Irrigation Scheduling Part 1 - Calculating Orchard Water Use

Scheduling of irrigation must take into account the variables of weather, water availability, and plant stress. All of these variables change throughout the irrigation cycle, providing difficulty in determining irrigation timing and amounts of water applied.

Today, lets start with a brief discussion on how to calculate irrigation needs based upon the weather. This weather driven demand for water by the almond tree is called evapotranspiration (ET). ET accounts for the loss of water through surface evaporation as well as the loss of water through the opening and closing of the stomates. We can calculate ET by knowing two things: the demand for water on a reference crop (ETo), and the crop coeficient (Kc) The Kc transforms the reference crop water use (ETo) into almond tree water use (ETc). The reference crop of use throughout California is grass pasture. Therefore, the multiplication of the reference crop water use and the almond crop coefficient will give us water use by an almond tree - or ETc = ETo x Kc.

When we access CIMIS to view weather conditions and water use, the values are always presented for reference crop. Remember to transform these to represent almond water use.

Since almonds change in canopy coverage throughout the year, the corresponding Kc will also change. Below is a list of crop coefficients as provided by the UN FAO* for almond orchards experiencing light to moderate winds with and without cover crops:

Almond Orchard Kc by Month	Dec/ Jan	Feb	Mar	Apr	May	June/ July/ Aug	Sept	Oct	Nov
With cover Crop	0.85	0.85	0.85	0.95	1.05	1.15	1.10	0.90	0.85
Without Cover Crop	0	0	0.50	0.70	0.85	0.90	0.80	0.75	0.65

Remember that these coefficients are based upon research and further research may refine the values listed above. There is currently ongoign research within California to review these numbers.

So, now that we have our water use by our reference crop and the crop coefficient almond, lets look at a sample calculation of water use by a mature almond orchard. We will use the month of May and a Merced County orchard with a cover crop as an example:

Week	ETo for the week (Grass water use) provided by CIMIS	Kc	ETc for the week (Almond Water Use)	Cumulative Total of water use by the Almond Orchard w/ cover crop
May 1st- 7th	1.65	1.05	1.74
8th - 14th	1.20	1.05	1.26
15th- 21st	1.39	1.05	1.46
22nd-28th	1.19	1.05	1.25
29th- 31st	0.72	1.05	0.76	6.47

As we can see above, a mature almond ochard grown under the described conditions used nearly 6.5 inches of water in May of 2010.

Young orchards, less than 7th leaf, will use a slightly lower crop coefficient depending on their size. Canopy coverage of the orchard should be estimated at mid-day by guessing the area of the orchard floor that is shaded by the tree. This percentage should then be doubled and then multiplied by the corresponding crop coefficient. For example, a 3rd leaf orchard covering 40% of the orchard floor will use 80% of the water that a mature orchard would use. Once the canopy shades 50% of the orchard floor, we assume that it will need full ETc.

Next week, we will discuss irrigation timing and soil water holding capacity differences.

*Dorenbos, J. and W.O. Pruitt, 1984:

Crop Water Requirements - Guidelines for Predicting Crop Water Requirements. - FAO Irrigation and Drainage Paper 24, FAO, Rome. ISBN 92-5-100279-7

April/May/June Almond Nut Development - Rationale for Proper Irrigation and Fertilization

The cool spring has brought up a few questions about almond development that I will do my best to answer today.

Does the cool weather slow nut development?

Yes, it does. By reducing the heating units, almond development is delayed. Similar to peaches, the cooler the weather, the longer it takes to complete the fruit sizing and kernal formation. This usually means that later season events will be delayed - such as hullsplit and harvest.

How can we determine if nut development is complete? 

By pulling almonds off of tree and taking cross-sections, it is easy to observe the development of the embryo. As seen in figure 1, the embryo will grow from the tip and eventually fill the entire shell. Preceding embryo development is the endosperm and nucellus which makes up the "jelly" of the almond. The endosperm tends to be a bit more cloudier than the nucellus and proceeds embryo development. Once the embryo is completely developed (i.e. the kernal has filled the shell), weight accumulation will begin in the kernal. This generally tends to happen around early June and continue to hullsplit.

Figure 1: Cross section of a developing almond. Courtesy of the UC IPM Almond Manual.

Why is knowing when the completion of nut development important?

Most of our UC recommended practices regarding irrigation and fertilization are based around nut development. If you are running short on water due to a curtailment, you might have heard that water can be cut back in Mid-June to help stretch your budget. This point in mid-June refers to when the embryo is completely developed and the dry weight accumulation is nearly done. Cutting water sooner than this will lead to reduction of crop weight, shrivels, and in some cases, nut abortion. In a cooler year, this point may be delayed - so if you are planning on deficit irrigating this summer, make sure your kernal development is complete.

