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).     

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.     

Increased severity of Rhizoctonia root rot in sugar beet treated with systemic insecticides

The systemic insecticides aldicarb 15G (15% granules) at 2·6 kg active ingredient (a.i.)/ha and phorate 1OG (10% granules) at 1·7 kg a.i./ha, applied as side dressings about 1 month after planting in 1979 and 1980, significantly increased the severity of root rot, caused by Rhizoctonia solani Kühn, in sugar beet (Beta vulgaris L.). Carbofuran 10G (10% granules) at 2·2 kg a.i./ha also increased root rot, but not significantly. Numbers of harvestable roots were reduced by all treatments but significantly by phorate only. Both aldicarb and phorate were slightly fungistatic to R. solani when the pathogen was grown on potato-dextrose agar incorporating 0·5, 5·0, and 25 μg a.i./ml. Trichoderma sp., a potential antagonist of Rhizoctonia, was slightly inhibited by aldicarb and phorate initially, but soon overcame the effect. Thus, the increase in disease severity in the field may be attributable to some metabolic or physiological effect of the chemicals either on the host or on the infection process of the pathogen. Indiscriminate use of these insecticides should therefore be avoided in areas where root rot is prevalent but where insects are not a problem.     

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.     

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.     

The use of asulam to control Bromus sterilis in ryegrass crops grown for seed

Asulam applied in April 1981 and 1982 gave good control of established plants of Bromus sterilis growing in Italian and perennial ryegrass crops grown for seed. Doses of 1–3 kg a.i./ha reduced numbers of weed inflorescences by 65–90%. The results also showed that there was no effect on crop heading and further suggested that seed yield had not been reduced. Two pot experiments also indicated the efficacy of asulam at 0·5-2 kg a.i./ha applied pre-emergence and further study of such treatment in the autumn during the establishment of a ryegrass seed crop is warranted.     

Initial and residual activity of glyphosate and SC-0224 in a sandy soil

Initial and residual herbicide activity of glyphosate and SC-0224 (trimethylsulphonium carboxymethylaminomethylphosphonate) when applied to a sandy soil was investigated. A bioassay employing wheat (Triticum vulgare L., cv. Mericopa) was used to determine the residual activity of the herbicides on different characteristics of plant growth. At 5 kg/ha both herbicides significantly reduced shoot length. This was observed in wheat planted immediately as well as 10 days after application. SC-0224 was more active than glyphosate, significantly reducing shoot length at the 2·5 kg/ha rate 10 days after application. Root length was reduced by both herbicides at 2·5 and 5 kg/ha in wheat planted 10 days after application. Reductions in fresh and dry weight were also observed for both shoots and roots. It is apparent that SC-0224 and glyphosate have residual herbicide activity in sandy soil, at least up to 10 days after application, and that SC-0224 has more herbicidal activity than glyphosate in this respect.     

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.     

Epidemiology and control of chocolate spot (Botrytis fabae) on winter field beans (Vicia faba)

Dispersal of Botrytis fabae spores and the development of chocolate spot lesions were monitored in crops of winter-sown field beans during the 1980/81, 1981/82 and 1982/83 seasons. The greatest numbers of B. fabae spores collected on horizontal sticky slides exposed in crops were associated with periods of heavy rain and numbers declined if weather was dry. Amounts of chocolate spot developing on leaves of young potted plants exposed in crops near the slides followed the same trends as spore numbers. When numerous spores were collected, abundant chocolate spot developed on the leaves of tagged plants in the crops. Benomyl sprays were applied (at 0·5 kg a.i./ha) either after peaks in numbers of spores collected or according to crop growth stages. Sprays applied in January–April generally gave no increase in yield whether or not timed according to spore peaks. The greatest yields were obtained from plots sprayed in late May, at the midflowering stage of crop growth.     

Colonization of rice fields by Nilaparvata lugens (Stål) and its control using a trap crop

Colonization of rice fields by the brown planthopper, Nilaparvata lugens (Stål) (Homoptera: Delphacidae), was monitored using yellow pan oil-water traps. In approximately 3 months, 35 788 immigrant macropters (1·0 ♂: 1·2 ♀) were caught in 512 traps installed over a 0·352 ha rice field. The trend of daily trap catches conformed closely to the number of macropters visually counted on rice hills. In sub-plots with a trap crop planted 20 days earlier than the main crop on a quarter of the total crop area, more macropters were recorded on trap-crop than on main-crop rows up to about 75 days after transplanting the main crop. In control sub-plots with one planting, more hoppers arrived on the middle than on the border rows. A blanket spray application of Perthane (0·75 kg a.i./ha) was made on the crop in control sub-plots, whereas only the trap crop was sprayed in trapped sub-plots. The combined yield in each treatment with trap crop was significantly higher than in the control treatment.     

Residues of carbaryl,lindane and monocrotophos on rice treated for control of rice bug, Leptocorisa oratorius (Fab.)

