Article

Influence of living mulches on vole populations and feeding damage to apple trees

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Abstract

Voles of the genus Microtus are considered the major mammalian pest species affecting tree fruit crops in North America and Europe. During winter, voles feed on bark, vascular tissues, and sometimes roots of trees. Rodenticides continue to be the major method used to reduce vole populations in orchards, but an alternative approach could be a living mulch along tree rows that would provide weed management, have a low growth habit, and be repellent to voles. We examined four living mulches installed in young apple orchards: hairy vetch (Vicia villosa Roth), birdsfoot trefoil (Lotus corniculatus L.), sweet woodruff (Galium odoratum (L.) Scop.), and creeping thyme (Thymus serpyllum L.). Forage grasses were used as a “control” in two experiments. Efficacy of these mulches was evaluated by their growth and effects on (1) abundance of total orchard herbaceous plants, (2) abundance of montane voles (Microtus montanus Peale) , and (3) feeding damage to apple trees in field trials at Summerland, British Columbia, Canada in 2007-2010. A sixth treatment, glyphosate herbicide, was added in Experiment 2. Hairy vetch and birdsfoot trefoil did not suppress herbaceous vegetation along tree rows, but birdsfoot trefoil had fewer voles than either hairy vetch or forage grasses. Sweet woodruff and creeping thyme both reduced abundance of orchard herbs compared with the control forage grasses and this effect was maintained for two of three growing seasons. Forage grasses and sweet woodruff had increasing proportions of mulch dominating the growing sites, whereas creeping thyme did not. Both sweet woodruff and creeping thyme seemed to repel voles with reduced damage to trees in two winters, but not summer 2010, compared with the forage grasses sites. Vole numbers were, on average, 1.4 to 4.9 times higher in the forage grasses than the other two sites. However, the relatively high degree of feeding damage (> 45% mortality) to young apple trees (except for 16% mortality for creeping thyme in one winter) in all three seasons was a major limitation. These tree mortality levels are unacceptable economically and suggest strongly that living mulches may not be a practical solution for weed management in organic or conventional orchards. Orchard-scale experiments that emulate real-world farming practices might yield living mulch habitats that are not as desirable for voles as those examined in our study. Herbicide sites had the lowest abundance of herbaceous vegetation, voles, and provided complete protection of apple trees compared to any of the other treatment sites.

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Chapter
IntroductionVolesOther Vertebrate PestsConcluding Remarks
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Field method for evaluation of rodenticides for control of Microtus pinetorum in apple orchards
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Byers, R.E. 1981. Field method for evaluation of rodenticides for control of Microtus pinetorum in apple orchards, p. 77-85. In: E.W. Schafer and C.R. Walker (eds.). Vertebrate pest control and management materials: Third conference. ASTM STP 752. Amer. Soc. Testing Materials, West Conshohocken, PA.
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U.S. Department of Agriculture. 2000. National Organic Program: Final rule. Fed. Regist. 65(246):80643.