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National Weather Service Issues Excessive Heat and Elevated Wildfire Danger Warnings

California Avocado Commission — The National Weather Service has issued excessive heat and elevated wildfire risk warnings in California this week beginning Tuesday, July 6 through Sunday, July 11. The conditions will pose a high risk for heat-related illnesses with possible record temperatures for the Antelope Valley area of Southern CA and brief critical fire weather conditions for the interior region. There also is a slight change of monsoonal thunderstorms and dry lightning from Wednesday through Sunday in the interior regions of Southern CA, most notably the mountain and desert areas.

From Tuesday, July 6 through Thursday, July 8, the NWS notes there will be widespread highs of 95˚F – 105˚F in the inland valleys, mountains and deserts with warm overnight lows (about 70˚F) in the foothills and deserts. These conditions will pose a high risk of heat-related illnesses for those who work outdoors. During this same timeframe, humidities will lower to 5% – 15% and winds may gust from 25 – 45 mph during the afternoon and evening. The strongest gusts are predicted for the Antelope Valley and Santa Ynez Range. These high winds, low humidities and abnormally dry fuels will lead to elevated critical fire weather conditions over the mountains and interior valleys.

From Friday, July 9 through Sunday, July 11, NSW predicts very hot conditions with temperatures ranging between 105˚F – 112˚F in the interior areas and Antelope Valley. Overnight lows will be in the mid to upper 70s in the deserts. Low humidities (5% – 15%) and gusty winds will continue the brief critical fire conditions in the mountains, deserts and inland valleys of this region.

Employers should take special precautions to prevent heat-related illnesses from occurring. It’s important to provide ample water, provide shade and frequent rest breaks, and ensure supervisors and employees are aware of heat illness symptoms and those that require immediate medical attention. For more information, read “Reduce heat illness risk for employees” on the California avocado growers website.

To ensure California avocados maintain their superior quality it is imperative growers manage their trees and harvest their fruit according to best management practices as outlined below.

IRRIGATION
Growers should be irrigating their trees now, in advance of the heat, to ensure their trees are fully hydrated. It is recommended that an additional 50% of the budgeted amount of water be applied the day before a heat wave. For extended heat waves, daily pulses of irrigation are recommended to maintain the trees’ water status. A well-watered tree will tolerate the stress of a heat wave much better than a tree that is suffering from water stress. Signs of heat damage to trees include fruit drop, shoot damage, leaf burn and in severe cases leaf drop.

HARVESTING

Every attempt should be made to harvest fruit when temperatures are below 90 °F, and no harvesting should take place when temperatures exceed 95 °F. Temperature in the shade should be monitored during harvesting and, when possible, harvesting crews should be moved to the coolest, least exposed areas of the grove.

Field bins should be placed under the trees while being filled to protect the harvested fruit from sunburn. Once filled, bins should be moved to a shade structure (open-sided roofed building), or covered with bin covers or light-colored tarps if they cannot be immediately transported to the packinghouse. Never leave filled bins exposed to the direct sun. The surface layer of fruit can easily heat up to more than 15 °F above ambient temperature when exposed to direct sun. Acute sunburn will only show on fruit after it is packed and is a major quality detractor.

To avoid water loss and decreased fruit quality do not hold fruit too long after harvest. Transport fruit to the packinghouse at least once per day, if not twice daily. Bins should not be left in the grove for more than 8 hours after harvest. Cover bins during transport to avoid sunburn and to reduce water loss.

For more information about managing heat in avocado groves, growers can view the following articles on the California avocado growers’ website:

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