Potential organic methods for management of pear scab

• Published in: Acta horticulturae no. 9092; pp. 527 - 530
• Main Authors: Sugar, D, Hilton, R.J
• Format: Journal Article
• Language: English
• Published: International Society for Horticultural Science 2011
• Subjects: Cacopsylla pyricola; calcium hydroxide; copper hydroxide; cultivars; disease control; economic threshold; kaolin; mites; natural enemies; organic production; pears; pests; potassium bicarbonate; rain; spring; trees; Venturia pirina; Oregon
• ISSN: 0567-7572

Pear scab, caused by Venturia pirina, can be a limiting factor for successful organic production of pears in climates conducive to scab development. Hydrated lime (calcium hydroxide, 1 and 2%), potassium bicarbonate (Eco-Mate Armicarb “O”, 1 and 2%), and copper hydroxide (Kocide, 1.0-2.4 g L-1) spray treatments for pear scab control were evaluated in 2008-2010 in ‘Golden Russet Bosc’ pear trees in southern Oregon (42.3°N; 122.8°W, elevation 455 m, average annual rainfall approximately 450 mm). Under very low scab pressure in 2008 and 2009 (3 and 10% fruit scab, respectively, in untreated trees), all treatments provided excellent disease control. However, spring of 2010 had a high number of scab infection periods, resulting in 100% fruit infection in untreated trees. Under these conditions, hydrated lime 2% treatments did not significantly reduce scab infections. Potassium bicarbonate 1% and copper hydroxide (Kocide 3000 1.0 g L-1) treatments reduced fruit scab infections by 94.3 and 87.5%, respectively. Both potassium bicarbonate and copper hydroxide treatments caused unacceptable levels of fruit russet when applied to ‘Comice’ pears. Hydrated lime treatments did not cause russet in ‘Comice’ pears. While there were no apparent negative effects from potassium bicarbonate or copper hydroxide in the naturally russet ‘Golden Russet Bosc’ trees, their use may not be appropriate in some green-skinned cultivars where a russet-free finish is desired. The effects of repeated applications of hydrated lime on insect and mite populations were assessed in 2010. Natural enemies of pear pests were slightly reduced in the hydrated lime treatment versus an untreated control but the application of kaolin (Surround), either alone or in combination with hydrated lime, reduced the presence of natural enemies. However, pear psylla (Cacopsylla pyricola) populations rose to well above the economic injury level in all treatments.