Sensitivity of <i>Venturia inaequalis</i> and <i>V. pirina</i> to dodine in New Zealand

Abstract

The sensitivity of Venturia inaequalis and V. pirina to dodine was evaluated during the 1997/98 season using EC 50 and EC 95 values for colony growth on amended agar. Seventy one orchards with known fungicide application histories were sampled in the six main apple growing districts of New Zealand and Venturia isolates were tested. Sensitivity values were 19% lower in 1998 than indicated by data from 1994. No relationship between sensitivity and orchard fungicide spray history was detected. Despite its frequent use, dodine is still an effective fungicide for controlling apple black spot (V. inaequalis). Baseline sensitivities of V. pirina (pear black spot) for dodine were established from eight orchards in Hawkes Bay, Auckland and Central Otago. No dodine resistance was detected in this pathogen.

Sensitivity of <i>Venturia inaequalis</i> to myclobutanil penconazole and dodine in relation to fungicide use in Hawkes Bay apple orchards

“…However, as for the DMI fungicides, the isolates from organic orchards tended to have low EC 50 values and the isolates from orchards in which resistance management guidelines were exceeded tended to have higher EC 50 values. The overall mean EC 50 value of 0.24 mg/litre (Table 1) was lower than the values of 0.85 mg/litre reported by Bakker et al (1995) and 0.527 reported by Bakker (1999).…”

“…As was the case for myclobutanil, isolates from the three organic orchards had amongst the lowest EC 50 values and isolates from IFP orchards that exceeded resistance management recommendations (orchards 7, 8 and 9) had relatively high EC 50 values. The overall mean EC 50 value for penconazole of 0.12 mg/litre (Table 1) was considerably higher than the national mean of 0.039 mg/litre reported by Whelan et al (Whelan et al 1992), 1993-94 (Bakker et al 1995 and 1997-98 (Bakker 1999 (1992), but was only slightly greater than the mean of 0.10 reported by Bakker et al (1995). Previous Hawke's Bay EC 50 values for penconazole were 0.033 mg/litre (Whelan et al 1992) and 0.11 mg/litre (Bakker et al 1995).…”

“…Dodine has been in use worldwide since 1959 and although widespread resistance has reduced its use overseas (Chapman et al 2011), dodine still appeared to be effective in New Zealand in 1993-94 with a mean EC 50 of 0.85 mg/litre (Bakker et al 1995), and in 1997-98 with a mean EC 50 of 0.527 mg/litre (Bakker 1999). Current New Zealand guidelines are for a maximum of three dodine applications per season (Beresford 2005b).…”

“…It also investigated relationships between fungicide sensitivity, fungicide use and fungicide resistance management guidelines. Of five DMI active ingredients currently registered for use on apples in New Zealand, myclobutanil and penconazole were chosen because they have been widely used in New Zealand since the early 1980s and their sensitivity has previously been quantified (Whelan et al 1992;Bakker et al 1995;Bakker 1999).…”

Resistance of <i>Venturia inaequalis</i> to demethylation inhibitor and dodine fungicides in four New Zealand applegrowing regions

“…A survey of Hawke's Bay apple orchards in the 2010-11 season (Beresford et al 2012) indicated that DMI sensitivity in V. inaequalis had decreased since surveys in the 1990s (Whelan et al 1992;Bakker et al 1995), to a degree where loss of black spot control could now be expected in some orchards. There was no evidence of a loss of sensitivity to dodine in Hawke's Bay since the 1990s (Bakker et al 1995;Bakker 1999).…”