The date palm (Phoenix dactylifera L.) made its way to California through the Spanish missions in the late seventeenth century. In its native ranges of North Africa and the Middle East, the date provided food, fiber and shelter. As commercial date production established in the interior valleys of California and Arizona, growers sought out new varieties. Introductions of varieties from Algeria, Tunisia, Egypt and Iraq between 1890 and 1922, laid the foundations of the modern California date industry. W.T. Swingle brought offshoots of ‘Deglet Noor’ to California in 1900. Recognized as a superior variety for three hundred years in the oases of Algeria and other North African countries, ‘Deglet Noor’ is now one of the most significant cultivars in California and worldwide. In 1927, Swingle also introduced the ‘Medjool’ date to California. ‘Medjool’, probably originated in the Tafilat district of Morocco, takes its place beside ‘Deglet Noor’ as one of our most important date varieties.

From its beginnings as few thousand imported offshoots, the California date industry has grown to annual harvests totaling $23-30 million dollars, according to 2001 USDA statistics. The approximately 5,600 acres of date palms in California account for more than 95% of the U.S. industry, supplying dates for consumption and mature trees for the expanding landscape market. The varieties ‘Deglet Noor’ and ‘Medjool’, amongst a few others, remain the mainstay of this strong niche landscape industry. While there have been no important cultivars introduced into the U.S. in recent years, there are over three thousand different cultivars grown worldwide. Examining these cultivars and making comparisons with those cultivars grown in California, will allow researchers to make new introductions best suited for our industry.

The long history of cultivation has obscured the origins of the date palm, thought to be a native of western India or possibly southern Iraq. Identifying cultivars can be difficult, as this is done primarily through morphological characteristics such as the fruit, leaf bases or spines. Environmental factors such as soil or weather can influence these characteristics, which are generally only observable on mature trees of at least 3-5 years of age. The names associated with date cultivars also create some confusion. In some parts of the world, a date known by one name at an oasis might be called something completely different a few hundred miles away. To add to the confusion, dates also exhibit intra-varietal variations. These variations, such as differences in fruit size, ripening time or vegetative characteristics, were first reported in the early 1920’s. Researchers originally thought the differences between palms of one variety were due to the chance that the plant had come from a seedling instead of an offshoot thus having different varietal characteristics because it was a hybrid and not a clone from the parent plant. Those plants were grown and marketed under the name of the parent cultivar. Modern researchers, using amplified fragment length polymorphism (AFLP) markers, a polymerase chain reaction (PCR) based molecular markers, can now evaluate genetic diversity and fingerprinting of the date cultivars. In a recent study at UC Riverside, we examined 23 samples of ‘Medjool’ and 33 samples of ‘Deglet Noor’ date using AFLP markers (The Journal of Horticultural Science and Biotechnology, 2003, 78(5): 405-409). The samples for this study were collected from the USDA National Clonal Germplasm Repository for Citrus and Dates at the UC Coachella Valley Research Station, Thermal, CA and from commercial date gardens in the Coachella Valley. Our results showed that there is almost no genetic difference amongst the 33 ‘Deglet Noor’ date samples; however we identified a wide range in genetic variation within the ‘Medjool’ samples. Among 23 ‘Medjool’ date samples tested, 3 had the same genetic profiles. In total, we identified 20 different types of ‘Medjool’ dates. How can we explain such large difference found in ‘Medjool’ dates in California? The differences could have originated when horticulturists originally introduced ‘Medjool’ into California in the early 1900s. The plants could have been mistakenly identified, mislabeled, or mistakenly propagated from seedlings instead of clonal offshoots. Another possible explanation for the genetic variation could be that ‘Medjool’ palms have a high rate of mutation. The differences we found in ‘Medjool’, however, are too large to be explained by a high mutation rate, we believe another explanation is more likely. We propose that the ‘Medjool’ date that was introduced into California originated from a “landrace” variety in the Tafilalt district of Morocco, where ‘Medjool’ was initially selected. A “landrace” variety means that the variety is endemic to an area (in the case of ‘Medjool’ in the Tafilalt district of Morocco), it is a mixture of different genotypes and well adapted to the local environment. It is possible that the initial introductions of ‘Medjool’ were in reality different genotypes of ‘Medjool’ and these different genotypes exist in current plantings. On the contrary, all 33 ‘Deglet Noor’ dates that we tested are almost the same genetically. ‘Deglet Noor’ seems to exist as a pure variety without much variation.

