Ground Cover Management and Nutrient Source Affect Weed Density, Vole Damage, and Survival During Establishment of An Organic Apple Orchard

Primary problems in organic orchards are ground cover management and application of sufficient nutrients to sustain growth. An unintended consequence of ground management practices may be an increase of new pests in the orchard. An experiment was established in 2006 to evaluate the main effects and interactions of four ground cover management systems and three nutrient source strategies that may be used in an organic orchard.  The four ground cover management treatments were 1) municipal green compost (GC), 2) wood chips (WC), 3) shredded white paper (SP), and 4) managed vegetation with a mow-and-blow mulch system (MB).  The three nutrient source treatments were 1) control (NF), 2) composted poultry litter (PL), and 3) certified organic commercial poultry litter based fertilizer (CF).  In the NF treatment, nutrients were provided by the four ground cover treatment provided above.  Trees of ‘Enterprise’/M26 were planted in 2006 at a density at a 600 trees/acre and trained to a modified vertical axis system.   Experimental design was a split plot with main units completely randomized in 6 blocks.  Main units were groundcover treatments (n=4) and sub-units were fertilizers (n=3).  Weed density during the season was measured with a color-difference photographic system to differentiate vegetative cover from ground cover surface.  In the first two seasons, the GC and MB treatments had significantly higher weed density than either the WC or SP.  Beginning in year 3 of the study, surface cultivation under the trees was begun.  Cultivation resulted in a strip approximately 50cm wide on either side of the tree with a 50cm vegetation strip contact tree to tree.  After cultivation, weed density was similar for GC, WC and SP (approximately 15-20%), but significantly higher in the MB treatment (40%).   There was no difference in weed density among the nutrient source treatments.   During a snow and ice episode in winter 2008, significant vole activity and damage occurred in the orchard.  Damage was rated and number of trees damaged counted.  Damage ratings were highest and most severe in the MB treatments and lowest in the WC.  The GC and SP treatments were intermediate.  There was no significant difference among the nutrient source treatment for vole damage ratings.  The greatest tree death (approximately 35% of all planted trees) occurred in the MB treatments while the GC and WC had less than 5% tree loss.   Tree death was relatively uniform across the nutrient source treatments.