- Author: Ben Faber
Reflections on Water – People and Trees
Coastal California is a hard environment to decide when to irrigate. Fog and rain vary from season to season and day to day. Depending on the proximity to the coast and elevation, average rainfall in Ventura is about 18 inches. That is the average of some years when we get over 40 inches with those when we get 4 inches. Below average is more the norm than above that figure. Late rains into June can happen, but the latest significant rains can also happen in January. So what is average? And based on rainfall, how do you know when to irrigate?
May grey/June gloom adds to the confusion of what might be an appropriate irrigation cycle. That cool, moist, low wind condition fog reduces water use by plants. Fog drip also adds soil moisture that the plant can use. But, as soon as the fog lifts, the wind kicks in and sucks out the soil moisture.
Water moves from the soil, though the roots, up through the plant stem and through the leaves. It's pulled by the conditions outside the leaf. The longer the air outside the leaf is dry, windy and warm, the more water is pulled out of the plant. And then the plant pulls it out of the soil to replace the water lost from the plant. It's called the cohesion-tension theory of water movement. Water molecules stick together and pull themselves along, the way a train locomotive pulls a string of freight cars. This happens whenever the conditions outside of the leaf are “drier” than inside the leaf. It happens in the winter and summer, when the soils are cold and when they are warm. It's a passive, physical process.
When plants lose water through their leaves, it's called transpiration. It's mediated by stomata in the leaves. These openings or pores are similar to the pores in our skin. People lose water off their skin and it's called evaporation or sweating. Water loss from leaves is similar to water loss from skin.
Evaporation from the skin and from leaves cools the surface. This cooling helps prevent heat stress. The leaf and skin both act as radiators. When this water loss stops, both plants and humans can go into heat stress. So water loss has an important function in both plants and humans. For plants, the stomata also need to be open in order to take in carbon dioxide to make sugar by way of photosynthesis.
The weather factors that drive water loss – water that needs to be replaced or the bodies begin to into heat stress – are the mount of light (day length, cloud cover), relative humidity (it dries faster when air is dry and it's slower when it's humid – think desert versus Florida), and windy (more wind, more drying). When water can't be delivered fast enough to the leaf, it wilts, when the human body starts drying out, the skin wrinkles and dries out. In both cases, water needs to be taken in to reverse the loss.
Temperature is important in water loss, but not as important or as much as the other drivers or humidity, day length and wind. When it's cold, leaves and skin both dry out – think freeze-drying, a very successful process for removing water from fresh food to make a light, backpacking food. Often humans respond more to temperature than these other driving factors of water loss. If it's cool, it's not necessary to irrigate the trees. A common grower refrain is, “it's winter, I don't need to irrigate.” After five years of drought, we know better about winter irrigation.
However, this “winter and it's cool, so it's not necessary to drink water while working outside” refrain is common, too. And this can be a real human health problem. Dehydration is something serious and we should all be aware of the need to drink water during these cool, windy days of spring.
Heat stress and irrigation are both more complicated than just being aware of the weather, but below are some helpful guidelines from Cal/OSHA to follow to avoid heat stress in humans. Hey, also might not be too far off for plants, as well.
- Author: Ben Faber
Advances in Citrus Water Use
Workshop & Field Day
Tuesday, March 26, 2019
8 Am - 3 PM
Strathmore, CA
Attend the Advances in Citrus Water Use Workshop & Field Day and join UC Davis Irrigation Specialist Daniele Zaccaria as well as other water experts and specialists from the University of California Cooperative Extension, the California Department of Water Resources, and the Citrus Research Board to learn about research advances in water use and irrigation for citrus production. Gain firsthand practical knowledge of the latest developments in the citrus industry and become familiar with methods and tools to measure evapotranspiration (ET) and crop coefficients (Kc), tree water status, and monitor soil moisture to inform irrigation planning and scheduling decisions for citrus.
What to expect?
Session topics include:
- Current research
- Water management and regulation
- Optional Field Session on irrigation technology
View a tentative agenda here.
Registration Details
$35 registration fee includes admission to the field day, coffee, refreshments, and lunch.
Register online, here. Fee will increase on March 13.
Limited to the first 150 participants
Logistics and Registration
ANR Program Support, Julia Kalika, (530) 750-1380 or Shannon Martin, (530) 750-1328
/span>- Author: Ben Faber
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Register NOW!!!
https://ucanr.edu/sites/citrusfieldday/Registration/
About the Field Day |
Attend the Advances in Citrus Water Use Workshop & Field Day and join UC Davis Irrigation Specialist Daniele Zaccaria as well as other water experts and specialists from the University of California Cooperative Extension, the California Department of Water Resources, and the Citrus Research Board to learn about research advances in water use and irrigation for citrus production. Gain firsthand practical knowledge of the latest developments in the citrus industry and become familiar with methods and tools to measure evapotranspiration (ET) and crop coefficients (Kc), tree water status, and monitor soil moisture to inform irrigation planning and scheduling decisions for citrus. |
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Contacts for More Information |
Logistics and Registration ANR Program Support, Julia Kalika, (530) 750-1380 or Shannon Martin, (530) 750-1328.
Course Content Daniele Zaccaria, UC Cooperative Extension Specialist, Agricultural Water Management |
- Author: Ben Faber
So a question comes in about a problem with a backyard avocado tree. And it would seem the first question would be about the overgrowth happening at the base of the trunk. This a ‘Fuerte' avocado that is grafted on a seedling avocado rootstock. It's not unusual to see an overgrowth, but this is the most extreme example I have ever seen. So it's basically an incompatibility between the graft and the rootstock. In many cases this is no big problem and trees can live a long time, as this tree has.
But the homeowner wasn't asking about the unusual growth at the base, but the canker that had appeared in the center of the trunk near the base.
This has the classic white sugar exudate that occurs with a wound of any kind in avocado. The sugary sap that contains the unusual mannoheptulose 7-carbon sugar characteristic of the laurel family to which avocado belongs will ooze out of the wound and result in a white crust (Read more about this sugar at: https://www.sciencedirect.com/science/article/pii/S0254629911001372 ).
Anyway, so this backyard tree is in an area that is getting 10 minutes of lawn watering a day. Lawns and avocados don't get along. And avocados don't get along with short, shallow irrigation that result in salt accumulating in the root zone. Which is what has happened here. Salt stress and the result is an infection of bacterial canker (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7920 ).
It's not fatal in an old tree like this, but it can predispose the tree to root rot. And that's not something that is easy to treat in backyard settings.
- Author: Ben Faber
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
http://ceventura.ucanr.edu/Com_Ag/Subtropical/Publications/Frost/A_Frost_Primer_-_2002_/
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: