Heat : Preventing Damage toAvocados

Lisa FyffeRipe Horticulture Pty LtdMeadowvale, QD

As modified by Ben FaberUCCE, Ventura, CA

Tristate Climate Challenges

High pH Soil, ranges from 6 to 9.

High limestone presence

Low Organic Matter and Carbonlevels

Soil types range from Sandy loam to SandyClay Loam

South Australia has high salt presence.

Water availability can be an issue during drought

High Temperatures in Summer (80 – 113 degrees F, 0-30 % humidity)

Cold temperatures in Winter – chill hours 700+

High Winds inSpring

Temperature variability and fluctuations

Impacts ofextreme heat

Floral abscission

Fruit drop

Reduction in Fruit size

Reduced photosynthesis

Root death

Preventing Heat Damage

Environment

Protectants

Nutriti0n

Environment

Manipulating your surrounding environment to improve the Micro Climate

Orchard Setup – WATER - Misting system, Irrigation, Mulch, Windbreaks, Inter-rowcropping, cover crops

CO2

H2O

H2O

A plant must

lose water

in order to

grow

When stomata close, they stop growing……..

smaller fruit

Stomata-

openings on leaves

open closed

They close with insufficient light, high temperature and high evaporative demand

The stomata must be open for transpiration to occur

Otherwise the plant heats up, and sunburn occurs.

Evaporative COOLING

And cools the plant

Evapotranspiration is driven by:

Sun – day length, clouds

Wind

Humidity

Temperature

Santa Ana Winds are Water Suckers

Stomata close under: Light stress – low intensity, shadedWater Stress – droughty, wind windsHeat Stress - >85 deg F

Heath and Arpaia http://www.avocadosource.com/ARAC/Symposium_2006/HeathRobert2006b.pdf

Tree needs to behydrated prior to heatin order to keep stomataopen

Water stressed tree cant respond to heatHeat stressed plants cant respond to water demand

WATER

Overhead Misting System

Useful to reduce heat in the Orchard and increase humidity during flowering

Sprinkler Size dictated by the size of your Mainline, pump capacityetc.

Need 100% Coverage of the Orchardarea

Sprinklers need to be clear ofTrees/vegetation

Need to be turned on at the correct time, 93 degrees F.

Depending on system/ water availability- may need to Pulse or leave on.

Temperature /humidity /wind monitoring

Can reduce temperatures in the Orchard by 9-15 degrees F-dependent on wind speeds, sprinkler output and temperatures.

Above canopyIrrigation

Overhead over every treesprinkler at every other tree.In Australia. Has become standardin last 10 years.

Overlap Ojai, CA since 2019

Temp Effect 10/16/20

started sprinklers @ noon

Temp Time Therm 1 Therm 2

103 12 93 93

103 12:30

102 13 93 88

103 13:30 96 85

102 14 95 92

102 14:30 93 89

102 15 91 87

102 15:30 90 89

Pulsed every 30 minutesrotating through 5 blocks

About 10 deg difference

System successfully controls temperaturessignificantly reduced fruit dropno significant adverse effects6 emitters per acre$1000 per acre installed

Before installation of overhead in 2019

Sprinkler spacing 60 X 60 every 4th row70 ft patternw/ 5-10 ft overlapin Santa Paula

Sept 6, 2020 temperature reached 115.3 deg and overhead sprinklers with flow rate of 3,168 gph dropped air temp 5-7 deg. No damage or fruitloss to trees covered by sprinklers. Installation cost for 1.5 acres ~ $1,200

0.4 acres ~$600

Expanding system to newly plantedtrees

Mitigating Heat

A big thank you to our Speakers

Speaker & Topic:Giulia Marino, UC Davis Tree Physiologist -

How Heat Affects a Tree and What Options Are there to Reduce the Effect.

Grower Panel on Overhead Irrigation -Four Examples of Growers Modifying Overhead Irrigation to

Affect Tree Heat.Lisa Fyffe, Australian Consultant –

How It’s Done Down Under.

https://www.youtube.com/watch?v=r0agynp_u7oGo to CAS –Seminars website

WATER

Irrigation & Irrigation Monitoring

Irrigation Audit – check that sprinklers are running within product specs, lines are clean, pressures are correct and good coverage, Shadow lines

Soil Moisture Monitoring -Capacitance probes – monitoring at 4 depths

Mulch

Excellent Mulch layer applied annually will keeproots cool,

Reduce evaporation

Provide a barrier to heat stress

Reduce root death

Improve water holding capacity of soil

Improve Organic Matter

Improve Soil Biology

Expensive…..But is it?

Mulch – Ryecorn, Oats, Barley, Rice Straw,Woody mulch, Blends, Grape Marc

Mulch

Soil Radiation

Ambient temperature of 104 degrees, reflection off bare soil can burn foliage,

Soil temperatures can reach over 86 degrees at 3 inch depth, cooking roots, particularly in the absence of Mulch

PollenViability

Exposure to temperatures above 93 degrees for several hours causes pollen to become unviable.

