Glyphosate formulations – What’s the difference (and what the heck is a “salt”)?

Cross post from UC Weed Science blog 12/20/17 Glyphosate is one of the most widely used herbicides in the world and is extremely important in many of our orchard, vineyard, and annual crops as well as in non-crop and home situations. However, it can be confusing to understand some of the differences among various formulations of glyphosate herbicides. I’ll paraphrase a recurring extension question like this: “I’m trying to compare the rates and cost-effectiveness of two glyphosate herbicides. One lists the active ingredient as ‘41% glyphosate as the isopropylamine salt’ and the other as 48.7% glyphosate as the potassium salt’.  How do I compare these two herbicides?” First important point, glyphosate is a weak acid herbicide.  The various salt formulations have major impacts on how the herbicide behaves in the jug, and to some degree on how it gets into the plant.  But once in the plant, it is the glyphosate acid that binds to the target enzyme in susceptible plants and causes the herbicidal effect. What is a salt? From a chemistry perspective, a salt is simply a compound formed by ionic bonding of two ions of opposite charge.  Glyphosate acid has a weak negative charge and the salt is formed when the glyphosate acid is bound to a base that has a positive charge.  In the cartoon below, this is illustrated a little incorrectly – you can see the negatively charged glyphosate acid on the left (C3H8NO5P); however, the “salt+” tagged on the right should really be labeled  “base+” (the combined molecule is actually the “salt”).   (image from www.wheatgrowers.com)  ((the “salt” on the right should more accurately be labeled “base”)) What are some common glyphosate salts? There are several glyphosate salts currently available in the market and others have been in the past but are less common now.  Four examples (below) include:

December 20, 2017

2016 Mid-Spring Update

The crop is developing nicely in many areas across the areas of the San Joaquin Valley in which I observed. Crop loads vary, depending on last season’s stress or crop-load, but generally look good. Looking forward to this week, there area few pointers to keep in mind. Rain is forecasted for this weekend with chances through next week. This will have minimal impacts on the physiological development of the crop. It will, however, impact the amount rates of evapotranspiration and soil moisture. This variance should be accounted for by either using soil moisture monitors or plant based measurements. If possible, rain gauges (or other measurement tool) should be placed at the various farms as rainfalls can be variable. Last year, for example, a thunder cell dropped around 3/4″ of rain in a farmer’s field on the North side of Livingston, while his block on the south side received less than 1/4.” Accounting for these differences can prevent the “stalling-out” of growth from over-irrigation. Even though it warmed up this week, it might be wise to question the start of the irrigation season. Only two out of four plots in which we are measuring stem water potential have indicated the need to irrigate. The other two are still reading around baseline…one is even in a Delhi sand. Plant based measurements should be used to help determine the need to irrigate. Remember: the tree is essentially a giant tensiometer with a lot larger volume of soil impacting the result. Disease update: Multiple days of rain are predicted. This could mean conditions suitable for Bacterial Spot (especially on ‘Fritz’ and ‘Padre’), Anthracnose (for ‘Monterey’), Scab, and Shot-hole. Lingering infections of green fruit rot may also progress. If a treatment is warranted, check the fungicide efficacy table. Remember to rotate away from the last spray

April 8, 2016

Almond Set and Nut Drop

Annually, I receive several questions on nut set. Many are aware that not all of the flowers on the tree will set a nut, but how many do? This, of course, can range  between 15-40%.  Most orchards, however, set between the 20-30% range, with average orchards around 25%. This percentage varies year-to-year, and is dependent on flower density, temperature at bloom and post-bloom, and tree health. Spur dynamics play a key role in fruit bud density and the ability for a flower to set. Research by Tombesi and colleagues found that a fruiting spur, if maintained in a position with ample light for photosynthesis, tends to alternate bear. These spurs may flower the year after cropping, but rarely set a nut. This is believed to be due to carbohydrate and nutrient depletion within the spur. Surprisingly, tagged spurs that double or triple crop die, regardless of light position. Therefore, orchards that have a high set percentage deplete the spur pool, leading to a reduced set in the following year (i.e. alternate bearing). Generally, however, most orchards are able to re-develop spur positions which lead to sustained yields. Farmer practices come into play in developing and maintaining spurs- they include PROPER irrigation and nutrition, as well as adequate potassium levels to reduce spur mortality. Tagging studies have also found that set percentage is generally inversely related to flower density. This means that trees that have fewer fruit buds/flowers will set at a higher percentage than trees with a high fruit bud/flower count. This most likely is due to a greater amount of resources able to be allocated to a fewer number of buds. This compensation for the lower bud count, however, does not typically lead to a higher yield. Temperature can impact set as well. Almond pollination and fertilization can occur over

