The 2011 ASHS Annual Conference

California’s Delta European pear trees are up to 100+ years old and are intensively farmed in a highly sensitive waterway.  Production for fresh market has largely supplanted emphasis on canning pears and quality can be influenced by a number of factors.  We are investigating nutrient effects on fruit quality and disorders and management by K fertigation (annual vs biennial) and Ca (foliar and fertigated). ‘Black end’ (BE) disorder occurs sporadically, mainly on Asian rootstocks, and has been proposed to be caused by rootstock metabolites, water stress, poor drainage and/or nutrient imbalance (typically lower fruit calcium, magnesium, and manganese, and higher nitrogen and phosphorus). In several affected orchards (mostly ‘Bartlett’) we found no water potential differences, strong rootstock effects, and high K:Ca, N, K (fruit) and high K, low N (leaf) for BE trees.  Soil associated with BE trees was lower in K and N, however.  Foliar and fertigated Ca were ineffective against ‘black end’. K fertigation frequency (Year1 vs Year1+2) to ‘Bartlett’/P. calleryana trees with low N application (~63 lb/A) and preharvest soil-applied CaNO₃, was tested for nutrient effects on fruit quality.  July and October analysis of leaves from shoots (SL) and bearing spurs (BSL) were compared for K treatment effects.  No K differences were found between July leaf types, and levels were adequate.  July ‘Year1+2’ BSL levels of N, P, S, Cu, (K+Mg):N, K:Ca, Mg:Ca, and N:Ca were significantly higher, and Ca, Mg, Fe, Mn significantly lower than ‘Year1’ levels. Similar results were found with July SL, and to a lesser degree ‘Year1+2’ SL were low for K, Ca and Mn.  October SL and BSL potassium was much higher in ‘Year1’ vs ‘Year1+2’; Ca was higher in SL and Mg lower in ‘Year1+2’ BSL vs ‘Year1’.  Conditioned fruit ripening 6 days postharvest was uniform in the ‘Year1’ treatment, but ‘Year1+2’ fruit tended to not ripen and where ripening occurred it was not uniform.  ‘Year1+2’ fruit firmness was reduced by ~2 lb after storage compared to ‘Year1’ fruit; after ripening 4 days, ‘Year1+2’ fruit showed increased internal browning.  Strong negative correlations for July BSL nutrients included: N with K, (K+Mg):Ca, K:Ca, Mg:Ca;  P with Ca, Mg, Zn, Mn, Fe; B with Ca, Mg, Zn, Mn, N/Ca.  Strong positive correlations for July BSL included:  N with S; P with B, (K+Mg):Ca, K:Ca, Mg:Ca and N:Ca.  Firmness was positively correlated to N:K and Zn and negatively to Cu in July BSL.