- 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: 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.
- Author: Ben Faber
Citrus is a messy botany. It loves to cross with anything and in so doing creates very complex ancestry. C-35 rootstock is a citrange and was created for its tolerance to cold, but is also good in Phytophthora situations and creates a slightly smaller tree. Oddly, it is deciduous, a cross between Poncirus and Citrus. It's a trifoliate hybrid. 'Meyer' lemon is the same mess, a cross between a lemon and an orange/mandarin. You would think these two messed up cousins might do well, but in several instances there is an incompatibility. 'Meyer' has been grown successfully on 'Macrophylla' and 'Yuma Ponderosa', both of which are also complex hybrids.
- Author: Neil O'Connel
Installing tree wraps on young trees provides protection to the trunk from applications of herbicides during weed management operations. Additionally, the wraps minimize light interception by trunk tissue thereby reducing sucker growth. During hot weather tree wraps provide shade to the trunk and reduce the incidence of sunburn. With the increasing incidence of earwigs, damage to young trees and the tendency for the insect to congregate under the wraps, tree wraps are being removed in some cases. Recent laboratory data from Dr. Beth Grafton-Cardwell (confirmed by observations in the field) suggests that as the season progresses adults become less and less interested in feeding on leaves (peak of feeding in March and April, declines to next to nothing by June). So, a management consideration would be to check the earwigs in the wraps in the summer, and if there are only adults present there is less concern than if there are immatures present. Another point would be to consider treatment with an insecticide such as Lorsban if wraps are to be left on for sunburn protection.
If wraps are removed a uniform coating of sun protective material should be applied to the trunk to protect against sun damage. Trunk surfaces should be monitored to ensure that a uniform coating is in place. Sun damage to unprotected trunk tissue can result in partial or complete girdling of the tree.
- Author: Ben Faber
Jane Delahoyde, a PCA here in Ventura, recently found an unusual scale in lemon here. It is barnacle scale with a typically long Latin name - Ceroplastes cirripediformis. It is unlikely to be any worse than other scales, but it's something to keep our eyes on. This is one of the soft scales, often called wax scales because of the wax they produce. It turns out that this has been described as being in Southern California for years, but some years they are just more present. For more on "Wax" scales see the Texas A&M site
or our UC IPM website