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Effects of California Pecan Orchard Management Changes During the Last Five Years
Written by: Brian Blain, Pecan Grower
Visalia, California
 


This paper will discus changes that took place over the last five years on 750 acres of pecans grown by Blain Farms in Tulare and Kern counties of California. Due to the small size of the California pecan industry, many of the changes to our orchard were also seen in other California pecan orchards and are so noted. Pecan orchard management in California has changed dramatically during the last five years. To preface illustration of these changes, some California pecan history and coincident problems are important. 


1975 – 1994

Pecans were a relatively new industry in California at this time. Most commercial orchards were planted in the late 70’s, long after walnuts, almonds and pistachios had been established. Nut growers in CA were quite familiar and adept at growing our traditional nut crops and incorrectly assumed that growing pecans would be similar. We also, incorrectly, assumed we could follow examples of growers in W. Texas, New Mexico and Arizona, where similar varieties were grown in the arid conditions and soils typical of the West. That assumption also got us into trouble.

As a result, the California industry became unprofitable, producing poorly filled nuts every year, with high percentages of pre-germ sprouting. Production was declining to a point where our “on” years averaged 1700 lbs/ac and “off” years 700 lbs/ac. By 1995, “on” cycle years were producing an entire crop of #2 quality pecans, barely exceeding 50% edible kernel. Orchards were being removed and replanted with other permanent crops. The pecans that remained were losing money, forcing growers to spend less and less on their orchards, further compounding the problem.


1995 Observations 

Alternate bearing: We noticed trees were “individual” in their alternate bearing cycles. That is, in any given year, 1/3rd of the trees in orchards were either “on” or “off” while the other 2/3rds were on the opposite cycle; trees in their “off” year would have less than 20 nuts while the tree next to it would have ~12,000 nuts, equivalent to 7,000 lbs/ac if every nut had filled. Such tree-tree variability was widespread, commonly seen in every tree row.

Intra-orchard alternate bearing severely effected profitability. Trees in their “on” cycle simply couldn’t fill that many nuts and low kernel yields were the result. Further, the crop stress on those trees substantially reduced their yield the following year. As a result, our “off” years, which should have produced high quality nuts, were now producing the same poor quality as “on” years; both years included heavily cropped trees that reduced quality of the crop over all. 

We feel several situations unique to California result in the problems we have experienced.

Aphids: The only insect pest of pecan in California is the pecan aphid complex (yellow and black aphids). Although these aphids are major pests of pecan elsewhere, damage is worse in the central valley of California as there is no summer rain. As a result, honeydew and resulting sooty mold accumulate on the leaf surface. Experiments in California by Wood and Sibbett and those done elsewhere show sooty mold to reduce photosynthesis up to 50%. In addition to the direct feeding damage, such a reduction in photosynthesis severely compromises the tree’s ability to produce good crops of high quality pecans.

Aphid control with registered insecticides was only marginally effective and quite costly; they either had short residual or aphids developed resistance to them. Biological controls, including inundative predator releases and providing orchard conditions that encouraged lady-bird beetles (including Harmonia) and lacewing development, were also unsuccessful because aphid populations could not be kept low enough to preclude honeydew/sooty mold development. 

Nut drop: California orchards do not experience the degree of “nut drop” seen in other growing regions. Some nut drop is beneficial; there is a crop thinning effect reducing crop load. This does not occur in California, making the “on” year even heavier. To compensate for heavy cropped trees, California growers try to provide optimal water and nutrients to achieve good nut filling. However, doing so also provides excessive nutrients to the “off” year trees scattered throughout the orchard. This encourages even heavier yields from these trees the following year. 

Tree size and shading: As elsewhere, California trees grow to heights that can approach 60 feet. At our initial planting distances of 30’ x 30’, severe shading occurs that must be dealt with. New wood diminished significantly, and the existing fruitwood was dying back in the trees’ interior to the point where they developed a “transparent” look due to reduced leaf surface. The traditional program of tree thinning (removal) used elsewhere was begun in many orchards to improve sunlight penetration. This had limited success. Hedging was also tried with little success due to the fact that both “on” and “off” trees existed in every row and while the hedging would help one it would aggravate problems of the other. We also didn’t have hedgers able reach the treetop, and hedging only the lower sides of the tree just made things worse.


