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Influence of living mulches on vole populations and feeding damage to apple trees
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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Sustainability is a primary goal of organic farming systems, particularly with regard to environmental factors. Modern orchard systems in general benefit from the perennial nature of the crop and the reduced impacts to soil and water with the absence of tillage. In the Pacific Northwest region of the USA, most pome and stone fruit orchards utilize herbicides to manage weeds in the tree row, and a perennial grass cover in the drive alley to reduce dust and provide a stable surface for machinery traffic. Organic orchards in the region do not have an acceptable herbicide option, and thus typically rely on weed control through soil tillage, which can compromise soil quality. Tillage was compared with wood chip mulch and an undisturbed control in a 3-yr trial. Tillage did not lead to consistent soil quality decline; however, it did lead to poorer tree performance relative to the control, while wood chip mulch improved tree performance. Both options provided good weed control. Related trials with living mulch in the tree row showed soil quality benefits and meaningful N contribution, but had severe competition with trees and elevated vole populations. Results to date suggest that an integration of practices will be needed to optimize sustainability.
This study was conducted to compare various orchard groundcover management systems (GMSs)—including a crownvetch “living mulch” (CNVCH), close-mowed (MWSOD) and chemically growth-regulated (GRSOD) sodgrasses, pre-emergence (NDPQT) and two widths of post-emergence (GLY1.5 and GLY2.5) herbicides, hay-straw mulch (STMCH), and monthly rototillage (tilled)—during the first 6 years in a newly established apple ( Malus domestica Borkh.) planting. Mean soil water potential at 5 to 35 cm deep varied substantially among treatments each summer, and treatment × year interactions were observed. During most growing seasons from 1986 to 1991, soil water availability trends were STMCH > NDPQT > GLY2.5 > GLY1.5 > tilled > GRSOD > MWSOD > CNVCH. Soil organic matter content increased under STMCH, CNVCH, and MWSOD and decreased under NDPQT and tilled treatments. Water infiltration and saturated hydraulic conductivity after 4 years were lower under NDPQT and tilled, and soil under STMCH and GRSOD retained more water per unit volume at applied pressures approximating field water capacity. Mid-summer soil temperatures at 5 cm deep were highest (25 to 28C) in tilled and NDPQT plots, intermediate (22 to 24C) under GRSOD, and lowest (16 to 20C) under CNVCH and STMCH. These observations indicate that long-term soil fertility and orchard productivity may be diminished under pre-emergence herbicides and mechanical cultivation in comparison with certain other GMSs.
Meadow vole ( Microtus pennsylvanicus Ord) populations, feeding activity and damage to young apple ( Malus ×domestica Borkh.) trees were monitored for several years in a New York orchard by direct observation, trap counts, and a feeding activity index in various groundcover management systems (GMSs). Meadow vole population density differed among GMSs, with consistently higher densities and more trees damaged in crown vetch ( Coronilla varia L.), hay-straw mulch, and red fescue ( Festuca rubra L.) turfgrass tree-row strips. Vole densities were high in autumn and low in spring each year. Anticoagulant rodenticides and natural predation did not adequately control voles in GMSs providing favorable habitat. Groundcover biomass per m ² was weakly correlated with vole densities in 2 of 3 years, while the percentage of soil surface covered by vegetation was not significantly correlated with vole populations. Applications of thiram fungicide in white latex paint were better than no protection, but less effective than 40-cm-high plastic-mesh guards for preventing vole damage to tree trunks. A combination of late-autumn trapping, close and consistent mowing of the orchard floor, trunk protection with mesh guards, contiguous habitat for vole predators, and herbicide applications within the tree rows provided effective control of meadow-vole damage to trees at this orchard during 3 years without applications of rodenticide baits. Chemical names used: Tetramethylthiuram disulfide (thiram)
The semiarid climate of the Pacific Northwest allows for the production of organic, temperate tree fruit relatively free of disease and with fewer key insect pests compared with other regions of the United States. Weed control and soil fertility are two of the higher cost areas for organic tree fruit where alternatives are being sought through research and on-farm innovation. Mulches, both living [e.g., white clover [(Trifolium repens)] and inert (e.g., wood chips) show promise for controlling weeds, conserving water, providing nitrogen (N), or improving tree growth, but potentially have system trade-offs such as increased rodent pests and unwanted late-season N. Growers need orchard floor management practices that help them maintain or improve soil quality per the requirements of the National Organic Standards.