This study investigated the correlation between insect mortality and insecticide residue levels in rice grain during the developing stages and at harvest, and also determined the relative toxicities of three insecticides, monocrotophos (Azodrin 16·8 EC), lindane (Agrocide 26 DP), and carbaryl (Sevin 85 WP) to Leptocorisa oratorius (Fab.), (Hemiptera: Alydidae). The insecticides were applied on field plots at 0·75 kg a.i./ha at the start of the milk stage of the developing grains. Sampling was conducted at 2 hours and 1, 2, 3, 4 and 5 days after spraying, which covered the milk stage to the soft dough stage. Mortality of insects exposed to the treated grain, the residue analysis of the treated grain during development and at harvest, and the LD₅₀s of the insecticides were determined. Monocrotophos was the most effective insecticide against the rice bug; lindane provided control for only one day; carbaryl was ineffective. Maximum residue levels of lindane and carbaryl in the harvested grains were below the established tolerance limits provided by FAO/WHO. There is no established tolerance for monocrotophos in rice.     

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.     

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.     

The effect of systemic fungicides,applied as seed treatments or early foliar sprays,on speckled leaf blotch of wheat, Mycosphaerella graminicola (Fuckel) Schroeter

Control of speckled leaf blotch (Mycosphaerella graminicola) of wheat (Triticum aestivum) with systemic fungicides used as seed treatments or foliar sprays was studied. Seed treatment with either imazalil (1·125 g/kg seed), nuarimol (0·2 g/kg), thiabendazole (1·5 and 0·75 g/kg), triadimenol (0·3 and 0·2 g/kg) or Shell WL 47675 (0·415 g/kg) reduced the number of infected plants by 28–62% when assessments were made 11 weeks after sowing. Thiabendazole (1·5 and 0·75 g/kg) and triadimefon (0·3 and 0·2 g/kg) slowed the development of speckled leaf blotch for c. 15 weeks after sowing. A single foliar spray of triadimefon (125 g/ha) slowed the development of the disease for c. 10 weeks, but a single spray of benomyl controlled it for the whole season. There was no additional benefit from combining a seed treatment of triadimefon (0·225 g/kg) with the foliar spray.     

Daily application of ultra-low-volume (ULV) insecticides at low dosages to control insect pests of cotton in Malawi

ULV carbaryl and DDT were applied to cotton (Gossypium hirsutum) at two sites, five times a week, using five swath widths from 4·5 to 18 m, representing high to low dosages. Sprays were applied between 0830 and 1400 h during the day or between 1830 and 2100 h during the evening. Subsequently, Bemisia spp. (whitefly) and Paurocephala gossypii Russell (psyllid) populations were significantly larger on plants treated with lower dosages applied over wide swaths. Yields of seed cotton were significantly lower from plants treated with low dosages (< 0·5 kg a.i./ha weekly) but the results of spraying in the morning and in the evening were comparable, at both sites.     

Control of stem nematode, Ditylenchus dipsaci, in tulip bulbs with aldicarb and oxamyl

In the Netherlands complete elimination of the stem nematode Ditylenchus dipsaci (Kühn, Filipjev) in tulip by destruction of infested lots and sterilization of infested soil is the aim of the Plant Protection Service. Elimination of stem nematode in narcissus bulbs is achieved by hot-water treatment, but this treatment is not appropriate for tulip bulbs because these are damaged at temperatures of 43 · 5°C and higher. As the effects of the systemic nematicides aldicarb and oxamyl looked promising, these were investigated further. Aldicarb, 6 kg a.i./ha, was applied once in the autumn and once in spring. Oxamyl, 2 · 88 kg a.i./ha, was applied three times in spring. The efficacy of these nematicides was shown not only by a reduction in the numbers of infested bulbs but also by a reduction in nematode numbers in the bulbs, shown here in the frequency distribution of infested bulbs over nematode numbers. However in some bulbs, probably those which had the highest number of nematodes before planting, a few stem nematodes could still be detected, having survived high dosages of nematicides. Therefore, complete elimination of stem nematodes from infected bulbs with very high nematode numbers is probably impossible. It is expected, however, that repeated treatment will increase the percentage of nematode-free bulbs and will lead to almost healthy tulip-bulb stocks.     

The effects of incorporating small quantities of straw in grass/grass silage-based diets for dairy cows

