- Author: Ben Faber
Plant-out-of-place photo galleries:
http://wric.ucdavis.edu/photo_gallery/photo_gallery.htm
http://ipm.ucanr.edu/PMG/weeds_intro.html
Horseweed - Conyza canadensis
Herbicide treatment table for citrus:
http://ipm.ucanr.edu/PMG/r107700411.html
And if you are wondering what herbicide damage might look like on various plant species (this is heavily weighted to annuals and landscape plants):
http://herbicidesymptoms.ipm.ucanr.edu/index.cfm
Blueberry herbicide damage
- Author: Brad Hanson
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 as “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").
In case it's been a while since your last organic chemistry class, here's a quick refresher on nomenclature. In the isopropylamine salt, that simply means it as a 3-carbon chain (that's “propyl”) and amine group (NH), and the chain is connected in the middle (the “iso” position) rather than on one end. Dimethylamine indicates two (di) methyl groups and an amine. Trimesium is a shortened name for trimethylsulfonium which means three methyl groups and a sulfur. Potassium means, well that one's pretty straightforward and means potassium (K).
How does the salt formulation affect the herbicide? The salt formulations are those of us managing weeds for a couple of important reasons.
- First, the different glyphosate salts have different solubility in water (or other solutions). This doesn't have much, if any, effect when we have the herbicide diluted in water to make a spray application (eg. quarts of product in 10 or more gallons of water). However, it has a big impact on how concentrated the herbicide can be in the formulated product. (It's useful here to note that pure glyphosate is actually a solid crystal that is dissolved in liquid to make the products we use in the field.) In the example I started with, that is the big driver behind why one product has 41% active ingredient and the other has 48.7%. From a packaging, shipping, storing, and handling perspective, it's far more efficient to have more concentrated materials (eg less water). So, we can assume the potassium salt is quite a bit more soluble than the isopropylamine salt form of this herbicide.
- Second, the different glyphosate salts have different weights. Remember the periodic table of the elements? The atoms that make up the salts (and any other chemical structure for that matter) have markedly different weights on an atomic scale. For our purposes, we can think of this as a carbon (C, atomic number 6) weighing six times a hydrogen atom (H, atomic number 1) and a potassium (K, atomic number 19) weighs about three times what carbon does. Of course, the glyphosate acid weight is the same C3H8NO5P in each formulation – only the salt is different. So, it is important to remember that in these herbicides the “active ingredient” (AI) is the salt formulation (eg glyphosate isopropylamine) and that each of the different active ingredients has a slightly different weight.
How can I use the percent active ingredient to compare products? I'll be honest here, I find it very confusing to think about the percent AI list on the label of a glyphosate herbicide. As I indicated above, this does not allow a straight across comparison for two different salts (eg a potassium salt glyphosate is not the same weight as a dimethylamine salt). More importantly, the percentage listed on the label is actually on a weight basis (weight of glyphosate salt per weight of formulated herbicide). I don't know about any of you, but I typically measure glyphosate herbicides by volume (fluid ounces, quarts, milliliters) rather than by weight (ounces, pounds, kilos). So knowing the amount of glyphosate per pound of Roundup Powermax isn't very helpful to me when I don't weigh the liquid.
Instead of focusing on the percent active ingredient, look on the label just below where the percentages are listed for the active ingredient and acid equivalent information. (I'm looking at a Roundup PowerMax label and a Credit41 label, but there are dozens of examples). In these two herbicides, you can see:
- Credit41 has 4 lbs per gallon of glyphosate as the isopropylamine salt, which is equivalent to 3 lbs per gallon of glyphosate acid.
- Roundup PowerMax has 5.5 lbs per gallon of the glyphosate potassium salt, which equates to 4.5 lb/gal of the acid.
So, once we're comparing on an acid equivalent (AE) basis, we can see that that one product is 50% more concentrated than the other (3 lbs vs 4.5 lb ae). If you wanted to make an equivalent rate (AE per acre) you'd have to apply 50% more of the 3 lb product to have the same amount of glyphosate acid. Similarly, in making cost comparisons, you should be thinking about it in terms of cost per unit of glyphosate acid. In the above example, if making an equivalent AE rate per acres, the breakeven point would be if the 3 lb material costs 2/3 of what the 4.5 lb material costs. Don't make the mistake of assuming a quart of one glyphosate is the same as another (or that a 2% solution of two different products is equivalent!
Check out this publication we did a couple years ago On the second page, there's a chart that illustrates this concept – if you wanted to apply a rate of ¾ lb ae per acre, you'd need to apply 32 fl oz of a 3.0 lb ae/gal material (eg Credit41, Roundup Original) but only 22 fl oz of a 4.5 lb ae/gal material (eg Roundup PowerMax).
What else is different among the formulations? This is a really good question without a really clear answer.
Besides the glyphosate-salt that makes up the active ingredient in each formulation, there are other components of the herbicide product. Some of these influence physical properties that affect handling, storage stability, etc. Others are surfactants and other adjuvants that impact how the herbicide penetrates the leaf surface. The surfactants (types and loading) are proprietary information and are not reported in the same way as the active components are so this can be difficult to ascertain. However, one way that price points can be reduced in this competitive market (lots of generic glyphosate herbicide due to loss of patent protection) is to reduce or change the surfactant packages. Thus, even if the active ingredient is the same between two products, they could have substantially different surfactant loading which can impact weed control efficacy (amount of herbicide getting to the target enzyme in the plants). If you use a low-surfactant-load glyphosate product, you should consider adding appropriate surfactants to make up for it.
I'll wrap this up by saying that I think a weed manager can get similar levels of weed control performance with the wide range of glyphosate herbicides currently available on the market. However, it is really important to make sure you're comparing apples-to-apples in determining rates needed from the various salt formulations and concentrated products. In my experience, at equivalent AE rates, a 3 lb glyphosate plus a good surfactant can perform similarly to a higher AE and higher surfactant load formulations; however, be sure to sharpen your pencils to make sure the savings from the cheaper AI isn't offset by higher required rates and surfactant additions.
N.B. https://www.epa.gov/pesticides/epa-releases-draft-risk-assessments-glyphosate
- Author: Caio Brunharo and Brad Hanson
Article written by UC Davis PhD student Caio Brunharo from his dissertation research. It was originally posted in the September 2017 "Weed Management Notes" newsletter from the UC Cooperative Extension office in Glenn County by new weed science and agronomy Farm Advisor Mariano Galla (also a UCD PhD student in weed science!).
Take care, Brad
Italian ryegrass management in perennial crops in California
Caio Brunharo1 and Brad Hanson2
1PhD Candidate, UC Davis; 2UCCE Weed Science Specialist, UC Davis.
Italian ryegrass (Lolium perenne L. spp. multiflorum (Lam.)Husnot) causes yield losses in a variety of cropping systems around the world (Figure 1). This species is highly competitive with annual crops but may also compete with perennial crops particularly during the establishment years when they are most vulnerable to direct competition. In orchards and vineyards, ryegrass infestation can also interfere with cultural practices during the bearing years.
Repeated herbicide use has selected Italian ryegrass populations resistant to a variety of herbicide mode of actions across the world. Glyphosate-resistant Italian ryegrass populations were first reported in California in 2008, and the evolution and spread of these populations in the state made alternative postemergence herbicides an important management strategy against this troublesome species.
Recently, poor control of Italian ryegrass with Gramoxone 2.0 SL was reported in a prune orchard near Hamilton City, California. Greenhouse dose-response experiments and field trials were carried out to evaluate Italian ryegrass response to several postemergence and preemergence herbicides.
Our greenhouse studies confirm that the Italian ryegrass population from Hamilton City is resistant to Gramoxone 2.0 SL, Envoy Plus, Roundup PowerMAX and Osprey, whereas Fusilade DX, Rely 280, Simplicity CA, Matrix and Poast controlled both a known-susceptible and resistant Italian ryegrass population (Table 1). (note: Osprey and Simplicity CA, which are not registered in perennial crops, were included in the study for comparison purposes). Our criteria were that whenever the resistance index (RI) was larger than two and the comparison between biotypes was statistically different (P <0.05), the population was considered as resistant to that particular herbicide. Matrix is an exception, however, because this herbicide controlled both biotypes at well below its recommended field rate.
The field experiment with postemergence herbicides corroborates with data from the greenhouse studies, since glyphosate and paraquat did not adequately control the herbicide-resistant population from Hamilton City. On the other hand, most of the treatments containing Rely 280 were effective for control of the resistant population (Figure 2).
From the preemergence herbicide trial, all treatments containing Alion controlled the resistant population up to 150 days after herbicide application. Chateau, Surflan AS, GoalTender, Prowl H2O, and the tankmixes of Chateau + Prowl H2O and Chateau + Surflan AS exhibited control percentages above 90% with long lasting residual activity (up to 150 days after treatment; Table 2).
Even though several postemergence herbicides controlled Italian ryegrass in our research, it should be noted that ryegrass populations resistant to Fusilade DX, Rely 280 and Poast have been reported elsewhere in the state (data not shown), and overreliance on these herbicides will increase the chances of selection of further cases of resistance. A chemical weed management program in areas infested with Italian ryegrass should include a preemergence herbicide with long residual sprayed in the winter (Alion, Chateau, Surflan, GoalTender or Prowl H2O are possible options) tankmixed with an effective postemergence herbicide. In areas where herbicide-resistant weeds are known to be present, alternative herbicide chemistries should be adopted (rather than increasing the herbicide rate sprayed) in both the winter and spring application. In some cases, a short residual grass herbicide included with the post-harvest burndown application may help reduce recruitment of early-germinating Italian ryegrass plants which will reduce weed pressure and densities to be managed later in the season.
- Author: Patrick Moran
Editor: Guy B Kyser
The giant invasive grass arundo (Arundo donax), one of the weeds targeted under the USDA-ARS-funded Delta Region Areawide Aquatic Weed Project (DRAAWP), has been re-acquainted with one of its natural enemies imported from arundo's native range. A tiny insect called the arundo armored scale (Rhizaspidiotus donacis) has been successfully released in the Sacramento River watershed and in the Delta.
Arundo forms dense stands across at least 10,000 acres in California, and over 100,000 acres in other arid riparian areas such as the Lower Rio Grande Valley of Texas and Mexico. Other control methods such as herbicide application, mechanical removal, mowing or burning have been used to reduce arundo populations in California, costing tens of millions of dollars. However, arundo is a tough plant and takes advantage of human disturbance and fire in riparian habitats along creeks, sloughs, rivers and reservoirs. Arundo populations in California thus exceed the capacity of these other control methods. In the absence of control, arundo consumes and wastes scarce water – a single plant can consume as much water as corn when growing in moist soil under hot, sunny conditions. Dense arundo stands block access to water for irrigation and recreation, and also obstruct flood control structures such as drainage ditches. Arundo also displaces native plants and animals and alters geomorphology and water flow dynamics in riparian habitats in ways that make it difficult for the natives to come back even if the arundo is controlled.
Biological control of invasive weeds focuses on the characterization, release and evaluation of insects (or plant pathogens) from the weed's native range into areas where the weed is non-native. The arundo armored scale was collected originally in southern France, Spain, and Italy. Studies by Spanish collaborators showed that, even in its native range with its own natural enemies, the arundo armored scale reduces shoot growth and rhizome size by 50%.
Biological control agents undergo rigorous testing to ensure they are not a threat to native plants or crops. After a permit review process, the USDA granted a permit for field release of arundo armored scale in 2010. (This is one of two insects that have been released for biological control of arundo in North America.) Since 2011, this biological control agent has been released in the Lower Rio Grande Basin. Initial releases of this agent in California began in 2014, and it was found that the scale insect had become established at one site in the northern Sacramento Valley by November of that year.
Armored scales are small insects that spend most of their lives in an immobile state, covered by their waxy secretions (‘armor'). Adult females produce ‘crawlers' that disperse locally (typically just a few feet) to find new buds coming up from the arundo rhizomes or lateral shoot buds above ground. The crawlers then lose their legs and antennae and insert their stylet-like mouthparts into the arundo tissue to feed on the fluids in the plant's vascular system. Crawlers molt to a second immature phase, and about six to eight weeks later, short-lived adult males emerge from their armor and mate with the immobile adult females. The females continue to feed and slowly develop embryos. A new generation of crawlers then emerges from the females. The life cycle takes four to six months.
Top row, left to right: Tiny (0.5 mm) crawlers emerge from females and settle on rhizomes or lateral shoots. Second-instar immature scales continue to feed and expand. Winged adult males emerge from their oyster-like scale covering. Females (armored scale cover removed) are shriveled and skinny right after molting. Mature females are plump and turn a darker color when they are full of crawlers ready to emerge. Bottom row, left to right: Adult females form aggregations on arundo rhizomes and shoots. The presence of armored scale populations causes shoot distortion and reduces both shoot growth and rhizome size.
In 2015, we tested a new release technique using arundo ‘microplants'. We soaked arundo shoot fragments in water for one month, then planted them in pots where they produced new shoot buds and roots. Armored scale crawlers were released onto the microplants. After about six months, we planted the infested microplants at field sites in the Delta – Andrus Island on the Sacramento River, and at Big Break near Oakley – and along Stony Creek in Glenn and Butte Counties north of the Delta. We established the microplants adjacent to large arundo shoots, and we cut off some of the established shoots to encourage production of new rhizome buds and lateral shoots. We watered the microplants as needed to keep them alive for about 6 months.
