A computer program using the language and statistical procedures available from SAS (Statistical Analysis System) was written in order to identify the most highly correlated meteorological factors with the incidence of wheat head blight (caused by Fusarium graminearum Schwabe) at Pergamino, in the humid pampeana region. Applying linear regression techniques, different models from simple up to a maximum of three independent variables were fitted to the data (1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990). The meteorological variables were processed in a time segment beginning eight days prior to the heading date (50% of emerged ears) and finishing when 530 degree days were accumulated (26-32 days). The number of two day periods with rainfall and relative humidity >81% in the first day and relative humidity >78% in the second (NPPRH) was the variable that showed the strongest association with disease incidence (FI) (R 2 = 0.81). After examining the models in several ways (1t 2, Adjusted R 2, PRESS statistic), two equations were selected: FI% --20.37 + 8.63 NPPRH -0.49 DDXNT (R 2 = 0.86) and FI% = 16.39 + 5.43 NPPRH -0.45 DDXNT + 2.95 DPRH (R 2 = 0.886), in which DDXNT represents the daily accumulation of the residuals resulting from subtracting 9 to the minimum temperature values (<9 ~ C) and the exceeding amounts of maximum temperatures from 26 * C and DPRH is the number of days with precipitation and relative humidity greater than 83%. Successful local predictions of incidence of scab for the years 1991-1993 (reserved for validation purposes) were achieved using both equations.

Fe and Có rdoba provinces, respectively (Galich and Galich, 1996). Assays in Pergamino (Buenos Aires prov-In Argentina, head blight (caused by Fusarium graminearum ince) showed that kernel number rather than kernel size Schwabe), is a highly risky disease of wheat (Triticum aestivum L.was seriously affected as a consequence of pathogen emm. Thell), although its occurrence is sporadic, depending on prevalent environmental variables. This unpredictability has stimulated the action (Annone and Frutos, 1988). development of predictive models of head blight occurrence that, ifInfection begins when spores are windblown onto successful, would help growers in the selection of control strategies. exposed anthers of wheat heads. The probability of in-As a result of our earlier work, empirical equations for predicting fection is greater when the anthers are exposed for a head blight incidence were developed at Pergamino INTA Experilonger period of time. This period with exposed anthers ment Center (Lat., 33؇ 56S), associating temperature and moisture lasts approximately 30 d in a commercial wheat field variables with mean disease observations from many wheat cultivars. (Reis, 1987). The critical period for infection extends In the current study our objective was to validate two of these meteofrom the beginning till the end of flowering, the crop rological based equations developed for Pergamino to predict wheat being less susceptible when grain filling starts. The anhead blight incidence and severity at Zavalla (Lat., 33؇ 1S) and Olithers constitute an important nutritional substrate for veros (Lat., 32؇ 33S) in moderately susceptible to susceptible cultivars the fungus, enhancing its rapid growth towards the ovafor the years 1993 to 1995. Even though the t-test determined nonsignificant differences between mean observed disease values versus ries and developed grains. Under proper environmental predicted values, a graphic method and a deviation examination conditions, the fungus grows into the kernels, glumes, or showed an underestimation at high disease levels. Simple analyses of other head parts (McMullen et al., 1997), thus producing sensitivity were able to detect the improvement in incidence and flower abortion early in the season and shriveled grain severity goodness of fit estimations that resulted from increasing the later. The pathogen overwinters in cereal residues and maximum temperature threshold and the heat accumulation defining secondary hosts until it is hydrated the next growing the length of the wheat critical period for infection. This study showed season, causing it to produce perithecia which release that meteorological based empirical equations developed for Pergamspores to infect another crop.ino can be useful for predicting disease intensity at more northern According to Galich and Galich (1996), Argentine locations in the Pampas region, making only a few changes in temperawheat cultivars have demonstrated two degrees of sensiture thresholds.

Citrus canker is an important bacterial disease of citrus in several regions of the world. Strains of Xanthomonas citri type-A (Xc-A) group are the primary pathogen where citrus canker occurs. After Xc-A entered the Northeast of Argentina in 1974, the disease spread rapidly from 1977 to 1980 and then slowed down and remained moving at slow pace until 1990 when it became endemic. Citrus canker was detected in Northwest Argentina in 2002. This paper presents the main steps in the fight of the disease and the management strategies that have been used to control citrus canker at this time. We think the process might be usefull to other countries with the same situation. Results from more than 40 years of research in Northeast (NE) Argentina indicate that we are at the limit of favorable environment for the disease. The severity of citrus canker is greatly affected by the environment and El Niño Southern Oscillation (ENSO) phenomenon which causes cyclic fluctuations on the disease intensity in the NE region. Weather-based logistic regression models adjusted to quantify disease levels in field conditions showed that the environmental effect was strongly modulated by the distance from a windbreak. Production of healthy fruits in citrus canker endemic areas is possible knowing the dynamics of the disease. A voluntary Integrated Plan to Reduce the Risk of Canker has been in place since 1994 and it allows growers to export unsymptomatic, uninfested fresh fruit to countries which are free of the disease and require healthy, pathogen free fruits. The experience from Argentina can be replicated in other countries after appropriate trials.