March 7, 2016

Whole Orchard Soil Re-incorporation: an Alternative Orchard Removal Strategy

Written by Brent Holtz (UCCE San Joaquin) and David Doll (UCCE Merced) You may have heard the news—co-generation plants are limiting the amount of chipped biomass they are accepting.  This is reducing the rate in which old orchards are removed, impacting the orchard redevelopment process. The soil incorporation of chipped or ground almond, peach, plum, or cherry trees during orchard removal could provide an alternative to co-generation plant or burning and could add valuable organic matter to our San Joaquin Valley soils.  Traditionally, many growers feared that wood chips or grindings would stunt tree growth by either allelopathic compounds or reduced nitrogen availability due to the high carbon to nitrogen ratio.  Interestingly enough, recent research has found this not to be true if the ground material is spread across and incorporated into the soil In 2008, University of California Farm Advisors and a USDA Plant Pathologist undertook a project at the UC Kearney Research and Extension center to compare the grinding of whole trees with burning as a means of orchard removal.  Twenty-two rows of an experimental orchard on nemaguard rootstock were used in a randomized blocked experiment with two main treatments, whole tree grinding and incorporation into the soil with ‘The Iron Wolf,’ a 50-ton rototiller, versus tree pushing and burning.  We examined second-generation orchard growth and hypothesized that soils amended with woody debris will sequester carbon at a higher rate, have higher levels of soil organic matter, increased soil fertility, and increased water retention.  Second generation almond trees (Nonpareil, Carmel, Butte) were planted in January/February 2009. The whole tree grinding did not stunt replanted tree growth.  In 2015, Greater yields were ultimately observed in the grind treatment, when compared to the burn (previous year’s yields were similar). In 2013, 2014, and 2015, soil analysis revealed  significantly more calcium,

November 14, 2015

Understanding and Applying Information from a Soil Test, Part 4: Boron, Chloride, Copper, Iron, Manganese, Molybdenum, Nickel, and Zinc

Allan Fulton, UC Farm Advisor, Tehama County and Roland D. Meyer, Extension Soil Specialist Emeritus This article (Part 4) discusses micronutrients and the use of soil tests to evaluate their levels in orchard soils.  Micronutrients are essential to almonds and other nut crops, yet are required in much smaller amounts than macronutrients such as nitrogen (N), phosphorus (P) and potassium (K) or secondary nutrients  such as calcium (Ca), magnesium (Mg), or sulfur (S).  The eight micronutrients are boron (B), chloride (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), and zinc (Zn).  They fulfill important roles in the plant.  For instance, zinc is needed for plant cell expansion and it influences pollen development, flower bud differentiation, and fruit set while boron is a building block for the plant cell wall and strongly influences pollen tube germination and growth.  Flower abortion in almond and walnut has occasionally been associated with boron deficiency.  Nickel has recently been determined to be an essential nutrient and there are no known deficiencies in California. Zinc, iron and manganese deficiencies are not as commonly found in the Sacramento Valley as in the San Joaquin Valley.  Zinc deficiency is most common in almond and other nut crops.  Other micronutrient deficiencies that are occasionally seen in almond include B, Fe, and Mn.  Copper (Cu), Mo, and Ni deficiencies have not been documented in almonds; however, Cu deficiency is common in pistachios. Five of the micronutrients (Cu, Fe, Mn, Ni, and Zn) largely exist in the soil as positively charged metal cations bound as minerals or adsorbed to the surfaces of colloids or soil particles.  Several factors in orchard soils may affect the solubility and availability of these metal cations to trees.  Soil pH greater than 7.5 has the major influence of reducing the tree availability of

November 6, 2015

Salinity Management for Fine Textured Soils

AUTHORS NOTE: The following article discusses salinity management considerations for FINE TEXTURED SOILS (e.g. loams, silts, and clays). This is a follow-up to the previous article, “Salinity Management for Sandy Soils.” For the most part, this article describes issues with the WEST SIDE of the San Joaquin Valley. NOT ALL SOILS ARE THE SAME. Please note that the following guidelines may need site-specific adjustments. Starting with the soil, we often use the term cation exchange capacity (CEC), which is the amount of cations (positively-charged ions like sodium, magnesium, calcium, potassium, etc.) that can bind to the soil particle surface. In fine textured soils across the State, CEC values can be very high, with values ranging between 15-40 meq/100 g of soil. Generally, sandy loams are in the teens through 20s, and silts and clays are in the 30s to 40s. This CEC value is important as it indicates the amount of cations the soil particles can hold. The higher the CEC, the more cations that stick to the soil, preventing them from entering the soil water (soil water is the amount of water that is held between soil particles – it is what the tree drinks), reducing salt exposure to the roots of the tree. Regardless of the CEC, once the soil is saturated with cations, the excess will stay within the soil water. As soil salinity increases, the tree’s roots salt exposure is increased. High soil salinity affects the osmotic movement of water, and this impacts the tree roots’ uptake of water (e.g. essentially making the tree work harder for water), leading to eventual toxicity. Salt toxicities within fine textured soils can vary based on the element involved. Chloride toxicity can occur rapidly, showing up within a year or two when applying poor quality water. This is due to chloride being an anion, and due

