Articles
WINTER CHILL MODELS IN A MILD SUBTROPICAL AREA AND EFFECTS OF CONSTANT 6°C CHILLING ON PEACH BUDBREAK
Article number
409_1
Pages
9 – 18
Language
Abstract
It is necessary to estimate, accurately and simply, winter chilling in different subtropical areas.
While the Richardson unit (RU) concept is widely used in South Africa, Erez’s dynamic model portions (DMP) have given a better estimation of winter chilling in areas with warmer winters in the Cape Province.
At Pietermaritzburg (29°40 S, 30°25 E, altitude 767 m), the number of hours above 10°C increases progressively throughout winter and is from slightly, to 2.6X greater, than in the Cape areas.
Twice, during the past three winters, there have been negative RU totals because of the high day temperatures.
By simply adding the RU totals, on days when there is a positive total, a progressive increase in total "units" accumulates during the winter months, which follows the same trend as with DMP. (A table of positive RU according to daily maximum and minimum temperatures can be used as a guide). Totals of 11–16 DMP and 150–225 positive RU, accumulated by the end of rest in numerous low-chill cultivars that produce well in this area.
Container grown trees exposed to constant 6°C have given earlier vegetative than floral budbreak, resulting in reduced fruit set as a result of competitive sinks.
Paclobutrazol drenches reduced the competitive effect of the earlier vegetative shoot growth.
While the Richardson unit (RU) concept is widely used in South Africa, Erez’s dynamic model portions (DMP) have given a better estimation of winter chilling in areas with warmer winters in the Cape Province.
At Pietermaritzburg (29°40 S, 30°25 E, altitude 767 m), the number of hours above 10°C increases progressively throughout winter and is from slightly, to 2.6X greater, than in the Cape areas.
Twice, during the past three winters, there have been negative RU totals because of the high day temperatures.
By simply adding the RU totals, on days when there is a positive total, a progressive increase in total "units" accumulates during the winter months, which follows the same trend as with DMP. (A table of positive RU according to daily maximum and minimum temperatures can be used as a guide). Totals of 11–16 DMP and 150–225 positive RU, accumulated by the end of rest in numerous low-chill cultivars that produce well in this area.
Container grown trees exposed to constant 6°C have given earlier vegetative than floral budbreak, resulting in reduced fruit set as a result of competitive sinks.
Paclobutrazol drenches reduced the competitive effect of the earlier vegetative shoot growth.
Publication
Authors
P. Allan, G. Rufus, G.W. Matthee, G.C. Linsley-Noakes
Keywords
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