This same principle is also the basis of most fertilizer timing recommendations. Fertilizer should be applied when the tree is growing and kernal is developing, but should cease or be reduced once kernal development is completed. Typically, the last recommended  nitrogen application is the first week of June. Nitrogen applied after the kernal is developed will be directed into the hull, not benefiting our harvest yields, and increasing our chance for hull rot. It is important to note that once the nuts are shaken from the tree, nitrogen should be applied to help with shoot and bud formation.

Is nut abortion increased during a cool spring?

Can be. Since the time period to nut maturity is extended, any stress during the various stages of development can lead to nut abortion/crop loss. If the trees are exposed to water stress, excess water, nutrient deficiency, or extremes in temperatures, then nut abortion rates may be higher. 

Peach Twig Borer and May Spray Timing

Peach Twig Borer (Anarsia lineatella) (PTB) is a long time pest of almonds, being first reported in California in the 1880s. It was considered to be the worst pest of almonds until the arrival of the Navel Orange Worm in the 1940s. Today, it still remains an important pest because of its direct damage to the nuts, damage and feeding on green and new shoots - killing terminal growth, and the preference of PTB damaged nuts by navel orange worm.

PTB can be found overwintering as a worm (larva) in a tiny cell (hibernaculum) within the crotches of one to three year old wood. They may also survive in pruning wounds and bark cracks. Larvae emerge around bloom and migrate up the twigs and branches where they tunnel inside the branch, killing the terminal shoot. This loss of terminal shoots and subsequent delay in growth can be very problematic for young orchards.

Figure 1: Damage to terminal branches caused by Peach twig borer.

PTB adults begin to emerge around late March/ early April. Adults are gray in color and are about a 1/4 to a 1/2 inch in length. The adults lay eggs on twigs during May and June which give rise to the second flight of moths in Late June/Early July. Second generation moths then repeat the cycle, causing damage and laying another generation of eggs.

Figure 2: Peach twig borer larva causing damage inside an almond fruit/hull.

Nuts become more susceptible to damage as they near harvest. Feeding on green nuts by PTB makes them more attractive to NOW. Branch damage, although problematic on young trees, is not considered an issue on mature trees. Cultivars differ in their susceptibility to nut damage, Merced and Thompson are the most susceptible, followed by Nonpareil, Fritz, Price, and Ne Plus Ultra.

PTB has three different management options throughout the growing season. Dormant season applications can be made to kill the larvae overwintering in the hibernaculum, bloom time sprays can be made to kill the larva with insecticides that do not target bees, and May spray timing can be made to kill adult moths and their first generation of larvae and eggs. Hull split timing is not recommended due to the difficulty of timing.

Figure 3: The adult peach twig borer moth.

Since we previously discussed different treatment options for the dormant and bloom period in a previous article, lets focus briefly on options for the "May Spray" timing. The May spray should be made 400-500 degree days after the first few moths are caught (biofix). To trap the first moths, pheromone traps should be placed in the orchard by the last week of March in order to catch the first emerging adults. Once the first few moths are caught, degree day accumulation begins. To make calculating degree days easier, the UC IPM website has developed a day degree calculator based upon a CIMIS weather station in proximity to your farm.

Figure 4: Damage to almond kernals by the peach twig borer.

Timing for the "May Spray" PTB usually occurs in early to mid May - hence "May Spray." This year, biofixes were later than normal, due to the cool weather and its effect on insect development. This week, many orchards are approaching 500 DD. Applications of either Spinetoram (Delegate), Chlorantraniliprole (Altacor), Flubendiamide (Belt), Methoxyfenozide (Intrepid), Spinosad (Entrust, Success), Phosmet (Imidan), Esfenvalerate (Asana XL), and Bacillus thuringiensis (BT) can be made to target moths, larvae, and eggs. Broad spectrums such as phosmet and esfenvalerate will kill non-targetted pests possibly causing flare ups and/or have drift, water, and environmental concerns. Bt provides an organic option for PTB control. Please see UC IPM for more information and rates.

Mating disruption has been shown to work, but have not provided reliable control when used alone. Future development of technologies will hopefully improve the efficacy of mating disruption. Bio-control does help reduce the population, but treatments are usually still needed in most orchards.

Figure 5: The California gray ant, Formica aerata, is one of the most effective predators of peach twig borer in the Central Valley. As apparent above, it feeds on larvae found within the tree.

So, now a question comes to mind: If there are three treatment options, which one is best? The answer depends on your familiarity of your orchard and products, timing of other sprays, and the need to control other insect pests. The dormant timing should be considered if another spray application is planned to be made (i.e. scale treatment). Applying a tank mix of fungicides and PTB specific insecticides can be made at bloom - and has been shown to be very effective. Spring spray timing often overlaps with NOW, providing great control for PTB and okay control for NOW. So, timing really depends on the problems that are specific to your orchard and your management strategies for the crop year.

