Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: wind

Frost and Rain?

It is that time of year and we should be alert to threat of freezing weather and damage to trees. Last winter was one of the warmest on record, but there was still a sneak cold blast around December 25 that caused some problems in some areas. Wet winters tend to have lower frost threats, and even though wet is forecast for this winter, the forecast is erratic, as usual. That still leaves January which historically is when most of our damaging frosts occur. Fox Weather on the CA Avocado Commission is forecasting some cold weather coming up, so growers need to be prepared for the worst.


Here are some links to frost information, preparing for frost and managing frost damage to trees.

A Frost Primer

Methods of Frost Protection

Protecting Avocados from Frost

Rehabilitation of Freeze-Damaged Citrus and Avocado Trees

The forecast is for north winds, which often means cold, dry air and often with winds. Winds mean no inversion and no warm air that can be introduced at ground level to warm trees. If this occurs, running a wind machine can make the damage worse. Wind machines and orchard heaters work on the principle of mixing that warmer air higher up – 20-100 or so feet higher than ground level which has colder air. When temperatures drop, the air is dry (wet-bulb temp below 28 deg F) and there is no inversion, running a wind machine can just stir up cold air and cause worse conditions (freeze-drying). It's better to not run the machine. The only thing left to do is to run the microsprinklers during the day so that the water can absorb the day's heat. Then turn the water off before sunset so that evaporative cooling from the running water isn't accentuated. Then when temperatures drop near 32 at night and the dewpoint is much below that, it's time to start the water again and let it run until sunrise (when risk is less). Running water works even if the water freezes. This is due to the release of heat when water goes from liquid to frozen state. This 1-2 degrees can mean the difference between frost damage and no damage. Also, ice on fruit and leaves can insulate the fruit. As the ice melts at the surface of the plant, it releases heat, protecting the plants. If there is not sufficient water to run the whole orchard, it's best to pick out the irrigation blocks that are the coldest or the ones you definitely want to save and run the water there continuously. Running the water and turning it off during the night to irrigate another block can lead to colder temperatures in both blocks.


Keep warm this winter.

and check out this Wind Machine You Tube:

Wind Machine frost
Wind Machine frost

Posted on Wednesday, January 9, 2019 at 4:46 PM
Tags: avocado (289), citrus (338), frost (19), irrigation (80), water (49), wind (5)

What Damaged the Citrus this Winter? Frost? Herbicide?

Something hit the citrus trees of Riverside in late December 2017. Some vandal spraying herbicide? It was too widespread. It was all over town, orchards and backyards. It was on the north and east sides of trees. It didn't happen in Ventura or Santa Barbara. It probably happened to a lot of other plant species, but our correspondent had eyes only for citrus.

It sure looks like it could have been a cold, freezing wind, but on closer consultation with our Citrus Specialist, Peggy Mauk who also directs the Agricultural Operations at UC Riverside – it was the demon wind. The Satan Wind. The Santa Ana that dried out the trees that had not gotten sufficient water to cool themselves and had dried out on the windward side of the tree and orchard. Burned, in effect. This is the side of the orchard that dries out the most. It's what's called the “clothes line” effect. The margins that dry first because of the greater exposure to wind, sun and usually lower humidity. In this case, way lower. And by the time the damage was noticed a week later, the winds had been forgotten. Expect more water stress in our future.                        

citrus dieback 2
citrus dieback 2

citrus santa ana damage 1
citrus santa ana damage 1

Posted on Thursday, February 22, 2018 at 5:17 AM
Tags: citrus (338), drought (41), heat (6), lemon (100), navel (11), orange (69), Santa Ana (1), stress (10), wind (5)

Fire Disaster Workshop for ALL Ventura/Santa Barbara Producers

The USDA's Farm Service Agency and Natural Resources Conservation Service will have workshops to aid agricultural producers; including cattle, tree, nursery, vegetable, and berry farmers in filing for federal assistance programs.  Appointments can be arranged now for filing applications during these workshops.


The California Avocado Commission and University of California Cooperative Extension (UCCE) are coordinating with the USDA's Farm Service Agency (FSA) and the Natural Resources Conservation Service (NRCS) the availability of field appointments for growers who have been impacted by the Thomas Fire. Personnel from both FSA and NRCS will be available to assist growers with the necessary paperwork to apply for federal assistance.

Currently, two days of appointments are available (information below). To schedule an appointment for either of the following two days, please call (805) 645-1434.

Tuesday, December 19th, 2017
Santa Paula Agriculture Museum
926 Railroad Ave, Santa Paula
8:00 am – 4:00 pm

Wednesday, December 20th, 2017
University of California Cooperative Extension
669 County Square Drive Suite #100, Ventura
8:00 am – 4:00 pm

Federal relief personnel will be available to assist growers with the paperwork, and growers are asked to provide the following information:

  • Business entity information (e.g. individual, limited liability corporation, etc.)
  • Social Security Number and/or Employer Identification Number
  • Location/size of the farm
  • Extent of damage

In addition, as we reported yesterday, it's important that California avocado industry members who have been impacted by the recent wildfires and/or Santa Ana winds contact their crop insurance agent within 72 hours of the event to determine possible applicable coverage. Both fire and wind events may be included in certain crop insurance coverage, but agents must be notified within 72 hours.

