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Development of Integrated Pest Management Strategies for Apple Fruit Russet 2000

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Project Leader: Thomas J. Burr, Dept. Plant Pathology, NYSAES-Cornell University, Geneva, NY 14456

Cooperator: Mary Catherine Heidenreich, Research Technician IV,

Dept. Plant Pathology, NYSAES-Cornell University, Geneva, NY 14456

Non-technical summary of the relevance of research results and how they impact IPM:

We have discovered that two common fungi, A. pullulans and R. glutinis are able to cause russet on apple and pear and we believe that they are important causes of russet in NY orchards. A. pullulans causes the most severe russet and therefore most of our research has been focused on it. It has been determined that several varieties are affected by russet and that A. pullulans is commonly found sporulating in russeted tissues. Isolates of A. pullulans from several different sources were all able to cause russet. A grower/processor/consultant survey provided additional information on apple varieties that are most affected by russet, factors that growers and consultants have observed that contribute to russet and information on the monetary significance of russet on apple in NY state.

Research this year suggests that A. pullulans may induce russet after a short contact period with fruit. However additional experiments will be needed to prove this point. Such information suggests that once A. pullulans reaches a certain population level on fruit, it can induce russet within 48 hours. Therefore, we are attempting to determine which factors affect population buildup and then it will be possible to circumvent the russet process.

Related research with Dr. Martin Goffinet this year also provides evidence suggesting that the fungus induces russet rapidly after reaching a certain population threshold. This was done by making observations of fungus-fruit interactions using electron and light microscopy. Previously it was observed that the fungus causes erosion of the fruit wax and cuticle layers. This year it was first observed that the fungus induces cell divisions in outer apple tissues that are associated with the classical wound response. Additional research is needed to explain why often only certain segments of the fruit become russeted following inoculation of the entire fruit.

Although some fungicides, such as captan, are inhibitory to russet fungi, control is erratic. We discovered that this may result because a certain component of the fungal population is resistant of the fungicide. It may be that isolates from apple (having been exposed to captan) are more likely to be resistant than are isolates from other plants that are not sprayed. Further research is needed to determine whether the fungus is resistant to other fungicides that could be used to reduce russet severity (Polyram, Sovran). The adjuvant, penetrant, acidifier, LI700, also significantly reduced russet on some varieties. It may be that the material is altering the fruit surface in a way that the fungus does not survive well. This could provide an alternative to fungicides for russet control and therefore warrants further investigation.