Farm Progress is part of the Informa Markets Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Serving: East

Serr walnut drop solution all about timing

Firmly touch the pads of your thumb and middle finger together. Hold the V-shape it forms at the fingertips skyward as you peer into your walnut trees beginning to bloom.

According to University of California Cooperative Extension farm advisor for Kings and Tulare counties, Bob Beede, this unorthodox evaluation method to evaluate the early stages of female walnut flower development should begin in the Central San Joaquin Valley this year about April 10. Walnut catkins should be about 6 inches long then.

“The chilling hours have been good and when the weather starts to warm, walnuts will come out fast,” Beede predicts.

Don't worry about what your neighbors or people driving by may think as they spy you strolling through the orchard with one arm outstretched toward the tree. It could be worth a lot of money to look a little strange if you are a walnut grower or his pest control advisor. Even if your eyesight is perfect, use binoculars to peer into the upper reaches of more stately, older walnuts forming the V.

Do this for sure in Serr variety blocks and maybe Tulare and Tehama. Don't waste your time in Chandlers.

According to Beede, when 30 percent to 50 percent of the blooms look like that fingers-formed V, Serrs are very likely a good candidate for an application of an ethylene inhibitor plant growth regulator aptly named ReTain because that's what it has proven to do — retain walnuts that would otherwise fall off the tree at bloom. (Valent, manufacturer of ReTain, recommends spraying from 5 percent to 30 percent bloom.)

The malady that has been causing growers to lose as much as a ton of Serr walnuts per acre for four decades is called pistillate flower abortion/abscission (PFA). This is caused by too much pollen collecting on the receptors of female flowers, causing an overdose of ethylene resulting in flower abortion and yield loss. It is more commonly known at the coffee shop as “Serr drop.”

PFA quickly became evident in the early 1970s shortly after the highly edible, early maturing Serr variety was released by the University of California. Scientists have been trying to come up with a reasonable solution ever since. The solution became so elusive that many Serr orchards have been pulled out in Northern California.

Scientists early on discovered that the PGR from Valent BioSciences reduced the ethylene, but it was Beede leading a team of UC farm advisors who discovered how to economically use it, applying it at early bloom.

Timing is everything and the application window is open only a short time, Beede told growers and PCAs in a series of early season tree and vine crop updates in the state sponsored by Valent.

“When the bloom starts to look like Elmer Fudd's exploding shotgun, it's too late for ReTain,” says Beede in a timing description that is even more scientifically unconventional than the V-shaped finger evaluation.

(Valent has produced a brochure that includes pictorial examples of Beede's V and Elmer Fudd shotgun descriptions of walnut blooms.)

The ethylene inhibitor is not the only way to solve the problem. Researchers have long recommended growers with a serious Serr drop problem consider spring shaking of trees to drop or scatter pollen. Beede says it works, but it could take several shakings at a cost of $60 to $65 per acre.

One properly timed application of ReTain equals four catkins shakings, Beede said, at an early season tree and vine production meeting sponsored by Valent in Selma, Calif.

Timing is also everything in catkin shaking. However, not all walnut growers own tree shakers normally used for harvesting nuts. Many growers contract for harvest and therefore do not have mechanical shakers.

Beede discovered the best timing for ReTain in trials beginning in 2005. His best test result was a 1,100-pound yield increase.

Mark Testerman, Valent sales rep, says the average yield increase from correcting PFA the company has validated has been a little more than 1,500 pounds per acre.

Location, location, location is also as critical a factor in diagnosing and correcting PFA as it is in the real estate business.

“There is an older walnut orchard in Kingburg that is Serr and Vinas down the row — a kiss of death for PFA,” says Beede because of the pollen coming out the Vinas and on to the Serrs causes incalculable PFA. This is an orchard where Beede has had some of the most dramatic results from his ReTain trials.

Serr drop also can affect only a portion of a Serr orchard, explained Beede. He has seen a PSA very severe on as few as 15 rows on one side of an orchard because of adjacent, nearby orchards producing the excess pollen on the Serrs.

Although PFA can dramatically impact yields, Beede says nine out of 10 producers with PFA-susceptible varieties do not know they have it. They think it is something else.

A strong walnut producing orchard can be expected to yields 2.5 to 3 tons of walnuts per acre. A Serr orchard with PFA can lose as much as a ton or more of potential yield. Tulare and Tehama are two other PFA-susceptible varieties Beede has demonstrated can benefit significantly from ReTain.

However, Chandler, he adds, has not shown any effect from ReTain. “If you are losing a ton per acre on Chandlers, something else is wrong.”

“If you are getting 3 tons of walnuts from an orchard, don't expect ReTain to take that up to 3.5 tons. Remember, walnuts are alternate bearing and typically do not crank out huge crops.”

Beede and Testerman admit ReTain is an expensive product to use. Although walnut prices are down sharply from the $1.20 per pound last season, it can still pay if the orchard has a severe PFA problem the product resolves.

ReTain is packaged in 333-gram water soluble pouches. One pouch per acre is recommended in at least 100 gallons of water.

Beede strongly recommends 200 gallons of water per acre for thorough coverage in taller trees. On very large trees, Beede says two-thirds of the spray should reach the top of the canopy.

“Go slow when spraying,” he urges. “You have to hit the target flower with the product to make it work.”

While ground applications are recommended, Beede says growers have recorded good results with helicopter applications when the ground is too wet for a ground rig. Some growers have made split applications from the ground and air.

“Growers have been very creative in applying this product,” he adds.

Although yield improvement has been very dramatic with ReTain, Beede warns that it also can be variable with the degree of PFA, application timing, as well as the duration of the female bloom.

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.