Two studies were conducted to examine the effects of incorporating small quantities of straw in the diets of dairy cows. In Experiment 1, forty Holstein Friesian dairy cows were used in a 2 × 4 factorial design experiment, with factors examined consisting of two parities (primiparous and multiparous animals) and four levels of straw inclusion in the diet (0, 0·08, 0·16 and 0·24 of forage dry matter). The basal forage offered in this study was grass silage, and the primiparous and multiparous animals were supplemented with 9·0 and 11·0 kg concentrate d^–1 respectively. In Experiment 2, forty‐eight Holstein Friesian dairy cows were used in a 2 × 3 factorial design experiment, with factors examined consisting of two basal forage types (grass silage and zero‐grazed grass) and three levels of straw inclusion (0, 1·0 and 2·0 kg d^–1). All animals were offered 7·0 kg d^–1 of a concentrate supplement. Both experiments were partially balanced changeover designs, consisting of two, 4‐week periods. In Experiment 1, the total dry‐matter intake followed a significant quadratic relationship (P < 0·05), increasing with low levels of straw inclusion and decreasing at higher levels of inclusion. With increasing levels of straw inclusion, there was a linear decline in milk yield (P < 0·001) and milk protein concentration (P < 0·05), but milk fat concentration was unaffected (P > 0·05). In Experiment 2, the effect of straw inclusion on total dry‐matter intake was quadratic (P < 0·001), with intakes being maximum at the 1·0‐kg level of straw inclusion. Milk yield exhibited a linear decrease (P < 0·001) with increasing level of straw inclusion. Milk fat concentration was lowest at the 1·0 kg rate of straw inclusion (P < 0·05), but milk protein concentration was unaffected by straw inclusion. There were no significant interactions between basal forage type and level of straw inclusion for any of the variables examined (P > 0·05). Despite small increases in total dry‐matter intake at a low level of straw inclusion, there was no evidence that straw inclusion improved either nutrient utilization or animal performance. The reduction in milk yield observed with straw inclusion reflects, to a large extent, a reduction in metabolizable energy intake.     

Influence of different tillage methods and pre-emergence herbicides on weed control in cowpea (Vigna unguiculata (L.) Walp.)

In the early and late cropping seasons of 1983, three different methods of tillage (minimum tillage, conventional tillage, and tilled and ridged) were evaluated for their influence on the performance of some pre-emergence herbicides used during the production of cowpea. Four varieties of cowpea (Ife Brown, H 144-1, TVx 3236, and Black-eyed bean) were planted in the early season while five varieties (Ife Brown, H 144-1, TVx 3236, H64/3 and Vita-5) were planted in the late season. A single spray application of 3·0 kg/ha alachlor, 3·0 kg/ha metobromuron + metolachlor and 3·5 kg/ha metolachlor was carried out one day before planting. Cyanazine at 3·0 kg/ha was included in the late season trial. The plots were either minimally tilled, conventionally tilled or tilled and ridged at the Teaching and Research Farm of the University of Ife. Results showed that the performance of all three herbicides used in the early season, as measured by weed control and grain yields, was best on the conventionally tilled, while the performance of the four herbicides in the late season was best on tilled and ridged plots. Metobromuron + metolachlor performed consistently better than each of the other herbicides irrespective of the method of tillage during both seasons. Conventional tillage enhanced the performance of metobromuron + metolachlor over minimum tillage plots and tilled and ridged plots in the early season; however, in the late season, the performance of metobromuron + metolachlor was best on tilled and ridged plots. Alachlor did not effectively control competing weeds in both seasons but did not injure any cowpea line. On the other hand, cyanazine did not control weeds effectively but was phytotoxic to Ife Brown variety of cowpea. In both seasons, the control of the broad-leaved weeds Ageratum conyzoides, Amaranthus spp., Euphorbia heterophylla, Ipomoea spp., Spigelia anthelmia, Synedrella nodiflora and Talinum triangulare was not adequate. The control of the grassy weeds Brachiaria deflexa, Cynodon dactylon, Imperata cylindrica and Eleusine indica was, however, effective.     

Control of stem nematode,Ditylenchus dipsaci,in narcissus with aldicarb

The efficacy of aldicarb in controlling stem nematode, Ditylenchus dipsaci (Kühn, Filipjev) in narcissus in the field was investigated. Although the proportion of infested narcissus bulbs was reduced when aldicarb (Temik 10G) granules were applied at 6kg a.i./ha in the autumn and spring, some infested bulbs remained and it is concluded that complete eradication of D. dipsaci is not possible.     

Chemical control of sorghum head bugs (Hemiptera: Miridae)

Eight contact and three systemic insecticides, and an enriched neem extract were tested for the control of sorghum head bug, Calocoris angustatus Leth. at the ICRISAT Center. The insecticides were applied at the complete-anthesis and milk stages (at 500 1/ha) with a knapsack sprayer. On the basis of effectiveness of head bug control, grain yield and 1000-grain mass, carbaryl (at 500 g a.i./ha) was the most effective insecticide followed by fenvalerate (at 50 g a.i./ha), and chlorpyrifos (at 250 g a.i./ha). Among the systemic insecticides, demeton-S-methyl (at 250g a.i./ha), was the most effective. Demeton-S-methyl and dimethoate were also effective for the control of other head bug species—Eurystylus bellevoyei Put. and Reut. and Campylomma sp. Plots sprayed with demeton-S-methyl gave higher grain yields than those treated with carbaryl, which was the best contact insecticide. Two sprays of carbaryl (at 500g a.i./ha) applied at the complete-anthesis and milk stages have been found to be effective for head bug control. Dichlorvos, fenitrothion and monocrotophos were highly phytotoxic and resulted in burning and drying of entire leaves. Dimethoate resulted in a slight drying of leaf tips and margins.