OK! Let's Strategize. There are four steps for everybody to consider, it doesn't matter if you have a backyard lawn and landscape or if you have 700 acres of avocados.
1. Maintenance: Irrigation System and Cultural Practices
2. Improve Irrigation Scheduling
3. Deficit Irrigation
4. Reduce Irrigated Area
a. Irrigation System.
- Fix leaks. Unfortunately, there are almost always leaks for all kinds of reasons. Pickers step on sprinklers, squirrels eat through polytube, branches drop on valves, coyote puppies like to chew….the system should be checked during every irrigation
- Drain the lines. At the beginning of each year every lateral line should be opened in order to drain the fine silt that builds up.
- Maintain or increase the uniformity of irrigation so that each tree or each area gets about the same amount of water. Common problems include different sized sprinklers on the same line or pressure differences in the lines. Where there are elevation changes, every line should have a pressure regulator, they come pre-set to 30 psi. Having all of your lines set up with pressure regulators is the only way you can get an even distribution of water to all of the trees, and it solves the problem of too much pressure at the bottom of the grove and not enough at the top.
- Clean the filters often. You don't have a filter because you think that the district water has already been filtered? Hah! What happens if there is a break in the line in the street and the line fills with dirt during the repairs? All of your sprinklers will soon be filled with dirt.
- Is water flow being reduced at the end of the lateral line? It could be because scaffold roots are growing old enough to pinch off the buried line. The only cure is to replace the line.
b. Cultural Management.
- Control the weeds because weeds can use a lot of water.
- Mulch? Mulching is good for increasing biological activity in the soil and reducing stress on the trees, but the mulch will not save a lot of water if you are irrigating often….the large evaporative surface in mulches causes a lot of water to evaporate if the mulch surface is kept wet through frequent irrigation. Mulches are more helpful in reducing water use if the trees are young and a lot of soil is exposed to direct sunlight.
2. Improve the Irrigation Scheduling.
- CIMIS will calculate the amount of water to apply in your grove based on last week's water evapotranspiration (ET). You can get to CIMIS by using several methods; for avocado growers the best method is to use the irrigation calculator on the www.avocado.org website. If you need further instruction on this, you can call our office and ask for the Avocado Irrigation Calculator Step by Step paper. You need to know the application rater of your mini-sprinklers and the distribution uniformity of your grove's irrigation system.
- CIMIS tells you how much water to apply, but you need tensiometers, soil probes or shovels to tell you when to water.
- “Smart Controllers” have been used successfully in landscape and we have used one very successfully in an avocado irrigation trial The one we used allowed us to enter the crop coefficient for avocado into the device, and daily ET information would come in via a cell phone connection. When the required ET (multiplied automatically by the crop coefficient) reached the critical level, the irrigation system would come on, and then shut down when the required amount had been applied. Increased precision can be obtained by fine tuning these devices with the irrigation system precipitation (application) rate.
3. Deficit Irrigation.
- Deficit irrigation is the practice of applying less water than the ET of the crop or plant materials. Deficit irrigation is useful for conserving water in woody landscape ornamentals and drought tolerant plants where crop yield is not an issue. Water conserved in these areas may be re-allocated to other areas on the farm or landscape.
- There hasn't been enough research on deficit irrigation of avocado for us to comment. We suspect, however, that deficit irrigation will simply lead to dropped fruit and reduced yield.
- Stumping the avocado tree could be considered a form of deficit irrigation. In this case, the tree should be stumped in the spring, painted with white water-based paint to reflect heat, and the sprinkler can be capped for at least 2 months. As the tree starts to re-grow, some water should be added back, probably about 10-20% of the normal water use of a mature tree.
- Regulated Deficit Irrigation for Citrus is an important method for saving water, and in some cases will reduce puff and crease of the peel. In one orange trial done by Dr. David Goldhammer in the San Joaquin Valley, an application of 25% of ETc from mid-May to Mid July saved about 25% of applied water for the year and reduced crease by 67%, without appreciably reducing yield.
