Assessing effects of an alfalfa cover crop on biological control and tree nutrition in organic pear orchards

Organic pear growers must balance the conflicting pressures between nitrogen levels and densities of pear psylla, a nitrogen-loving pest of pears. We are assessing in 3 certified organic orchards and 1 experimental orchard whether planting of alfalfa leads to improved tree nutrition and biological control of psylla. Alfalfa was planted in 2 ft wide strips in 3 organic pear orchards in spring 2008; at the experimental orchard, aisle-wide strips of alfalfa had been planted in spring 2006. Each alfalfa plot was paired with a control (grass) plot. Sampling at the 3 commercial orchards was initiated in spring 2009; sampling of arthropod densities, predator movement, predator feeding, and tree nitrogen was begun in 2007 at the experimental orchard. There was no effect of alfalfa on pest or predator densities in the tree canopy. Tree nitrogen was slightly higher in the cover crop plots than control plots. The movement data have yet to be fully analyzed, but initial results show that tree-collected predators have evidence of having visited orchard floor vegetation; no striking differences were noted between alfalfa and control plots. The feeding data have yet to be analyzed.

Grant Information

  • Project ID: 047
  • Project Status: Complete