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.     

Chemical weed control in rainfed upland rice in Nigeria

Abstract

Two field experiments on chemical weed control in Faro 41 upland rice (Oryza sativa L.) variety were conducted at a rainforest site near the National Cereals Research Institute, Amakama Substation in 1989 and 1990. The herbicides tested were a coformulated mixture of pretilachlor and dimethametryne at 1.5, 2.0 and 2.5 kg a.i./ha, a co‐formulated mixture of piperophos and propanil applied at 3.16 and 3.95 kg a.i./ha, and Oxadiazon at 1.0 kg a.i./ha. Two hand weedings and a ‘no weeding’ treatment were included. The herbicides were applied 5 days after planting. All were safely selective to the crop. Most provided adequate weed control through 8–12 weeks after planting. Weeds controlled included Cynodon dactylon, Commelina benghalensis, Dlgitaria horizontalis, Eleusine indica, Panicum maximum and Pennisetum purpureum as grass weeds. The broadleaf weeds were Emilia sonchifolia, Ageratum conyzoides, Portulaca oleraceae, Richardia brasiliensis and Ipomoea Involuncrata. The sedges Mariscus alternifolius and Cyperus esculentus were encountered in the plots. Pretilachlordimethametryne at 2.5 kg a.i./ha had the best weeding score. Twoyear average grain yields of 1.7–2.6 t/ha were obtained from the herbicide treatments. With only 0.4 t/ha from the unweeded treatment, yield losses of more than 80% were recorded.     

Evaluation of herbicides for maize production in three ecological zones of Nigeria

Abstract

Maize cultivation in Nigeria has increased rapidly in the last few years as fertilizers have become more readily available to farmers. Without the use of herbicides however, the area of land that can be brought under maize production will be limited. The following herbicides were evaluated in three ecological zones of Nigeria: atrazine and mixtures of atrazine and simazine, atrazine and metolachlor and atrazine and cyanazine. All herbicide treatments were applied at the rate of either 1.0 or 2.0 kg a.i./ha. The plots that received 1.0 kg a.i./ha also received one supplementary hand weeding. All treatments gave yields comparable to the weed free control, with the exception of the unweeded higher rate of the atrazine and cyanazine treatment which gave the lowest grain yield as a result of poor weed control.     

Herbicide Performance in Rainfed Cabbage

Abstract

The effectiveness of butralin (2.0 and 4.0 kg a.i./ha pre-plant, 2.0 and 4.0 kg a.i./ha pre-em), chlorthal-dimethyl (10.0 and 12.0 kg a.i./ha pre-em), trifluralin (0.6 and 1.1 kg a.i./ha pre-plant) chloramben (2.0 kg a.i./ha pre-em) and nitrofen (2.0 kg a.i./ha pre-em) in controlling weeds in transplanted ‘Kono Cross’ cabbage and the influence of these treatments on the yield and quality of marketable heads and on the economics of weed control were evaluated in three replicated field experiments on River Estate loam soil in Trinidad during the wet seasons of 1976 and 1977. While herbicides did not affect the size of the cabbage plant population or the date to maturity of the crops, they reduced the cost of weed control by over 30% and increased the net returns relative to the clean-weeded control by over 9%. Butralin at 4.0 kg a.i./ha pre-plant and pre-em and the trifluralin treatments were superior to nitrofen which gave good weed control up to five weeks and higher yields than the clean-weeded control. Chlorthal-dimethyl gave encouraging results but caused slight, temporary stunting. The application of one of these treatments followed by one hand weeding at about four weeks should give full-season weed control and an acceptable yield of marketable heads with increased financial returns. Chloramben was the least effective herbicide tested and its use may not be justified under similar conditions to those of this study.     

A World-Wide Organization to Promote the Development of Biological Control

Abstract

Three experiments were conducted to evaluate the efficacy of metribuzin in tea fields. These were a field trial in plots infested with a wide range of weeds, a pot experiment using Paspalum conjugatum and a microplot experiment with 100 Ageratum conyzoides plants/plot. Metribuzin at 0.70, 1.05, 1.40 and 2.10 kg a.i./ha was applied in 450 l water/ha. All rates were satisfactory after 1 week but residual activity increased with application rate; metribuzin at 2.10 kg a.i./ha was significantly superior after 6 weeks. Control after 8 weeks was reduced due to the presence of resistant species. Against Paspalum conjugatum metribuzin at 1.40 kg/ha gave good control for 8 weeks but 2.10 kg/ha was necessary for 12 weeks control. All rates compared favourably with dalapon (4.48 kg a.i./ha). Against Ageratum conyzoides metribuzin at all rates gave good control for up to 12 weeks and significantly better than 2, 4-D at 1.12 kg a.i./ha. Most other grass and broadleaved weeds were satisfactorily controlled at 1.40 kg a.i./ha. Metribuzin with its marked post-emergent effect and prolonged soil residual activity from 6-12 weeks after application, depending on weed species, may become an important tool in pre-monsoon weed control programmes in tea fields. It did not induce any phytotoxic symptoms on mature tea.     

