Chemical control of weeds in wheat (Triticum aestivum L.) in Iran

Experiments were conducted in 2006–2007 at six research stations of the Iranian Plant Protection Research Institute to study the efficacy of different herbicides to control weeds in wheat. Treatments included mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (WG) at 45 + 45 + 135 g a.i./ha, respectively, sulfosulfuron at 21, 31.5, 42 and 51 g a.i./ha, chlorsulfuron at 15 g a.i./ha, bromoxynil plus MCPA at 600 g a.i./ha with clodinafop propargyl at 64 g a.i./ha, sulfosulfuron plus metsulfuron-methyl at 36 g a.i./ha, mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (OD) at 15 + 3 + 45 g a.i./ha, respectively, and a full season weed-free control. Herbicides were applied at wheat tillering. Results showed that sulfosulfuron plus metsulfuron-methyl, and bromoxynil plus MCPA with clodinafop propargyl resulted in satisfactory weed control and wheat grain yield at most locations. Weed control efficacy of both formulations of mesosulfuron-methyl plus iodosulfuron-methyl-sodium was variable across locations. Efficacy of the OD formulation appears to depend upon location, so that application of this herbicide at Shiraz and Gorgan resulted in better weed control compared to use of the WG. Satisfactory performance of the OD formulation at Gorgan and Shiraz could be attributed in part to the even pattern of rainfall distribution during the growing season and wheat cultivar used, respectively. With respect to grain yield, however, the OD formulation was better than WG formulation at most of the locations.     

Weed control with pre-emergence herbicides in vegetable soybean (Glycine max L. Merrill)

Field and laboratory experiments were conducted in the early and late rainy seasons in Thailand to evaluate the effect of pre-emergence application of herbicides and determine the herbicide residues on vegetable soybean (Glycine max L. Merrill cv. No. 75) production. No visible crop injury was observed after application of alachlor 469 g a.i./ha, clomazone 1080 g a.i./ha, metribuzin 525 g a.i./ha, pendimethalin 1031.25 g a.i./ha, tank-mixed clomazone 960 g a.i./ha + pendimethalin 928 g a.i./ha, or tank-mixed metribuzin 350 g a.i./ha + pendimethalin 928 g a.i./ha. However, acetochlor 1875 g a.i./ha, isoxaflutole 75 g a.i./ha, and oxadiazon 1000 g a.i./ha caused visible crop injury. Plant bioassay of herbicide residues in the soil after harvest showed no phytotoxic effect on baby corn (Zea mays Linn. cv. Suwan 3), cucumber (Cucumis sativus L. cv. Pijit 1), pak choi (Brassica chinensis Jusl. cv. Chinensis), and soybean (G. max L. Merrill cv. CM 60). Gas Chromatography-Mass Spectrometry (GC–MS) analysis showed no significant herbicide residues on crop yield (or MRLs < 0.01 ppm) for all herbicides used in this study. The application of metribuzin at 525 g a.i./ha was sufficient to provide satisfactory full-season control of several weed species and gave the highest crop yield. In addition, pendimethalin at 1031.25 g a.i./ha, and tank-mixed metribuzin at 350 g a.i./ha + pendimethalin at 928 g a.i./ha can provide a similar level of weed control as an alternative to reduce herbicide dosage thereby increasing food and environmental safety in vegetable soybean production.     

Efficacy of a new glyphosate formulation for weed control in maize in southwest Nigeria

