Excessive Valley Heat Poses Challenge for Almond Harvest

No one needs to tell Valley farmers it’s been very hot, even by local standards.

The Fresno region set a record for the most consecutive days of 100-degree temperatures in July. In fact, everyone endured 30 straight days of triple-digit weather until the high temperature fell to a cool 99 degrees on August 5.

Almond field scout Jenna Mayfield adds there has been little relief at night with the lows hovering in the 70s this past month. “We haven’t had a break. We welcome the days when it’s in the 90s,” she says. Jenna adds:  “The air is so unhealthy. There’s smoke from the wildfires. It’s hard to breathe.”

NASA photo shows smoke covering the Central Valley.

Add in smoke and hot weather and “it makes you more tired. “It’s hard on workers in the fields,” Jenna says. “They’re toughing it out.”

Jenna says the excessive heat may be affecting the pests as well. “The mite pressure is down in almonds. Navel orangeworm numbers are low.”

Jenna thinks the heat coupled with the addition of miticides in the hull split sprays are keeping mites down. Mite populations usually explode during the hot summer days.

Right now, growers are moving around harvesting equipment and a few have started shaking nuts off the trees. Harvesting should begin picking up this week.

“Everything has been slow. We really haven’t seen much harvesting yet,” Jenna says. The prolonged heat spell prompted growers to figure out the best strategy to irrigate during hull split and prior to harvest.

More growers should start harvesting almonds this week.

Extreme heat triggers more evaporation and dry ground heats up more quickly than wet soil.
Here’s the quandary: If growers irrigate too much, they increase the risk of diseases, shaker damage and delayed harvest. If they don’t provide enough water, the trees become over stressed, mite activity could explode and kernel weights might decrease. “It’s a balancing act,” Jenna says.

Pomologist David Doll of UC Cooperative Extension in Merced County advises growers to maintain the same frequency of irrigation during hull split but make adjustments during irrigation sets.

“Reductions to irrigation (i.e. 50 percent at the onset of hull split) to apply a stress can be made by reducing the duration. Trees should be monitored by either a pressure chamber or observations (i.e. wilting) to identify stress levels. If the trees are over/under-stressed at the end of the cycle, adjust the duration,” he writes in his Almond Doctor column.

Here are some recommendations at this time:

·         Pre-Harvest week: 20-50 percent reduction to help begin a slight dry down of the orchard.
Harvest week: 30-50 percent evapotranspiration (ET) – some water should be applied, but with enough time to allow orchard floor drying for shaker movement.

·         Post Harvest: 100 percent ET – stress should be minimized at this stage as the tree prepares for next year.

Growers need to adjust irrigation schedules during harvest.

“The recommendations are made for micro, drip, or solid-set irrigation systems, but the recommendations would be very difficult to achieve using flood irrigation,” Doll writes. “With flood irrigation, growers will want to adjust their irrigations so that some trees show signs of water stress between irrigations during hull split, and harvest will be delayed until the wettest part of the field is dry. Increasing distribution uniformity by taking into account soil differences with different checks may help with a uniform harvest.”