- Author: Ellie Marie Andrews
- Author: Elizabeth J Fichtner
Olive orchards entering an OFF year in 2024 may benefit from pre-bloom foliar boron (B) applications to support reproduction and yield. Because the 2023 California olive crop varied widely both within and between olive-growing regions, the value of boron applications should be considered at the individual orchard level. For example, in the southern San Joaquin Valley, the 2023 ‘Manzanillo' table olive crop was OFF due to the high temperatures at bloom whereas many oil cultivars in the region were unaffected by the heat and had heavy production. Those orchards that had a heavy ON crop in 2023 may benefit from pre-bloom boron application in the 2024 season.
Boron is an essential micronutrient for plant growth and reproduction. Boron deficiency affects plant reproduction by reducing pollen viability and germination and limiting pollen tube growth. Deficiency also limits the proportion of flowers that set fruit and reduces the retention of developing fruit. The influence of boron deficiency on multiple stages of reproduction may negatively impact yield. Boron also plays a role in vegetative growth and metabolism, ensuring cell wall and membrane integrity and facilitating sugar transport and cell division. Because boron plays a crucial role in reproduction, boron is translocated from vegetative tissues to reproductive tissues resulting in higher concentrations of the nutrient in reproductive organs than leaves. Due to this high demand, reproductive boron deficiency can occur even when vegetative boron and available soil boron are sufficient.
Studies conducted across numerous global olive-growing regions demonstrate the beneficial effects of foliar boron application on yield, particularly in advance of an OFF crop. The influence of boron application on productivity in olive orchards may relate to increases in photosynthesis, an increase in the number of perfect flowers (those with both male and female reproductive parts) (Figure 1), and an increase in pollen viability, or pollen tube growth. Olives are considered andromonoecious, a reproductive strategy in which plants bear both hermaphroditic (perfect) flowers and male flowers. Stress prior to bloom may cause pistil abscission in a fraction of buds resulting in a higher percentage of male flowers. Several research studies have demonstrated that pre-bloom foliar boron application can increase the percent of perfect flowers on trees, thus increasing the number of flowers capable of producing fruit. In olive, boron is readily mobilized from both young and old vegetative growth to support flower and fruit production; therefore, a portion of boron applied throughout the year may be utilized to support reproductive processes. During the pre-bloom season, however, cool temperatures and the corresponding reduced physiological activity may limit the uptake and translocation of boron in olive. Additionally, flowers are not as strong a boron sink as fruit; therefore, the pre-bloom foliar application may render the micronutrient available at a short-lived, yet critical, time in crop development.
Both oil olives and ‘Manzanillo' table olives have been shown to benefit from foliar boron applications. For example, ‘Arbequina' receiving pre-bloom foliar application of boron exhibited increased bloom and a 27% increase in yield in an OFF year. In the ‘Arbequina' study, no value of boron was observed in an ON year, and boron was found to have no effect on vegetative growth. In another study, boron applications to ‘Frantoio' resulted in increased concentration of chlorophyll and soluble sugars, as well as changes in the profile of endogenous plant growth regulators within the leaves. In California, pre-bloom boron applications on ‘Manzanillo' resulted in increased percentage of perfect flowers and improved fruit set and yield, particularly during an OFF year.
The recommended foliar boron concentration for olives ranges from 19-150 ppm. Values below 14 ppm boron may result in boron deficiency, whereas values above 185 ppm may result in boron toxicity. A foliar nutrient analysis only provides a snapshot of the status of the plant at the time of leaf collection; however, low boron status of leaves has been found to correlate well with symptoms of deficiency. Symptoms of boron deficiency in olive include dead leaf tips with a characteristic yellow band and green leaf base, as well as twig and limb dieback (Figure 1). Boron deficiency may first become apparent in the meristems, the growing tips of shoots. Boron deficiency may also result in misshapen and defective fruit (Figure 1), low fruit set, and premature fruit drop. The value of boron application for improved fruit set is not limited to orchards with visual symptoms of boron deficiency or foliar boron levels below the recommended range. In fact, the numerous research studies that demonstrate the value of pre-bloom foliar boron applications for enhanced fruit set and yield were conducted in orchards with no boron deficiency. Based on these findings, foliar analysis alone may not be a useful predictor of benefits from pre-bloom foliar boron application.