Growers in California have observed differences in fruit quality and yield of ‘Medjool’ date in the past, but the variation always have been attributed to xenia effect, location, environmental, or management practices. Our results imply that the differences in production between ‘Medjool’ date palms may be due to genetic differences and not just cultural differences. Field testing is needed to determine if the differences in fruit quality and yield between plants is related to genetic differences between plants. For this, we need to plant a trial where we are able to evaluate genetically different strains of ‘Medjool’ palms grown under the same environmental conditions. Potentially, some strains of ‘Medjool’ may have higher yield and better fruit quality than other selections; these can be selected for propagation thereby having the potential to increase grower’s returns.

In the future, we would like to examine 30-50 different ‘Medjool’ samples collected from Morocco using the AFLP markers to confirm or dispute the possibility that ‘Medjool’ date exists as a landrace variety in Morocco. We also are collecting samples of offshoots from the same ‘Medjool’ palm to determine if high mutation rate exists in ‘Medjool’ dates. By learning more about the varieties grown in California and abroad, we hope to select varieties that would increase the vitality of the date industry in California.

 

This is the story of a remarkable avocado rootstock trial that was set up in 2004, lost to the freeze of January 2007, recovered (mostly) and had its first harvest in spring of 2010. But the real story is how some of the rootstocks bore at a really high rate with water that was so saline that almost killed most of our California rootstocks.

As part of Crowley and Arpaia's salinity rootstock trial, in cooperation with farm advisors and several growers, and funded by the California Avocado Commission, this particular trial was planted in 2004 at the Nick Stehly Ranch in Valley Center. The trial had 10 different rootstocks all grafted with Hass scions. Twenty trees of each rootstock were planted in a randomized and replicated block design: the rootstocks were Duke 7, Spencer, Parida, VC 44, VC 207,VC 801, VC 218, PP14 (Uzi), PP 16 (Rio Frio) and PP24 (Steddom). The VC series are rootstocks selected in Israel for tolerance to salinity, and the PP series are rootstocks selected for root rot tolerance by Dr. John Menge at the Plant Pathology Dept., U.C. Riverside. At the time of planting it was not known how the PP trees would react to salinity.

In Spring 2005 we planted six Hass/Dusa trees into vacant spots in the trial. These trees were left over from a Bender irrigation trial on another part of the ranch.

The trees were grown with highly saline irrigation water with an average EC of 2.5 and chloride levels of approximately 300 ppm. Needless to say, most of these trees suffered greatly with severe tip-burn and some of the trees almost died. But some looked better than others and we were waiting for the first harvest. In Spring 2006 some the trees set fruit and we expected the first harvest to be in 2007. But then disaster struck!

In January 2007 we had a serious freeze in San Diego County. Nick Stehly called us to let us know that he recorded a temperature of 18° F in our plot. All of the trees looked like they had died and we gave up on this plot and went on to other trials.

But the irrigators didn't give up! They kept pruning the dead wood out of the trees that did not die and gradually brought most of the trees back to life. But the trees were still being irrigated with the saline water, except for one important difference.

The Stehly family liked to swim in the reservoir about three times during each summer. So they would fill the small reservoir at the end of the ranch that supplied our trial, with Metropolitan Water District water with an EC of 0.7 – 0.9. After swimming they used this water for an irrigation of the trial. Amazingly, this “leaching” irrigation was apparently enough to keep the trees growing without too much tip-burn, and the irrigator reported to Nick in January, 2010 that we had enough fruit for a harvest.

The first harvest was completed in March,2010. The data for mean pounds of fruit per tree is presented in Figure 1. The number of surviving trees after the freeze of 2007 is presented in Table 1.

