- Author: Neil O'Connell
Since the first publication of this article on vole damage in citrus, a recent field observation regarding vole activity is worth noting. Voles prefer a situation where there is cover and shelter generally from weed or grass. In some orchards established in the last few years a plastic strip has been installed along the tree row for weed management (Fig 1). These strips appear to be offering a sheltered environment for vole activity in some cases (Fig 2). Recent observations in two such installations, one a block planted in 2013 and the other an eight year old planting exhibited significant vole activity. The young orchard at this point does not exhibit obvious tree damage although active tunneling is apparent (Fig 3). In the older orchard feeding damage to the trunks is very obvious (Fig 4).
Meadow Mice (Voles) can cause serious damage in a citrus orchard resulting in partial or complete girdling of a tree (Fig 5). Trees often exhibit damage to the bark of the tree from the soil line up 6-8 inches (Fig. 6 ). On close inspection, an open hole 1-1.5 inches in diameter may be found at the base of the tree (Fig 7).
Five species belonging to the genus Microtus are found in California, two of which “Microtus californicus” and “M.montanus” are reported to cause damage. Damage has been reported in permanent pasture, alfalfa, hay, artichokes, Brussels sprouts, carrots, cauliflower, potatoes, sugar beets, tomatoes, grains, nursery stock and the bark of apple, avocado, citrus, cherry and olive trees.
Microtus are often found where there is grass cover. They generally do not invade cultivated crops until the crop is tall enough to provide food and shelter. Meadow mice are active all year round. They forage at any time during the day or night but are chiefly nocturnal. They are usually found in colonies marked by numerous 2-- inch wide surface runways though matted grass. Small brownish fecal pellets and short pieces of grass stems along the runways are evidence of activity. The burrows consist of extensive underground tunnels, nest chambers and storage chambers. Home range is typically small, less than a 60 foot radius in the case of “M.californicus”. All meadow mice swim well. Therefore, irrigation ditches will not serve as effective barriers against meadow mice movement into fields. Meadow mice may forage beyond the sheltered runways. Food consists of tubers, roots, seeds, grain, and succulent stems and leaves.
Females breed at 4 to 6 weeks of age with litter size of “M.californicus” averaging around 4. Under natural conditions a female Microtus may produce from 5 to 10 litters a year. The major breeding season corresponds with the season of forage growth. Microtus populations build up to a peak every 3 to 4 years, followed by a rapid decline during the next breeding season. The exact causes of the cycle of buildup and decline are not known, though disease, food shortages, physiological stress from overcrowding, and other factors may be involved. It is assumed that in cultivated areas Microtus populations are permanently based in favorable habitat such as roadsides, canal banks or adjacent noncultivated land. Invasion of cultivated cropland occurs when the population builds up or when the wild habitat becomes unfavorable. Coyotes, badgers, weasels, snakes, hawks, owls, herons and gulls are among the principal predators. It is believed that predators are not able to prevent or control a population eruption because of the birth rate of the fast breeding Microtus population. Meadow mice are classified as nongame mammals by the California Fish and Game Code. Nongame mammals, which are found to be injuring growing crops may be taken at any time or in any manner by the owner/management. The most effective management options in an orchard situation are a reduction in ground cover and the use of toxic baits. Meadow mice are cover dependent. In situations where cover removal is not possible or is insufficient to solve the problem, the next best option is the use of toxic baits. Many bait carriers are used (e.g., oat groats, wheat bait). Baits: Crimped oat groats are the most satisfactory bait although crimped whole oats are used (e.g., oat groats, wheat grains, pelletized formulations, etc., but crimped oat groats have typically been most effective). The primary toxicants used for meadow mouse control include zinc phosphide, diphacinone, and chlorophacinone. Directions for management including baiting can be obtained by contacting the Agricultural Commissioner's Office. * Portions taken from J.P.Clark Vertebrate Pest Control
- Author: Ben Faber
Most growers know the N-P-K numbers on fertilizer, but that doesn't tell you what else might be in the material, either as a contaminant or something purposely added to the material. CA Department of Food and Agriculture has a website that according to manufacturer and material there is a full listing of what is in the product. The website is: http://apps4.cdfa.ca.gov/fertilizerproducts/
What's startling is the shear number of producers on the market
- Author: Gary Bender
After a 30-year career as the farm advisor of subtropical fruit crops in San Diego County, I've decided to retire to do some other things, including some fishing. According to my wife, that seems to mean some painting, re-tiling the floor, re-landscaping and cabinet work. I'm not sure we are speaking the same language!
First, I'd like to thank all of the really great growers in this county. When I first started I knew a lot about dry root rot of citrus (since that was my research topic in college) and quite a bit about avocado root rot. And I had a pretty good background in diseases and other problems that bother plants. But not much else! I learned a lot about irrigation, frost protection, gopher control etc. from growers and the extension specialists. I even learned how to turn on wind machines and light orchard heaters at 3:00 am from grower John Hankey in Pauma Valley.
Prior to being a farm advisor, I spent four years in grad school at UC Riverside under Dr. John Menge. And he was a great mentor. He understood how important field research was for growers to be successful and he encouraged me to go into extension work.
