A Cumulative Degree-Day-Based Model to Calculate the Duration of the Incubation Period of Guignardia bidwellii

Abstract

Molitor, D., Fruehauf, C, Baus, O., and Berkelmann-Loehnertz, B. 2012. A cumulative degree-day-based model to calculate the duration of the incubation period oí Guignardia bidwellii. Plant Dis. 96:1054-1059.The duration of the incubation period of Guignardia bidwellii on leaves and clusters of Vitis vinifera strongly correlates to temperature. To describe this relationship mathematically, a new, cumulative degreeday-based model was developed. According to this model, first symptoms on leaves appear after reaching a threshold of 175 cumulative degree-days (calculated as the sum of average daily temperatures between 6 and 24°C starting on the day after the infection). On clusters, the duration of the incubation period is additionally affected by their respective developmental stages. For 'Riesling', the duration of the incubation period on clusters corresponds to the duration on leaves until reaching £he phenological stage "berries beginning to touch" but extends continuously with ongoing phenological development. Therefore, a correction factor recognizing cluster phenology was derived to calculate the cumulative degree-day thresholds for the occurrence of first symptoms on clusters after reaching "majority of berries touching". Hence, this present model allows the estimation of fungal development and forecasts the appearance of new symptoms on leaves as wel as on clusters, enabling growers to more precisely schedule curative as well as protective fungicide applications against grape black rot.

Accurate prediction of black rot epidemics in vineyards using a weather-driven disease model

“…In the model used in this research, an incubation period ended when 175 degree‐days (using 6 and 24 °C as the cardinal temperatures) were accumulated after infection, and symptoms continued to appear until 305 degree‐days were accumulated . Molitor et al found that disease symptoms first became visible on leaves when 165.6–198.2 degree‐days had accumulated after infection.…”

“…In the model used in this research, an incubation period ended when 175 degree‐days (using 6 and 24 °C as the cardinal temperatures) were accumulated after infection, and symptoms continued to appear until 305 degree‐days were accumulated . Molitor et al found that disease symptoms first became visible on leaves when 165.6–198.2 degree‐days had accumulated after infection. A similar incubation duration was observed for clusters when clusters were inoculated between growth stage BBCH 68 (80% of flowerhoods fallen) and BBCH 77 (berries beginning to touch); the incubation duration was longer for later inoculation dates in Riesling vines because of ontogenic or age‐related resistance .…”

“…Molitor et al found that disease symptoms first became visible on leaves when 165.6–198.2 degree‐days had accumulated after infection. A similar incubation duration was observed for clusters when clusters were inoculated between growth stage BBCH 68 (80% of flowerhoods fallen) and BBCH 77 (berries beginning to touch); the incubation duration was longer for later inoculation dates in Riesling vines because of ontogenic or age‐related resistance . This variability in incubation duration strongly supports our inference that most of the false negative predictions of infection in the present work were related to variability in incubation duration rather than to errors in predicting infection occurrence.…”

“…Gadoury et al also developed a set of simple rules to define the criteria for black rot infection based on a combination of wetness duration and temperature. Recently, Molitor et al developed a disease prediction system based on suitable conditions for infections and duration of incubation . The model was validated against 330 observed disease assessment data on leaves only; the model failed to predict a true infection in 41 of the 165 assessments with new disease symptoms and predicted an infection that did not occur in 79 of the 165 assessments with no new disease symptoms.…”

Epidemiology, identification and disease management of grape black rot and potentially useful metabolites of black rot pathogens for industrial applications – a review

“…The duration of the incubation period of P. ampelicida on leaves and clusters of V. vinifera correlates negatively (Spotts, ) and linearly with temperature and can be expressed as cumulative degree days (Northover, ; Hoffman et al ., ; Molitor et al ., 2012 a ). For instance, under Central European conditions on grape ( V. vinifera cv.…”