 

 

 

The mean wt of Hass avocados for the VC 801 rootstock was 92.2 lbs, and the mean wt for the Dusa rootstock was 139 lb. If this is compared to the San Diego County average yield of 7000 lbs per acre (about 70 lbs per tree), it would indicate that we might be making progress in finding some better rootstocks for use with some of our saline irrigation waters. However, as we all know, you can't base any conclusions on one year of yield data. We need to have at least three years of yield data to even begin to make a conclusion.

Our hats off to the irrigators at the Stehly Ranch, and to the Stehly family for their cooperation (and their reservoir/swimming pool). You never know what might show up in some of these older rootstock trials.

 

Recently a six-year old W. Murcott orchard was evaluated for causes of tree  decline. A high percentage of the trees exhibited damage to the bark of the tree generally from the soil line up 6-8 inches. (Fig.2) In some instances the tree had been almost totally girdled. On close inspection of the trunk, an open hole 4-5 inches in diameter was found at the base of the tree. (Fig.3)

Meadow Mice (Voles) can produce serious damage in a citrus orchard resulting in partial or complete girdling of trees.(Fig.1). 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 piles of brownish feces 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 liter 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. If cover is the management of choice - typically weed or grass, the cover can be removed from around the base of a tree, this often solves meadow mice problems. 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 is 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

Agricultural spray adjuvants are materials added to the spray tank when loading the sprayer. They include products classified as activator adjuvants and marketed as wetters/spreaders, stickers, humectants, and/or penetrators. Activator adjuvants are marketed to improve the performance of pesticides and foliar fertilizers.

Activator adjuvants can have a place in tree (and vine) crop sprays, but matching the material to the job can be tricky. A bad match can lead to minor or major losses to the grower. Minor losses can result from excess spreading and pesticide runoff from the target plant. Phytotoxicity can cause major damage.

This article describes ingredients and functions of activator adjuvants commonly sprayed on tree and vine crops. Suggestions regarding activator adjuvant selection are offered. Growers must make their own activator adjuvant use decisions based on experience, particular needs, and risk tolerance.

Do I need to add an activator adjuvant?

Read and follow the specific instructions on the label. If the pesticide or foliar fertilizer label indicates the product should be used with certain types or brand of adjuvant(s), that’s what you need to use.

Do I want to add an activator adjuvant?

If the label includes phrases such as "use of an adjuvant may improve results" or “complete coverage is needed for best results” then you may want to look into selecting and using an appropriate activator adjuvant. Before proceeding with use of an activator adjuvant, first look at your existing spray program. Are you already doing the best spray job you can? Good spray coverage begins with proper sprayer calibration and set up. Is your sprayer calibration dialed in for different stages of canopy development?

Optimum sprayer set up – gallons of spray per acre, ground speed, fan output, and nozzle selection/arrangement-- changes from dormant to bloom to early growing season to preharvest sprays. Adjusting your sprayer to best match orchard and vineyard conditions at each general stage in canopy development is the foundation of an effective, efficient spray program. An activator adjuvant will not make up forexcessive tractor speed, poor nozzle arrangement and/or worn nozzles. Your money is best spent first dialing in your sprayer(s) for the whole season, before considering an extra material in the tank (that is not required on the label). If you have your sprayer(s) dialed in for each orchard and stage of growth, now is the time to say “OK, I want to think about a little extra boost to my spray job”.

Which activator adjuvant properties do I want?

First, know the properties of the pesticide you will use. Does it work on the plant surface or inside the plant? This is a key point in selecting adjuvants. Here is a quick review of the main classifications and characteristics of activator adjuvants as they currently appear in the field. Note: Certain products can provide more than one adjuvant property – that can be beneficial in the field. For example, non-ionic surfactants can work as surfactants and penetrators, depending on use rate.

Wetters/spreaders: These materials contain surfactants that decrease the contact angle and increase the spreading of the spray droplet on the target. High rates of wetters/spreaders may also increase penetration of pesticide into the target tissue (leaves or fruit), potentially causing phytotoxicity. Excessive spreading of pesticide spray solution and runoff from the target may result when using a new or higher rate of spreader -- especially when using silicon “super-spreaders”. Test new combinations of spreader material(s) and spray volume before regular use. Spray volume per acre or adjuvant use rate will probably have to be reduced if a labeled rate of adjuvant provides excessive spreading.

To check for excessive spreading, place alength of black plastic sheeting under several trees or vines in a row. Secure the plastic with spikes, wire staples, and/or weights. Spray the new adjuvant and pesticide combination using your current sprayer set up. Reenter the field right after spraying, wearing appropriate PPE, and evaluate coverage. If material is pooling at the lower portion of leaves and/or fruit, excessive spreading is occurring. Check to see if pooling is occurring only in a certain area(s) of the canopy or throughout the canopy. If more spray solution is landing on the black plastic tarp under the trees/vines than between them, then runoff is occurring. [Some ground deposit should be expected from standard airblast sprayer use.]

Compare the results of your adjuvant test with a similar application of your current pesticide/adjuvant combination on another portion of the row. If there is no pooling or runoff with the new adjuvant in the tank, you can use the adjuvant with confidence. A lack of pooling or run off with the new adjuvant also might mean that your old sprayer setup and tank mix didn’t deliver adequate coverage. If the test with the new adjuvant showed pooling on leaves and/or runoff on the ground, you have several choices.

1. You can reduce spray volume per acre by replacing some or all nozzles with smaller nozzle sizes on the sprayer in an effort to reduce overspreading. If you saw overspreading on some portions of the canopy, but not others, reduce nozzle size only on the part of the spray boom that targets the over-sprayed part of the canopy. Recheck spray coverage if nozzling changes were made.
   
   
2. Reduce the adjuvant rate and recheck coverage/spreading.
   
   
3. You can just go back to your established program without the new adjuvant. What’s the “best” course of action? That depends on your farming operation.Reducing spray volume per acre means more ground covered per full spray tank – a potential time and cost savings. If spraying is done during the heat of the day in hot, dry climate, spray water evaporation is a major issue and it may be best to keep the higher spray volume and reduce the spreader rate or eliminate it entirely. Checking coverage and overspreading allows you to make the best decision possible; avoid damage and, hopefully, save money. All farming operations are different. Make the choice that best fits your farm.

Stickers: These adjuvants can increase the retention time of the pesticide on the leaf and reduce rain wash off. They may limit movement of systemic pesticides into the plant, and are probably most beneficial when used with protectant materials (cover sprays). Do you overhead irrigate? Is there rain on the horizon? If you answer yes to either one of these questions, you may benefit from using a sticker.

Humectants: Under low humidity conditions humectants can help reduce spray droplet evaporation before and after deposition on the plant. This is especially valuable when small droplets and/or materials that must be absorbed into the plant (systemic pesticides, PGRs, nutrients, etc.) are used in the summer under high temperature and low relative humidity conditions.

Penetrators: Frequently used with herbicides, these products include oils (petroleum, vegetable, or modified vegetable oils) and non-ionic surfactants used at higher rates. In crop sprays, penetrators can be used to increase absorption of systemic pesticides (for example, oil with Agri-Mek) as well as translaminar materials. Penetrator adjuvants should be used with caution oravoided entirely with surface active pesticides such as cover sprays or else phyto may result. Finally, some penetrators can increase the rain-fastness of some pesticides.

Which adjuvant material should I select?

Use a product intended for crop spraying. Many activator adjuvants were developed and intended for use with herbicides. Products that are advertised for use with plant growth regulators should have a higher chance of crop safety compared with those that don't. This is still no guarantee of a phyto-free application. Ask for help from your PCA or the adjuvant manufacturer’s sales rep. How much do they know about the particular activator adjuvant in the spray mix you are planning? Can they show you the kind of information on a single product similar to what you can find at: http://www.ast-us.com? (This website is intended as an example, not an endorsement of the web pages it contains including specific adjuvants.)

Will the adjuvant I selected work in the spray I’m planning?

If you choose to use an adjuvant that is not specifically listed on the pesticide or foliar fertilizer label, jar test the planned spray solution first. Use the same spray water source. Include all leaf feeds, other adjuvants, and pesticide(s) that you plan to put in the spray tank. Do this before tank mixing these materials. A lot of time and money rides on effective pesticide application. Do your homework before the spray tank is filled and you will be well on your way to solid results.