level and first-level IPM blocks. Such lack of differ- 

 ence suggests that growers were applying understory 

 management and drop pick-up practices equally to both 

 types of blocks, even though our recommendation 

 called for more intensive management of the second- 

 level blocks. 



As shown in Table 1, there was a marked tendency 

 toward increasing incidence of vole establishment with 

 increasing height of grass. Orchards treated with herbi- 

 cide or in which height of understory growth did not 

 exceed 5 inches at time of sampling in October showed 

 an average incidence of 10% of the shingles with vole 

 activity, which we consider to be a comparatively non- 

 damaging population level. In contrast, orchards in 

 which understory growth exceeded an average of 21 

 inches showed an average incidence of 48% of the 

 shingles with vole activity, a potentially very damaging 



population level. 



As shown in Table 2, there 

 was no clear relationship between 

 numberof drops and incidence of 

 voles. Ifanything, vole establish- 

 ment beneath shingles tended to 

 be slightly greater in blocks with 

 fewer drops than in blocks with 

 greater numbers of drops. 



Conclusions 



We conclude form this two- 

 year study that growers who 

 maintain understory plant growth 

 at a low height during autumn 

 months have a much better 

 chance of escaping establishment 

 of voles than growers who do not. This conclusion may 

 be particularly applicable to meadow voles. Many 

 factors can affect the numberof voles immigrating into 

 an apple orchard during autumn and becoming estab- 

 lished beneath the trees. For example, a high abimdance 

 of alternate food such as acorns might tend to discoiu-- 

 age vole immigration into orchards. But in years when 

 alternate food is sparse or in locales where orchards 

 closely border woods containing many oak or ever- 

 green trees, growers could substantially lower the risk 

 of vole invasion by frequent mowing. 



Acknowledgments 



This study was supported by grants from the Mas- 

 sachusetts Society for Promoting Agriculture and the 

 USDA Northeast Regional 1PM Program. 



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Fruit Notes, Fall, 1994 



11 



