Pink mould of pecan kernels in the southeastern USA is associated with scab, above-normal temperatures, and humidity during nut maturation

Abstract

SummaryPink mould is a disease caused by the common saprophytic fungus Trichothecium roseum (Pers.:Fr.). Pink mould rarely infects kernels of pecan [Carya illinoinensis (Wangeh.) C. Koch] in the southeastern USA, but the disease was a major problem in 2002. T. roseum enters the pecan fruit via scab lesions on the shuck caused by the fungus Fusicladoporium effusum, (G. Winters) Partridge & Morgan-Jones. This study examined the association between pink mould and weather during nut maturation. Average daily temperatures and two or more consecutive days of rainfall were identified as critical factors in 2002, and were compared with weather data between 1963 – 2001 when there was no recorded evidence of pink mould. Both the average daily temperatures and the number of consecutive rainy days during nut maturation were above the 40-year average in 2002. Consecutive rainy days during the nut drying period in 2002 were more than double the 40-year mean, implicating humidity as a critical factor in mould development at this time. Normal variations in temperature were minor factors in disease development following the initial infection. Thus, the onset of mould was associated with the development of scab lesions in late July, a combination of warm temperatures in September and October, and above-average humidity in September and during nut drying from mid-October until mid-November. This combination of factors occurred in only one year out of the past 41 years, explaining the rarity of the disease. The incidence of mould was sigmoidal, with the log-phase overlapping the period of rapid sugar accumulation in the kernel, and potential substrates for the mould to grow.