October 18, 2015

Salinity Management for Sandy Soils

AUTHORS NOTE: The following article discusses salinity management considerations for SANDY SOILS (e.g. sands, loamy sands). A follow up post will be made for finer texture soils (loams, silts, and clays). For the most part, this article describes issues with the EAST SIDE of the San Joaquin Valley. NOT ALL SOILS ARE THE SAME. Please note that the following guidelines may need site-specific adjustments. During low rainfall years, salt burn often shows up in sandy soils. This salt burn is a combination of accumulation of sodium within the soil, the use of well water, and the low exchange capacity of the soil. Starting with the soil, we often use the term cation exchange capacity (CEC) which is the amount of cations (positive charged ions like sodium, magnesium, calcium, potassium, etc.) that can bind to the soil particle surface. In the sandier areas on the east side of the San Joaquin Valley, CEC values can be quite low, with values less than 10 meq/100 g of soil. To put that in perspective, sandy loams are in the teens through 20s, silts and clays are in the 30s to 40s. This value is important as it indicates the amount of cations the soil particles can hold. The higher the CEC, the more cations that stick to the soil, preventing them from entering the soil water (soil water is the amount of water that is held between soil particles – it is what the tree drinks), reducing exposure to the roots of the tree. Regardless of the CEC, once the soil is saturated with cations, the excess will stay within the soil water. As the soil salinity increases, the tree’s roots have a greater exposure impacting them by affecting the osmotic movement of water (e.g. essentially making the tree work harder for water) and  eventual toxicity.

October 10, 2015

Understanding and Applying Information from a Soil Test, Part 3: Secondary Plant Nutrients: Calcium (Ca), Magnesium (Mg), and Sulfur (S)

Written by Allan Fulton, Farm Advisor, Tehama County and Roland D. Meyer, Extension Soils Specialist Emeritus This article (Part 3) discusses the use of soil tests to evaluate levels of the secondary nutrients calcium (Ca), Magnesium (Mg), and sulfur (S) in orchard soils.  It is a follow up to a series of articles on intrpretation of soil sampling results. These nutrients are considered secondary because while they are essential to crop development, seasonal crop uptake is usually lower than for the primary nutrients N, P, and K but considerably higher than the micronutrients zinc (Zn), iron (Fe), Manganese (Mn), copper (Cu), boron (B), and chloride (Cl). Calcium and Magnesium Plant uptake, cation adsorption and desorption in soil, leaching from rainfall and irrigation, and weathering of minerals all contribute to the concentration of water soluble Ca and Mg available to meet tree nutritional needs.  Water soluble cations are determined from the saturated paste extract soil test procedure while the exchangeable cations are determined with the ammonium acetate procedure.  Also important are the concentrations of exchangeable (non-water soluble) Ca and Mg which help to promote favorable soil structure.  Soil chemistry is in a constant state of change attempting to reach equilibrium between the soluble and non-soluble (exchangeable and mineral) phases.  The May 2009 newsletter discussed this dynamic process.  Calcium and magnesium share similar chemical properties in soils.  Both Ca and Mg are “double positively charged (divalent) cations in the soil-water phase and on soil cation exchange sites.  Calcium is adsorbed to soil exchange sites preferentially and more strongly than Mg.  When Ca and Mg are abundant in the soluble phase tree roots absorb these nutrients by mass flow.  If Ca and/or Mg are less abundant or limited by soil moisture, uptake occurs more slowly through diffusion. Table 1 provides ranges of exchangeable

September 21, 2015

Leaf analysis and salinity monitoring

Written by Joe Connell, Butte County Farm Advisor Leaf analysis for the full range of nutrients is best done in July when nutrient levels in leaf tissue are stabilized. Published July critical values established for almond by U.C. researchers can help guide you in your fertilization practice.  Analysis can reveal specific nutrient deficiencies or can alert you to developing trends when results are compared from one year to another.  Keeping trees in the adequate zone for nitrogen can save on fertilizer costs by helping to avoid over fertilization. 

July 4, 2014

2013 Top Ten Articles

Following a long standing tradition of developing a “Top 10” list to celebrate the old and bring in the new year, I compiled the top 10 articles read on The Almond Doctor in 2013.

December 31, 2013