Factors affecting flower and immature fruit loss in pincherry and chokecherry
Shiell, Kevin John
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The objectives of this study were to quantitatively define the timing, extent and causes of flower and immature fruit loss for pincherry (Prunus pensylvanica L.) and chokecherry (Prunus virginiana L.). An estimated 75% of flower and immature fruit loss in both pincherry and chokecherry occurred just after full bloom and was attributed to inadequate pollen transfer. The remainder of the flowers and fruit lost was attributed to insect damage. In 1995, insect damage to reproductive structures accounted for 14% of flower and immature fruit loss in pincherry and 8% in chokecherry. The major insect pest of pincherry fruit was a sawfly (Hoplocampa sp.) which accounted for 11% of total fruit loss. The major insect pest in chokecherry was the leaf-roller (Archips argyrospila), which was responsible for 7% of the total amount of flower and fruit loss. Diseases were not a factor in flower or immature fruit loss in either pincherry or chokecherry. Pincherry in this study was found to have a growing degree day requirement (GDD5°C) of 144±8 for full bloom and 780±8 for fruit ripening. Chokecherry in this study had a GDD5°C requirement of 224±20 for full bloom and 1099±23 for fruit ripening. Pincherry required an average of 59±6 days from full bloom to harvest while chokecherry required 76±3 days. Yields of mature fruit in pincherry calculated from non-destructive sampling were 4.3% of potential yield (the total number of flowers at full bloom) in 1994 and 32.6% of potential yield in 1995. Based on destructive sampling, yields were 38% and 48% of potential yield in 1994 and 1995. The yields of mature fruit in chokecherry calculated from non-destructive sampling were 7.5% of potential yield in 1994. In 1995 yields from two separate sites were 8.6% and 5% of potential yield and in 1996, 3.7% of potential yield. From destructive sampling yields for chokecherry were 19% of potential yield in 1994 and 17% of potential yield in 1995. Studies on the role of pollen source and the effect of supplemental cross pollination of pincherry and chokecherry suggest that the majority of abscissions result from a lack of adequate pollen transfer. Pincherry was found to be self-incompatible, requiring cross-pollination to ensure maximum fruit-set. In 1996, flowers that were cross-pollinated by hand produced a yield increase of 55.6% in comparison to yields from flowers that were open-pollinated. Chokecherry was found to be partially self-compatible, producing fruit yields of 7.1% of potential yield in 1995 and 18.8% of potential yield in 1996 in flowers that were self-pollinated by hand. Flowers that were cross-pollinated by hand resulted in a significant (p=0.05) 42.9% and 16.3% increase in yield in 1995 and 1996 respectively, as compared to flowers that were open-pollinated. Pincherry flower buds were susceptible to freezing temperatures ranging from -4 to -12°C during the first stage of flower bud development designated as green bud. Chokecherry flower buds in the green bud stage were susceptible to freezing in the range of -8 to -20°C. Flower buds and flowers were susceptible to freezing temperatures in the range of -2 to -4°C for pincherry from the first-white stage until post bloom and for chokecherry from the open cluster to post bloom stages. Orchard cultivation of both pincherry and chokecherry seems plausible but pollination management strategies and insect pest control will be required to maximize yields.