Showing papers on "Leaf spot published in 1984"

The influence of foliar diseases and their control by selective fungicides on a range of groundnut (Arachis hypogaea L.) genotypes

Abstract: SUMMARY Twenty groundnut genotypes were grown with various spray treatments which controlled either, only rust, or only leaf spot diseases, or all of these diseases or none of them. The genotypes varied in their resistance to these diseases, some having resistance to only one disease and some having resistance or susceptibility to all the diseases. Chemical control of the diseases resulted in variations in leaf area protection and in yield which were specific to each genotype. For some genotypes the diseases had little influence on yield and foliage, while for others yield and remaining green leaf were varied greatly by the control of diseases. For many of the genotypes the yield achieved was well related to variations in the green leaf remaining at maturity as a result of the spray treatments. Genotypes with good levels of genetic resistance did not have high yield potentials while those with the best yields when diseases were controlled were the most susceptible to these diseases.

Nursery diseases of eucalyptus in Kerala

Abstract: Survey of Eucalyptus (E, grandis and E. tereticornis) nurseries in Kerala State indicates that the most prevalent diseases are damping-off, web blight and seedling blight in seedbeds and stem canker, leaf and shoot blights and Phaeoseptoria leaf spot in container plants. Cylindrocladium spp., Rbizoctonia solani and Pythium spp. arc the main serious pathogens. Pythium myriotylum, P. deliense, R. scilani, Cylindrocladium camellias, C. clavatum and Sclerotium rolfsii are recorded for the first time on Eucalyptus.

Resistance of wheat to leaf spot caused by Bipolaris sorokiniana

Abstract: Leaf lesions caused by Bipolaris sorokiniana on resistant cultivars of wheat (Triticum aestivum) inoculated at the threeto five-leaf were fewer and smaller and sporulated less than lesions on susceptible cultivars. In crosses growth stage. involving four resistant and four susceptible wheats, resistance was dominant in the F1 progenies. The effect of host genotype on lesion Disease reactions of the F2 indicated that resistance was conditioned by two genes in the cultivar development and on sporulation of the Motia and in lines E 5895 and HD 1927 and by one gene in line DT 188. pathogen was studied on resistant or susceptible cultivars and lines inoculated when in the boot growth stage and kept in Leaf spot of wheat (Triticum aestivum hr, then removed to greenhouses where a moist chamber for 48 hr. Seven days L.) caused by Bipolaris sorokiniana temperatures were 18-27 C. after inoculation, disease severity was (Sacc. in Sorok.) Shoem. occurs Disease severity was estimated on estimated in flag leaves and the lesionson throughout the wheat-growing regions of inoculated leaves 7 days after inoculation, leaves were counted. Five lesions were cut India and probably ranks close to leaf when lesions appeared to have reached from each leaf and measured for size, rust in destructiveness. The disease has maximum size, using a scale of 0-5: 0 = then placed in 5 ml of distilled water and been managed by use of cultivars with free of spots; 1 = necrotic spots without shaken vigorously for 1 min. Spores of B. moderate resistance, but greater resistance chlorosis, up to 5% of the leaf area sorokiniana in the water were counted is needed. The purpose of this work was involved; 2 = necrotic spots with light with a hemacytometer and the number of to identify sources of resistance, to study chlorosis, 6-20% of the leaf area spores per 100 mm 2 of spot surface was its inheritance, and to provide information involved; 3 = necrotic spots with calculated. The experiment was repeated. on how the resistance influenced the pronounced chlorosis, 21-40% of the leaf pathogen's development, area involved; 4 = 41-60% of the leaf area RESULTS involved; and 5 = spots merging, more Six hundred twenty-five wheat lines MATERIALS AND METHODS than 60% of the leaf area involved, were tested for resistance to B. sorokiniana. Inoculum was prepared from an isolate A total of 625 spring wheat lines Kalyansona, Sharbati Sonora, Sonalika, of B. sorokiniana that had produced obtained from breeding programs in and P.V.18 (commercially grown cultivars) severe leaf spot in nine of 10 cultivars and northwestern India were examined as had disease ratings of 4-5 and were lines tested. The one line that it did not potential sources of resistance. Theywere considered fully susceptible. These severely infect was HD 1927, which was grown in pots 15 cm in diameter, with five cultivars were typical of 591 of the resistant to all isolates of the pathogens to plants per pot. The trial was repeated. cultivars and lines tested. There were 18 which it was tested. This isolate was Plants were inoculated at the threeto moderately resistant wheats (disease grown at about 25 C on a mixture of five-leaf growth stage. ratings between 1 and 2): PKD 66, PKD autoclaved barley, oats, wheat, and rice. Inheritance of resistance was studied in 74, PKD 75, HD 1623, HD 1670, HD About equal volumes of the different eight crosses. Kalyansona and Sharbati 1706, HD 1801, HD 1827, HD 1902, HD grains were used in the mixture. Conidia Sonora (susceptible commercially grown 1917, E 4900, E 5070, E 5533-1, MACS 5, were washed from the seeds and strained cultivars) were crossed with resistant lines CA 528, HS 40, DT 192, and CPAN 980. through cheesecloth. Plants were sprayed HD 1927 and E 5895 and susceptible lines There were 16 resistant wheats (disease with inoculum containing about 12,000 HD4500and HD4501 wercrossed with ratingsnotgreater.than 1): PDK42, PDK conidia per milliliter of water and two resistant Motia and DT 188. Progenies 57, PDK 65, HD 1470, HD 1620, HD drops of Tween 20 (polyoxyethylene from F1 and F2 populations and the 1927, HD 1956, B 5895, DT 188, D 144, sorbitan monolaurate) per 100 ml until parents were evaluated for leaf spot DA491-5, N 3199, W 3, NP 876, NP 891, dripping wet. After inoculation, plants were kept in a moist chamber for about 48 Table 1. Inheritance of resistance to Bipolaris sorokiniana in plants of the F2 generation of crosses of wheats that were susceptible or resistant Paper 13,538, Scientific Journal Series, Minnesota Agricuiturai Experiment Station, St. Paul 55108. No. of plants Total p Mode of

Fungicide effects on light leaf spot, canker, crop growth and yield of winter oil-seed rape

Abstract: Field experiments with rape ovs Primor, Jet Neuf and Norli during 1979–83 tested the effects of benomyl, prochloraz, imazalil, thiabendazole, metalaxyl or triadimefon sprays applied at different times on disease, crop growth and yield. The principal disease in all experiments was light leaf spot (Pyrenopeziza brassicae).A single spray in autumn of benomyl or prochloraz at 0·5 kg a.i./ha consistently decreased incidence and severity of light leaf spot and sometimes decreased stem canker (Leptosphaeria macvlans). Under severe disease conditions in cv. Primor an autumn spray of fungicide contributed more to disease control than a spray in spring; a decrease in light leaf spot incidence was detectable up to 8 months after application. The autumn spray maintained plant population density, increased leaf area index, dry matter, crop growth rate, earliness of flowering, and yield by up to 0·69 t/ha; an autumn + spring spray increased yield by up to 0–83 t/ha. Effects on crop growth and yield were due to disease control not direct chemical stimulation of growth. Measurements of crop growth and population per unit area revealed the effects of fungicides more clearly than traditional disease assessments based solely on randomly selected plants.Triadimefon sprayed on rape stubble at high dose rate (1 kg a.i./ha) decreased incidence and severity of light leaf spot throughout the growing season of a subsequent rape crop, with beneficial effects on plant population density, growth, flowering and yield.Electrostatically charged rotary atomizer and conventional hydraulic spray applications of fungicide were equally effective in disease control. A reduction to one quarter in dose rate of prochloraz and 100–fold reduction in amount of water carrier (125 g a.i. in 4·3 1/ha) when applied electrostatically in autumn or autumn + spring had similar effects on disease, crop growth and yield to those obtained with a conventional sprayer delivering 500 g a.i. prochloraz in 410 1/ha.Fungicides, spray timing and methods of application are discussed in relation to the epidemiology of light leaf spot and canker and the economics of disease control.

Assessment of resistance to Cercospora arachidicola in peanut genotypes in field plots.

Abstract: Reactions to early leaf spot, caused by C. arachidicola [Mycosphaerella arachidis], were evaluated at Perkins, Okla. in 1981 on 151 groundnut entries representing genotypes of cultivated Arachis hypogaea, wild A. spp. and hybrids. Plants were grown in single-row, 3 m plots that were irrigated weekly (2.5-3 cm); leaf spot was evaluated 115-120 days after planting. A subjective scale index of 1-5 (low to high response) was used to describe each of the following criteria: amount of leaf necrosis; degree of sporulation of M. arachidis; leaf defoliation. A leaf spot reaction index (LSRI) for each entry was obtained as the product of the leaf necrosis and sporulation indices, where the lowest and highest values of the LSRI were 1 and 25, respectively. The Kruskal-Wallis one-way analysis of variance by ranks and multiple-comparison test were used to test the equality of the effects of genotypes on these criteria. The Spearman rank correlation for each pair of criteria was calculated for each genotype. Significant positive correlations between LSRI and defoliation and between amount of leaf necrosis and defoliation were obtained for all genotypes. Information obtained from this statistical analysis is useful for evaluating resistance of groundnut entries

Cercospora leaf spot and powdery mildew of fenugreek, a potential new crop in Canada

Abstract: Two diseases, Cercospora leaf spot and powdery mildew, were observed on the foliage of research plots of fenugreek ( fibonella foenum-graecuml in 1983. The leaf spot, caused by the fungus Cercospora traversiana, resulted in serious defoliation and also affected the stems and pods. It appears that Cercospora leaf spot possesses the potential to be a serious constraint to the production of fenugreek in Canada. Powdery mildew was not serious. Can. Plant Dis. Surv. 64:2,33-35, 1984. Deux maladies, la rayure nervale et le blanc, ont bt6 observbes sur le feuillage du fenugrec ( 7kigonella foenum-graecum) croissant sur des parcelles de recherche en 1983. La rayure nervale, caus6e par le champignon Cercospora traversiana, provoque une defoliation importante et affecte aussi la tige et les gousses. II semble que la rayure nervale puisse gener serieusement la production du fenugrec au Canada. Le blanc, quant A lui, ne fait pas de dommage sbrieux.

Purple spot and Stemphylium leaf spot of asparagus

Abstract: Not available – first paragraph follows: For several years, California asparagus growers have noticed purple spots that develop near the base of the spears before harvest. The condition is worse following cool, wet weather and was more severe during 1982 and 1983 than in previous years, resulting in higher rejection rates during cutting and packing.

Some effects of climate and plant growth on the development of light leaf spot in cauliflowers

Abstract: In laboratory and climate chamber studies with Pyrenopeziza brassicae Sutton and Rawlinson, most conidia germinated at l6°C, mycelial growth was most rapid (about 1 mmjday) over the range 15–20°C, and symptom development on cauliflower leaves was greatest at 18°C High relative humidity (98–100%) was required for conidial germination but symptom development was inversely proportional to atmospheric saturation Results of field studies are discussed in the light of these findings Conidia rarely germinated on newly emerged leaves, but the proportion germinating increased as the leaves expanded and was optimum on fully expanded leaves Symptoms did not usually appear on leaves during the early stages of leaf expansion

Orchard Efficiency Analysis of Litchi

Abstract: There is considerable variation in the average annual yield of individual plants in an orchard and between orchards of litchi cv. Bombai. The orchard efficiency indicating yield potential varies from 33 to 54 per cent. The mean annual yield per plant for four years varies from 718 to 4458 fruits. The variation in yield has significant correlations with leaf nitrogen content, infection of leaf spot, red rust and mite and feeder root density. The yield is positively correlated at 5 per cent significance with the leaf nitrogen before flowering (0.428), and negatively correlated at 1 per cent significance with leaf spot, red rust, mite and fruit rot. The yield has also significant positive correlations at 1 per cent level with the feeder root densities, both in April and October, at the depths of 0–30 cm, 30–60 cm, 60–90 cm. Hence the variation in yield is associated with the leaf nitrogen content, and pest and disease infection. It is suggested that the actual guidelines for better management of orchards to attain higher yield should be determined after detailed experimentation using fertilizers, fungicides and pesticides.

Evaluation of Agropyron intermedium for Reactions to Various Leaf Spot Diseases

Abstract: Twelve cultivars or strains of intermediate wheatgrass (Agropyron intermedium) were evaluated plots at Mandan, ND, between 26 August for reactions to leaf spot diseases under field conditions at Mandan, ND. The cultivars or strains and 3 September 1980. Four hundred were Greenleaf, Mandan 759, Slate, Trigo, PI345526, Nebraska 314054, Swift Current 13702, Swift plants of each entry were spaced 0.9 m Current 13713, South Dakota 50, South Dakota 2-15, South Dakota 4-14, and South Dakota apart in a plot of 10>( 10 plants in each of 10-14. A total of 4,800 spaced plants were established in 1980 and evaluated for 3 yr. Disease four replicates in a completely randomized reactions differed significantly among years and among cultivars or strains. South Dakota 2-15 was block design. Plants were allowed to rated the most resistant and Trigo the least resistant for all 3 yr. Neither heading date nor plant establish in 1980, and no disease ratings height were associated with resistance or susceptibility. Cochliobolus sativus was considered the were taken. Ammonium nitrate fertilizer most important leaf-spotting pathogen because it was isolated from nearly all plots evaluated and was applied at 90 kg N/ha in late fall of was present on 41% of the plated leaves. Pyrenophora trichostoma, Leptosphaeria nodorum, and a 1980, 198 1, and 1982. Plants received Leptosphaeria sp. were also widely distributed in the plots. about 250 mm of water from April

Aerobiology and epidemiology of certain diseases of bajra

Abstract: The present report deals with the aerobiological investigations carried out with reference to certain diseases of bajra e.g., Downy mildew, Ergot Leaf spot and Rust diseases of bajra. The atmospheric concentration of pathogenic spores, their seasonal variations, effect of meteorological factors and disease incidence with reference to growth stages of plants have been investigatd. These observations and conclusions drawn would serve as a usful step forward in the treatment of disease of bajra

Evaluation of chemicals inhibiting the bacterial leaf spot pathogen of betelvine

Abstract: A betelvine leaf spot pathogen was isolated from infected leaves and identified as Xanthomonas campestris pv. betlicola (Patel, Kulkarni & Dhande) Dye. Five antibiotics, two phenols and a naphthoquinone at 50, 100 and 250 ppm were screened for their in vitro toxicity against the pathogen. Streptomycin proved most effective followed by tetracycline and ampicillin giving maximum zonal inhibition diameters (39–40 mm) at 250 ppm. During field evaluation streptomycin was found to be most effective (80–90% disease control) followed by menadione (78–80% and resorcinol (68–72%). No phytotoxic effect was observed. Thus, besides streptomycin, menadione and resorcinol have also emerged as promising agricultural bactericides.

Two mycelia sterilia parasitic on foliage of hardwood seedlings in Kerala State, India

Abstract: Rhizoctonia solani and Sclerotium rolfsii are newly reported causing a seedling web blight of Eucalyptus and a leaf spot of teak respectively in Kerala, India.

Effect of leaf growth in cucumber on deposit dilution and the control of angular leaf spot.

Abstract: Tropically grown cucumber exhibits massive increases in foliar area within a short space of time. New leaves are produced at a rate of 1 leaf/vine/day and emerging leaves expand by a factor of 20 within 4–5 days. Foliar protection using the traditional 10‐day spray interval is difficult because many leaves remain unprotected throughout their main period of growth and deposits applied to newly emerged leaves are diluted to inactive levels within several days. Angular leaf spot poses particularly acute problems because it spreads and develops most rapidly when deposits are under the most intense weathering pressure, and its appearance on the leaves coincides with the stage of rapid leaf expansion. Indications are that control may be improved by shortening spray intervals to four or five days so that all leaves receive spray during the critical 4–6 days after emergence when they are susceptible to angular leaf spot but have already completed most of their expansion. Increased costs through higher sp...