Many plants have mechanisms of physical or chemical resistance that protect them from herbivores in their environment. The ornamental plant Pachysandra terminalis Sieb. and Zucc is highly unpalatable to voles, but the nature of this resistance is not fully understood. Extracts of P. terminalis were prepared to determine the extent to which chemical constituents could account for its avoidance by voles. A bioassay in which samples were mixed with applesauce showed that ethanolic extracts were highly deterrent to captive prairie voles (Microtus ochrogaster Wagner, 1842). Bioassay-guided fractionation of ethanol extracts showed that antifeedant activity was present in both polar and non-polar fractions. Further separation of each fraction by open column chromatography and high pressure liquid chromatography revealed that combinations of compounds were responsible for the deterrent activity. Preliminary ultraviolet and mass spectroscopic analyses indicated that steroidal alkaloids that are characteristic of this plant are likely to be involved.
Little is known about the effects of cover crops on soil properties in organic orchards. To fill this gap, this work aimed
at examining the effects of several cover crops on soil fertility, nitrate dynamics, populations of nematodes and tree performance
in an organic orchard of apple cv. Royal Gala/EM 26 planted in 1994 at 4×2m. In 1999 the following treatments were randomly
applied to the inter-row spaces of 20 tree rows each: permanent cover of alfalfa (Medicago sativa L.) plus fescue (Festuca arundinacea Schribn.), Alfalfa/fescue (AF); permanent cover of strawberry clover (Trifolium fragiferum L.), Strawberry clover (SC); seeding of common vetch (Vicia sativa L.), Vetch (V); and Control (C) (natural vegetation of grasses and legumes with the soil disked twice in late winter, which
is the traditional management system used by growers in this region). The cover crops were mowed 3 or 4 times during the growing
season and the clippings were left on the ground for decomposition. The trial was conducted in the northern Patagonia region
of Argentina in a sandy loam soil with a pH of 7.6 and initial organic matter content of 1.5%. A commercially available certified
organic fertilizer containing 5% total N, 2% total P and 4% total K was added annually at a rate of 1.0kg per tree in equal
amounts to each treatment in a radius of 0.4m around the trunk. After 6years, soil organic matter in the top soil was 31,
27.9, 23 and 18.6gkg−1 for SC, AF, V and C treatments, respectively. Total soil N followed the same trend. Apple leaf N declined steadily in all
treatments especially in AF and C from year 3 to 5 with values below 1.8% and it was therefore necessary to increase the rate
of organic fertilizer. Nitrate concentrations remained under 7.5mg kg−1 during the winter months in all treatments and increased in spring and summer. A sharp increase in soil nitrate, up to 100ppm,
was observed in late spring in V due to rapid biomass decomposition after maturation of the common vetch. Populations of nematodes
especially bacterivores and herbivores increased from September (late winter) to March (fall) in the V treatment. Significant
differences were observed when we compared the effects of treatments on the entire nematode population. Tree growth as measured
by trunk cross sectional area and canopy volume was significantly lower in the C treatment. Apple yield was also lower in
the C treatment in years 5 and 6 while no differences were found among the seeded cover crops. Thus, our soil management treatments
did affect soil properties, tree growth and yield. Disking is not a recommended practice because it may decrease the concentration
of soil organic matter and leads to poor tree vigor that corresponds to low fruit bearing potential. However, even with the
use of permanent cover crops the addition of organic fertilizers is needed in order to sustain yield and tree vigor.
Removal of all vegetation with herbicides over the total orchard floor or only in tree rows significantly reduced montane vole ( Microtus montanus Peale), meadow vole ( M. pennsylvanicus Ord), and northern pocket gopher ( Thomomys talpoides Richardson) populations and damage. Herbicide treatments in four test orchards were carried out during May, July, and Sept. 1983 to 1985. Average overwinter abundance of voles was reduced 53% to 99% on treatment areas. Several vole populations went to extinction in the third year of herbicide treatment. Incidence of tree damage was 40.6% and 9.6% with feeding intensities of 17.2 cm ² and 0.4 cm ² of bark and tissues removed per tree on control and treatment blocks, respectively, during a peak year in abundance of voles. Pocket gopher populations and damage were significantly lower in treatment than control blocks. Deer mouse ( Peromyscus maniculatus Wagner) and yellow pine chipmunk ( Eutamias amoenus J.A. Allen) populations generally increased on treated areas. Use of herbicides to control orchard floor vegetation is an effective means of rodent damage control.
(1) Field voles, Microtus agrestis, and bank voles, Clethrionomys glareolus, are pests in Scandinavian forestry and horticulture. Damage to forest seedling or fruit trees, for example, is inflicted mainly at, or just after, population peaks. Changes in population density, using standardized trapping techniques, are laborious and expensive to follow. Therefore the value of various signs as indices of vole abundance was examined. (2) The abundance of M. agrestis on abandoned fields was correlated with grazing intensity in spring and autumn and with runway numbers in autumn. Seasonal and annual changes in catches of M. agrestis were related to various signs but variations in the latter were generally more even. The abundance of C. glareolus in mature forests was correlated with numbers of runways in spring and autumn and with grazing intensity in spring. Other signs such as earth holes or faeces did not correlate so well. Long-term predictions could not be made. (3) In order to make short term predictions, M. agrestis abundance on abandoned fields and other habitats with few other small rodent species should be assessed in terms of grazing intensity. In areas where C. glareolus is also common, e.g. reforestations, the number of runways should also be recorded.
