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

Posts Tagged: water

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 (266), citrus (295), frost (17), irrigation (72), water (44), wind (5)

Soil Moisture/Nitrogen Workshop

Irrigation and Nutrient Management Field Day

Monday January 14, 2019
555 Las Varas Canyon Road Goleta 7:30 am - 11:30 pm, lunch is provided The event is FREE

but please register -

Learn all about soil moisture sensor systems -
•     Using sensors to save water, energy, & fertilizer
•     Monitoring & interpreting soil moisture data
•     Checking & fixing common system problems
•     System configurations & funding opportunities
•     Practical and common sense considerations

Attendees get a
FREE Soil Nitrate
Quick Test Kit

The Cachuma Resource Conservation District, with funding from the Department of Water Resources, is
pleased to offer this FREE field day event in partnership with:

Parks Land and Cattle Company The Irrometer Company
Natural Resource Conservation Service

Picture:  Soil Moisture Testing by the" Feel Method"

Posted on Monday, January 7, 2019 at 5:42 PM
Tags: soil (21), testing (4), water (44), workshop (3)

Ready! Set! Split! Navel Orange Time.

These are hard days for navel oranges.  Drought stress.  Salt stress due to drought. Then a heat wave in July that messed the trees up.  And now we head into a weird fall with maybe rain. Maybe no rain. Maybe a little rain. This is ripe for navel splitting. This time of year when they are starting to build sugar, they are also ripe for splitting.

Years of drought, and a stressed tree are a perfect set up for navel oranges and fruit splitting.
The days have turned cooler and suddenly out of nowhere there is rain. That wonderful stuff comes down and all seems right with the world, but then you notice the navel fruit are splitting. Rats! No, a dehydrated fruit that has taken on more water than its skin can take in and the fruit splits. This is called an abiotic disease.  Not really a disease but a problem brought on by environmental conditions.

Fruit splitting is a long-standing problem in most areas where navel oranges are grown. In some years, the number of split fruit is high; in other years it is low. Splitting in navel oranges usually occurs on green fruit between September and November. In some years, splitting may also occur in Valencia oranges but it is less of a problem than in navel oranges.

Several factors contribute to fruit splitting. Studies indicate that changes in weather including temperature, relative humidity and wind may have more effect on fruit splitting than anything else. The amount of water in a citrus tree changes due to weather conditions and this causes the fruit to shrink and swell as water is lost or gained. If the water content changes too much or too rapidly the rind may split. In navel oranges the split usually occurs near the navel, which is a weak point in the rind.

Proper irrigation and other cultural practices can help reduce fruit splitting. Maintaining adequate but not excessive soil moisture is very important. A large area of soil around a tree should be watered since roots normally grow somewhat beyond the edge of the canopy. Wet the soil to a depth of at least 2 feet then allow it to become somewhat dry in the top few inches before irrigating again. Applying a layer of coarse organic mulch under a tree beginning at least a foot from the trunk can help conserve soil moisture and encourage feeder roots to grow closer to the surface.  

If trees are fertilized, apply the correct amount of plant food and water thoroughly after it is applied.  If the soil is dry, first irrigate, then apply fertilizer and irrigate again.

navel split
navel split

Posted on Friday, November 2, 2018 at 4:55 AM
Tags: citrus (295), irrigation (72), navel orange (2), rain (17), water (44), weather (8)

A More Water Efficient Avocado?

Here's a pretty technical report of water efficiency in avocado - the amount of water it takes to make fruit.  It looks like there might be some varieties that could produce more fruit with less water. It's a promising start to selecting a tree that could produce under the increasing drought conditions found in avocado growing areas.


Evaluation of leaf carbon isotopes and functional traits in avocado reveals water-use efficient cultivars

Plant water-use efficiency (WUE) describes the ratio of carbon gain to water loss during photosynthesis. It has been shown that WUE varies among crop genotypes, and crops with high WUE can increase agricultural production in the face of finite water supply. We used measures of leaf carbon isotopic composition to compare WUE among 24 cultivars of Persea americana Mill (avocado) to determine genotypic variability in WUE, identify potentially efficient cultivars, and to better understand how breeding for yield and fruit quality has affected WUE. To validate carbon isotope measurements, we also measured leaf photosynthetic gas exchange of water and carbon, and leaf and stem functional traits of cultivars with the highest and lowest carbon isotope composition to quantify actual WUE ranges during photosynthesis. Our results indicate large variation in WUE among cultivars and coordination among functional traits that structure trade-offs in water loss and carbon gain. Identifying cultivars of subtropical tree crops that are efficient in terms of water use is critical for maintaining a high level of food production under limited water supply. Plant functional traits, including carbon isotopes, appear to be an effective tool for identifying species or genotypes with particular carbon and water economies in managed ecosystems.


Read the article:

avocado fruit
avocado fruit

Posted on Wednesday, June 20, 2018 at 6:24 AM
Tags: drought (41), production (8), salinity (12), water (44), water use efficiency (1), WUE (1)

Irrigation Emitters - Do They Operate as Advertized?

The Irrigation Training & Research Center (ITRC) of Cal Poly San Luis Obispo tested 28 different pressure-compensating models of microirrigation emitting devices from a total of nine manufacturers in order to compare independent laboratory testing with manufacturer specifications.

The test results indicate that:

The majority of ~0.5 gallon-per-hour emitters (drippers), regardless of manufacturer exhibited:

  1. Good uniformity of manufacturer

  2. Had excellent response to pressure variation

  3. Had consistent flow rates within the nominal operating pressure range 

    But that the percentage of well-performing products decreased as the designed flow rate increased. Many of the emitters designated as microsprinklers or sprayers, although pressure compensating did not compensate at the normal operating pressures. Often the pressure compensating feature did not start performing until much higher pressures were achieved. Often this occurred when clogging occurred and this clogging often occurred where the pressure diaphragm was located and was not performing. Sediment would get in back of the diaphragm.  Effectively the emitters were not pressure compensating. The testing procedure of numerous medium and high flow models also found individual pieces were found to be defective. These faulty emitters had a measurable effect on the evaluation for those models.

    Read more at:

    An example of the comparisons that ITRC canbee seen here of their results, compared to the manufacturers' values:

emitter performance from ITRC
emitter performance from ITRC

Posted on Wednesday, June 6, 2018 at 12:07 PM

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