Boron is typically introduced to orchards either as a solid mineral broadcast on the soil surface, or in solution as a foliar spray. The pre-bloom foliar application is designed to specifically enhance fruit set and yield and should be applied three weeks prior to bloom. Boron is generally sold as borax, sodium borate, sodium tetraborate, boric acid, or Solubor® (Table 1). The boron content varies between formulations; therefore, all calculations should be based on the equivalents of active ingredient (ie. pounds of boron). For example, for soil-applied boron in olive, 5-10 lbs/acre of boron is broadcast, which equates to approximately 45-49 lbs/acre of borax (11% boron) or 24-48 lbs/acre Solubor® (20.5% boron). In California, foliar application of boron three weeks prior to ‘Manzanillo' bloom, particularly in OFF years, at rates of 1 or 2 lb./acre Solubor® in a 100 gallon/acre (246 or 491 mg/L boron at 935 L/hectare) was demonstrated to improve yield by approximately 30%. The baseline boron level in this California study site was 16 ppm boron, a level just below the established critical level, but high enough to avoid deficiency symptoms.
The value of boron applications on orchard health and economic return varies based on the status of the alternate bearing cycle in the year of application, the baseline boron status of the tree and soil, and other climate factors that may influence yield. Plants have a narrow range between boron deficiency and toxicity. Be sure to read the product label carefully to avoid over-application and conduct annual leaf tissue analyses to gather baseline information on the boron status of orchards. More information on fertilizer rates for olives and other California crops may be found on the CDFA FREP California Crop Fertilization Guidelines website (https://www.cdfa.ca.gov/is/ffldrs/frep/FertilizationGuidelines/).
![Figure 1 Figure 1](/blogs/blogcore/blogfiles/104475.jpg)
![Figure 2 Figure 2](/blogs/blogcore/blogfiles/104476.jpg)
![Figure 4 Figure 4](/blogs/blogcore/blogfiles/104477.jpg)
- Author: Luis Espino
- Author: Bruce Linquist
We have gotten several calls about the use of zinc (Zn) fertilizers to address potential Zn deficiencies. The price of zinc is going up, and it is prompting growers to look more carefully at the use of zinc. Use of zinc fertilizers became widespread in the late 1970s after it was discovered that the “alkali disease syndrome” was caused by zinc deficiency. The problem was widespread in the Sacramento and San Joaquin Valleys and affected young seedlings after the first true leave emerged. The syndrome consisted of yellowing of leaves from the base up, weak leaves that floated in the water, and plants eventually dying 4 to 6 weeks after seeding, resulting in thin stands. Cool temperatures during the early part of the season can exacerbate zinc deficiency problems.
Currently, we do not know how widespread zinc deficiency is. We know that zinc deficiency is more common in alkaline soils (pH higher than 7). In such soils a level below 0.5 to 0.8ppm (obtained by theDTPA method) suggests a deficiency. In soils with pH lower than 7, the threshold for zinc deficiency is 0.3ppm. Duringtillering stage, a Y-leaf Zn concentration of
Based on research out of the 70s, you can correct for Zn in a couple of ways. First by applying a Zn fertilizer. This is most often done by adding some Zn containing fertilizer (e.g. zinc sulfate, chloride, or nitrate) to the starter fertilizer blend. In most fields, no more than 8 lbs of Zn/ac was needed to correct deficiencies. Another option is to coat the seed with Zn before planting. When coating seed, 2 lb of Zn per 100 lb of seed was enough.
If you are reassessing the need to use Zn, use the pH and Zn content of your soil to decide if the investment in Zn is justified. Also, if you are using a starter fertilizer that has Zn in it, you may be supplying enough to address any deficiency.
![]() |
![]() |
Field with suspected zinc deficiency.