The organic market has grown exponentially in Europe during the last ten years. However, the organic fruit industry in European states still has a relatively low market share of less than 1-5% compared with organic vegetables, milk and eggs that have achieved market shares of close to 10% of the total market. As well, conventional fruit growers still hesitate to respond to the generally good organic market demand. A major reason for this behaviour is the continuing high production risk due to less availability of effective management tools for the control of pests, diseases, weed and biennial bearing. The key pests and diseases in apple and pear include scab, sooty blotch, and fire blight as well as rosy apple aphid, pear sucker and codling moth, as well as post-harvest diseases like Gloeosporium rot. Another reason that holds up organic fruit expansion is that in fruit production, in contrast to milk or wheat, new and organic-specific marketing attempts are necessary for organic cultivars, less cosmetic "beauty", etc.) but are presently scarce. In an ideal organic production system, all possible measures that lead to improved stability and self-regulation of the agro-ecological system have to be implemented (e.g. resistant cultivars, bio-diversity areas, lower planting densities, measures to avoid inoculum build-up, soil fertility). At present, most organic orchards have almost the same design as found in conventional production and often do not include system stabilising elements. Therefore, organic fruit production still depends largely on direct pest and disease control methods. In the last decade effective compounds and techniques have been developed such as Neem preparations, granulosis viruses, and mating disruption to control pests. Some new plant protection techniques e.g. clay powders, resistance inducers, better spray technique and spray timing models have been introduced. The introduction of new equipment, compounds, cultivars and decision support systems will further improve yield stability. However, for other limiting factors, such as weed competition, crop load regulation and market demands in respect to quality, innovative solutions have to be developed. The challenge for the future is to build up a credible ("true-organic") and high quality multi-factor oriented organic fruit production that combines single factor solutions to a self-regulating, and possibly even organic pesticide-free, production system. Progress in this direction will lead to innovative organic production and marketing concepts that are clearly different from conventional ones. To achieve these goals, creative efforts along the whole chain involving producers, consumers, retailers, advisory services and researchers are essential.
The food preferences of the meadow vole (Microtus pennsylvanicus) were tested against an array of 30 plant species from a wide variety of habitats; eight of the 30 were introduced species. In the food-preference sequence established by this experiment, forage crops and adventive plants characteristic of the old-field habitat occupied eight of the top ten ranks. White clover (Trifolium repens) was the most preferred plant; alfalfa (Medicago sativa) and red clover (Trifolium pratense) were next in rank, followed by dandelion (Taraxacum officinale) and horsetail (Equisetum arvense). Four of the remaining five ranks among the first ten plants were occupied by adventive grasses. The 12th to 20th positions were occupied by native monocotyledonous plants. Native boreal and bog plants occupied the last eight positions.
This study was designed to determine the abundance and diversity of vascular plant and small mammal communities in a mosaic of orchard and non-crop habitats in an agricultural landscape. Study areas were located at Summerland, British Columbia, Canada where seven replicate habitats: old field, sagebrush, dwarf, and conventional apple orchards, ponderosa pine forest, hedgerow, and riparian were intensively sampled for vascular plant (1999) and small mammal communities (1999–2003). Total plant species sampled included 104 herbs, 26 shrubs, and 9 trees. Mean crown volume index of herbs was similar among sites. Hedgerow and riparian habitats had substantial shrub layers, and the conventional orchard, pine forest, and riparian habitats had the highest biomass of trees. Total mean species richness of plants was similar, but did range from 12.3 species in old field sites to 32.3 species in sage sites. Overall plant species diversity and structural diversity were highest in the sage, hedgerow, and riparian habitats. Total structural diversity was positively related to total species richness and species diversity of vegetation. Mean total abundance of small mammals ranged from 28.1 to 37.0ha−1 across old field, sage, and riparian habitats compared with a range of 6.2–16.7animals/ha in the other habitats. Old field and sage habitats generally had the highest levels of species richness and diversity of small mammals, although the other non-crop habitats were similar to these in some years. Structural diversity of vegetation appeared to be a reasonable indicator of biodiversity, at least for vascular plants and small mammals, and should be included in future assessments of diversity in agroecosystems.