Prior to getting my Ph.D. in plant pathology I worked one year for the Riverside County Ag Dept, four years for the Orange County Ag Dept as a plant pathology technician and 3 years as a staff research associate at UC Riverside in Entomology, Nematology and Plant Pathology. Oddly enough, it was the Riverside County job that changed the course of my career. I was a floating “problem solver” that basically diagnosed diseases and other problems for growers and homeowners and I got to drive to the calls in a really fast car turned in by the retired sheriff. And I did such a good job I got a “promotion” to being in charge of all the fruit fly trapping from Indio out to Blythe. And this happened in the summer! That's when I decided it might be in my best interest to go back to grad school under Dr. Menge and work on the cause of a citrus trunk disease.
I have worked on a lot of projects over the years with the professors, specialists and other farm advisors. Just a few highlights from over the years:
Dr. Mary Lu Arpaia and I started an avocado rootstock trial in 1986 that evaluated the yield of some of our new rootstocks in “clean” soil (without Phytophthora cinnamomi root rot). It turned out to be a very important trial because it showed that the G755 series (our most resistant rootstock to root rot) was actually very poor at producing fruit when it was grafted to Hass. From there Dr. Arpaia and I and the other farm advisors all worked on irrigation trials and fertilizer trials in order to establish some basic information on the water and NPK requirements for Hass avocados.
I conducted a reclaimed water trial with the City of Escondido from 1991 to 1996 and the results showed that, because of the high salt content in their reclaimed water, yields were reduced by 40% compared to district water. But that set the stage for a current trial by Dr. David Crowley with the City of Escondido in which reverse osmosis will be used to separate the brine out and have it go out to the ocean in their outfall. The less saline reclaimed water will then be piped to the backside of Escondido to be used for agriculture. I think, with our high water prices that may be the future in our county.
Ben Faber and I conducted avocado pruning trials in the late 90's and early 2000's, which showed mixed results, but taught us some lessons. Pruning should be done early in the year, and not in the summer because that's when fruiting wood is forming for the following spring. These results will be described again in a future article.
At the same time, Ramiro Lobo and I started blueberry variety trials and eventually irrigation trials. This work, along with work by advisors Faber and Mark Gaskell, set the stage for a new crop in California: low chill early season blueberries. Unfortunately, this is definitely not a low water-using crop. In fact, in a Valley Center trial, we got our best yields when we irrigated with 40% more water than avocados (on an acre basis).
For the last five years I have worked on IPM techniques to control the Diaprepes citrus root weevil along coastal San Diego and Orange counties (in conjunction with Jim Bethke, Joe Morse and Loretta Bates). We used a special landscape cloth under the lemon trees to block the adults from emerging from the soil and it also blocked the young weevils that had just hatched on the leaves from entering the soil. Blocking the entrance and exit turned out to be a great IPM technique for controlling this pest. We also imported parasites from Florida and released them, and the parasites established. These releases have apparently slowed down the spread of this invasive pest because we do not see that they are spreading away from the original quarantine zone. Without the parasites, I doubt that our citrus along the coast would be surviving today, based on all of the sick and dying lemon trees we saw at the beginning of this project.
Currently I have a project with the California Avocado Commission which is taking a look at two pruning styles for a high density planting of Hass and Lamb Hass. Connected to this project are classes for new avocado growers. I will continue this project at least for the next three years as an emeritus farm advisor. Why? Because I think high density has the potential to increase yield per acre substantially, and it's just so darn interesting!
Now, I'm going to do some fishing, and a little house painting.
- Author: Ben Faber
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- Author: Gary Bender
- Author: Dave Shaw
By now almost everyone growing tree crops in California is undergoing some amount of mandatory water cutbacks, especially if they are buying water from water districts. Some districts in the San Joaquin Valley have had really severe cuts, up to 80%. For a lot of growers who are not buying water, they may be facing severe water shortages due to water tables that are dropping.
San DiegoCounty is a good example. In 2008 all of the avocado and citrus growers in San Diego
County had a mandatory 30% water cutback, if they
were in the water discount program known as the Interruptible Ag Water Program. Fearing that the cuts would be even higher in 2009 if they stayed in the program, most growers opted out, but were then faced with paying full price for their water. Now, it looks like most of these growers will be faced with a mandatory cut of about 8% (this depends on the water district), and will have to pay full price for ag water. But wait! Because the districts aren't selling as much water, they need to raise prices to cover their fixed costs. For instance, Fallbrook
Public Utility District recently announced they were raising prices 13%. Many districts in San DiegoCounty have simply followed water wholesalers (MWD and SDCWA) in their price increases.
Please make sure that you are in touch with your local water district. They may have a different cutback rate than the 8% mentioned as well as conservation guidelines and regulations. You are responsible for knowing this information and you could be looking at some hefty fines for using more water than allowed.
So what can you as a grower do when faced with this scenario? Before we start with our recommendations, let's start by thinking about what you can't do. (This always confuses the issue, so let's get this off the table).
- You can't make it rain more. We are in a prolonged drought, this happens periodically in California, and that's just the way it is. Can you lobby for more storage for when it does rain in excess? Yes!
2. You can't solve the Delta smelt issue, not unless Congress cancels the Endangered Species Act. A solution for bypassing the Delta with a pipeline from the Sacramento River down to the State Water Project canal which supplies Southern California would certainly help. Researchers at UC Davis have determined that the canal would be the most economically feasible way to fix the delta issues. However, given California's budget woes, it probably won't happen soon.
- There are no magical solutions that work to “inactivate” the salts in your well water. There are a lot of devices sold that make lots of claims, but there is no University research evidence that shows that any of them work. The only thing that does work is reverse osmosis, but be careful because these systems produce brine which must be disposed of legally. The brine cannot go into the local creek.
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 JoaquinValley, 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.
- 4. 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.