- 3. Reduce Irrigated Area.
- Taking trees out of production. Trees that are chronically diseased and do not produce fruit (or the fruit is poor quality) should be taken out of production during this period. Also consider: trees in frosty areas, trees in wind-blown areas, trees near eucalyptus and other large trees that steal the water from the fruit trees.
- Changing crops. You may want to take out those Valencias during this period and replant to something that brings in more money, like seedless, easy-peeling mandarins. The young trees will be using a lot less water.
- Fallow Opportunities. You may decide to do some soil preparation, tillage or cultivation, or even soil solarization of non-irrigated areas.
We have found that this four step process is a logical way to achieve water cutbacks with least impact. It is possible to achieve a ten percent reduction in water by only improving irrigation system uniformity and scheduling procedures. Often, these two measures also result in better crop performance and reduced runoff. Reducing irrigated area or taking areas out of production should be a last resort and a well thought out decision. Plan for the future, hopefully water will be more available in future years.
I recently went out to an avocado orchard on sandy soil that had had sudden leaf drop after a Santa Ana condition. The problem is that the orchard had had an ongoing leaf blight problem that had been accentuated by two years of drought and with the Santa Ana more pressure had been put on the trees. This is a condition that has become more and more pronounced over the year and with little rainfall is going to be something to watch out for this coming irrigation season.
Stem and leaf blights are symptoms that appear for various reasons – high rainfall or humidity, spray burn, chewing insect infestation. Here in California we can add other causes, such as drought and salinity burn. These conditions can cause wounding of leaf and stems allowing entry of fungal spores that can cause leaf and stem dieback. This condition is most common near the coast where weather conditions can change from mild and low temperatures to extremely high temperature with winds, such as the Santa Anas or the Sundowners in Santa Barbara. Leaves suddenly dry out, causing cracking either at that time or when they are rehydrated with irrigation. This allows spore entry into the wounds and permits the pathogen to grow in the dead tissue. Symptoms appear 7 – 10 days after the stress. These are decay fungi that create these spores and they are the ones that cause decay of dead tissue on the ground. So their spores are everywhere.
The greater part of a tree is dead – the woody part of the branches and trunk. And it is dead tissue that these fungi are feeding on. Most trees will limit the growth of the fungus by sealing off the infection with gums of various sorts. In that case, the disease is limited and you may only see a leaf or small branch dying back. In mature trees it is possible to see a small branch here and there that has died back, but the bulk of the canopy is still green. It has been called “salt and pepper syndrome”, because of that speckled appearance. In the case of young trees with their smaller root systems and a lesser ability to seal of the disease process, a whole tree can die.
Since this is a severe water stress or salt stress induced problem, the most important management issue is to watch the weather forecasts predicting unusual hot, dry weather and make sure the trees are adequately irrigated going into the stressful period. Shallow rooted trees like avocados are more prone to dry out rapidly in these high water demand situations, but it can be occur in other trees (citrus, apple, peach) and shrubs if the weather conditions are severe enough. With poor leaching due to low rainfall, this can be more of a problem
The only solution to the symptoms is to cut out the diseased parts to prevent its further spread. Once the disease starts spreading, the fungus can produce copious amounts of spores, which in the case of avocado can cause cankers and rots on the fruit.
Some symptoms of leaf blight. Spots that progress into marginal necrosis can occur or just general necrosis.
The talk of drought and water restrictions in the State has created a time for serious decisions. What can be done with avocado citrus trees that have been invested with time and money when there are allocations of water? Although this article is addressed to subtropicals specifically, the guidelines are generally applicable to all fruit trees.
Irrigation systems and scheduling
One of the surest, although not necessarily the cheapest, ways of managing with a decreased amount of water is to improve its application and scheduling. Insure that equipment is working properly, that nozzles are not plugged or worn, that pressures in the irrigation blocks are uniform, that leaks are repaired, and that no runoff or deep percolation are occurring. Many Resource Conservation Districts have Mobile Labs that can help make a system evaluation.