/table>- Author: Whitney Brim-DeForest
2019 Annual Rice Grower Meetings
Sponsored by UC Cooperative Extension
-------------- 5 Locations --------------
WHERE & WHEN
Richvale: Thursday, Jan. 17, 8:30am, Evangelical Church, 5219 Church St., Richvale
Glenn: Thursday, Jan. 17, 1:30pm, Glenn Pheasant Hall, 1522 Hwy 45, south of Glenn
Colusa: Friday, Jan. 18, 8:30am, Colusa Casino Resort, 3770 Hwy 45, Colusa
Marysville: Friday, Jan 18, 1:30pm, Yuba County Government Center, 915 8th St. Marysville
Woodland: Tuesday, Jan. 22, 8:30am, Cracchiolo's Market, 1320 E. Main St. Woodland
TIME: Doors open at 8:00 am and meetings start at 8:30 am at Richvale, Colusa, and Woodland.
Doors open at 1:00 pm and meetings start at 1:30 pm at Glenn and Marysville.
Program
8:00 a.m. (1:00 p.m.) Doors open, sign‐in, coffee
8:30 a.m. (1:30 p.m.) Call meeting to order
California Rice Commission Referendum – Tim Johnson, CRC
8:50 a.m. (1:50 p.m.) Rice Research Board Nominations – Dana Dickey, Rice Research Board
9:00 a.m. (2:00 p.m.) Rice Pesticide and Regulatory Update – County Ag Commissioner
9:15 a.m. (2:15 p.m.) Weedy Rice and Emerging Weed Issues – Whitney Brim‐DeForest, UCCE
9:35 a.m. (2:35 p.m.) Arthropod and Disease Update – Luis Espino, UCCE
10:05 a.m. (3:05 p.m.) Season Review and Fertility Update – Bruce Linquist, UCCE
10:35 a.m. (3:35 p.m.) Weed Control Update – Kassim Al‐Khatib, UCCE
11:05 a.m. (4:05 p.m.) — ADJOURN —
****Applied for DPR and CCA CE credits****
- Author: Konrad Mathesius
- Contributor: Mark Lundy
After a dry beginning to the season, wheat growers might be trying to decide how to proceed with their nitrogen fertility program. If not irrigated, most wheat planted in the Sacramento Valley during November will likely have been stunted by the relatively dry conditions during the second half of November and throughout December (see Fig. 1, below). Some of the crops out there may need to be replanted entirely. If you're trying to work out how your stand is doing, consider some population sampling.
To get a rough estimate of your field's population, take several plant counts from random locations in the field. Lay a yard stick parallel to a row and count how many plants are still present in that row. Do this several times throughout the field and get an average. Multiply that number by 4 and divide the new number by your row spacing (in inches, typically 7).
Above: Checking wheat stand at tillering. Photo: University of Missouri Cooperative Extension
Example:
After counting several times, your average is 35.5 plants per 3 feet.
(35.5 x 4) / 7 => 142/7 => 20.29 => Roughly 20 plants per square foot.
Table 1: Relationship between plant stand and ideal yield potential adapted from Penn State Extension.
If your average comes out at less than 23 plants per square foot (or 1 million plants per acre) when you planted/planned for 1 million plants per acre, your crop yield potential would be less than 100%. At this stage of growth, the crop can make up ground by producing relatively more tillers than a full stand. But, you might need to adjust your fertilization plan to the lower than expected plant population. (Keep in mind, if you planted at a relatively low seeding rate for any number of reasons, your plant stand might not be the result of any significant losses due to moisture stress).
For example, if you were planning to apply 100 units of N at tillering you might consider decreasing that amount to match the reduction in yield potential. If your stand is down to 18 plants per square foot (roughly 75% yield potential), adding 75 units instead of 100 might make sense.
Figure 1: Cumulative Rainfall from estimated planting date for wheat in the southern Sacramento Valley
Timing is critical. If your plant stand is low, plants will respond by producing more tillers to fill the gaps as long as they have sufficient nitrogen available at this time to tiller aggressively. There are two scenarios to consider depending on whether or not you applied pre-plant N:
1) If you applied a heavy pre-plant application of N and have not irrigated, it is unlikely that the soil is deficient because the lack of rain this year would not have pushed much of the pre-plant fertilizer too deep into the profile. In this case you might wait a bit longer and decide on top-dressing based on soil N (See information on soil nitrate quick tests here and here and contact your UCCE Agronomy Advisor to assist with assessing this). If you applied extra nitrogen in a high-N reference strip, you can use it to monitor deficiencies that begin to appear as the plants are tillering.
