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Hedgerow Makes Cents

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UC study gets good results on tight spacing.

Maybe Jerry Brown had it right when he declared, "Less is more!" Or so it appears when that vaporous philosophy is applied to crowding almond trees together into smaller spaces.

According to UC Farm Advisor and Nickels Soil Lab Manager John Edstrom, "Through the sixth season, our tightly-spaced almond hedgerow on Marianna 2624 rootstock appears to be an economically viable orchard."

Detailed records of growth and yields for four common varieties of almonds planted at the Nickels lab on Marianna 2624 rootstock at 10 feet by 20 feet spacing show strong growth and comparable yields to an adjacent planting spaced 15 feet by 20 feet on Lovell rootstock. Edstrom points out that previous research at the Nickels laboratory proved that a wide variety of almond cultivars can be very productive when matched with Marianna 2624 plum rootstock. "In fact," he adds, "Mission, Ruby and Padre cultivars have shown excellent compatibility with M2624 rootstock."

The earlier productivity trials were based on equal planting distances and a variety of rootstocks. However, considering that tree size varies with rootstocks, yield data expressed on a per tree basis may not accurately compare rootstock per acre yield potential, Edstrom explains.

"Trees planted on size-reducing rootstocks such as M2624 may then appear to be lower in yield when compared to trees on invigorating rootstocks," he says. To more accurately test the commercial yield potential of almonds on M2624, the current trial employed tighter planting distances of 10 feet by 20 feet.

Another concern that was addressed in this trial was the history of inconsistent performance of the Butte cultivar on M2624. According to Edstrom, "Numerous tree failures have been reported amid blocks of acceptable Butte/M2624 combinations."

Growers having such problems have removed bad trees and replanted a second or even a third time before healthy plantings were established, he says. In addition, viruses have been implicated in similar graft union disorders in the Butte/M2624 combinations.

Taking these issues into consideration, the laboratory staff established a test planting in 19889 designed to evaluate four almond cultivars in a closely-planted hedgerow on M2624 rootstock. All Butte trees used in the trial were certified virus free. Commercially harvestable replications were designed into the test for yield data collection. Butte, Mission, Ruby and Padre almonds were planted in single rows at 10 feet by 20 feet spacings for a 218 trees per acre density.

Yields climbed rapidly from the third to fifth year. Then, Edstrom notes, yields declined in 1994. "Generally, the yields last year were acceptable given the young age of the planting, but they were disappointing given the exceptional productivity the previous season," he said.

He speculates that the yield decline in 1994 "could be the result of the heavy crop in 1993 in combination with water stress during and after the 1993 harvest, which resulted in considerable defoliation. Shoot vigor during 1994 was unacceptably weak and could also reflect those stresses." Kernel sizes, however, were larger in 1994 compared to 1993, he said, but represented historical averages for the varieties in the trial.

Butte Surprises

In addition tot eh good Butte yields, Edstrom was pleased to note that survivability of Butte on Marianna rootstock equaled that of all three other cultivars. And trunk size falls within the expected range, he added.

However, there has been a problem with necrotic leaf symptoms on the Butte/M2624 trees for two consecutive seasons. First noticed on a few trees in July 1993, the problem was thought to be herbicide damage. The following year, 17 percent of the Butte/M2624 trees showed severe marginal necrosis. Affected branches appeared stunted and produced little current season shoot growth. Only some scaffolds on the affected trees had symptoms while others on the same tree appeared normal.

Lab tests of affected trees were negative for almond leaf scorch and leaf mineral analysis showed acceptable levels of sodium, boron and chloride. Edstrom observes that the affected trees are located on sidehills and that their situation, compared to similarly-affected older Butte M2624 trees, suggests that water stress may be involved.

Still, overall plot yields for Butte, Padre and Mission compare favorably to the adjacent sixth-leaf, wider-spaced planting on Lovell rootstock.

Edstrom adds that tree vigor in all of the cultivars is not quite as good as it could be throughout the planting. Consequently, the staff is focusing on that aspect this year with nitrogen and potassium fertilization and more careful management of future harvest irrigations.

Perhaps a future report will prove once and for all that, indeed, less is more in the application of size-reducing rootstocks to almond cultivars.