In the Ventura area, oranges use about 30 inches of water per year, however , the monthly amount varies with weather. Applying water in the amounts and at times for optimum production can be improved by using tensiometers. A gauge reading near 40 centibars has been recommended for the one foot tensiometer. The three foot tensiometer can be used to determine the amount of moisture stored in the lower horizon and to determine whether the irrigation was effective, whether the irrigation water infiltrated down to that depth.
Whatever reading is used there is no substitute for observation of the trees themselves and the soil.. Use a soil sampler or shovel to verify the depth of water applied. If time clocks are being used, turn them off or at least adjust them frequently enough to accommodate changing weather patterns. Use of CIMIS weather data can aid in correcting schedules to changing weather.
If water applications need to be curtailed, there will be a decline in yield and fruit size. Applying something less than about 75% of tree requirement will give reduced yields not only for this year, but will lead to dieback and low yields for 3 -4 years after. Abandoning the trees altogether will also yield little or no crop and dieback, but the trees will often return to normal yields in 3 - 5 years. If little water is available, it may be best for commercial operators to reduce the number of trees irrigated to those that can receive 85% of their water requirement and abandon the rest, hoping for more water in future years.
Since it is the leaves that are the site of water loss , the best way to reduce water loss is to reduce the amount of leaves present. This is the ideal time to thin an orchard, get rid of those trees that are shading each other and reducing the per tree yield of fruit. This is a good time to topwork trees to better varieties, since the smaller trees will use less water. A good weed management program will reduce competition for water, and mulching the wetted area of the sprinkler will reduce evaporative loss from the soil surface. Once the leaf area is reduced, it is necessary to adjust the irrigations to reflect the decreased need for water.
This is an opportunity to identify the least productive trees in an orchard and cut of water to them. Trees with root rot or frost damage; trees growing on limy/iron chlorosis sites. Trees growing on ridges that receive the full force of the wind and have a lower yield per gallon of water should be considered first. Trees growing on the perimeter of an orchard also will transpire more water for a given amount of fruit. If all trees in the orchard look good, then these perimeter trees should be targets for saving water. If production records have been kept for different blocks of trees, it might be possible to identify low yielding areas that could be sacrificed.
This is an opportunity , as well. Many growers have kept poor producing parts of groves going because it is an emotional issue to cut up a tree. Seize the day and take advantage of the situation.
For more, check out the powerpoint
A trial planted in Oxnard involved eight different pollinizer varieties at three different distances from 'Hass' tree rows. Yield data collected from 2002 – 2005 suggest that the presence of pollinizer varieties in close proximity enhance the total number of fruit harvested from ‘Hass'. The influence of pollinizers on yield diminishes as the distance from the pollinizer variety increases. Differences were detected between pollinizer varieties in terms of influencing ‘Hass' yield. The highest ‘Hass' yields were observed when ‘Fuerte', ‘Zutano' and ‘SirPrize' were used as the pollinizer. The lowest cumulative yield was observed when ‘Harvest', an A-Flower type was used. Small but significant differences were also detected in percent dry weight, fruit and seed length/width ratio and seed size. For a more complete description of the trial see:
A new publication, "How to Attract and Maintain Pollinators in Your Garden," (Publication 8498) has been added UC Agriculture and Natural Resources (ANR) catalog. The document is a collaboration of UC experts which includes an entomologist, laboratory assistants, landscape designer, photographer, and pomology expert.
Pollination is crucial to the survival of much of our ecosystems and maintaining viable environments for them to thrive provides not only benefits to personal outdoor space, but adds to the well being of the community at large.
This publication focuses on ways to make your garden and outdoor environment, including avocado orchards more attractive to pollinators by identifying pollinators and the plants and landscaping practices that appeal to them.
ANR Publication 8498 is free of charge and available as a downloadable PDF.
You can download this publication here.