Almond N - P - K Crop Use and Variety Differences

Each year when the almonds are harvested, a significant amount of nutrients are removed from the orchard. Research by Dr.Patrick Brown  (UC Davis) and colleagues has shown that approximately 58 pounds of nitrogen, 7 pounds of phosphorous, and 51 pounds of potassium are removed for every 1000 pounds of kernals harvested. Nutrients must be either supplied by the parent soil material (as the case with phosphorous and potassium) or re-applied back to the orchard through fertilization. Furthermore, the amount of nutrients removed per pound of kernals is relatively the same for each variety; thus varieties can be fertilized to match the respective yields in order to increase nitrogen use efficiency. Young trees (less than 8 years) may need more fertilizer to maintain crop production AND vigorous growth.

For example, lets say a 12th leaf 50%-25%-25% Nonpareil, Monterey, and Sonora orchard yields 3200, 3000, and 2500 lbs/acre, respectively giving an average of 2975 kernal pounds per planted orchard acre. Within this 50%-25%-25% planting, total N-P-K usage by Nonpareil is 93, 11, 82 lbs/planted orchard acre, respectively (50% of 185,22, and 163 lbs of N-P-K that would be utilized by a fully planted acre of Nonpareil); Monterey 44, 6, and 39 lbs of N-P-K/planted orchard acre, respectively (25% of what would be used by a fully planted acre); for the Sonora 34, 5, 32 lbs of N-P-K/acre, respectively (again, 25% of what would be used by a fully planted acre). As expected, a larger amount of nutrients are needed by the tree for the higher yielding varieties. (NOTE: Applying only the amount of each nutrient used by the tree will eventually lead to deficiency due to the inefficiency of nutrient applications. This is especially true with nitrogen, which can vary significantly in its application efficiency. This was covered in an earlier blog)

In many cases growers would apply fertilizers to match the average yield of all three varieties (2975 lbs/acre). In this scenario, the lower-than-average yielding varieties would receive the same rate of nutrients as the higher-than-average yielding variety. This would lead to an excess of nutrients being applied to the lowest yielding variety, while a deficient amount of nutrients would be applied to the higher yielding varieties. Another possibility is to fertilize to match the maximal variety yield. In this case, excess nutrients would be applied to the varieties yielding less than 3200 pounds/acre.

So, why should we and how can we apply the right amount of nutrients to each of the differing varieties?

By applying different rates of nutrients to varieties, nutrient use efficiency will increase, decreasing our nutrient use (and saving money) while also reducing environmental concerns.  One way is to establish the orchard with different irrigation manifolds/systems for each variety. By doing this we could fertigate the different amounts on to each of the varieties by adjusting the duration of  fertigation. Currently this would be time consuming, but hopefully future technologies will provide some tools to help manage this type of application. Another possibility - and a bit more practical - is to apply the nutrients through a variety of application techniques. By using fertigations, broadcast, and banded applications, varied rates can be made by making multiple passes and  extra applications. In this case, the nutrients used by the lowest yielder would be the "baseline." The baseline nutrient amount would be applied to all trees, while the varieties needing more nutrients would receive extra applications to meet their needs.

I will admit that this concept may be premature. Never-the-less, with the impending regulations that will regulate the amount of nutrients applied per acre, it will become necessary to increase our application efficiency. Applying to match varietal needs will become important in order to maintain crop yields and orchard sustainability.

May 5th IPM Update posted online

Trece has posted their May 5th, 2010 Field Reporter.

Biofixes of Note for Merced County:

Peach Twig Borer: April 15th, 201 DD;

Codling Moth: April 9th, 237DD;

Oriental Fruit Moth: April 14th, 616DD.

European Grapevine Moth Found in Fresno...an article from Western Farm Press explains.

2010 Subjective Almond Crop Estimate

As reported by USDA-NASS (National Ag Statistics Survey):


RESULTS
The initial forecast for the 2010 California almond production is 1.53 billion pounds. This is 8.5 percent above last year's revised production of 1.41 billion pounds. Estimated bearing acreage for 2010 is 740 thousand. This forecast is based on a telephone survey conducted April 23 - May 4 from a sample of almond growers. Of the 485 growers sampled, 317 reported. Acreage from these reports accounted for 28 percent of the total bearing acreage. Despite a variable spring, weather in 2010 had few negative effects on the developing almond crop. Bee activity was reported to have been hampered some by the rain, but overlap of varieties was excellent. Nut sets looked good. Acreages in the San Joaquin Valley that experienced frost damage in 2009 show heavy sets this season. High winds resulted in some nut and tree losses, but damage was not significant. Wet weather increased concerns about fungal infections and rot, but additional sprays have kept the problem in check. A benefit of the cool weather has been low insect pressure; overall, the trees are growing well and the crop is developing in good condition.

PROCEDURES
Results of the subjective survey are based on opinions obtained from growers. The sample of growers changes from year to year and is grouped by size of operation, so all growers will be represented. Each selected grower is asked to indicate their almond yield per acre from last year and expected yield for the current year.

ACKNOWLEDGMENTS
A special thanks goes to the many almond farm operators and owners who provided information on their operations. The support was outstanding and we appreciate the time they spent completing telephone interviews.

The full report can be found here.

Tree and Vine Consulting Link and Updates

Gary Gliddon, consultant, owner, and operator of Tree and Vine  Consulting, posts a weekly update at his website, found here.He gives weekly updates regarding IPM and water use for the Stanislaus/Merced/Madera areas. The updates are on the right-hand column under the title "Recent Posts."

USDA/NASS 2009 California Almond Acreage Report

For brevity, here are the survey results provided by the USDA/NASS:

"California’s 2009 almond acreage is estimated at 810,000 acres, up 2 percent from the 2008 acreage of 795,000. Of the total acreage for 2009, 720,000 acres were bearing and 90,000 acres were non-bearing. Preliminary bearing acreage for 2010 is estimated at 740,000 acres.

Nonpareil continued to be the leading variety, followed by Carmel and Butte. Monterey, Wood Colony and Aldrich varieties showed significant acreage increases. Kern, Merced, Stanislaus, and Fresno were the leading counties. These four counties had 64 percent of the total acreage, unchanged from the previous year."

Link for further results/information can be found here.

Guide to Help Identify Common Ants in the Almond Orchard

I hope this will help you identify some of the common ants in your orchard.
Almond Orchard Ant Identification

Managing Orchard Ants - time to scout for activity!

Pavement and Fire ants can cause significant damage to the almond crop. Feeding throughout the year on seeds of grasses and broadleaves, ants are only problematic once the almonds are shaken to the ground. Ants can completely hollow out the nut, leaving only the pellicle behind. Damage increases the longer the almonds are on the ground.

Within the San Joaquin Valley, the southern fire ant has a wider distribution and usually causes more damage than the pavement ant. Pavement ants are found in the northern San Joaquin Valley and into the Sacramento Valley. Within Merced County, we have both the Southern Fire Ant and the Pavement Ant. Recently, Merced County has had infestations of the Red Imported Fire Ant (RIFA), a third problematic ant for almond growers, requiring quarantine actions to control this invasive pest. Please see Guide to Identifying Orchard Ants to help identify ants.

Ants tend to be problematic on drip or sprinkler irrigated orchards. Within flood irrigated blocks, ants are limited to tree berms. Moist, cool temperatures increase above ground activity of ants; hot temperatures drive the ants deeper into the colony. Varieties with a tight shell seal are more resistant to ant damage, or with shell splits less than 0.03 inches wide. Shell seal can vary greatly year to year depending on crop load, nut size, and horticultural practices.

The orchard should be surveyed for ant colonies 2-3 days after an irrigation in the months of April – May in order to determine if a treatment is needed. Once the temperatures increase, problematic ant surface activity decreases, giving an inaccurate count of the population. In scouting for ants to determine if treatment is necessary, choose five survey areas per orchard, each about 1000 sq. ft., including the soil area from mid-alley to mid-alley beneath trees. Count the number of active colonies in each area, sampling five different areas of the orchard. Total all the ant colonies to get the number in a 5000 square foot area and compare it to the table below which gives an indication of the amount of damage you can expect at harvest. A survey sheet can be found here, and also can be found at the UC IPM website.

Several strategies can be employed to help control ant populations and prevent the corresponding damage. Letting the almonds dry longer on the tree and rapidly removing them from the field after harvest will prevent damage, but not always possible due to other harvest activities, nut moisture content, and navel orange worm pressure. In these cases, baits and conventional sprays can be used to help reduce the populations to a reasonable level. Baits are slow acting insect growth regulators; they need to be applied several weeks before harvest. They are selective for ants and highly effective, weakening or killing the entire colony. Baits should not be used within 24 hours after an irrigation or 48 hours before an irrigation. Baits absorb moisture, which reduces its attractiveness to the ant. Do not keep baits year-to-year as they will go rancid. Conventional sprays of chlorpyrifos can also be applied to control ant populations at harvest, but will only kill foraging ants. Spraying two weeks prior to harvest is the recommended timing for these types of applications.

Please see the UC IPM Website for updated pest management strategies and materials. An entry later this week will help in identifying orchard ants.

Almond Orchard Ant Monitoring Form - UC IPM

Almond Antcolony Monitoring