The montane vole, Microtus montanus, exhibits multiannual fluctuations in population density in northwestern Wyoming. Multiannual fluctuations in precipitation during May were also observed in the area. For data from the past 19 years, there is a significant negative correlation (r = −0.61, p < 0.01) between precipitation during May and vole population dynamics. Furthermore, there was a correlation between cycle phases of May precipitation and of population density. Peak precipitation in May (1970, 1974, 1977, 1980, 1984) was correlated in the same year with the decline phase in the population cycle. A trough in the May precipitation cycle (1969, 1973, 1976, 1979, 1983, 1985) was correlated in the same year with a population peak. It is hypothesized that spring precipitation may contribute to the population dynamics of Microtus montanus in north-western Wyoming by influencing the survival and reproductive success of these rodents at a critical time, the onset of the breeding season.
The aim of the present study was to relate food choice of meadow voles (Microtus pennsylvanicus) living in a variety of habitats to the presence or absence of two families of chemical compounds (alkaloids, tannins) that are widespread in plants. Voles seemed to prefer resources that possessed one or both of the compounds and to reject others even if they had no alkaloids or tannins. Several abundant species were not used by voles whether or not they possessed alkaloids or tannins. Our results show no pattern of association between the presence or absence of alkaloids and tannins and vole food preferences.
IntroductionVolesOther Vertebrate PestsConcluding Remarks
An experiment was conducted near Ithaca, New York, to compare orchard soil and groundcover management systems (GMSs) in a silty clay loam soil (mixed, mesic, Glosaquic Hapludalf). Three replications of four GMS treatments were randomly assigned to 12 plots and maintained since 1992 in 2 m-wide strips within tree rows: (1) Sod: Red fescue (Festuca rubra) turfgrass mowed biweekly; (2) Post-HBS: Post-emergence applications of glyphosate herbicide in May and July annually; (3) Pre-HBS: Pre-emergence applications of paraquat, diuron and norflurazon herbicides each May; and (4) Mulch: A 15-cm depth layer of shredded hardwood bark mulch, renewed triennially. After eight years of continuous treatments, we compared soil physical conditions and hydraulic properties in these GMSs. Bulk density was lower and soil porosity greater under Mulch than other GMSs. Infiltration was more rapid under Mulch than other GMSs, and under Post-HBS than Sod. Saturated hydraulic conductivity ranged from 6 10–4 m.s–1under Sod to 12 10–4 m.s–1 under Mulch plots, and was equivalent in Sod and Pre-HBS, lower in Sod than Post-HBS or Mulch treatments, higher in Post-HBS than Pre-HBS, and higher in Mulch than all other GMSs. Volumetric soil water content at field capacity ranged from 0.47 under Mulch to 0.40 under Sod, and was not significantly different among GMSs between 0.99 and 39.22 kPa of pressure. GMS treatments and related management practices at this orchard had substantially different long-term effects on soil physical conditions. Compaction and reduced infiltration in Sod compared with other GMSs were attributed to tractor wheel traffic during mowing. Mulch treatments improved soil conditions relative to other GMSs. Greater infiltration rates and hydraulic conductivity under Post-HBS compared with Pre-HBS suggest relative advantages of post-emergence herbicides.
This study was designed to test the hypothesis that continuous removal of northern pocket gophers (Thomomys talpoides) from natural habitats and tree fruit orchards would result in successful population reduction. A secondary objective was a detailed analysis of demographic responses (reinvasion dynamics) of gopher populations in control and removal sites. Pocket gopher populations were intensively live-trapped in replicate control and removal sites in natural and orchard habitats at Summerland and Vernon, British Columbia, Canada. New pocket gophers readily colonized removal sites in the natural habitats, particularly during spring, summer, and fall months. Fewer gophers colonized vacant sites during winter months (⩽1 per ha at Summerland and ⩽9 per ha at Vernon). Mean abundance of gophers ranged from 15 to 31 per ha on control sites. Population increases due to recruitment on control sites were reflected in periods of high reinvasion of removal sites. Spring reproduction and subsequent dispersal of juvenile gophers resulted in high colonization of vacant habitat. The recovery ratio (colonization rate) of gophers in natural habitats averaged 26.9% in summer and 0.9% in winter at Summerland, and averaged 44.2% in summer and 40.4% in winter at Vernon. Recovery ratios to previous densities on removal sites averaged >100% in summer at Summerland and in both seasons at Vernon. A relative recruitment index also followed this pattern at both study areas. New adult gophers that reinvaded removal sites produced young there despite continuous removal of animals. Mean body mass of gophers was significantly higher in control than removal populations at Summerland, but not Vernon. This study is the first intensive live-trapping evaluation of reinvasion dynamics of northern pocket gophers in removal sites. It seems likely that colonization of sites treated with toxicants or kill-trapping will be at least as high as the reinvasion rates recorded in our study. The timing of removals is crucial to achieving an overwinter reduction in gopher abundance.
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