A field trial in 2003 and 2004 assessed the efficacy of a new formulation of glyphosate, Touchdown Forte HiTech (glyphosate-TF) and two older versions, Roundup (glyphosate-RP) and Touchdown (glyphosate-TD) for weed control in Nigeria. Treatments were glyphosate-TF at 0.25–1.25 kg a.i./ha, glyphosate-RP at 1.8 kg a.i./ha, and glyphosate-TD at 1.0 kg a.i./ha. Weeded and unweeded treatments were controls. Visual evaluations of weed control at 4 and 8 weeks after treatment (WAT) in both years indicated that glyphosate-TF at all doses gave moderate to complete control of all major weeds (50–100%). At 4 WAT, control of Ageratum conyzoides L., Commelina benghalensis L., Ipomoea involucrata P. Beauv., Brachiaria comota [Hochst ex A. Rich] stapf, and Acalypha ciliata Forssk was at a level similar to that in the weeded control. In 2003, all herbicide formulations and the weeded control reduced Imperata cylindrica (L.) Beauv. shoot dry biomass to the same level at 8 WAT (91–100%) and at maize harvest (83–88%). In 2004, 0.50–1.25 kg a.i./ha of glyphosate-TF and 1.8 kg a.i./ha of glyphosate-RP gave 95% reduction at 8 WAT and 97% at harvest, similar to the weeded control. Maize grain yield in the weeded control and herbicide treatments was 2.8 times higher than that in the unweeded control in both years. These results indicate that glyphosate-TF is effective for weed control in maize at herbicide doses lower than the older formulations.     

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

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

Peanut variety response to postemergence applications of carfentrazone-ethyl and pyraflufen-ethyl

Field experiments were conducted in the south Texas and Texas High Plains area in 2005 and 2006 to evaluate peanut variety tolerance to carfentrazone-ethyl and pyraflufen-ethyl. Lactofen was used as the standard. Carfentrazone-ethyl at 0.03 and 0.04 kg ai/ha, pyraflufen-ethyl at 0.003 and 0.004 kg ai/ha, and lactofen at 0.22 kg ai/ha were applied 35 days after planting (DAP) in south Texas and 51–56 DAP in the High Plains area in weed-free plots. Peanut cultivars selected for evaluation were those normally used in each area. In south Texas, Tamrun 96, Tamrun OL 01, and Tamrun OL 02 were evaluated while in the High Plains area, Flavor Runner 458, GP-1, and Tamrun OL 02 were evaluated. No peanut cultivar by herbicide interaction was observed in south Texas but an interaction did occur in the High Plains. In south Texas, peanut stunting was 10% or less with both herbicides and rates. In 2005, carfentrazone-ethyl at 0.04 kg/ha resulted in a yield reduction when compared with the untreated check while in 2006 both rates of carfentrazone-ethyl and the high rate of pyraflufen-ethyl reduced yield compared to the untreated check. No grade differences were noted among herbicide treatments. In the High Plains area, the high dose of both carfentrazone-ethyl and pyraflufen-ethyl caused the greatest peanut injury (at least 25%) compared with lactofen (6% or less). In 2005, the high dose of pyraflufen-ethyl and lactofen reduced yield compared with the untreated check while in 2006 both carfentrazone-ethyl and pyraflufen-ethyl reduced yield compared with the untreated check.     

Insecticidal control and economic damage of sugar-cane wireworm, Agrypnus variabilis (Candèze) in maize

Six insecticides (terbufos, chlorpyrifos, ethoprophos, phoxim, bendiocarb and lindane) were tested against sugar-cane wireworm Agrypnus variabilis (Candèze) in maize. The first five insecticides were applied at 0·25, 0·5 and 0·75 kg a.i./ha (2·27, 4·55 and 6·82 g a.i./100 metres of row) while lindane was applied at the registered rate of 0·29 kg a.i./ha (2·64 g a.i./100 metres of row). In addition, bendiocarb was applied as a seed treatment at the rates of 4000 and 6000 ppm. The insecticides were applied at planting as insecticide/fertilizer mixtures in 18 cm wide bands, 2–3 cm below the soil surface and 3–5 cm above the seed. The minimum effective rates were terbufos 0·25 kg a.i./ha, lindane 0·25 kg a.i./ha and chlorpyrifos and ethoprophos both at 0·5 kg a.i./ha. These treatments gave at least 5 weeks' residual control. The bendiocarb seed treatments were phytotoxic. No residues were detected in the cobs or grain at the minimum effective rates of the terbufos, chlorpyrifos or ethoprophos treatments. The positive linear relationship between plant population and yield showed that for every 1% loss in plant stand below the optimum range of 60 000–65 000 plants/ha, there is a 0·72-0·74% loss in grain yield respectively. Control measures would be economically justified with only a 2·3% reduction in plant stand (assuming $20/ha for cost of control and $150/tonne for maize).     

