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  • Author or Editor: P. J. Porpiglia x
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Net photosynthesis (Pn) rates of greenhouse-grown apple leaves were unaffected for at least 24 hours after shoot detachment. With shoots detached from orchard trees, overnight holding did not affect Pn rates nor stomatal resistance. Use of detached shoots for Pn and dark respiration (Rd) determinations in apple leaves was concluded to be a valid technique.

Open Access

Three studies were conducted to evaluate the effect of post-infection sprays of prohexadione-calcium on the severity of naturally occurring fire blight infections on 3- and 4-year-old 'Gala' apple trees on blight-susceptible or blight-resistant rootstocks. Although post-infection prohexadione-calcium reduced the dry weight of fire blight strikes removed by pruning in one commercial orchard site, this treatment did not reduce mortality of young 'Gala' trees on M.9 or M.26 rootstocks, and did not reduce the incidence of scion or rootstock cankers on any of the rootstocks tested. We conclude that post-infection treatment with prohexadione-calcium is of no practical value in reducing fire blight symptoms on apple. Our results suggest that resistant apple rootstocks will be very valuable in increasing orchard survival in a fire blight epidemic.

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