Response of transplanted rice to nitrogen fertilization under different weed management practices

Abstract

Rice yield increased significantly and consistently up to 120 kg N/ha when weeds were not controlled. But when weeds were effectively controlled by two hand weedings (20 and 40 days after transplanting) or by use of thiobencarb at 1–0 kg a.i./ha rice yield increased significantly up to 80 kg N/ha. The optimum dose of N for transplanted rice under mid‐hill conditions of Himachal Pradesh (Palampur) was 82 kg/ha when two hand weedings were done and 86 kg/ha when weeds were managed using thiobencarb. The yield response per kg of N in the respective treatments was 20 and 24 kg of grain. The weed dry weight was significantly lower in thiobencarb and hand weeded plots compared with unweeded check though the difference in weed dry weight due to the former two treatments was not significant.     

Herbicide Research on Groundnut and Sorghum under Farmer Conditions in the Indian Semi-arid Tropics

Abstract

Plots 17 × 5 m were laid out in farmers' fields in three villages. Treatments (replicated thrice) included atrazine (0.5 or 1.0 kg a.i./ha) on sorghum and nitrofen (0.75 and 1.5 kg a.i./ha) on groundnuts with or without hand-weeding or farmers normal weed control. Groundnuts were unfertilized, sorghum received 20 or 80 kg N/ha. Cooperating farmers were allocated plots for traditional weed control, other operations were carried out by research staff. Some plots were discounted because farmers withdrew cooperation or did not participate correctly or because of flooding. In groundnuts nitrofen alone was inferior to nitrofen + one hand-weeding. In sorghum there were no differences between high and low fertilizer regimes. Atrazine gave superior yields to farmers' weed control. All treatments were better than the unweeded control. Generally farmers fields had low weed populations due to good, timely control and low soil fertility. Herbicides are not economic at present. Problems associated with research in farmers fields included: selection of farmers who would participate correctly, variability between different farmers' weeding practices and between different fields due to previous crops and cultural practices; lack of control of farmers weeding operations and the distance of experimental plots from the research station. The authors suggest that small experiments with only 4-6 treatments are easier for participating farmers to comprehend, selecting suitable size and shape of plots is important and that if many farmers are involved the number of replicates can be reduced.     

Weed interference and control in white yam (Dioscorea rotundata Poir)

The climbing growth habit of white yam (Dioscorea rotundata) coupled with its inability to shade the ground completely at any stage of its growth and development makes it very susceptible to weed interference. The critical period of weed interference in white yam was between the 8th and 16th week after planting (w.a.p.) for yam planted at the onset of rains. Keeping yam plants weedy for 16 w.a.p. or beyond significantly reduced tuber yield; keeping them weed-free for the same period resulted in a significant increase in tuber yield. A minimum of three weedings within 16 w.a.p. are necessary to minimize yield reduction caused by weeds. The lowest weed weight and highest crop yield from herbicide treatments were obtained where a mixture of fluometuron and metolachlor each at 2.0 kg a.i./ha was used for pre-emergence weed control.     

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.     

The Institute of Phytopathological Research

Abstract

Further work with the herbicide C 19490 (S-(2-methyl-1-piperidyl-carbonylmethyl)-O,O-di-N-propyl dithiophosphate) in the mixture C 288 with the triazine C 18898 in the ratio 4:1, and with 2,4-D isopropyl ester (2,4-D IPE) in the ratios 2:1 and 3:2 have been completed. New toxicological data show that the risk of toxicity hazards to the user or to other mammals by contamination is low. Residue work shows that C 19490 leaves very low or undetectable residues in rice grain and soil, though C 18898 was detected in both, but never at more than 0.28 ppm in soil or more than 0.04 ppm in grain. There was no interaction between either C 19490 or C 288 and commonly used insecticides. Uptake of the products by plants was shown to be preferentially through emerging shoots, and less through roots.

Field trials resulted in recommendations for around 2 kg C 288 total a.i./ha in Japan, optimum timing depending on the prevailing temperature. Successful control was achieved in Taiwan with C 288 at 1 kg a.i./ha in both the cool and warm season crops, applied 7–12 days after transplanting. In equatorial Asia, mixtures worked well: C 288 at 0.75–1.25 kg a.i./ha, C 19490 at 0.75–1.0 + 2,4-D IPE at 0.5 kg a.i./ha and the 3:2 mixture at 0.75 + 0.5 kg a.i./ha (granular), applied four DAT on dense weed stands, but up to ten DAT on stands comprising predominantly moderate infestations of Echinochloa crusgalli, Monochoria vaginalis and annual Cyperus spp. These recommendations resulted in yields which were never significantly different from those of hand-weeded areas. On light, permeable soils, e.g. in Pakistan, C 288 at 1.0–1.25 kg a.i./ha, 8–10 DAT was less harmful to the crop than lower rates applied earlier, and was better than the 2,4-D IPE mixture for weed control. In Egypt, C 19490 + 2,4-D IPE at only 0.375 + 0.25 kg a.i./ha was successful, because of the susceptible weed flora.     