Weed control and wheat (Triticum aestivum L.) yield under application of 2,4-D plus carfentrazone-ethyl and florasulam plus flumetsulam: Evaluation of the efficacy

Three field experiments were conducted at the research fields of Plant Protection Research Institute, Iran, at different locations in 2004–2005 to study the efficacy of different broadleaved herbicides to control weeds in wheat. Treatments were the full-season hand weeded and weed-infested controls, and post-emergence applications of florasulam plus flumetsulam at 8.75, 10.50, and 12.25 g a.i./ha, 2,4-D plus carfentrazone-ethyl at 210, 245, 280, and 490 g a.i./ha, bromoxynil plus MCPA at 75, 100, and 150 g a.i./ha, 2,4-D at 560, 720, and 1120 g a.i./ha, tribenuron methyl, and 2,4-D plus MCPA. Herbicides were applied at wheat tillering stage. Naturally occurring broadleaved weed populations were used in experiments. Results indicated that bromoxynil plus MCPA at 150 g a.i./ha, 2,4-D plus MCPA, and 2,4-D plus carfentrazone-ethyl at 490 g a.i./ha were the best options to control weeds. Bromoxynil plus MCPA at 150 g a.i./ha and 2,4-D plus MCPA also resulted in the highest wheat yield. Overall, it could be concluded that rotational application of bromoxynil plus MCPA at 150 g a.i./ha, 2,4-D plus MCPA, and 2,4-D plus carfentrazone-ethyl at 490 g a.i./ha would be the best option to achieve satisfactory weed control, high grain yield and prevention of evolution of herbicide-resistant weeds.     

Chemical weed control in direct-seeded irrigated rice in the Lake Chad Basin,Nigeria

Two field experiments were conducted at Ngala in the Lake Chad Basin during the 1981 and 1982 wet seasons to investigate chemical weed control in direct-seeded, irrigated rice (Oryza sativa L.). Pre-plant-incorporated, pre- and post-emergence herbicides and their mixtures were tested in replicated, completely randomized block trials. Rice variety IR 28 was drilled each season at 125 kg/ha and fertilized with N (150 kg/ha) and P₂O₅ (40 kg/ha). In both seasons, the post-emergence herbicides propanil + oxadiazon at 3·0 + 1·0 kg a.i./ha, propanil+fluorodifen at 1·4 + 1·8 kg a.i./ha, propanil + bentazone at 3·6 + 1·5 kg a.i./ha and propanil at 3·6 kg a.i./ha as well as thiobencarb applied pre-emergence at 5·0 kg a.i./ha controlled the weeds effectively and gave similar grain yields to that from hand-weeding twice, and significantly higher grain yield than the unweeded control treatments. Grain yields similar to those from the ‘two hand-weeding control’ were achieved also by use of the herbicide dymrone at 3·0 kg a.i./ha, either soil-incorporated pre-sowing or sprayed before weed emergence. The herbicides gave satisfactory control of the weeds, which were predominantly the broad-leaved weed Luffa echinata Roxb., together with the grasses Sorghum aethiopicum (Hack.) Rupr. ex Stapf., Echinochloa colona (L.) Link, Eleusine indica (L) Gaertn, Digitaria sanguinalis (L.) Scop., Oryza longistaminata (Chev. & Roehr.), and sedges Cyperus rotundus L. and Cyperus esculentus L. The studies indicate that effective weed control by these herbicides and herbicide mixtures are dependable alternatives to hand weeding for direct-seeded, irrigated rice cultivation in the Chad Basin area.     

Yield response to pre-emergence control of broad-leaved weeds in winter cereals with isoxaben in France

A series of 59 trials was designed to assess the yield response to the control of broad-leaved weeds in winter cereals in the 1982/83, 1983/84 and 1984/85 seasons. When apllied pre-emergence to winter cereals, isoxaben provided season-long control of a wide spectrum of broad-leaved weeds including Veronica spp., Viola spp., Stellaria media, Aphanes arvensis, Papaver rhoeas and Matricaria spp. In 22 trials on winter barley and 37 trials on winter wheat treated pre-emergence with isoxaben in the autumn, mean yield increases of 0 · 22 t/ha and 0 · 14 t/ha respectively were recorded over that produced by herbicide combinations applied as post-emergence treatments in the spring. The mean yield increases with isoxaben over untreated controls were 0 · 30 t/ha and 0 · 26 t/ha on winter barley and winter wheat respectively.     

