadazine-2,1,3 one-4 dioxyde-2,2] et le 2,4-D [acide 2,4-dichlorophénoxyacétique] ont permis une lutte efficace contre S. maritimus mais pas contre les graminées. La maîtrise de S. maritimusétait insuffisante quand les traitements herbicides ont été appliqués en prélevée ou en postlevée précoce. Une forme granulée de bensulfuron-methyl, appliquée 6 ou 8 jours après le repiquage ou le semis (stade deux- à quatre-feuilles de l'adventice) a permis une lutte efficace contre S. maritimus ainsi que les adventices annuelles E. glabrescens, E. crus-galli ssp. hispidula et Monochoria vaginalis (Burm. f.) Presl. Une réduction dramatique dans le peuplement de S. maritimus a suivi l'emploi alterné de techniques humides el sèches dans la préparation du sol. Ni l'intensité du labourage ni l'emploi de variétés de riz modernes de hauteur moyenne n'ont eu d'influence sur l'enherbement. Bekämpfung der Strand-Simse (Scirpus maritimus L.) und einjähriger Unkräuter in Nass-Reis (Oryza saliva L.) mit chemischen und Kulturmethoden Mit Herbiziden wie Bentazon und 2,4-D konnte Scirpus maritimus, nicht aber die einjährigen Gräser Echinochloa glabrescens Munro ex Hook, und Echinochloa crus-galli ssp. hispidula (Retz.) Honda bekämpft werden, wenn sie im 6- bis 8-Blatl-Stadium (20 bis 28 Tage nach dem Pflanzen oder der Saat des Reises) behandelt wurde. Die Bekämpfung war aber unzureichend, wenn die Herbizide vor oder kurz nach der Keimung ausgebracht wurden. Mit bensulfuron-methyl Granutat 6 oder 8 Tage nach dem Pflanzen oder der Saat (2- bis 4-Blatt-Stadium der Unkräuter) konnten Scirpus maritimus und Echinochloa glabrescens sowie E. crus-galli ssp. hispidula und Monochoria raginalis (Burm. f.) Presl. Bekämpft werden. Die Verschiebung der Bodenbearbeitung von nass nach troeken verringerte die Verunkrautung mit Scirpus maritimus erheblieh. Der Unkrautbestand wurde weder durch verschiedene Intensität der Bodenbearbeitung noch durch die neuen mittellangen Reissorten herabgesetzt.     

Effect herbicides on weed control, yield and quality of eggplant (Solanum melongena L.) in Trinidad

The effects of six herbicides on weed control, yield and quality of transplanted.‘Early Long Purple’eggplant (Solantam melongena L.,) were evaluated in two replicated field experiments during the wet seasons (June to December) of 1976 and 1977 on River Estate loam soil in trifluralin 0 kg and had gave the best yield and excellent weed control for 8 weeks. Benfluralin (kg and ha) isopropalin (1.5 kg m.a ha) and diphenamid (5.0 kg and ha) gave acceptable weed control for 8 weeks and satisfactory yields, but chlorthal-dimethyl (1 kg a ha) and hotra (40 kg a ha) were less satisfactory. All the herbicides tested controlled weed for 4 weeks. There was no crop injury. Effet des herbicides sur le desherbage de sendement et la qualite de l'aubergine (Solanum melongena L.,) d Trinidad Les effets de herbicides sur le desherbage, le rendement et la qualite de preds transplantes d'aubergine (Solantum melongena L.,) var ‘Farly Long Purple’, ont ete evalues dans deux experiences au champ, durant les sarsons humides (june to December repetees en 1976 et 1977, sur un sol argileux de River Estate a Trinidad La triflurraline 1.0 kg m a has donne le meilleut rendement et un excellent desherbage pendant S sernames I a benfluraline (1.1 kg m.a. ha) l'isopropaline (1.5kg ma. Ha) et le diphenamide (5.0 kg m.a ba) ont donne un desherbage acceptable et des rendements satisfaisant mais le chlorthal dimethyl (10.0 kg m.a ha) et la butraline (4.0 kg m.a ha) ont ete moins satisfaisants Tous les herbicides essayes ont maitrise les measures herbes pendant 4 semaines II n'y a pas eu de degats sur la recolte. Emsatz von Herbizalen in Eterfruchen Solanum melongena in Trinidad Wirkane aut Unkraut. Ertrag und Qualdat. Es wurde die Ergnung von wchs Herniziden fur die Unkraut-bekämpfung in gepfltanzten Eterfrüchten (Solaman melongena L.) der Sorte ‘Early Long Purple’ sowie the Wirkung aut Ertrag und Qualität in zwer Feldversuchen wahrend der Regen zen (Juni bis December) in den Jahren 1976 und 1977 auf einem River-Estate-Lehmnoden in Trinidad gepruit. Mit Trifluralin (1.0 kg ha AS) wurden die hochsten Ertage und cine ausgezetchnete Unkrauthekämpfung über acht Wechen erzielt Benfluralin (1.1 kh ha AS) Isopropalin (1.5 kg ha AS) und Dephenamid (5.0 kg ha AS) wirkten uber acht Wochen zufriedenstellend und führlen zu mittleren Ertagen; Chlorthaldimethyl (10.0 kg ha AS) und Butralin (4.0 kg ha AS) befriedigten weniger. Alle gepruften Herbicide bekämpften die Unkrauter uber cine Zeit von 4 Wochen. Schaden an der Kulturpflanze konnten nicht festgestellt werden.