- Author: Allison Rowe and Ben Faber
How to irrigate is probably the most common question in irrigated agriculture, even with 10,000 years of cultivation knowledge to guide us. The complexities of irrigation and the unique situation for each grower makes this question so difficult. Not enough water, and plants have diminished growth or the propensity for disease and disorder 1. Too much water leads to root disease and nutrient problems 2. So, it can't be too much or too little, but just right. There are times when citrus can handle a little more water stress than other times, which can lead to water savings 3, especially in a drought year or in areas where water costs are crucial. Salinity further compounds the question of irrigation where striking a balance determines the health of your tree. Staying in tune with your orchard and using appropriate methods to measure water need, water use, environmental water demand, and soil water-holding capacity will help inform irrigation management decisions.
There are all kinds of ways of estimating tree water need 4 , a valuable piece of information for irrigation decision making. An inexpensive and often overlooked method of estimating tree water requirements is grower observation in the orchard to assess leaf color, leaf size, the look of the leaves, and canopy fullness. Pure observation and knowledge of your trees yields a lot of valuable information regarding irrigation management. Beyond observation, a direct measure of the tree with a porometer, pressure gauge (bomb), sap flow meter, dendrometer or other device gives an absolute or relative number of tree performance. Technological advances, such as telemetry and imaging with drones or satellites, holds promise, but are still being perfected for general irrigation use. In general, technological devices yield informative data, but tend to be expensive, delicate, and require manual monitoring to account for tree-to-tree variation in the orchard.
Soil moisture sensors can be an effective method of evaluating water use by the tree. The most basic way to measure soil moisture is with a human powered shovel or soil tube 5. While it requires an operator who knows what they are doing, the technique is easily learned and repeatable. A human and shovel can move around an orchard checking out different suspicious spots that are not easily done with fixed-in-place sensors. Installation of soil moisture sensors systems range in cost and capabilities, yet provide specific data on water use. Integrating certain systems into communication relay systems allow for the monitoring of multiple sites at once. Some sensors can measure soil salinity, as well as soil moisture, to give a sense of whether the water in the soil will be useable by the tree. If soil moisture sensors are used, correct placement of where roots are taking up water is imperative to get an accurate assessment of water uptake. Overall, it is critical to keep the entire orchard in mind and understand that fixed sensors only take a specific location's reading.
Another great technique to inform irrigation scheduling is an estimate of the demand that drives water use. An evapotranspiration estimate either by CIMIS, a private weather station with ET-calculation or atmometer gives not only an amount to apply but also when to apply that amount based on the water holding capacity of the soil and the rooting depth of the crop. Soil moisture holding volume can be complicated, but can be estimated from the NRCS table in the previous paragraph5 or from tables in the Web Soil Survey 7.
Simply running an irrigation system for a specific amount of time and probing for depth of water penetration and extent of wetted area is the best way to get an estimate of soil moisture holding capacity. This knowledge is needed in order to decide whether the active rooting volume is getting wetted sufficiently or too much is being applied. Emitters are rated by gallons per hour, but that 1 gph, 5 gph, 20 gph emitter output might differ according to water pressure that can vary over an irrigation period. On the flip side, monitoring soil moisture depletion over time can give an approximation of how depletion compares to ET estimates. Soil moisture depletion can be measured by soil moisture sensors or by shovel and feel. This estimate of applied water compared to output and ET only needs to be done once at a given growth stage of the orchard. If the orchards is young, it will need to be done each year as the trees fill out. An estimate of canopy growth can also be used to better approximate young orchard ET.
All of these methods suppose that a grower has the capability to irrigate when, where and for how long they need to. If water delivery is on a fixed schedule and the amount of water can be controlled it is valuable to understand specific water needs. Knowing the rated applied amount of an emitter is important, but that amount shouldn't be assumed, especially considering natural wear and tear, damage from harvest, poor filtration, clogging, or damage by wildlife. Maintenance to insure good distribution uniformity is critical to the operation and the correct application of water to trees and for the maintenance of tree health. Low-pressure systems are wonderful but they should be evaluated on a yearly basis and tuned up in preparation for every irrigation season. Many growing areas have mobile irrigation labs that will evaluate system performance and make recommendations for improvement.
All said, knowing the orchard and evaluating tree health will inform irrigation management decisions. Applying technology where technology is appropriate will help. Using it to help advise irrigation decisions is valuable, but new tools will not always be the answer.
It's important to know what is being applied.
Trust but verify.
Water Measurement and Reporting Course
This training will be held on
Friday June 7th, 2019
from 1:00 p.m. – 4:30 p.m.
At the Santa Ynez Community Services District,
1070 Faraday St., Santa Ynez, CA 93460
Senate Bill 88 requires that all surface water right holders who have previously diverted or intend to divert more than 10acre-feet per year (riparian and pre1914 claims),or who are authorized to divert more than 10acre-feet per year under a permit, license, or registration, to measure and report the water they divert. Detailed information on the regulatory requirements for measurement and reporting is available on the State Water Resources Control Board “Reporting and Measurement Regulation” webpage. The legislation as written requires that for diversion (or storage) greater than or equal to 100 acre-feet annually that installation and certification of measurement methods be approved by an Engineer/Contractor/Professional. Diverters across CA were concerned about this requirement.
California Cattlemen's Association heard from their membership and worked with Assemblyman Bigelow on a bill that would result in a self-certification option. Assembly Bill 589 was passed and became law on January 1, 2018. This bill, until January 1, 2023, allows any diverter, as defined, who has completed this instructional course on measurement devices and methods administered by the University of California Cooperative Extension, including passage of a proficiency test, to be considered a qualified individual when installing and maintaining devices or implementing methods of measurement. The bill requires the University of California Cooperative Extension and the Board to jointly develop the curriculum for the course and theproficiency test.
