Seasonal variation in the response of Hagberg falling and liquefaciton numbers to propiconazole fungicide in wheat

Summary The hypothesis was tested that seasonal differences in the response to propiconazole fungicide of hagberg failling and liquefaction numbers are related to grain drying rate, as indicated by potential evaportranspiration. The response of Hagberg failling and liquefaciton numbers to late‐season applicaitions of propiconazole was calculated using data from a field experiments in each of the years 1981 to 1990 on winter wheat ( Triticum aestivum ) cv. Agalong grown with similar husbandry at one site. Cumulative potential evapotranspiration was calculated over seven different periods during grain ripening. No visible sprouting occurred in any experiment and Hagberg falling number was above 250 s in nine of the 10 years. Disease severity on the flag leaf was less than 7% in nine of the 10 years, and diseases were generally controlled well by propiconazole. There were no significant relationships between the response of Hagberg falling number and any of the potential evapotranspiration variables. The response of liquefaction number was exponentially related to each of three cumulative potential evapotranspiration variables which covered periods before the estimated date of 40% moisture content. Years with lower cumulative potential evapotranspiration gave the greater responses, but the relationships were considerably influenced by the two lowest potential evapotranspiration years. It was concluded that these data provide indirect evidence that the response of Hagberg falling number (when transformed to liquefaction number) to fungicide is mediated through grain drying rate, and furthermore that the results are compatible with the hypothesis that pre‐maturity alpha‐amylase activity is stimulated by slow grain drying.