Recent Developments in the Use of Herbicides in Rubber and Oil Palm

Abstract

Recent developments in the use of herbicides during the establishment of leguminous cover crops and the mature phases of rubber and oil palm plantings are discussed. Results of 12 semi-commercial and commercial scale trials showed that chemical weeding using paraquat and diuron post-emergence or oxyfluorfen pre-emergence with supplementary manual or chemical control was considerably cheaper than exclusive manual weeding during the six months following the sowing of legumes. Reductions in weeding costs ranged from 6 to 66%. In the mature phase a wide range of herbicide treatments involving extensively used herbicides such as paraquat, MSMA, 2, 4-D amine and sodium chlorate for the suppression of weed growth along rubber tree rows and in oil palm circles and harvesters' paths were compared. Results indicate that there are several suitable alternatives to sodium arsenite, a formerly widely used herbicide which is now banned for general weed control. In both crops, the most cost effective treatments for controlling mixed vegetation were Ustinex Special (MCPA + diuron + amitrole, 2:3:6) at 1.48 kg a.i.ha + Gramoxone (paraquat) at 0.22 kg a.i./ha and Paracol (paraquat + diuron, 1:1) at 0.56 kg a.i./ha + DMA Amine (2, 4-D) at 0.50 kg a.e./ha.     

Plant Diseases

Abstract

Field experiments conducted at Punjab Agricultural University, Ludhiana during 1972–73 and 1973–74 showed that post-emergence application of oxadiazon at 1 kg a.i./ha in transplanted onion gave remarkable weed control and maximum crop yield. Other treatments which performed well include pre-planting alachlor at 2.5 kg a.i./ha plus post-emergence propanil at 1.8 kg a.i./ha and also pre-planting nitrofen at 1.25 kg a.i./ha plus post-emergence nitrofen at 1.25 kg a.i./ha. Herbicides did not significantly influence the bulb quality, soil microflora or the emergence and yield of following crops of okra, bitter gourd and radish.     

Weed and fertility management using maize/soyabean intercropping in the north‐western Himalayas

Abstract

In a field experiment conducted on a moderately fertile silty clay loam soil in the north‐western Himalayas, growing one or two rows of soyabean (Glycine max L.) as an intercrop in maize (Zea mays L.) reduced weed numbers and weights significantly and increased maize yields. Sowing two rows of soyabean had a better effect than one row, with maize at a constant sowing density. The maize equivalent yield increased significantly with intercropping in the ratio 1:2 (maize:soyabean rows) as compared to maize alone or maize + soyabean in alternate rows, when all these trials were supplied with the full recommended amount of fertilizer. The maize yield in trials with half the recommended fertilizer amount in the intercropped system was similar to that of maize alone supplied with the full fertilizer dose. The weeds were effectively controlled and yields of maize and soyabean were increased with pre‐emergence application of alachlor at the rate of 2.5 kg a.i./ha or with three hand weedings.     

Weed control in rose-scented geranium (Pelargonium spp)

Abstract: Field investigations were carried out during 1999 and 2000 to identify effective chemical/ cultural methods of weed control in rose-scented geranium (Pelargonium spp). The treatments comprised pre-emergence applications of oxyfluorfen (0.15, 0.20 and 0.25 kg AI ha(-1)) and pendimethalin (0.50, 0.75 and 1.00kg AI ha(-1)), successive hand weeding, hoeing and mulching using spent of lemon grass (at 5 tonnes ha(-1)) 45 days after planting (DAP), three hand-weedings 30, 60 and 90 DAP, weed-free (frequent manual weeding) and weedy control. Broad-leaf weeds were more predominant than grass and sedge weeds, accounting for 85.8% weed density and 93.0% weed dry weight in 1999 and 77.2% weed density and 93.9% weed dry weight in 2000. Unrestricted weed growth significantly reduced geranium oil yield, by 61.6% and 70.6% in 1999 and 2000, respectively. Pre-emergence application of pendimethalin (0.75-1.00 kgAI ha(-1)) or oxyfluorfen (0.25 kg AI ha(-1)), successive hand-weeding, hoeing and mulching and three hand-weedings were highly effective in reducing weed density and dry weight and gave oil yield comparable to the weed-free check. Application of oxyfluorfen (0.15 or 0.20 kg AI ha(-1)) and pendimethalin (0.50 kg AI ha(-1)) were less effective in controlling the weed species in geranium. None of the herbicides impaired the quality of rose-scented geranium oil measured in terms of citronellol and geraniol content.     