At the workshop you will:
- Clarify reporting requirements for farms andranches.
- Understand what meters are appropriate for differentsituations.
- Learn how to determine measurement equipmentaccuracy.
- Develop an understanding of measurementweirs.
- Learn how to calculate and report volume from flowdata.
Registration is required; there is a fee of $25.
Registration link here.
For questions, please contact Matthew Shapero at (805) 645-1475 or firstname.lastname@example.org. For other helpful resources regarding water measuring, reporting, and AB 589, please visit: https://ucanr.edu/sites/AB589//span>/h1>/h1>/h1>/h1>/h1>
World Bee Day
And more things to learn in this slide set
Impacts of the invasive shot hole borer (Euwallacea kuroshio) are linked to sewage pollution in southern California: the Enriched Tree Hypothesis
By: John M. Bolandand Deborah L. Woodward
The Kuroshio Shot Hole Borer (KSHB, Euwallacea kuroshio) and the Polyphagous Shot Hole Borer (E. whitfordiodendrus; Coleoptera: Curculionidae: Scolytinae) have recently invaded southern California and are attacking live trees in commercial agriculture groves, urban parks and native riparian forests. Among native forests the worst impacts observed to date have been in the Tijuana River Valley in south San Diego County, where approximately 30% of the native willows (Salix spp.), or120,000 trees, have died as a result of a KSHB infestation. This paper examines wood densities, wood moisture contents, KSHB infestation rates, and KSHB-induced mortality rates in two willow species (Salix lasiolepis and S. gooddingii) at sites near and far from sewage input. Comparisons were made on two spatial scales: broadly among sites within San Diego County; and locally among sites within the Tijuana River Valley. The results showed that, on average, willow trees growing closest to sewage pollution had significantly lower wood density, higher wood moisture content, higher KSHB infestation rates, and higher KSHB-induced willow mortality rates than those growing farther away. We present the Enriched Tree Hypothesis to explain the link between sewage pollution and KSHB impacts; it is as follows: (A) Riparian trees subject to nutrient enrichment from frequent sewage pollution grow quickly, and their fast growth results in wood of low density and high moisture content. If attacked by the KSHB, the trunks and branches of these nutrient-enriched trees provide an environment conducive to the fast growth of the symbiotic fungi upon which the KSHB feeds. With an abundant food supply, the KSHB population increases rapidly and the trees are heavily damaged by thousands of KSHB galleries in their trunks and branches. (B) Riparian trees not subject to frequent sewage pollution grow more slowly and have denser, drier wood. Conditions in their trunks and branches are not conducive to the fast growth of the KSHB's symbiotic fungi. The KSHB generally ignores, or has low abundances in, these slow-growing trees. This new hypothesis explains current patterns of KSHB impact in San Diego County and focuses attention on the important roles of the environment and preexisting conditions of trees in determining the extent of KSHB impact .It highlights the Tijuana River Valley as an unusual site due to high sewage inputs and predicts that the high KSHB-induced willow mortality seen there should not occur in other natural riparian habitats in southern California. Most importantly, by identifying sewage pollution (or nutrient enrichment) as a major risk factor for KSHB impacts, the hypothesis ratchets down the KSHB-threat level for most riparian sites in southern California and directs attention to other nutrient-enriched sites as those most at risk.
The complete article can be found at:
Two newly published scientific journal articles that address SHB species delineation are:
- Gomez et al. Species Delineation Within the Euwallacea fornicatus. in Insect Systematics and Diversity, (2018) 2(6): 2; 1–11. (Attached) Richard Stouthamer and Paul Rugman-Jones, both with UC Riverside, are two of the co-authors
- Hulcr, J & Landers, J. January 7, 2019. So Many Shot Hole Borers: New research charts four nearly identical species. in Entomology Today. https://entomologytoday.org/2019/01/07/so-many-shot-hole-borers-new-research-charts-four-nearly-identical-species/
Examples of ambrosia beetle impact on willows. (A top) KSHB excavate galleries within a trunk and push the sawdust tailings out of their entrance holes. (B lower) Trees can be undermined by many galleries and snap in high winds. [These pictures show the extremes – infested trunks do not always look like A, and infested trunks do not always break, like B. Images: John Boland]
WESTMINSTER, Colorado - An article in the most recent edition of the journal Weed Science shows that cover crops can play an important role in slowing the development of herbicide resistant weeds.
Researchers conducted field experiments in Pennsylvania to explore how cover cropping tactics influenced the management of horseweed in no-till grain crops. Seven cover-cropping treatments were used over two subsequent growing seasons.
There were several significant findings. In comparison to fallow control plots, cover crop treatments reduced horseweed density at the time of a pre-plant, burndown herbicide application by 52% in the first year and 86% in the next. This reduced the herbicide "workload" and lowered the selection pressure for resistant weeds. Cereal rye alone or in combination with forage radish was found to provide the most consistent horseweed suppression.
Importantly, winter hardy cover crops also reduced horseweed size inequality - meaning fewer large horseweed plants were found at the time of herbicide application. Researchers say this reduces the chance of a size-dependent fitness advantage for horseweed biotypes that develop herbicide resistance.
"Our hope is that understanding the complementary relationship between cover crops and herbicides can lead to new weed control strategies that slow the development of herbicide resistance," says John M. Wallace, Ph.D., of Pennsylvania State University.
Full text of the article "Cover crop effects on horseweed (Erigeron canadensis) density and size inequality at the time of herbicide exposure" is now available in Weed Science Volume 67, Issue 3.