Dry matter and nitrogen accumulation,partitioning, and retranslocation in safflower (Carthamus tinctorius L.) as affected by nitrogen fertilization

Safflower (Carthamus tinctorius L.) is a deep-rooted crop which can tolerate water stress and can be grown in rotation with other crop species. Nitrogen is one of the most important nutrients for the growth and development of safflower; however, the effect of N level on dry matter, accumulation, partitioning, and retranslocation has not been extensively studied. A 2-year field study was therefore conducted with the objective to determine the effect of N fertilization on crop phenology, dry matter, N accumulation, partitioning and retranslocation of safflower grown under rain-fed conditions. Three rates of N were used (0, 100, and 200 kg N ha⁻¹) and two hybrids (CW9048 and CW9050) of safflower were selected. The experiment was conducted during the 2003–2004 (2004) and 2004–2005 (2005) growing seasons on a calcareous sandy loam (Entisols, Orthents, Typic Xerorthent) at the experimental farm of the Aristotle University of Thessaloniki, in Northern Greece. During 2004 spring was quite mild with significant rainfall whereas during 2005 spring was hotter with lower rainfall. Our study found that N fertilization increased biomass at anthesis by an average of 24% and at maturity by an average of 25% compared with the control. Total above ground biomass increased after anthesis in both years, in both hybrids and for all fertilizer treatments. N fertilization increased the dry matter partitioning in leaves + stems and heads at anthesis and also in leaves + stems, seeds, and head vegetative components at maturity. Dry matter translocation was not affected by N fertilization but lower values were found during the second year. N content was affected by the fertilization treatments and increased in those plants treated with fertilizer compared with the controls. In addition, N fertilization increased N retranslocation from the vegetative parts of the plant to the seed, but it did not affect N gain. During the second year, which was drier, there were significant N losses but also greater N translocation efficiency and higher contribution of pre-anthesis N to seed. Seed yield was correlated with the dry matter and N translocation indices, and was higher for the fertilized plants, compared with the control. The present study indicates that N fertilization promoted the growth of safflower and increased the dry matter yield, N accumulation, translocation and seed yield under rain-fed conditions.     

Pre-transplant herbicides for weed control in irrigated onion (Allium cepa L.) in northern Nigeria

Field trials were conducted at Samaru in the northern Guinea and at Bakuta and Kadawa in the Sudan Savanna ecological zones of Nigeria to identify suitable herbicides for weed control in irrigated onion. The herbicides tested were chlorthal-dimethyl, fluorodifen and oxadiazon. In the trials each herbicide treatment was compared with an identical treatment which received supplementary hand-weeding. The results of these experiments show that oxadiazon at 1·0–2·0 kg a.i./ha, with or without supplementary hoe-weeding at 6 weeks after transplanting, combined effective weed control with high bulb yields in irrigated dry season onions. While fluorodifen at 1·5 kg a.i./ha followed by supplementary hoe-weeding may be effective at sites with low weed infestation, a higher rate (3·0 kg/ha) may be desirable at sites with a higher broad-leaved weed infestation. Chlorthaldimethyl at 10·0 kg a.i./ha effectively controlled weeds at all the sites and gave high onion yields at sites with 6–12% clay; the selectivity was, however, lower at Bakura with very light soil. Uncontrolled weed growth caused 49–86% reduction in the bulb yields compared with the best herbicide treatments.     

