Almond Rootstock Evaluation Regional Trial
John Edstrom, Bill Krueger
UCCE Farm Advisors
Variations in growing conditions between the major almond districts
(ie. soil texture, rainfall, nematodes, diseases, tree vigor, etc.) have clearly shown
that new varieties and rootstocks need regional evaluation to determine local performance.
Rootstock trials were established in four almond counties representing different growing
conditions - Butte, Kern, San Joaquin and Colusa at the Nickels Soils Lab (NSL). This
cooperative project involves commercial nurseries, UC Davis Department of Pomology, UC
Cooperative Extension and grower cooperators. Large scale commercial plantings at each
site are evaluating seven different rootstocks grafted to either Nonpareil or Butte
varieties.
Replicated plots (8 plots X 24 trees) are being evaluated at NSL for
different criteria including: rootstock compatibility, tree growth characteristics,
harvest date, yield and crop quality.
The Nickels trial was planted to Nonpareils (1/2) in March 1997 at a
spacing of 22 feet by 24 feet to allow room for the large size of hybrid rooted trees.
Pollinator varieties include: Carmel (1/6), Aldrich (1/6), and Monterey (1/6) on Brights
PA Hybrid rootstock. The site was slip plowed on 10 foot centers N-S and on the diagonal
to the 5-6 ft. depth. A microirrigation system installed with two spinners per tree should
favor extensive root development and allow growth of a cover crop. The Nonpareil test
trees were pruned to facilitate eventual limb shaking. The trial includes an extra set of
Nonpareil plots to compare yields of short vs. standard pruning of primary scaffolds.
Progress
Initial trunk measurements taken on Nonpareil 8/31/98, 18 months after
planting, indicate that trunk circumference of the Nonpareils are equal between all seven
rootstocks. Tree survival rates are high and the same for all seven rootstocks, despite an
unusually wet 1998 season. Strong winds in the spring of 1998 resulted in some limb
breakage and loss of scaffolds, but overall tree development has been satisfactory.
Atlas PAPC Hybrid Dave Wilson 1/6 plum
+ 1/6 almond + ½ peach + 1/6 apricot
