Farm Progress

Almond growers are looking for ways to manage a crop that is worth more than $3 billion and is forecast to hit more than 2 billion pounds.

Dennis Pollock 1

May 16, 2013

7 Min Read
<p> Entomologist Walt Bentley found some spider mites on leaves at the base of an almond tree.</p>

Dozens of almond growers, pest control advisers and others gathered in a Fresno almond orchard for an up-close look at insect pests and to hear about ways to manage a California crop that is worth more than $3 billion and is forecast to hit more than 2 billion pounds and approach near record levels this year.

What they learned at that field day could help them achieve what was being forecast on the same day in Modesto, a federal estimate of 2.07 billion pounds for this year’s California almond crop, which would be about 300,000 pounds shy of the previous record in 2011.

Some growers brought samples of insect pests or the damage they caused as field day participants gathered for the event sponsored by the San Joaquin Sustainable Farming Project. It was hosted by Gina Rushing, a principal in LPGL Ranch.

Entomologist Walt Bentley opened the meeting with tips on finding spider mites and pinpointing the presence of pests that included the leaf footed plant bug, navel orange worm and stink bugs.

David Doll, who has been nicknamed the “almond doctor” and who is a Merced County University of California pomology farm advisor, closed the meeting with a discussion of hull rot and nutrient management.

Inside the orchard, participants saw eggs from a leaf footed plant bug, thanks to the sharp vision of Lacey Mount, an agronomist with Dellavalle Laboratory Inc. in Fresno.

And they saw Bentley, a retired UC Statewide Integrated Pest Management entomologist, worm his way into the branches of an almond tree and find evidence of some spider mites.

Bentley showed how to distinguish damage of almonds from weather conditions — spiking cold and warm temperatures — from insect damage caused by the leaf footed plant bug or stink bug. In both cases, there was some gumming on the nut.

But, he said, “The key is to walk the orchard, cut into the nut and see if there is a darkened, discolored area.” That, he said, is an indicator that the pests have injected saliva.

Almond varieties with softer shells such as Fritz, Sonora, Aldrich, Livingston, Monterey, and Peerless are more susceptible to leaf footed bug damage for a longer period during the season.

Butte and Padre trees comprise the orchard in Fresno. They, along with the Monterey, are hard-shelled varieties that mature late, making them particularly susceptible to damage from the navel orangeworm because they are all harvested during or after the third flight of that pest, Bentley said.

 “With Nonpareil nuts, they are down and off before that third generation comes on,” Bentley said.

Neighboring blocks

For Butte and Padre, he recommends more of a focus on disease management and less on insect pressure.

With Monterey and Fritz, Bentley said, there are more management pressures, and it may be necessary to do two or three sprays depending on when harvesting can take place.

Bentley said growers also need to take into account if there is a neighboring susceptible block. He pointed out that the navel orangeworm is able to overwinter at greater percentages at points further south in California.

One grower supplied a baggie containing green soldier stink bugs that had dropped to the orchard after application of a pesticide.

That pest is more likely to over-winter in an orchard, Bentley said.

He said that both insect pests leave a distinctive “thin curlicue, like a little pig tail” on the surface of the nut.

The stink bug leaves eggs that are “barrel shaped clusters,” which Fresno County grower Andrew Vargas said he found in his orchard on the county’s west side. Bentley said they may resemble a long, thin necklace “like macaroni strung together.”

“If you’re seeing them, treat,” Bentley said. “They’re not that easy to find.”

One way to detect that insect — or perhaps the leaf footed plant bug — is to rap the limb of the tree and get the insects to drop or fly off.

“You need to focus your eye on a smaller world,” said Bentley, who fishes as a pastime. “It’s like a hunter watching for a silhouette or a fish in the water.”

Bentley said Lorsban can be used to control both pests, but he advises against using that unless the orchard is “isolated from water” due to concern over contamination of groundwater.

“If I were in Mendota, there’s no way I would touch that material,” he said. Among alternatives he recommended is Bifentrin (Brigade).

Groundwater contamination

Bentley said regulation on contamination of groundwater is “a big deal big for you; it’s big for the industry. We don’t want this industry to get a black eye, it has one of the cleanest names right now, and we don’t want it to have a bad name.”

Because of a previous spray, there was a low level of mites in the LPGL Ranch orchard. Bentley was able to find some after considerable effort at the base of a tree. He advised wearing a long-sleeved shirt to protect against scratches while reaching into branches.

“See that white fuzz and speckling on the leaves,” he said. “That’s the key you look for early. You need to know your orchard and if you have a stressed orchard.”

Bentley said orchards that neighbor corn fields can have greater pressures from spider mites that blow in because growers of the corn cannot get into the fields after a certain point to spay.

The mites can bring defoliation, something Bentley said almond growers do not want before the nut’s shell opens.

Doll talked of nutrient and water needs and of how hull rot can be exacerbated by over-application of both water and nitrogen.

Previous farm advisors have likened hull rot to “the gout of almond diseases” or the “good growers’ disease” because it can result from “too much food and drink.”

Doll said the problem may be exacerbated this year as more growers, given water shortages, can be expected to rely more on groundwater they pump into the orchards.

That groundwater, he said, can contain “nitrate nitrogen, a great source of nitrogen for your orchard.”

But he cautioned that growers should take into account what that additional nitrogen could mean: “For every part per million of nitrate in your water, you should take that times .273 times for every acre inch of water applied. At 10 parts per million, you’re getting 2.7 pounds of nitrogen per acre.”

Because highly vigorous trees are an issue in hull rot, Doll said, that added nitrogen “will tie into later season management” of the crop.

Water deficit

He said it is important to reduce the amount of nitrogen and water during hull split, thereby cutting growth that might be more conducive to infection.

Some varieties, including Nonpareil, are more susceptible to hull rot, Doll said.

He recommends creating “a water deficit” before the nut begins to split, dropping applications by about 50 percent for a week.

If wilting occurs, he advises a second week at 70 percent of accustomed levels.

Then, he said, the grower should go back to full irrigation in order to prevent formation of an abscission layer that can lead to “stick-tights” and to avoid drawing moisture out of the kernel, which would mean lost weight.

Rolinda grower Nick Nazaroff said hull rot “nearly destroyed” his orchard, but he has gotten the problem under control by switching from irrigating all rows, starting in mid-May, to every other row.

Fungicides can be used on hull rot, but Doll said different products should be rotated to avoid developing resistance to sprays. He said the products do not need to be costly.

Most common in the southern San Joaquin Valley is the Rhizopus pathogen, he said, calling for application of a fungicide at hull split. It can be applied at the same time as products used to control navel orange worm, Doll said.

To the north, it’s more common to encounter a Monilinea pathogen, which is best treated in mid-May, Doll said.



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