CULTURAL TIPS: FREEZE PROTECTION
As California transitions to winter months, growers are confronted with few frost‐protection options. Therefore, tree health is an optimal means of mitigation heading into freeze conditions, and listed below are several tips for handling such:
Pre Freeze:
- Consistent irrigation, as recovery time has proven shorter in blocks irrigated a few days before arrival of cold temperatures (water‐stressed trees are physiologically less capable of enduring freezing temperatures)
- Consider management factors and nitrogen deficiencies that reduce leaf canopies, as they can further erode avocado trees during a freeze
- Weed control, as freeze‐damaged groves have historically shown severe damage - or death - when weeds are abundant
Freeze Indicators:
- Firm, brittle, curled leaves
- Water‐soaked or discolored wood or twigs
- Older branches and trunks splitting and losing bark
- Discolored avocados, with hues ranging from barely visible bronze to black
Protection During Freeze:
- Applying heat to the grove, via irrigation systems
- Helicopter use, when warm air near the inversion layer can be pushed down into groves
- Wind machine use, at low speeds, has historically provided adequate protection in citrus groves, which bear similar production traits to avocados
Post Freeze:
- Soon after leaves fall, whitewash defoliated trees with white‐latex or lime‐based paint that is water diluted (not too diluted, as paint should appear white on tree); will protect damaged wood from sunburn, which can cause further damage
- Suggested not to apply dressings - or additional paint‐on sealants - to cracked bark, as it might strengthen bacterial or fungal infections
- Pruning can be postponed until Spring, when new growth develops
- Because freeze‐damaged trees require less water, irrigation should be done judiciously and reduced in proportion to lost canopy, according to their evapotranspiration requirements (be cautious at this stage, as waterlogged root zones can further stress trees)
- Survey damaged trees before applying fertilizer, to identify what minerals are lacking, as nitrogen applications are likely to trend downward; suggested to withhold nitrogen fertilization until midsummer (or longer). However, zinc sprays often are applied to expanding young foliage
Post Freeze Picking:
- Stem‐damaged fruit should be picked first, assuming it is mature and not otherwise harmed by the cold; while stem damage may be apparent, fruit might be unscathed. When stems are completely girdled by a brown band, fruit will drop. Drops typically occur within seven to 10 days, following a freeze
- Do not pick any discolored avocados (barely visible bronze to black)
- For further picking advice during freeze conditions, growers should contact a University of California Cooperative Extension (UCCE) specialist and/or their respective handlers
Information compiled from the California Avocado Commission's "Frost & Freeze Watch, December 2009" newsletter, California Avocado Society 1991 Yearbook 75:63‐70, as shown on Avocadosource.com, and Ventura County Cooperative Extension's Fall 2010 Newsletter; the information is suggested and is not representative of all situations.