2) If your stand is low and your pre-plant application was light to non-existent, consider additional N applications sooner than later with the idea being that you are trying to ensure that N is available as plants tiller and expand their canopy potential.
If your stand count is sufficient. You might wait a little longer until applying depending on the maturity and nitrogen status of your crop and soil. Applying at tillering with sufficient water following your application to incorporate your fertilizer into the root zone will mean that peak N availability will match peak N demand.
More information about determining nitrogen status and how to decide on top-dress N applications can be found here. In general, keep in mind that in-field tests vary in efficacy depending on several factors, but employing more measurement tools (soil N tests, green canopy measurements with a high-N test strip…) improves your chances of making an informed decision.
- Author: Konrad Mathesius
- Contributor: Mark Lundy
After a dry beginning to the season wheat growers might be trying to decide how to proceed with their nitrogen fertility program. If not irrigated, most wheat planted in the Sacramento Valley during November will likely have been stunted by the relatively dry conditions during the second half of November and throughout December (see Fig. 1, below). Some of the crops out there may need to be replanted entirely. If you're trying to work out how your stand is doing, consider some population sampling.
To get a rough estimate of your field's population, take several plant counts from random locations in the field. Lay a yard stick parallel to a row and count how many plants are still present in that row. Do this several times throughout the field and get an average. Multiply that number by 4 and divide the new number by your row spacing (in inches, typically 7).
Above: Checking wheat stand at tillering. Photo: University of Missouri Cooperative Extension
Example:
After counting several times, your average is 35.5 plants per 3 feet.
(35.5 x 4) / 7 => 142/7 => 20.29 => Roughly 20 plants per square foot.
Plants/sq ft |
Yield Potential (%) |
30-35 |
100 |
22-28 |
100 |
18-21 |
90-95 |
15-18 |
75-80 |
12-14 |
60-70 |
Table 1: Relationship between plant stand and ideal yield potential adapted from Penn State Extension.
If your average comes out at less than 23 plants per square foot (or 1 million plants per acre) when you planted/planned for 1 million plants per acre, your crop yield potential would be less than 100%. At this stage of growth, it can make up ground by producing relatively more tillers than a full stand. But, you might need to adjust your fertilization plan to the lower than expected plant population. (Keep in mind, if you planted at a relatively low seeding rate for any number of reasons, your plant stand might not be the result of any significant losses due to moisture stress).
For example, if you were planning to apply 100 units of N at tillering you might consider decreasing that amount to match the reduction in yield potential. If your stand is down to 18 plants per square foot (roughly 75% yield potential), adding 75 units instead of 100 might make sense.
Figure 1: Cumulative Rainfall from estimated planting date for wheat in the southern Sacramento Valley
Timing is critical. If your plant stand is low, plants will respond by producing more tillers to fill the gaps as long as they have sufficient nitrogen available at this time to tiller aggressively enough to fill the gaps. There are two scenarios to consider depending on whether or not you applied pre-plant N:
1) If you applied a heavy pre-plant application of N, it is unlikely that the soil is deficient because the lack of rain this year would not have pushed any pre-plant fertilizer too deep into the profile. In this case you might wait a bit longer and decide on top-dressing based on soil N (See information on soil nitrate quick tests here and here and contact your UCCE Agronomy Advisor to assist with assessing this). If you applied extra nitrogen in a high-N reference strip, you can use it to monitor deficiencies that begin to appear as the plants approach tillering.
2) If your stand is low and your pre-plant application was light to non-existent, consider additional N applications sooner than later with the idea being that you are trying to ensure that N is available as plants tiller and expand their canopy potential.
If your stand count is sufficient. You might wait a little longer until applying depending on the maturity and nitrogen status of your crop and soil. Applying at tillering with sufficient water following your application to incorporate your fertilizer into the root zone will mean that peak N availability will match peak N demand.
More information about determining nitrogen status and how to decide on top-dress N applications can be found here. In general, keep in mind that in-field tests vary in the efficacy depending on several factors but employing more tools (soil N tests, green canopy measurements with a high-N test strip…) improves your chances of making an informed decision.