Management Changes

Nut Thinning to stabilize intra-orchard production variability: In 1995 we predicted the biggest crop in our history. The trees were obviously overloaded and poor quality was expected. Dr. Darryl Sparks convinced us that mid-summer mechanical nut thinning might be the answer to the severe cycle we were experiencing. His experimental procedure was tried on 800 acres. Trees with heavy crop loads, the equivalent of 7,000 lbs/ac (determined by shaking all of the nuts from representative trees) were marked with paint, and shook to remove approximately 50% of the nuts when the nuts were less than ¾ inch in size. Trees with no crop or normal crop were not shaken. The result was an orchard average crop of 2,100 lbs/ac with kernel yields of 60% edible and minimal sprouting. 

The next year we repeated the same procedure on unmarked trees; which were now overloaded. We achieved the same positive results. The marked trees which were shook in the previous season returned with an “off” year crop of 1,100 lbs/ac., up from 700 lbs in the last “off” year. Kernel yields were again 60% for both thinned and previously thinned trees. The procedure has been continued on an “as needed” basis, with less and less needed each year. Indeed the intra-orchard production variability was stabilized.

Hedging: In 1997 we began a program of regular hedging. We used the technique developed by Deane Stahmann in Australia and observed by Dr. Bruce Wood and Steve Sibbett during a trip there (Deane refused to thin trees from his orchard and instead developed a hedging technique to maintain production). Our initial cuts brought the trees down to a height of 35 feet, and a width of 26 feet, in orchards with a spacing of 40 x 40 ft. (Orchards with 30 x 30 spacing were topped at 30 ft. and hedged 20 ft. wide.) The process resulted in the removal of a significant amount of fruitwood, and an initial loss of some production. We phased in gradually over a four-year period; hedging alternate rows in alternate years. By 2000 the phase-in was complete, and a regular program of hedging every other middle, every year, is our current program. 

Our hedging cuts are considered conservative compared to some of the other hedging being tried in CA. Our cuts are approximately 10 feet from the trunk of the tree, however an experiment with closer cuts is being tried by Wood and Sibbett at the Skinner ranch in the Sacramento valley. In that trial, cuts are being made five feet from the trunk.

We are now re-hedging the same wood every other year, but each tree is hedged on one side or the other, every year. We have one 60-acre block where we have hedged both sides of every row, every year for five years, but it has exhibited more severe alternate bearing than other blocks. Overall, it appears that hedging has reduced the need for mechanical nut thinning, and stimulated new fruitwood, while arresting the die back from shading.

Aphid control: As mentioned, aphid control was difficult in California. Production and quality were definitely being influenced by aphid populations and resulting sooty mold development on their honeydew. In 2000, we began using the systemic insecticide aldicarb (Temik) for aphid control; other aphicides did not provide adequate or complete control. Formerly, aldicarb was only available in CA for experimental purposes. Steve Sibbett, Univ. of Calif. Cooperative Extension Farm Advisor and Dr. Bruce Wood, conducted research over a period of six years showing the benefits of aphid control using aldicarb as the aphicide. Test blocks showed significant increases in production, nut size and kernel yield due to aphid control and possibly an additive effect of the aldicarb itself. After many years of work, aldicarb was approved for use in CA and first applied to orchards in the summer of 2000. Essentially all pecan growers in California now use the systemic aphicide for aphid control and have realized the same results. In that it is well known aphids will develop resistance to aldicarb, new work is proceeding to register imidocloprin (Admire) for aphid control in California. 

The use of aldicarb has had a dramatic effect on CA orchards. In orchards where the only change in management practices over the last 5 years was the use of aldicarb, growers experienced increased kernel yields, increased production and a decrease in alternate bearing. In our orchards, where we have been using aldicarb in conjunction with hedging and mechanical nut thinning, the results have been even more dramatic. Production has doubled, edible kernel yields have increased by 10%, and we have not experienced any alternate bearing during the last two years.


Summary

Implementation of these management changes resulted in the largest crop of good quality nuts ever in 2000. A larger, good quality crop followed this record crop in 2001. Growers are using some, or all, of the new management practices discussed with good results. Growers with older orchards were more likely to use mechanical nut thinning, due to more severe alternate bearing. Younger orchards were able to use hedging to prevent the onset of severe alternate bearing cycles. Over 80% of the orchards are now hedged regularly, and 90% of the growers are using aldicarb. Pecan growers in CA have a renewed optimism that pecan production can be profitable with the use of these new management tools. Indeed, the problem is no longer production of good quality, but one of selling the crop for a profitable price.
Copyright 2016 by California Pecan Growers Association