Phytotoxicity of isazophos,lindane and heptachlor to sorghum applied as in-furrow and broadcast-incorporated treatments

Isazophos applied as an in-furrow spray at 0·5, 0·75 and 1·0 kg a.i./ha (4·65, 6·98 and 9·3 g a.i./100 m of row) reduced the establishment of Yates NK 212 sorghum by 37, 61 and 75% respectively. Similarly, heptachlor at 1·12 kg a.i./ha (10·42 g a.i./100 m of row) and lindane at 0·29 kg a.i./ha (2·7 g a.i./100 m of row) reduced establishment by 24 and 57% respectively. Heptachlor and isazophos, applied at the same rates but as broadcast-incorporated sprays and the lowest rate of isazophos applied as an in-furrow spray (0·25 kg a.i./ha, 2·33 g a.i./100 m of row) were not phytotoxic.     

Pre and postemergence herbicides for weed control in castor crop

Weed management is among the main factors limiting cultivation of castor (Ricinus communis) in extensive fields, particularly when labor is scarce or expensive. This experiment evaluated the efficiency of weed management programs using preemergence (clomazone, pendimethalin, and trifluralin) and a postemergence herbicide (chlorimuron-ethyl) applied at 20 days after emergence in castor plants cv. BRS Energia under rainfed conditions in Apodi, Brazil. No phytotoxicity was observed on the castor plants, and the postemergence herbicide significantly increased castor seed yield to 1466 kg ha⁻¹ complementing the weed control of preemergence herbicides treatments in which seed yield was 1207 kg ha⁻¹. Seed yield on weedy and weed-free treatments was 760 and 1971 kg ha⁻¹, respectively. Weeds were kept under a satisfactory control up to 40 days after emergence. This program resulted in reasonable weed control because the preemergence herbicides controled monocotyledon weeds, while the postemergence herbicide controlled broad leafed species being selective to castor plants.     

Broadening weed control with imazamethabenz combinations

Broad-spectrum weed control by use of imazamethabenz (AC 222 293) in herbicide combinations was investigated in the greenhouse. Imazamethabenz at rates ranging from 0·1 to 0·4 kg a.i./ha effectively controlled wild oats (Avena fatua L.). Additional control of redroot pigweed (Amaranthus retroflexus L.) was achieved when imazamethabenz, plus octoxynol surfactant, was applied in combination with MCPA (amine or ester) or commercial MCPA mixtures (bromoxynil/MCPA and cyanazine/MCPA). Only inclusion of propanil/MCPA in the combination reduced wild-oat control by imazamethabenz at the lower rate (0·1 kg/ha). Control of green foxtail (Setaria viridis (L.) Beauv.) was also obtained by use of fenoxaprop-ethyl in combination with imazamethabenz (plus octoxynol). Three-way mixtures of imazamethabenz (or plus octoxynol), MCPA alone or mixture, and fenoxaprop-ethyl may provide practical control of grass and broad-leaved weeds in the field.     

The response of onion couch (Arrhenatherum elatius ssp. bulbosum (Willd.) Schub. & Mart.) to glyphosate and other foliage-applied herbicides

Two experiments were conducted in which foliage-acting herbicides were applied to onion couch (Arrhenatherum elatius ssp. bulbosum). The first experiment used an artificially established population and investigated the effects of straw burning on the performance of autumn-applied treatments of glyphosate, aminotriazole and dalapon. Spring barley was sown without cultivation. The second experiment, conducted on a naturally occurring infestation, compared the performance of glyphosate applied at alternative autumn timings and a single application of flamprop-methyl made in the following spring, in the presence of a winter wheat crop. In the first experiment, assessments made after 15 months suggested that straw burning resulted in increased growth. In addition, herbicide performance appeared less effective after burning. In neither case were these differences significant. Glyphosate at 1·0 and 1·5 kg a.e./ha gave the highest levels of control of both shoots and bulbs, whereas control from aminotriazole at all doses (1·5, 3·0 and 4·5 kg a.i./ha) was poor. Dalapon (6·0, 12·0 and 18·0 kg a.i./ha) was intermediate in its effectiveness. In the second experiment, applications of glyphosate at 1·0 and 1·5 kg a.e./ha resulted in high levels of control of both shoots and bulbs with no significant difference between application dates. Flamprop-methyl at 0·52 kg a.i./ha reduced the number of shoots and bulbs by 55% and 58% respectively. All treatments significantly reduced the number of inflorescences present in July.     

