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Development of IPM Strategies to Control Russet of Apple Fruit 1997

Project Leaders: Tom Burr and Mary Heidenreich

Objectives:

1. Identify overwintering sites of A. pullulans in orchards.

2. Identify when during fruit development they are most susceptible to russet caused by A. pullulans .

3. Test the effectiveness of different biological controls and fungicides for control of russet in the orchard.

4. Measure natural populations of A. pullulans on different apple cultivars.

Results:

Re. objective 1: A. pullulans was present in high numbers in all tissues sampled, and higher A. pullulans levels were detected on Golden Delicious than on McIntosh. These data demonstrate that high populations of A. pullulans are present on apple year-round.

Re. objective 2: It appears that fruit can be susceptible to russet over a 6-week period if high enough inoculum is present. The next task will be to determine the effect of wetting periods at various stages of fruit phenology on populations of A. pullulans in relation to russet development.

Re. objective 3: Certain fungicides [shown in table 4, not included in this summary] and the growth regulator Provide were found to be effective for russet control. These same fungicides have in vitro activity against A. pullulans. Two microorganisms were tested as potential biological controls for russet in 1997, but neither significantly reduced the level of russet.

Re. objective 4: All eight cultivars gave very similar population curves. This result shows that differences in russet susceptibility among cultivars is probably not related to differences in epiphytic populations of A. pullulans that establish on them.