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TNFP0919-tim-hearden-fire-ice_BT_Edits.JPG Tim Hearden
Orchards in the San Joaquin Valley are shrouded in smoke in late summer of 2018. Wildfires last year led to grower concerns about smoke damage in their orchards.

Fire and ice: Surviving the fall season in California

Autumn’s arrival sparks memories of wildfires, cold snaps.

With the official start to the fall season just around the corner the elongated regions of the Golden State’s productive valleys are well into the harvest process for many of the nut and fruit orchards that dot the landscape.

Already the hot and often balmy days of summer are giving way to cooler nighttime temperatures while the wetter months of winter and spring have become mostly a distant memory even for northern reaches of the state.

If you’re a tree nut producer or vineyard operator, chances are you remember the fall of 2018 rather well. One reason may be because of the heightened fire season that gave us one of the worst wildfires on record, the infamous Camp Fire that destroyed property, claimed lives, desolated communities and hijacked headlines across the nation.

On the opposite side of the weather spectrum, the month of November last year set up odd weather conditions that played out like the plot of a George R.R. Martin epic novel that pitted fire against ice. Excessively warm daytime temperatures were countered by a few nights of exceedingly low temperatures, and University of California (UC) researchers say it may have been this drastic rise and fall of the mercury that brought about early freeze damage that was reported in some orchards.

While accurately predicting the weather the next seven days can be difficult given the changes in climate conditions in recent years, foretelling what the weather may bring 30 to 60 days down the road is even more difficult, and often unreliable. Based upon the unusual weather of last fall, some farmers are already wondering if there could be a repeat of last year when the season once again begins to change.

Unpredictability of weather forecasting

While technology has advanced the tools science uses to provide more accurate forecasts in recent years, even experienced forecasters are quick to point out there is much we do not yet understand when it comes to accurately predicting weather and climate changes from week to week and year to year.

Last year, 2018, and the start to 2019, are a case in point.

While snowpack accumulations in recent years have been incredibly low, beginning in the fall and stretching into the winter season, heavy snow blanketed the Sierra Nevada range, in some cases dropping 150 percent of the average and normal snow levels that were, until a few years ago, commonly expected. Combined with record-setting rains and some flooding in the spring season, weather over the last 12 months or so has been incredibly unpredictable in parts of California.

Now, as another fall season is about to launch, will farmers see much of the same type of weather they did last fall and winter season?

Preparing for the unexpected

Regardless what the weather may bring and when and how much it may change from a year ago, a review of last year’s fire and freeze season may be warranted.

“The sudden November 2018 freeze event that caused extensive damage in many walnut orchards is a stark reminder that we must do our best to prepare against extreme events,” Luke Milliron, UC Cooperative Extension (UCCE) Area Sustainable Orchard System Advisor in the Sacramento Valley, warned in a recent email exchange.

Milliron and recently retired Janine Hasey, UCCE Farm Advisor Emeritus, teamed together in a Sacramento Valley Walnut Newsletter article, “Preparing for Extreme Events: Freeze and Fire,” to offer advice to tree nut growers as the season changes this year. They suggest that growers withdraw irrigation of orchards throughout September until a terminal bud is set on the trunk of young trees to harden them.

“After the terminal bud has set you can resume irrigation to avoid tree stress and defoliation, without the fear of pushing new growth. If there has not been adequate rainfall by the end of October, irrigate young and mature orchards so the soil is moist going into November,” they advise.

Milliron says rainfall adequacy can be determined by monitoring soil moisture levels by hand or with sensors. Trees with adequate soil moisture are better able to withstand low temperatures without damage than trees that are dry.

“Water conducts and stores more heat than air spaces. Continue to actively monitor soil moisture and freeze predictions in November. If a freeze is predicted and the soil is dry, it should be wetted three to five days prior to a freeze event to fill the air spaces so the soil will store more heat. The top foot is the most important and should be at field capacity (not too wet).”

While the timing and amount of watering is tree and field specific and critical to avoid freeze damage, he also has a tip for preventing sunburn and drying damage. He advises to get your paint buckets and paint brushes ready for the season.

“Avoid water on the soil surface before a freeze since it will make the soil surface colder because of evaporative cooling. If freeze damage is suspected in the fall or winter, check the tissue for drying or browning. Subsequent sunburn can further damage tissue on the southwest side of the tree. Paint the southwest side of damaged trees with 50-percent diluted (1:1 water to paint) white interior latex paint. Painting up to a week after the freeze event can decrease damage by half or more.”

Notes about fire and smoke and orchard management

When it comes to fire and smoke vulnerabilities in an orchard, UCCE advisors generally agree tree nut operations are less susceptible than grape vineyards or fruit orchards. None-the less, an orchard often serves as a practical fire break and measures can be taken to help the orchard survive or suffer less damage.

Irrigating or flooding an orchard subject to an approaching wildfire may represent the best method of preparing for the intense flames and heat of a fire storm. Watering high into the canopy is advised and if water is available, a continual drip on the orchard floor can provide some protection.

They also advise that “a key fire management strategy is controlling weeds to avoid the buildup of dry biomass that serves as a potential fuel source and can act as a ladder for the fire to move from the orchard floor to the trees. Tilling a fire break along weedy orchard borders can help to stop the fire’s spread.”

In terms of smoke damage, not a great deal can be done, and many farm advisors say how much smoke may affect a healthy orchard is still unknown.

Regardless whether the year is normal, abnormal or completely different that any in recent memory, staying aware of November’s weather is advised to prevent unexpected damages this fall season.

For more news on tree nuts as reported by growers and farm advisors, subscribe to the Tree Nut Farm Press e-newsletter.

TAGS: Disaster
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