Effects of fungicides applied at seeding on stripe rust and common bunt of wheat

Control of stripe rust (Puccinia striiformis) and common bunt (Tilletia caries and T. foetida) of wheat (Triticum aestivum), with fungicides applied on or adjacent to seed at sowing, was studied. Etaconazole pellets (2800 g a.i./ha), fenfuram liquid seed treatment (17 · 5 g a.i./ha) and imazalil granules (5000 g a.i./ha) were phytotoxic, reducing the number of heads per plot. All treatments reduced the incidence of common bunt although benomyl granules (2500 g a.i./ha), benomyl pellets (1400 g a.i./ha) and imazalil granules (5000 g a.i./ha) were not as effective as the registered smut fungicides carboxin, fenfuram, fenaminosulf and triadimefon. Triadimefon pellets (7000 g a.i./ha), PP347 pellets (1400 g a.i./ha), triadimefon granules (1500 g a.i./ha), flutriafol pellets (1400 g a.i./ha) and etaconazole pellets (2800 g a.i./ha) reduced stripe rust severity 17 weeks after sowing by 90, 89, 88, 86 and 74%, respectively.     

Al toxicity effects on radiation interception and radiation use efficiency of Al-tolerant and Al-sensitive wheat cultivars under field conditions

Soil acidity and Al toxicity are highly extended in agricultural lands of Chile, especially where wheat is widely sown. To evaluate quantitatively the response of wheat biomass and its physiological determinants (intercepted radiation and radiation use efficiency) to Al toxicity, two field experiments were conducted in an Andisol in Valdivia (39°47′S, 73°14′W), Chile, during the 2005–2006 and 2006–2007 growing seasons. Treatments consisted of a factorial arrangement of: (i) two spring wheat cultivars with different sensitivity to Al toxicity (the sensitive cultivar: Domo.INIA and the tolerant cultivar: Dalcahue.INIA) and (ii) five exchangeable Al levels (from 0 to 2.7 cmol₍₊₎ kg⁻¹) with three replicates. Crop phenology and intercepted radiation (IR) were registered during the entire crop cycle, while 10 samples of above-ground biomass were taken at different stages between double ridge and maturity. Both biomass and leaf area index (LAI) were recorded in these 10 stages. Radiation use efficiency (RUE) was calculated as the slope of the relationship between accumulated above-ground biomass and accumulated photosynthetically active radiation intercepted by the canopy (IPARa). Crop phenology was little affected by soil Al treatments, showing only up to 17 days delay in the Al-sensitive cultivar under extreme Al treatments. Above-ground biomass at harvest was closely associated (R² = 0.92) with the crop growth rate but no relationship (R² = 0.14) was found between the crop cycle length. IPARa explained almost completely (R² = 0.93) the above-ground biomass reached by the crop at harvest under the wide range of soil Al concentrations explored in both experiments. On the other hand, a weaker relationship was found between above-ground biomass and RUE. The effect of soil Al concentration on IPARa was mainly explained by LAI as a single relationship (R² = 0.93) between IR (%) and LAI at maximum radiation interception showing a common light attenuation coefficient (k = 0.33).     

Herbicide evaluation studies in transplanted chilli pepper (Capsicum frutescens L.) in the Nigerian savanna

Field trials were conducted in the Nigerian savanna to evaluate the performance of various herbicide mixtures for weed control in chilli pepper (Capsicum frutescens L. var. Serrano chilli) during the wet seasons of 1982 to 1984 and in the 1982/83 dry season. Linuron at 0·5 kg or 0·75 kg a.i./ha in mixture with either alachlor at 1·5 kg, metolachlor at 1·5 kg, oxadiazon at 1·5 kg, or diphenamid at 3·0 kg, as well as metolachlor plus metobromuron at 1·0 + 1·0 kg and 1·5 + 1·5 kg a.i./ha all followed by supplementary hoe-weeding at 6 weeks after transplanting combined effective weed control with high chilli pepper fruit yields comparable to the hoe-weeded control in all the trials. Unchecked weed growth throughout the crop life cycle resulted in an 86–90% reduction in potential chilli pepper fruit yields.     