High temperatures cause pollen distortions in the grains and at 102-104 degrees pollen was unable to reach the embyro sac.

High temperatures damage the fertilisation and fruit set process

It has been found that cross pollination by other varieties (eg Edranol) increased fruit set and fruit retention in Hass

Inter-rowcropping

Windbreaks

Cover Crops can reduce temperatures by 3-8 degrees, dependingon height and density of cover crop.

Will use excess irrigation

Windbreaks help to reduce the intensity of the hot dry winds during a heat wave

Windbreaks create humidity, help improve overhead mistingsystem

Intercroppingas a covercrop

Pollination Gardens

Protectants

Sunscreen - Surround, Screen Duo, etc. – reflect heat/light

Vaporguard / Envy / WiltNot/Antistress – reduce water loss ???????

White Paint on trunks for sunburn protection

Heat Stress vs Water Stress

https://crw.org.za/home/document-home/news-articles/south-african-fruit-journal-safj/safj-2011/2542-sa-fruit-journal-april-may-2011-sunburn-reduction-on-miho-wase-satsuma-mandarin/file

Antitranspirants prevent transpiration and cooling

The best thing to do for water stress is to anticipate the stress and get the water on before itarrives – to hydrate the tree so that it continues to transpire and cool itself.

https://crw.org.za/home/document-home/news-articles/south-african-fruit-journal-safj/safj-2011/2542-sa-fruit-journal-april-may-2011-sunburn-reduction-on-miho-wase-satsuma-mandarin/file

Vaporguard / Envy / WiltNot/Antistress ??????? Might cause more heat stress

White Paint on trunks for sunburn protection after Santa Anas

Sunscreen - Surround, Screen Duo etc. work to cool, stomata don’t close but continue to cool

Heat Stress vs Water Stress

Nutriti0n

A healthy tree will withstand a heat event better than an unhealthy tree.

Healthy root system

Stimulants / Seaweeds /AminoAcids ?????

Summary

Protecting Avocados from Heat events starts with optimumOrchard setup and healthy trees

Successful Irrigation is crucial for a productive Orchard with good fruit size

Using the Irrigation systems strategically will achieve best results

Mulching tree berms, improving soil and tree health

Monitoring – Soil moisture and air temperatures

The use of Protectants (reflectants) products can be used to alleviate the stress of heat, usually provides a few degrees relief

Cover cropping and hedgerows increase humidity and evaporative cooling.

Drought Strategies for Avocados

Impacts of Drought • Avocado Not adapted to

hot, dry climates

• Shallow root system• 80% roots in top 12 inches

• Low salt tolerance

So what to do in a drought?

Analyze the Grove• Poor production areas:

• Cold temperatures?• Excessive salinity?• High soil pH?• Low bee visitation?• High wind areas?

• Irrigate the areas with good production record

Root Rot Infected Trees• Critical evaluation of crop

• No crop – cap sprinklers

Mulch

• Concentrate on most productive areas

• Mulching can reduce

evaporative loss

by up to 25%

But is expensive to apply

Sunblotch infected trees

• Deep grooving in fruit

• Rough bark on lower trunk

• Remove trees

• Cap sprinklers

Trees in wind-prone areas• Orchard edge trees use as windbreaks since

lose fruit every year

• Cap sprinklers

Tall trees

• Scaffold/stump to 6-9 feet

• Whitewash to protect bark

• Cap sprinklers for about 2 months

• Gradually increase watering

Thin the grove

• Remove every other tree and cap sprinklers

• Increase water to remaining trees

• Roots will have been growing into neighboring trees

• Change sprinklers to wider pattern

Prune• Removing half the foliage doesn’t

reduce water use by half

• Estimates would be 20-30% reduction• Increased light within canopy• Increased air flow

Kaolin (Surround, Snow Coat) has been

shown to reduce leaf temperatures

by 3 - 4 deg and reduce transpiration

by 22-28% (Abou-Khaled et al., 1970)

Drought Strategies

• Set priorities

• Irrigate productive blocks

• Fix and Maintain the irrigation system

When you know Santa Anas are comingIrrigate the trees in advance

Historically had 15 frost days each winter, when smudge pots were lit. Many fewer days now

2020 had two freeze events – not catastrophic

But two heat events – above 100 F and higher in many sites –that were catastrophic

118 *F is too hot formost plants

https://ucanr.edu/blogs/Topics/

frequent blogs on tree issues

http://ceventura.ucanr.edu/news/Topics

_in_Subtropics/

quarterly newsletter on trees

Read more about heat and avocados:Avocados and Cover CropsWhy and How to Cool Avocado TreesWhat's Happening to Climate?Mitigating Heat in the OrchardConnecting to the Changes Around UsMade in the ShadeWith Climate Change Will We Grow Cactus?Heat, Wind, Freeze, Wind, RepeatOptimizing Salt LeachingChanging Temperatures Affecting Herbicide Efficacy?Heat Stress AdviceAvocado Heat DamageHeat and Trees