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Studies were undertaken during 3 growing seasons at several locations on the Argentinean Pampas to investigate the relationships between environmental factors and black point incidence, and to develop predictive models. The strongest associations were observed throughout the critical period starting at 543 degree-days from heading to 861 degree-days (base temperature = 0°C). After a selection process, the best regression equation was: PI % = –6.50 + 0.07 DPrDDTd + 0.23 DRH, where PI is predicted disease incidence, DPrDDTd is a product of days with precipitation and the total degree-day accumulation of mean daily temperatures greater than 17°C (DDTd), and DRH is the total days with relative humidity above 62%. The equation accounted for 87% of the total variance in the disease incidence. Using logistic regression techniques, a model including precipitation frequency and DDTd could satisfactorily explain the probability of occurrence of severe, moderate, and light epidemics.

RESUMENDurante los años 2003 a 2008 se evaluó la severidad de las enfermedades de fin de ciclo (SevEFC, mancha marrón y tizón morado) en el estado fenológico R7 en localidades de las provincias de Santa Fe y Córdoba. Los valores de SevEFC (N=15) se categorizaron binariamente en función de un valor umbral en: epidemia severa (Sev EFC>36 %) y epidemia moderada a ligera (<=36 %). La variación de la SevEFC en R7 fue analizada en relación a variables ligadas a la precipitación, procesadas entre R3 y R5. Las variables se expresaron como frecuencia y precipitación acumulada en mm, que superan los umbrales: 1, 5, 7 y 10 mm. Las variables DPr7 (días con precipitación >7 mm), PrAc7 (acumulado de precipitaciones diarias >7 mm) y la interacción entre ambas (It7) resultaron ser las más fuertemente correlacionadas con los niveles epidémicos (coeficiente de Kendall Tau-b (r K = 0,74, 0,60 y 0,71 respectivamente). El modelo de regresión logística que incluyó a PrAc7 estimó correctamente la probabilidad de ocurrencia en 12 de las 15 observaciones de SevEFC. Los modelos logísticos que integraron las variables DPr7 o It7, obtuvieron precisiones de predicción de 93,3 %. Estos resultados podrían ser útiles para la predicción y control de las EFC. Palabras clave: Glycine max, enfermedades de fin de ciclo, modelos logísticos. were recorded at the R7 growth stage at several sites in Santa Fe and Córdoba Provinces. The annual LSDsev records (N=15) were grouped into two epidemic categories based on a threshold value (median of observed disease data): severe (LSDsev >36 %) and moderate to light (LSDsev <=36 %). Variations in epidemic levels were studied in relation to precipitation-based variables, processed in a time window limited by R3 and R5 growth stages. The variables were expressed as frequency (days) and total accumulation (mm) of daily precipitations greater than the thresholds 1, 5, 7 and 10 mm. The variables PrF7 (number of days with precipitations>7 mm) and AcPr7 (total accumulation of daily precipitations >7 mm) and the interaction (product) between them (It7) were the most strongly correlated, according to Kendall tau-b coefficients (r K =0.74, 0.60 and 0.71 respectively). Logistic regression model including AcPr7 correctly estimated the probability of occurrence of epidemic categories in 12 cases (out of 15). Logistic models integrating PrF7 or the interaction effect (It7) presented prediction accuracies of 93.3 %. These results could be useful for prediction and chemical control of LSD. Keywords: Glycine max, late season diseases, logistic models. logistic models. logistic models. ABSTRACT INTRODUCCIÓNDurante la campaña 2008/09, la Argentina alcanzó una siembra record de 17 millones de hectáreas de soja, constituyéndose en la mayor superficie sembrada en la historia del país con una única especie (SAGPyA, 2008). Casi la totalidad de la siembra correspondió a cultivares modificados genéticamente y la mayor parte se cultiva bajo siembra directa (SD). Este proceso de crecimiento estuvo acompañado por el avance de la frontera ...

Leaf rust epidemics of wheat, caused by Puccinia recondita f. sp. tritici, were analyzed for the 1972 to 1990 growing seasons. The disease severity values recorded for leaf rust in early and late bread-wheat planting dates at Pergamino were used to identify the best genetic and environmental predictors of disease severity. Leaf rust severity (early planting date) could be predicted (R2 = 0.88) as a function of heat accumulation (base daily mean temperature >12°C), days with relative humidity >70% without precipitation, and a cultivar resistance index. For late planting date, the predictive value of meteorological variables decreased, while the importance of the resistance index increased over that found for the early seeded trials. In general, predicted and observed leaf rust severity levels agreed during 1994 to 1996 at Pergamino, and for trials (1991) that were grown at some distance from the area where the original data for model development were recorded.

Net blotch caused by Drechslera teres is an important disease in most barley-growing areas. To prevent the introduction of this pathogen into the field, seed treatment is recommended. The objectives of this research were to evaluate different fungicides for eradicating D. teres from the seed and the role of both infected and treated seeds in the epidemiology of the disease under field conditions. The three fungicides tested in vitro (iminoctadine, guazatine, and thiram + iprodione) were able to eliminate D. teres at the highest dose used in this study. Under field conditions, eradication of the pathogen was not achieved, but net blotch was significantly reduced.