Monday, July 16, 2018

Hot, Humid Weather Worrisome for Almond Growers

Bing… A short text message arrived on field scout Jenna Mayfield’s cell phone, reading “Hulls stopped splitting!”

The almond grower’s text was rather tongue-and-check, yet insightful at the same time. It appeared a build-up of hot, humid weather over the several days last week seem to slow hull split in his orchard.

Adding to grower anxiety, a few summer showers fell in parts of the Valley last Thursday night, cranking up humility levels as the daily high temperature reached the 100s. “We usually get this kind of humidity in September. To have it in July is definitely not normal.”

Humid weather and sprinkles worried growers.
Weather experts blamed monsoon moisture coming from the Arizona area for bringing the Hawaii-like humidity to the Valley and Northern California.  Yes, it was unusual to see lots of clouds in the sky on Friday and a higher-than-normal humidity during the mid-afternoon.

“Almonds grow best when we have super dry climate,” Jenna points out. “If the humidity continues it could be a problem. It may slow hull split.” But forecasters say continued triple-digit temperatures and drier afternoons are on tap this week, easing the minds of many almond growers.

Still, Jenna says some growers are hedging their bets and adding fungicides to their hull split sprays for navel orangeworm.  Growers already were adding miticides to their hull split sprays.

Yes humidity in orchards can lead to foliar diseases such as alternaria leaf spot. The symptoms are large brown leaf spots that turn black as the fungus spreads on the leaf surface. The leaf spots develop quickly in July and potentially can cause defoliation. 

Orchard humidity also can trigger rust and scab, which is a relative of alertnaria. These two diseases also can cause defoliation and weaken trees, impacting future almond production.

Humidity can trigger alternaria leaf spot. (UC IPM photo)
Meanwhile, field scout Damien Jelen says bug pressure has dropped in cotton, which is good news after a recent uptick in crop-threatening lygus bugs. During his field visits, Damien snared an average of one to two lygus for every 50 passes of his sweep net. The results about normal for lygus this time of year.

Growers are leaving uncut strips of alfalfa near cotton fields.
Damien says alfalfa growers with fields near cotton have been doing a good job leaving uncut strips of alfalfa during recent cuttings. These strips create habitats for lygus to stay in alfalfa during harvest rather than migrate to cotton.
The worm counts are high in alfalfa. But growers appear to be holding off treatment, reasoning the worms issue dissipates after each cutting.  Damien advises growers to remain vigilant about pest issues in alfalfa.

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