Left to right: Microplant with gelatin capsules used to isolate scale crawlers from females (capsules had been opened and crawlers poured onto the base of the plant). Greenhouse bench with arundo microplants. Field plot with arundo shoots cut back to promote new shoot and rhizome growth. Base of an arundo shoot at the field site (arrow indicates location of adult female scales that developed from crawlers that had previously came out of the females on the microplants.
Almost one year after planting, in November 2016, we sampled arundo rhizomes and shoots from the areas where the now-dead microplants were placed. At the Sacramento River site, 150 females were found, and at a site on Stony Creek in Butte County, 72 females were found. The females were placed in gelatin capsules to capture crawlers. A total of 1,668 crawlers emerged by early January 2017. Since there are still many more arundo shoots around the microplant sites, these results indicate that the arundo armored scale has established reproductive populations at three sites in California. This is the first establishment of this biocontrol agent in the state. Additional releases are planned throughout the Delta and surrounding watersheds. Along with the arundo wasp (Tetramesa romana), the arundo armored scale is expected to significantly reduce the potential for arundo to grow, disperse and form damaging populations that threaten water resources.
This work is conducted under the USDA-ARS-funded Delta Region Areawide Aquatic Weed Project (DRAAWP). This portion of the project is led by Dr. Patrick Moran (Patrick.Moran@ars.usda.gov) of the USDA-ARS Exotic and Invasive Weeds Research Unit, Albany, CA. Dr. Moran is working with a postdoctoral researcher, Dr. Ellyn Bitume (Ellyn.Bitume@ars.usda.gov), on this project. Contact us if you have questions. The Sacramento-San Joaquin Delta Conservancy (Beckye Stanton) is collaborating with USDA-ARS to identify field sites in the Delta, connect with landowners, and integrate biological control with their chemical arundo control program. Dr. Moran cooperates with landowners and local Reclamation Districts to obtain access to field sites.
- Author: Sonia Rios
Shark (carfentrazone) has been currently labeled for use in California avocados. It's widely used in many tree and vine crops. It's a Protoporphyrinogen oxidase (PPO) inhibitor. PPO is an enzyme in the chloroplast cell that oxidizes protoporphyrinogen IX (PPGIX) to produce protoporphyrin IX (PPIX). PPIX is important because it is a precursor molecule for both chlorophyll (needed for photosynthesis) and heme (needed for electron transfer chains). Inhibitors of the oxidase enzyme, however, do more than merely block the production of chlorophyll and heme. The inhibition of PPO by inhibitors also results in forming highly reactive molecules that attack and destroy lipids and protein membranes. When a lipid membrane is destroyed, cell becomes leaky and cell organelles dry and disintegrate rapidly.
PPO Inhibitors have limited translocation in plants and sometimes are referred to as contact herbicides. PPO Inhibitors injure mostly broadleaf plants; however, certain PPO Inhibitors have some activity on grasses. PPO Inhibitors usually burn plant tissues within hours or days of exposure. PPO Inhibitors used in the United States belong to eight different chemistries. It is used in the same niche that Treevix, Venue, and the post rates of Goal are used although registrations vary among those of course (only Goal from that list is registered on avocado).
Carfentrazone is a broadleaf-only herbicide and is interesting in that it has a fairly narrow weed spectrum; it has some species that it is really good on, but misses some other broadleaves almost completely. For example, it is excellent on bedstraw, but pretty weak on fleabane and marestail. It can provide good an inexpensive top-burn of perennial weeds like field bindweed, but will not kill it. Take a look at the label and, if the grower's weed spectrum aligns with some of the labeled weeds, it's worth checking out. Just be aware that it is grass-only and doesn't get all broadleaves equally.
Injury symptoms can occur within 1 to 2 hours after exposure, appearing first as water-soaked foliage, which is followed by browning (necrosis) of the tissue. Symptoms will appear most quickly with bright, sunny conditions at application. Drift injury will appear as speckling on leaf tissue. The necrotic spots are sometimes surrounded by a reddish colored ring. Injury from soil applications or residues appears as a mottled chlorosis and necrosis.
Fig. 1. Phytotoxicity of Shark herbicide on non-target leaf (above)
Phytotoxicity of Shark herbicide on non-target leaf. Since the droplets landing on the
Mixing the formulation depends on the growers sprayer calibration. If applying 20 gal of water per acre, that would be 5 acres per 100 gal mix and would need 10 fl oz product.
For a “spot treatment”, there is a table on the Shark EW label with mix amounts “based on 1 gal of water evenly covering 1000 square feet”. Take a look at Table 4 on this label: https://s3-us-west-1.amazonaws.com/www.agrian.com/pdfs/Shark_EW_Label1q.pdf