Below, again, is a list of potential FSA programs that may provide disaster assistance to those avocado growers affected by the wildfires:

  • The Tree Assistance Program provides financial assistance to qualifying orchardists to help them replant or rehabilitate trees damaged by natural disasters (separate from crop insurance).
  • The Emergency Conservation Program offers funding and technical assistance to growers to help them rehabilitate land damaged by natural disasters. This program may provide cost share assistance for debris removal, land leveling and shaping, irrigation replacement, and cattle fencing.
  • Emergency loans are available to producers located in counties that receive a primary or contiguous disaster designation.

Remember, if you are an impacted grower you are asked to contact both FSA and your county agricultural commissioner's office as follows:

USDA-Farm Service Agency

Santa Barbara/Ventura County
Daisy Banda
Key Program Technician
805-928-9269 Ex.2

Riverside/San Diego Counties
Desiree Garza
County Executive Director
760-347-3675 ext. 107

Ventura County
Korinne Bell, Chief Deputy Agricultural Commissioner,
Henry Gonzalez, Agricultural Commissioner,
(805) 388-4343, Ext. 2

Santa Barbara County
Debbie Trupe, Deputy Agricultural Commissioner,
Stephanie Stark, Deputy Agricultural Commissioner,
(805) 681-5600

San Diego County
Vince Acosta, Information Technology Principal,
(858) 967-8623

Riverside County
Ron Bray, Assistant Agricultural Commission, RBray@RIVCO.ORG
(951) 955-3000

A complete list of FSA disaster assistance programs can be found online. For more information about available disaster assistance programs, contact your local U.S. Department of Agriculture office. You can find your local USDA service center by clicking on this link.

Tom Bellamore, President
Ken Melban, Vice President of Industry Affairs
California Avocado Commission

IMG 2031
IMG 2031

Posted on Saturday, December 9, 2017 at 12:45 PM
Tags: assistance (2), damage (24), fire (30), flood (3), usda (4), wind (5)

Was that a Worm Eating my Tree?

You come on a leaf with the margins munched on. It's got to be a beetle or a looper or some insect doing the damage, right? Not necessarily. It's not time to drag out the Raid. Look at the damage closely. In the photos below you can see the dead leaf margins caused by either salt damage or more likely leaf blight. Leaf blight is a disease that shows up with water stress and is caused by a fungus, one of the Botryoshpaerias. It causes an uneven marginal necrosis that goes along the margin in a somewhat irregular pattern and often not at the leaf tip. In this case it does affect the leaf tip, and since salt burn and leaf blight are caused by the same conditions of water stress, it's probably a bit of both.

Lepidopteran larvae will more commonly feed in a smooth pattern, not the rough pattern seen here. Now with this dead tissue, the wind blows it out, and what's left is the uneven margin. No it's not time to spray an insecticide. It's time to reflect on irrigation. There's a lot of this damage out there now. On avocados, citrus, landscape plants. It's going away until the leaves drop and are replaced with new ones, that will hopefully be well hydrated by rain and proper irrigation.

Top photo is salt/leaf blight damage

Bottom is necrotic tissue that the wind has blown out

leaf blight 1
leaf blight 1

leaf blight 2
leaf blight 2

Posted on Wednesday, January 27, 2016 at 1:59 PM
Tags: avocado (289), botryosphaeria (13), citrus (338), damage (24), leaf blight (8), salt (8), wind (5)

What to Expect of Young Trees or Teach your Children Well

The first years of a tree's life are for building a structure for the future. Many varieties of trees are precocious and will bear fruit when they should be building structure. Letting a tree carry fruit when it is too young (under 2 years of age in the ground and some say 5 depending on the tree species) delays future good production and distorts the tree's architecture. A young avocado tree can be completely humbled (brought to ground literally) by the weight of the 12 ounce fruit. ‘Lamb Hass' wants to grow upright, but if the young tree is burdened with fruit early on, it will grow squat and twisted.

Another problem with precocious trees recently came up with ‘Meyer' lemon. Along the coast, this is a tree that will carry fruit throughout the year. It is a small tree naturally, but also because it puts so much energy into fruit production. If allowed to fruit to its full potential early, the canopy development is delayed and the fruit grows unprotected from winds. It is much more subject to wind scarring. Imagine the wind flailing the fruit around with no branches or leaves to protect it. Now the grower has a small, twisted fruit tree and fruit that can't be sold.

Give your young trees a chance to grow without the burden of carrying fruit to early.  They are your children.


Imagine all this fruit on a one year old canopy

And this fruit is fully exposed to the elements and wind scarring

Lamb Hass pulling on tree
Lamb Hass pulling on tree

meyer lemon wound
meyer lemon wound

Posted on Wednesday, September 2, 2015 at 12:12 PM
Tags: avocado (289), bearing (1), canopy (5), fruit (18), Lamb Hass (1), lemon (100), Meyer (4), precocious (1), wind (5), young (1)
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