Intra-specific competition in maize: Early established hierarchies differ in plant growth and biomass partitioning to the ear around silking

Early interferences among plants within a maize stand determine the establishment of extreme plant types (i.e. dominant and dominated individuals). The development of these hierarchies takes place well before [from the seventh leaf stage (V₇) onwards] the start of the critical period for kernel set (i.e. a 30-day period centered in silking). Kernel number per plant (KNP) is significantly related to plant growth rate around silking (PGR_S) and biomass partitioning to the ear during this period. Previous evidence has demonstrated that at high stand densities, extreme plant types may exhibit similar PGR_S values but set different KNP. We tested the hypothesis that early established plant hierarchies differ in biomass allocation to the ears during the period around silking. Two hybrids of contrasting tolerance to crowding (DK752 and DK765 as the tolerant and the intolerant hybrid, respectively) were cropped at different interplant competition intensities (6, 12, 12 pl m⁻² thinned to 6 pl m⁻² at V₉ and 6 pl m⁻² shading from V₉ onwards) during 2003/2004 and 2004/2005 in Argentina. For all treatments, the coefficient of variation (CV) of plant biomass increased from V₃ (ca. 1.2%) to V_9-10 (ca. 22%). From V₇ onwards, plant growth rate of dominant individuals was higher (P < 0.05) than that of the dominated plants. Hence, dominant plants exhibited higher (P < 0.05) PGR_S (ca. 4.5 g pl day⁻¹) than dominated individuals (ca. 3.7 g pl day⁻¹). As PGR_S declined in response to increased plant population density (ca. 5.1 and 2.8 for 6 and 12 pl m⁻², respectively), biomass partitioning to the ear was reduced (ca. 0.44 and 0.33 for 6 and 12 pl m⁻², respectively). For all treatments, however, dominant plants exhibited a greater biomass partitioning to the ear (ca. 0.41) than the dominated individuals (ca. 0.36). Consequently, the former were the individuals with the highest ear growth rate (ca. 1.9 and 1.4 g per ear per day for the dominant and dominated plant, respectively) and KNP (ca. 623 and 490 kernels per plant for the dominant and dominated plant, respectively) of the stand. We identified three traits on DK765 related to the low tolerance to high-density stress of this genotype: (i) a higher plant-to-plant variability (CV ca. 26% and 19%, for DK765 and DK752, respectively), (ii) a lower biomass partitioning to the ear around silking (ca. 0.26 and 0.39 for DK765 and DK752, respectively), and (iii) a higher response rate of KNP to ear growth rate around silking (ca. 370–738 and 360–414 kernels per g, for DK765 and DK752, respectively). Hence, as stand density was increased, KNP of DK765 was sharply reduced, especially in the dominated individuals of the stand.     

Agronomic and economic assessment of intensive pest management of dry bean (Phaseolus vulgaris)

Two common production constraints of dry bean (Phaseolus vulgaris) in Ontario are annual weeds and anthracnose (caused by Colletotrichum lindemuthianum). Dry bean is not considered a competitive crop and weed interference can result in substantial yield losses, while anthracnose is considered one of the most devastating diseases in dry bean production. A study conducted in Ontario Canada, examined the effect of two herbicide programs on weed management, thiamethoxam insecticide treatment on plant enhancement and three fungicide programs on anthracnose development in a navy bean cv. ‘OAC Rex’. The premium herbicide program (s-metolachlor + imazethapyr) reduced percent weed ground cover relative to the economic herbicide program (trifluralin) in five of six locations. Thiamethoxam increased emergence and vigour at only one location, which contradicts reported benefits of thiamethoxam on plant health. The herbicide or thiamethoxam treatments did not affect anthracnose disease severity, visible seed quality, net yield or economic return. The fungicide seed treatment was often superior to the untreated control, for a number of the parameters measured. The application date of the foliar fungicide, relative to the onset of disease, varied between site-years. This dramatically influenced the fungicide’s effectiveness. Foliar fungicides increased seed quality and net economic return compared to the control when applied prior to disease development. The combination of fungicide seed treatment followed by a foliar fungicide provided the largest reduction in anthracnose severity.