摘要:

Early blight (Alternaria solani)is the most important foliar disease of potatoes in the humid highlands of Papua New Guinea. Late blight(Phytophthora infestans)is not found. Two trials compared copper oxychloride, mancozeb and chlorothalonil, applied by knapsack sprayer at 7‐ and 14‐day intervals, with an unsprayed control. Copper oxychloride, the least expensive fungicide, gave the greatest yield in the relatively dry season (May‐September) at Taluma (altitude 2570 m) and was the only fungicide consistently to increase yield in the wet season (November‐February) at Rakamanda (1920 m). The extra benefit from spraying at 7‐ rather than 14‐day intervals was small. When sprayed every 14 days, starting at 31 days after planting, copper oxychloride (2–0 kg a.i./ha) increased the yield of cv. Sequoia from 21–8 to 26.2 t/ha (SEd 1.75; 28 d.f.) at Taluma, and from 26.4 to 300 t/ha (SEd 1.69; 28 d.f.) at Rakamanda. Copper oxychloride increased average tuber weight and specific gravity at Taluma but not at Rakamanda.

ISSN:0143-6147    

DOI:10.1080/09670879109371552

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The incidence, distribution and severity of bacterial diseases of rice was studied in West Africa. Two bacterial diseases‐the bacterial leaf streak caused byXanthomonas campestrispv.oryzicolaand bacterial leaf blight caused byXanthomonas campestrispv.oryzae‐were detected. Both bacterial diseases were found to be more prevalent and severe in the Sahelian than in the forest zone of West Africa. They are rarely found in the more humid zone of West Africa. Bacterial leaf blight was found to be more widely distributed in the Sahelian region than the bacterial leaf streak. The incidence of bacterial leaf blight was found to be aggravated by high dosages of nitrogen. Lossese ranging from 2.7% to 41.0% in grain yiefd were inflicted on the rice crop by bacterial leaf blight. Some control measures are recommended.

ISSN:0143-6147    

DOI:10.1080/09670879109371553

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Field trials conducted with groundnut(Arachis hypogaeaL.) at three different locations in Niger, using seed‐protectant chemicals, showed a large reduction in plant stand on non‐treated plots. The reduction in plant stand was largely due to pre‐emergence seed and seedling rots, caused byAspergillus niger, A. flavus, Rhizoctonia solani, Macrophomina phaseolinaand species ofRhizopus, FusariumandPythium.Losses in pod yields in non‐treated plots were substantial and varied over locations. Seed treatment with thiram was very effective in improving plant stand and pod yields at all locations.

ISSN:0143-6147    

DOI:10.1080/09670879109371554

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Bacterial blight of tannia,Xanthosoma sagittifolium(L.) Schott., in Tanzania is described. Results of pathogenicity tests, cultural properties and electron microscopy studies indicate that the disease is caused byXanthomonas campestris.This represents the first report of the disease from East Africa.

ISSN:0143-6147    

DOI:10.1080/09670879109371555

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Head blast caused a significant reduction in grain yield, a result of reduction in spikelet length, grain weight and number of grains per head. The correlations between field infection and yield, and between field infection and percentage seed germination, were both statistically non‐significant.

ISSN:0143-6147    

DOI:10.1080/09670879109371556

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Leaf spots caused byAlternaria macrosporaandA. alternataare common in cotton crops around the world. Both species are, however, usually considered to be minor pathogens of Upland cotton(Gossypium hirsutum)butA. macrosporacauses premature defoliation with resulting yield loss in cultivars ofG. barbadensein Israel and in the USA.A. macrosporais also able to cause defoliation in Upland cotton if the crop is. predisposed to infection by environmental or physiological stress. In Zimbabwe the main predisposing factor is potassium deficiency. The paper discusses the disease in Zimbabwe against the background of work reported from other countries on its effect on yield and on its epidemiology and control.

ISSN:0143-6147    

DOI:10.1080/09670879109371557

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The evolution and design of two versions of a modified Micro‐Ulva hand‐held u.l.v. sprayer are described. These sprayers have resulted from the need by the Mali Millet Pest Control Project, under the auspices of the Overseas Development and Natural Resources Institute of the Overseas Development Administration, to develop equipment suitable for use by subsistence farmers in the control of grasshoppers and millet head miner or millet spike worm. The Mali‐1 sprayer has been used in 1987 and 1988. The Mali‐2 has been used in 1989.

ISSN:0143-6147    

DOI:10.1080/09670879109371558

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The use of dyes in the physicochemical evaluation of sprayers and spray application methods assumes 100% recovery from targets. Using a red and yellow dye on cotton plants it was shown that a significant percentage of dye was actually retained by the plants. The amount differed for different‐coloured dyes.

ISSN:0143-6147    

DOI:10.1080/09670879109371559

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Two field experiments were conducted with a granulosis virus infecting sugarcane shoot borer,Chilo infuscatellusSnellen. In both the experiments, application of the virus significantly reduced the borer infestation compared to untreated control. The first experiment was carried out to determine the effectiveness of the virus applied as high and low volume sprays. When virus was applied at 5.5 x 1012IB/ha as high volume (500 I/ha), 70.2% of the plants were protected from shoot borer infestation compared to 53.6% in low volume spray (150 I/ha). Significant reduction (P> 0.01) in shoot borer infestation was observed in plots treated with high compared to low volume spray. In the second experiment the effectiveness of the virus applied as crude and purified preparations was assessed. Both crude and purified preparations significantly(P >0.01) reduced the borer infestation compared to untreated check. No significant differences (P < 0.05) were observed between plots treated with crude and purified preparations of the virus.

ISSN:0143-6147    

DOI:10.1080/09670879109371560

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

During the 1988 wet season (May‐September), an experiment was conducted at the experimental farm of Abubakar Tafawa Balewa University, Bauchi, to investigate the effects of nitrogen and different weed competition durations with an improved sorghum(Sorghum bicolor(L.) Moench), variety BES, on the crop growth and yield, and determine the critical period of weed competition. The results showed that fertilized sorghum tolerated 2 weeks of early weed competition with minimal yield reduction. Weedy sorghum yield decreased as weed competition period lengthened from 2 to 7 weeks, primarily because sorghum plants under competitive stress had less panicle weight, fewer spikelets per panicle, lower 1000 grain weight and conseqently greatly reduced grain yield. Crop height was not significantly increased by nitrogen nutrition. However, sorghum plants under competitive stress were significantly taller than the weed‐free plants, probably as a result of severe competition with weeds for sunlight. Panicle weight, number of spikelets per panicle, weight of 1000 grains and grain yield were significantly increased by nitrogen nutrition. The mean reduction in grain yield due to weed competition decreased from 51% at zero nitrogen to 37.8% and 32.2% at 60 and 120 kg N/ha respectively, indicating that yield reduction decreased at medium and high fertility. Unweeded sorghum suffered a yield loss of 65% from severe competition with weeds that were predominantly made up ofRottboellia cochinchinensis. Setaria viridis, Cynodon dactylon, Striga hermonthica, Ipomoea cairica, Dichromena ciliata, Tridax procumbensandCyperus rotundus.

ISSN:0143-6147    

DOI:10.1080/09670879109371561

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor