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RESUMO O objetivo do presente trabalho foi avaliar o progresso temporal das doenças ferrugem polisora (Puccinia polysora), cercospora (Cercospora zeae-maydis), mancha branca (Pantoea ananatis) e helmintosporiose (Exserohilum turcicum) no milho, bem como sua correlação com as variáveis climáticas. O delineamento experimental foi o de blocos completos com tratamentos ao acaso. O modelo monomolecular foi o que melhor se ajustou às epidemias. Com os dados de severidade de cada doença, foram elaboradas correlações com as variáveis climáticas (DFtemp-dias favoráveis com temperatura entre 18-28ºC; DFumid-dias favoráveis com umidade relativa>60%; PrecAcc-precipitação acumulada; PrecDia- precipitação/dia e Prec10-precipitação>10mm) observadas durante o período de avaliação. Após as análises pôde-se inferir que a variável precipitação acumulada foi determinante para a ocorrência de epidemias das doenças estudadas. ABSTRACT The aim of the present study was to evaluate the temporal progress of the diseases southern rust (Puccinia hpspolysorahps), Cercospora leaf spot (Cercospora hpszeaehpsatn-atnmaydis), white spot (Pantoea hpsananatishps) and spot blotch (Exserohilum hpsturcicumhps) in corn, as well as their correlation with climate variables. Experimental design was in complete blocks with random treatments. The monomolecular model best fit to the epidemics. Using the severity data from each disease, correlations were established with the climate variables (DFtemp-favorable days with temperatures between 18-28 ºC; DFumid-favorable days with relative humidity>60%; PrecAcc-cumulative rainfall; PrecDia-precipitation/day, and Prec10- precipitation>10 mm) observed during the evaluation period. After analyses, it was possible to infer that the variable cumulative precipitation was determinant for the occurrence of epidemics of the studied diseases.

Gray leaf spot (Cercospora zeae-maydis) is a foliar disease of corn (Zea mays) that consistently reduces yields across the United States and is an annual concern in Indiana corn production. Field trials were conducted in West Lafayette, IN, over 3 years (2016 to 2018) to evaluate the effectiveness of 12-leaf collar stage (V12) foliar fungicide applications compared with tasseling (VT) applications for gray leaf spot management and yield. Results indicated that during years in which foliar disease severity was less than 4%, there was no effect of application timing on gray leaf spot severity. In 2018, when gray leaf spot levels exceeded 5%, significantly less disease was observed in treatments receiving VT applications compared with V12 applications. Application timing did not affect yield in any year of the experiment. In 2016, benzovindiflupyr + azoxystrobin + propiconazole resulted in greater yields compared with the nontreated control, and in 2018, pyraclostrobin + metconazole and benzovindiflupyr + azoxystrobin + propiconazole resulted in greater yields compared with the nontreated control. This research indicates that in high disease pressure environments and years, Indiana farmers may want to continue to apply fungicides at VT rather than apply prior to tassel.

Gray leaf spot is one of the major constraints of maize production in Ethiopia where warm humid environmental condition is prevailing. A field experiment was conducted in Gondar zuria district of western Ethiopia during 2016/17 and 2017/18 cropping season with the aim to evaluate effective maize varieties for the management of maize gray leaf spot disease. The experiment was laid out in Randomized Complete Block Design (RCBD) in three replications. Nine improved varieties, that is, SBRH, Gibie 2, Gibie 3, Argene, Jibat, BH-546, SPRH, Wonji, AMR-852 with one local maize were tested for GLS resistance. The genotype significantly varied and there were significant differences (P

Objetivou-se nesse trabalho investigar o potencial genético de populações locais de milho quanto a resistência à cercosporiose. Foram conduzidos três ensaios no oeste de Santa Catarina, sendo avaliados 12 tratamentos (10 variedades locais e 2 testemunhas) em delineamento de blocos completos casualizados, com três repetições. Foram efetuadas seis avaliações da severidade da doença. Os dados foram submetidos a análise de variância conjunta. Diferenças significativas (p

Gray leaf spot (GLS), caused by Cercospora zeae-maydis is an important and destructive foliar disease of maize (Zeae mays) mostly in the mid hills of Nepal. Considering its potential threat to maize production, a total of fourty two and thirty different maize genotypes were evaluated in the year 2012 and 2013 respectively with two replications in observation nursery at Kapurkot, Salyan (1480 masl) for resistance to GLS. Disease assessment was made using 1-5 scale at 15 days interval for three times starting from tasseling stage (65 days after sowing). The results showed that no immune and highly resistant genotypes were found in both the year. Response of 27 out of 42 genotypes of maize were identified as moderately resistant (2-2.5 score) and 15 genotypes showed moderately susceptible (3 score) to GLS during 2012. During 2013 out of 30 genotypes of maize 27 were identified as moderately resistant (1.75-2.5 score) and 3 moderately susceptible (2.75-3 score) to GLS. Among the tested genotypes, BGBYPOP, Rampur SO3FO4, Celaya OOHGYA*HGYB, O7SADVI, Manakamana-3, SO1SIYQ and local were found most promising and moderately resistant to GLS disease during 2012 and SYN312-SR and CML-395/CML-444 during 2013.

Controlled environment studies were conducted to determine the effects of temperature on the expansion of lesions of gray leaf spot, and the effects of temperature and relative humidity on the sporulation of Cercospora zeae-maydis on maize (Zea mays). For the lesion expansion experiment, potted maize plants were spray inoculated at growth stage V6, bagged, and incubated at 25 to 28°C and 100% relative humidity for 36 to 40 h. Symptomatic plants were transferred to growth chambers and exposed to constant temperatures of 25, 30, and 35°C. Lesion area (length by width) was measured at 4-day intervals for 17 days. For sporulation studies, lesions were excised from naturally infected maize leaves, measured, and incubated at constant temperature (20, 25, 30, or 35°C) and relative humidity (70, 80, 90, or 100%) for 72 h. Sporulation was estimated as the number of conidia per square centimeter of diseased leaf tissue. A quadratic function was used to model the relationship between log-transformed conidia per square centimeter at 100% relative humidity and temperature. Temperature had a significant effect on lesion expansion (P ≤ 0.05). At 25 and 30°C, the rate of lesion expansion was significantly higher than at 35°C (P ≤ 0.05). The largest lesions and the highest mean rate of lesion expansion were observed at 30°C; however, the mean lesion expansion rate at this temperature was not significantly different from that at 25°C. The interaction effect of temperature and relative humidity on the log of conidia per square centimeter of diseased tissue was significant (P ≤ 0.05). At 100% relative humidity, the effect of temperature on sporulation was significant (P ≤ 0.05), with maximum spore production occurring at 25 and 30°C. The quadratic model explained between 49 and 80% of the variation in the log of conidia per square centimeter at 100% with variation in temperature. These results suggest that the rapid increase in gray leaf spot severity generally observed during mid- and late summer may be due to favorable conditions for lesion expansion during this period. When relative humidity is >95%, expanding lesions may serve as a source of inoculum for secondary infections.

Maize crop is affected by several diseases, but Gray leaf spot (GLS), is the major disease that threat maize production in every year in mid-hills and high-hills of Nepal. To identify the source of resistant on gray leaf spot disease maize genotypes were screened/evaluated under hot spots during 2013 and 2014 summer seasons across the hill environment of Nepal. In the screening nursery both exotic(CIMMYT China) and NMRP developed genotypes were included and screened at Pakhribas, Dhungkharka, Supping and Salyan during 2013 & 2014 summer seasons under replicated conditions. The genotypes identified resistant and high yielding at Dhungkharka in 2013 were YML58/(CML226/CATETO//CML226/CATETO)F2-B-1-2-B,YML32/(P147-F2-108-S7/P45-C8-76-S5)-F2-B-30-1-3, YML32/Cel FSRYS9956-B-3-2-4-B and YML58/(G34/36/G33TSR)-F2-B-4-1-B. In case of Salyan none of the genotypes showed resistant reaction against GLS but eight genotypes namely; YML23/P502-C2-58-1-1-2-5-B, YML23/P502-C2-185-3-4-1-3-B-1-B, YML23/P502-C3-F2-10-8-1-1-B, YML23/GLSI01P502-B-25-2-B, YML23/MBR-C5W-F108-2-3-1-B, YS12Q-189, YS12Q-33 and YS12Q-189 reacted MR reaction. At Pakhribas two genotypes reacted resistant (R) reaction namely; YML23/GLS101HGA-B-4-1-B and YS12Q-189 and other ten genotypes responded MR reaction. None of the tested entries at Suping responded resistant reaction but four genotypes ZM-401, 07SADVI, ZM-627 and BGBYPOP responded MR reaction against GLS. During 2014 summer season a total of 20 genotypes both exotic (CIMMYT India) and NMRP developed were screened against GLS across the hill regions of Pakhribas, Dhungkharka and Salyan. From the result of Pakhribas the genotype P501SRCO/P502SRCO was recorded for resistant (1.3) reaction and three genotypes 05SADVI, Entry # 36 and Entry # 27 were responded for MR reaction. In case of Dhungkharka nine genotypes namely; ZM-401, ZM-627, 05SADVI, 07SADVI, TLBRSO7F16, ENTRY#33, ENTRY#24, ENTRY#32 and ENTRY#21 were recorded for MR reaction. The tested genotypes at Salyan revealed that six genotypes namely; 05SADVI, 07SADVI, ACROSS-9942/ACROSS-9944, BGBYPOP, ENTRY # 24 and ENTRY# 32 were reacted resistant reaction and the genotype 07SADVI produced significantly highest grain yield (8638 kg/ha).Int J Appl Sci Biotechnol, Vol 3(3): 504-512

Gray leaf spot (GLS), caused by Cercospora zeae-maydis, is an important foliar disease of maize (Zea mays L.) worldwide, resistance to which is controlled by multiple quantitative trait loci (QTL). To gain insights into the genetic architecture underlying the resistance to this disease, an association mapping population consisting of 161 inbred lines was evaluated for resistance to GLS in a plant pathology nursery at Shenyang in 2010 and 2011. Subsequently, a genome-wide association study, using 41,101 single-nucleotide polymorphisms (SNPs), identified 51 SNPs significantly (P

Gray leaf spot (GLS) is an important and destructive disease of maize in the hills of Nepal. The occurrence of this disease is recorded for the first time in the country in 2006. Several genotypes of maize supposed to be resistant to gray leaf spot in SARMP Zimbabwe and CIAT Colombia were evaluated together with other varieties in observation nursery conducted at farmer’s fields as well as at Khumaltar (NARC research station in the Kathmandu Valley) during 2008 and 2009. Ten out of 28 genotypes of maize were identified as resistant to moderately resistant to GLS. The disease incidence was higher on the open pollinated varieties of maize. The severity of GLS on genotypes of maize observed as 3.0 and 2.2, respectively at Baluwapati and Dhungkharka in Kavrepalanchwok and 2.0 at Khumaltar in Lalitpur during 2008. The severity of GLS was observed as high as 2.4 at Pakhribas in Dhankuta and 1.7 at Khumaltar in 2009. DOI: http://dx.doi.org/10.3126/ajn.v2i0.7524 Agronomy Journal of Nepal (Agron JN) Vol. 2: 2011 pp.93-101

Maize (Zea mays L.) is one of the most important cereal crops used in the human diet in large parts of the world as well as in Ethiopia and its production are limited by diseases such as grey leaf spot caused by a fungus Cercospora zeae-maydis. Currently grey leaf spot has become the most important threat to maize production in maize belt areas of Ethiopia causing significant yield loss. The objective of this study was therefore, to assess the distribution and importance of maize grey leaf spot in south and southwest Ethiopia. The field assessments were conducted during the year of 2014 cropping seasons by sampling 110 farmer fields in 11 districts selected from two zones of Oromia region and two zones of Southern Nation, Nationalities and People region (SNNPR). The result revealed that the disease occurs in the entire assessed districts having different agro-ecological zones. Maize grey leaf spot was prevalent in all surveyed farms of south and southwest Ethiopia, 74% of maize fields were infected by grey leaf spot. However, the mean incidence and severity of grey leaf spot on maize was significantly varied from district to district. The highest grey leaf spot incidence (71.2%) and severity (46.2%) was recorded in Boricha district, while Damote Gale had the lowest mean incidence (51.8) and severity (33.5%). Among the surveyed four zones in two regions, the highest incidence was found in Sidama (65.6%) and Illubabore (63.1%) followed by Jimma (62.5%) and Wolaita (57.6%). The highest mean severity of maize grey leaf spot was observed in Sidama (44.5%) followed by Illubabore (43.7%) and Jimma (42.63%) while the lowest severity was recorded in Wolaita (36.4%) zone. The disease was more severe in intermediate/humid areas with intermediate annual rainfall. The current study revealed maize grey leaf spot pressure in maize farms of south and southwest Ethiopia and the need to design an efficient, inexpensive and sustainable management approaches against the pests.

The fungal genus Cercospora is one of the most ubiquitous groups of plant pathogenic fungi, and gray leaf spot caused by C. zeae-maydis is one of the most widespread and damaging foliar diseases of maize in the world. While light has been implicated as a critical environmental regulator of pathogenesis in C. zeae-maydis, the relationship between light and the development of disease is not fully understood. Recent discoveries have provided new insights into how light influences pathogenesis and morphogenesis in C. zeae-maydis, particularly at the molecular level. This review is focused on integrating old and new information to provide an updated perspective of how light influences pathogenesis, and provides a working model to explain some of the underlying molecular mechanisms. Ultimately, a thorough molecular-level understanding of how light regulates pathogenesis will augment efforts to manage gray leaf spot by improving host resistance and disease management strategies.

Resistance of maize inbred lines to major leaf diseases should be characterized for the development of new hybrids in breeding programs. Thus, this study aimed to assess the severity of leaf diseases in maize inbredlines with different kernel hardnessand two sowingseasons. We assessed four inbred lines and one check hybrid with dent kernels and four inbred lines and a check hybrid with flint kernels. Treatments were conducted in two sowing seasons, one in October, and another in December 2013. The symptoms of gray leaf spot (Cercospora zeae-maydis), northern leaf blight (Exserohilum turcicum), and white leaf spot (a complex of Phaeosphaeria maydis and Pantoea ananatis) were assessed every 10 days from flowering. The area under the disease progress curve was also calculated. Severity level of the diseases was higher in inbred lines when compared to the check hybrds (AG8041 PRO and P30R50YH), regardless of kernel hardness. Dent-kernel inbred lines showed a higher severity of northern leaf blight symptoms when compared to flint-kernelones. It is worth mentioning that disease severity increased as sowing was delayed.

Isolates of Cercospora species from leaves displaying symptoms of grey leaf spot were collected in maize-producing areas of south-central Brazil in 2001 and 2002. Restriction digests of the internal transcribed spacer region of rDNA detected the presence of the same two Cercospora species described on maize in the United States, namely C. zeae-maydis and the recently described species, C. zeina . Genetic variability among isolates was assessed by analysing 104 amplified fragment length polymorphism loci. Cluster analysis confirmed the genetic separation of isolates into two species with a mean similarity of 35%. Similarity levels within species were high, averaging 93% and 92% among isolates of C. zeae-maydis and C. zeina , respectively. The mean genetic similarity between C. zeae-maydis and C. zeina and two isolates of C. sorghi f. sp. maydis was 45% and 35%, respectively. Results of this study showed that populations of the grey leaf spot pathogens in Brazil are similar to those in the United States regarding species composition and that C. zeina is also present in Brazil.

Light, scanning and transmission electron microscopy were used to study conidiophore formation and conidiogenesis by Cercospora zeae-maydis Tehon & Daniels, the causal organism of grey leaf spot on maize, Zea mays L. Hyphae aggregate in the substomatal cavity and give rise to fascicles of 1–2 septate conidiophore initials which emerge through the stoma. A single, aseptate conidium develops from the conidiogenous cell of the conidiophore initial. As the conidium matures, septa are laid down. Extension growth of the conidiogenous cell terminally, leads to the lateral displacement of the conidium on the conidiophore. Schizolytic secession results in the secession of the conidium from the conidiogenous cell. On secession, a slightly everted geniscar, with a granular wall deposit, is left laterally on the parent conidiogenous cell. After conidial secession, the conidiophore continues to grow, producing a second conidium from the conidiogenous cell at the apex of the extended conidiophore. The second conidium, ...

Grey leaf spot (Cercospora zeae-maydis Tehon and E.Y. Daniels) has seriously decreased the yields of maize in KwaZulu-Natal, South Africa, and has been identified in neighbouring provinces and countries. Since no commercially grown hybrids have been identified to be resistant to the disease, a study was initiated to assess the susceptibility of hybrids to the pathogen. The objective of the study was to identify high-yielding hybrids that were least susceptible to grey leaf spot, and to identify hybrids best suited to stubble and conventionally ploughed tillage systems. Linear regression of relative yield against relative disease severity identified high-yielding maize hybrids, including PAN 6480, that were least susceptible, SNK 2888, was tolerant, whilst PAN 6528 was most susceptible to disease. The susceptibility of hybrids to grey leaf spot was affected similarly by stubble and conventional tillage practices over the seasons of the study. In the 1993/94 season with adequate rainfall and favourable for ...

Gray leaf spot (GLS) is a major maize disease in Brazil that significantly affects grain production. We used Bayesian inference to investigate the nature and magnitude of gene effects related to GLS resistance by evaluation of contrasting lines and segregating populations. The experiment was arranged in a randomized block design with three replications and the mean values were analyzed using a Bayesian shrinkage approach. Additive-dominant and epistatic effects and their variances were adjusted in an over-parametrized model. Bayesian shrinkage analysis showed to be an excellent approach to handle complex models in the study of genetic control in GLS, since this approach allows to handle overparametrized models (main and epistatic effects) without using model-selection methods. Genetic control of GLS resistance was predominantly additive, with insignificant influence of dominance and epistasis effects.

Resumo - A resistencia obtida pelo componente genetico e um dos metodos mais eficientes de controle das doencas foliares da cultura do milho. Para avaliar a capacidade geral de combinacao (CGC), capacidade especifica de combinacao (CEC), reciprocos, efeito materno e nao-materno para resistencia a Cercospora zeae-maydis, cinco linhagens (A, B, C, D e E) foram cruzadas e os vinte hibridos obtidos foram utilizados em experimentos conduzidos em tres ambientes. Foram avaliados a severidade da cercosporiose (CP) no estadio fenologico R5 e o rendimento de graos (RG) na colheita. A analise dialelica demonstrou que ocorreu interacao significativa (P < 0,05) hibridos versus locais para as variaveis CP e RG. D e E foram os melhores genitores para a para a variavel cercosporiose de acordo com a CGC. Na media dos locais as melhores combinacoes hibridas, conforme a CEC foram AxD, BxE, AxE e BxC, com estimativa de aumento nos rendimentos de graos, devendo ser recomendado a continuacao destes hibridos no programa de melhoramento da empresa. Palavras-chave - Zea mays L. Analise dialelica. Cercosporiose. Rendimento.

Three populations derived from crosses of selected resistant inbreds (061, B37HtN, and DS:74:1071) with susceptible inbred FR1141 and a population derived from a cross of B37 × B37HtN were evaluated for gray leaf spot severity in 1992 and 1993 at Urbana, IL, and Andrews, NC. Populations included the susceptible parent (P1), the resistant parent (P2), F1 and F2 generations, backcrosses BCP1 and BCP2, and, when space and seed were available, one or more of the F3, BCP1S1, and BCP2S1 generations. Plants at Urbana were inoculated, and naturally occurring disease was relied upon at Andrews. Individual plants were rated by visually estimating the percent leaf area blighted (necrotic). Generation mean analysis of data combined over years or locations indicated that a simple additive-dominance model was able to explain the inheritance of resistance for all populations. Dominance effects were detected in all population evaluated. For the FR1141 × 061 and FR1141 × B37HtN populations, dominance was significant at early ratings, but not at late ratings. Results from generation mean analysis for individual years, locations, and rating were variable.

Gray leaf spot (GLS), caused by the fungus Cercospora zeae-maydis, is one of the most important foliar diseases of maize. This study was undertaken to estimate heritability of C. zeae-maydis resistance and examine the relationship between previously identified resistance loci and certain components of resistance including incubation period, lesion number, and maximum lesion length. Partially inbred progenies arising from hybridization between maize inbred lines VO613Y (high level of partial resistance) and Pa405 (susceptible) were examined in Ohio and South Africa. Heritability estimates of resistance were calculated based on severity and incubation period values. The range of heritability estimates based on severity was broad, with values ranging from approximately 0.46 to 0.81 (mean = 0.59). Estimates of mean heritability for incubation period were lowest (0.18), indicating that this component would likely be unsuitable for selection of germ plasm intended for deployment in diverse regions. Length of GLS lesions was significantly affected by host genotype, with resistant genotypes having shorter lesions from one site in Ohio during two seasons. Genotype also had a significant effect on incubation period and lesion number; the lower values for these components also were associated with resistant genotypes. The combined action of these resistance components resulted in lower overall disease severity.

Plant diseases hinder food production globally. Of the known crop plant pathogens, fungi are perhaps the most widely adapted organisms. For disease control, host resistance has been the main method used through major gene deployment. Equally important, has been the use of fungicides. Over the last two decades these two control strategies have been fraught with rapid resistance erosion commonly referred to as the “boom and burst cycle,”. This raises urgent concerns with regard to development of effective alternative strategies such as use of fungicides. The use of fungicides is an effective strategy but they are potential sources of pollution into the environment, pose serious health risks to humans and are uneconomical for low-resource farmers. In this article the potential of how improved disease management strategies embodied in integrated disease management (IDM) can be developed based on a clear understanding of the pathosystem is discussed. We demonstrate that population and molecular genetics can be used to define pathosystems, estimate the evolutionary responsiveness of pathogens and from the data, design appropriate durable control methods. Various population and molecular genetic methodologies are described and how they can be incorporated into standard pathogen characterisation studies. Using grey leaf spot of maize ( Cercospora zeae-maydis ) as a case study, we show how these techniques can be used to generate information on genetic variability, providing for logical development of a durable IDM programme. Key words : Cercospora zeae-maydis, disease management, genetic tools, molecular markers RESUME Les maladies de plante entravent globalement la production de nourriture. Des pathogenes de plante connus, les champignons sont peut etre les plus rependus organismes adaptes. Pour le controle de maladie, la resistance hote a ete la methode principale utilisee a travers le deploiement de gene majeur. Egalement important, a ete l'usage des fongicides. Pour plus de deux decennies ces deux strategies de controle ont ete angoissees avec une rapide erosion de resistance communement connu a nous comme “boom and burst cycle” (cycle de boom et d'explosion). Ceci souleve les inquietudes urgentes avec respect au developpement des strategies alternatives effectives comme l'usage des fongicides. L'usage des fongicides est une strategie effective mais ces fongicides sont des sources potentielles de pollution dans l'environnement, pose des risques serieux de sante aux humains et ne sont pas economiques pour les fermiers de faibles ressources. Dans cet article le potentiel de comment les strategies ameliorees de gestion des maladies incarnees dans une gestion integree des maladies (IDM) peut etre developpe base sur une comprehension claire du pathosysteme est discutee. Nous demontrons que la population et les genetiques moleculaires peuvent etre utilises pour definir les pathosystemes, estimer les non reponses evolutionnaires des pathogenes et a partir des donnees, concevoir des methodes de controle durables. Diverses populations et methodologies genetiques moleculaires sont decrites et comment elles peuvent etre incorporees dans les etudes de caracterisation de pathogene standard. Utilisant la tache grise de feuille de mais ( Cercospora zeae-maydis ) comme cas d'etude, nous montrons comment ces techniques peuvent etre utilisees pour generer l'information sur la variabilite genetique, pourvoyant le developpement logique d'un programme d'IDM durable. Mots cles : Cercospora zeae-maydis, gestion de maladie, outils genetiques, indicateur moleculaire African Crop Science Journal Vol.12(4) 2004: 327-342

A description is provided for Cercospora zeae-maydis . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. DISEASE: Grey leaf spot of maize. HOSTS: Zea mays (Gramineae ). GEOGRAPHICAL DISTRIBUTION: AFRICA: Cameroon, Ethiopia (WEGARY et al. , 1999), Kenya, Malawi, Mozambique, Nigeria, South Africa, Swaziland, Tanzania, Uganda, Zaire, Zambia, Zimbabwe. NORTH AMERICA: USA (Colorado, Delaware, Iowa, Illinois, Kansas, Kentucky, Maryland, Minnesota, Missouri, North Carolina, Nebraska, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia, Wisconsin, West Virginia). CENTRAL AMERICA: Costa Rica, Mexico, Trinidad & Tobago. SOUTH AMERICA: Brazil (São Paulo), Colombia, Ecuador, Peru, Venezuela. ASIA: China (Jilin). TRANSMISSION: By wind dispersal of airborne conidia and infection from debris of the previous year's maize crop.

In 1989, 1,396 corn (Zea mays) inbreds were evaluated for resistance to gray leaf spot at Urbana, Illinois, after inoculation with Cercospora zeae-maydis. Sixty-two inbreds were selected on the basis of low disease rating, restricted lesion type, and maturity most useful for breeding programs in the midwestern United States. In 1990, selected inbreds and F 1 crosses between selected inbreds and the susceptible inbred FR1141, with the hybrid FR1141×LH51 has a susceptible check, were evaluated. Crosses FR1141 with inbreds CI30, CI88A, DS:74:1071, H110, Mo18W, Mo22, and TEX 1 had ratings that were nearly as good as or better than their resistant parent and significantly better than the susceptible hybrid FR1141×LH51

Development of gray leaf spot (GLS) of maize (Zea mays), caused by Cercospora zeae-maydis, was evaluated in seven inbreds in 1990 and 19 inbreds in 1991 in field plots with naturally infested corn debris. In 1990, nine ratings over 35 days were made beginning 9 August. In 1991, 10 ratings over 43 days were made beginning 17 July. Individual plants were assessed by two methods: 1) a disease index (DI) score was assigned on a 1-5 scale (1=no lesions, 5=all leaves dead); and 2) disease severity (DS) was expressed as diseased leaf area divided by the total area multiplied by 100, assessed on the ear -1 leaf and all leaves above it. The mean of ratings over time and the area under the disease progress curve (AUDPC) rankings for seven inbreds were similar both years (.)

Sporulation of Cercospora zeae-maydis was detected from lesions on pieces of leaf blades and sheaths kept on the soil surface or buried 5-10 cm beneath the soil surface during the winter and spring months of 1990 and 1991. Sporulation was not detected after May on buried infected tissues. The mean number of conidia per square millimeter of lesion varied from 2.1 to 5,430.6 on leaf blade tissues at two locations and from 5.9 to 104.6 on leaf sheath tissues on the soil surface at one location. However, the coefficient of variation among replications of each treatment was high (.)

Grey leaf spot (Cercospora zeae-maydis Tehon and E.Y. Daniels) is a relatively new disease of maize in South Africa and is capable of reducing grain yields by 20–60% in KwaZulu-Natal. Fungicides are widely used for control, but must be applied at the correct stage of disease development. Repeated applications may be necessary for effective control to be achieved. There is a paucity of information on the economic justification of these control measures. The aim of this study was to estimate the economic benefits of single and multiple sprays applied to maize at different stages of disease development. The economic analysis was based on the average operating costs of 18 dryland maize farms in the Winterton and Karkloof areas, where fungicides have been used to control the disease. These costs were used in the analysis of data generated from trials at Cedara to determine the most effective times and frequency of fungicide application for the control of grey leaf spot. Triple-spray treatments under both high ...