Insect Pests of Cotton – Western Herbaceum Region of India

Abstract

Pre-plant and pre-emergence herbicides were tested for effective weed control in a seed crop of okra during 1974–75 and 1975–76. All treatments significantly decreased the weed population and increased the seed yield as compared to the unweeded control. Fluchloralin (0.90 and 1.20 kg a.i./ha pre-plant), alachlor (2.50 kg a.i./ha pre-em) and EPTC plus alachlor (3.75 kg a.i./ha pre-plant and 1.25 kg a.i./ha pre-em) proved to be the most effective and economical treatments. No residual effects were observed with any herbicide on the succeeding crops of radish, carrot, turnips, peas and spinach.     

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.     

Effects of weeding and nitrogen treatmerts on maize yields in Nigeria

The effects of handweeding and of varying timing of applications of nitrogen were examined in three experiments on maize grown in Southern Nigeria. At two weedy sites which had been cropped for several years, weed competition lowered maize yields by 50% and two hand weedings at 3 and 7 weeks after planting were as satisfactory as more extended weedings. At the third site after an extended fallow period weed competition was not severe. Splitting of nitrogen application generally had no advantage over a single application of the same amount. There was no significant interaction between nitrogen and weeding treatments at any site.     

Seventh British Insecticide and Fungicide Conference,Brighton, November 1973

Abstract

A field experiment was conducted during the wet seasons of 1980 and 1981 to find out the relative influence of weed control and applied nitrogen on performance of transplanted rice and nutrients uptake by rice and weeds. Propanil and thiobencarb, each at 2.0 kg a.i/ha, were found comparable to two hand weedings in increasing grain yield of rice and minimizing dry matter of weeds. The mean grain yield was increased by 28.06% while dry matter of weeds reduced by 84.04% over unweeded control. Application of nitrogen from 0 to 75 kg N/ha increased grain yield to the tune of 1631 kg/ha. Remarkable increase in grain yield was noticed when weed control treatments were associated with application of nitrogen. Higher uptake of N, P and K by crop and lower removal of same nutrients by weeds were observed in herbicides and hand weedings than unweeded control. N, P and K in the order of 11.49, 1.71 and 12.40 kg/ha respectively could be saved through weed control in transplanted rice.     

Study on the effect of four herbicides with and without applied phosphorus on weed control and seed yield of fenugreek (Trigonella foenum‐graecum L.)

Abstract

Field experiments were conducted at Jobner (Rajasthan) during the winter seasons of 1982 and 1983 to evaluate certain physical and chemical weed control systems in fenugreek at two levels of applied phosphorus. The experiments comprised four herbicides (fluchloralin, pendimethalin, thiobencarb, and chloramben) at two levels each, manual weeding at three levels; and an unweeded check. The second factor, namely, application of phosphorus was evaluated at 0 and 40 kg P₂O₅/ha. The soil of the experiment site was loamy sand, containing 0.16% organic carbon. The results showed that amongst the herbicides, preemergent pendimethalin at 0.75 kg/ha controlled the weeds most effectively and gave 8.91 q/ha fenugreek seed yield, which was more than twice the seed yield obtained from the unweeded check plots. The twice hoed plots were found to give 1.32 q/ha higher seed yield than the pendimethalin herbicide treatment, but the benefit‐cost ratio was found higher for the herbicidal treatment. Application of phosphorus at 40 kg P₂O₅/ha was found to bring about significant increase in the seed yield of fenugreek by 59 kg/ha over control, without any interaction with the weed control treatments.     

Weed control in irrigated dry seeded rice

Large losses in grain yields due to weed competition were found in studies conducted in irrigated dry seeded rice at Gezira Research Station, Sudan. These losses could exceed 50%. Weed competition lowered panicle number per unit area by 37%, number of filled grains per panicle by 13%, and weight of 1000 grains by 4%. Tillering was the critical growth phase most affected by weed competition. Grain yields were increased as number of hand weedings increased. The best yield (4.1 t/ha) was obtained from 3–4 weedings carried out at 15, 30, 45 and 60 days after rice emergence. Oxadiazon (0.5 kg/ha) gave good residual weed control of the dominant weed species, Phyllanthus niruri L., Leucas urticifolia L., Heliotropium F.W.Andr. and Echinochloa colona (L.) Link, for 6–7 weeks. The combination with continuous flooding from 6 weeks after rice emergence gave excellent weed control during the entire season, and comparable or even better yields than frequently weeded rice.