Subtropical Fruit Crops Research & Education
University of California
Subtropical Fruit Crops Research & Education

Posts Tagged: glyphosate

The Round UP on Glyphosate Use in Tree Crops

UC Ag Experts Talk:

Managing Glyphosate-Resistant Weeds in Orchard Crops

Description: One hour webinar about glyphosate-resistant weed management in orchards, delivered by Dr. Brad Hanson. One CEU (other) from the DPR is approved.

Time: Apr 24, 2019 3:00 PM in Pacific Time (US and Canada)

Recorded version will be published on UC IPM YouTube channel about a week after the webinar.

The link to register is https://ucanr.zoom.us/webinar/register/WN_96wd2GBMQl2Ou4i4oSwTTg

More information about the webinar series UC Ag Experts talk: https://ucanr.edu/sites/ucexpertstalk/

Speaker

Dr. Brad Hanson
Cooperative Extension Weed Specialist @UC ANR / UC Davis
Dr. Hanson, an associate Cooperative Extension specialist in the Department of Plant Sciences, specializes in weed management in tree and vine cropping systems. Hanson completed his Ph.D. in plant sciences (with an emphasis in weed science) at the University of Idaho and worked as a research agronomist with the USDA-ARS before joining the UC Davis faculty in 2009. His research interests include weeds, weed control, herbicide resistance, weed biology, invasive plants, pest control in fruit and nut crops and other agricultural production systems.

Webinar logo

horseweed bolting
horseweed bolting

Posted on Tuesday, April 16, 2019 at 8:18 AM
Tags: glyphosate (5), herbicides (15), resistance (12), round up (2), weeds (30)

Italian Ryegrass Resistance to Herbicides

WESTMINSTER, Colorado - November 23, 2018 - Herbicides have been instrumental in managing Italian ryegrass, a weed that frequently competes with perennial crops in California. Herbicide-resistant populations have become increasingly commonplace, though, including paraquat-resistant Italian ryegrass found recently in a California prune orchard.

A team of scientists set out to determine if the paraquat-resistant population might also be resistant to other postemergence herbicides. Seven other herbicides commonly used in fruit tree and nut tree crops were included in the study, including clethodim, fluazifop-P-butyl, glufosinate, glyphosate, pyroxsulam, rimsulfuron and sethoxydim.

Researchers found the paraquat-resistant population was also resistant to both clethodim and glyphosate. Among the remaining herbicides, glufosinate, rimsulfuron and sethoxydim were found to deliver the best postemergence control. Unfortunately, though, other populations of Italian ryegrass have developed resistance to the three herbicides, indicating their effectiveness may be short-lived.

"Overreliance on postemergence herbicides from a variety of chemical classes can result in weed populations that exhibit multiple resistances," says Caio Augusto Brunharo, a postdoctoral research fellow at the University of California, Davis. "Effective herbicide-resistance management programs are necessary for sustainable weed control."

The researchers recommended a number of preemergence herbicides as control options for Italian ryegrass in fruit and nut tree crops, including tank mixes containing indaziflam and flumioxazin.

###

Full text of the article, "Multiple Herbicide-Resistant Italian Ryegrass (Lolium multiflorum) in California Perennial Crops: Characterization, Mechanism of Resistance and Chemical Management" is now available in Weed Science Volume 66, Issue 6.

About Weed Science

Weed Science is a journal of the Weed Science Society of America, a nonprofit scientific society focused on weeds and their impact on the environment. The publication presents peer-reviewed original research related to all aspects of weed science, including the biology, ecology, physiology, management and control of weeds. To learn more, visit http://www.wssa.net.

italaian ryefrass resistance
italaian ryefrass resistance

Posted on Friday, December 14, 2018 at 4:54 PM
Tags: avocado (272), citrus (304), glufosinate (1), glyphosate (5), herbicides (15), orchards (7), paraquat (1)

Dust and Roundup

Agronomy and Weed Science Advisor, Merced County

It's getting hot and dry in the Central Valley and the movement of equipment in and out of fields/orchards/vineyards has the potential to stir up a significant amount of dust. Among its other impacts to agriculture (soil erosion, tissue damage, reduced photosynthesis, etc...), wind blown dust can reduce the efficacy of glyphosate, which is an important tool for the  management of weeds in trees and vines, along rights-of-ways, and in glyphosate-tolerant agronomic crops (e.g. corn, cotton, alfalfa) in CA.

The adoption of glyphosate has been facilitated, at least in part, by it's relative lack of soil activity (Miller et al. 2013; Zhou et al. 2006). Glyphosate can become tightly adsorbed to soil particles (depending on clay and organic matter content, pH, cation exchange capacity, etc...), thereby reducing the potential for crop injury via root uptake. The ability of glyphosate to bind to soil also contributes to it's reduced efficacy in certain situations. Specifically, dust that settles on weed leaf surfaces (Figure 1) can negatively impact glyphosate performance due to binding/inactivation.

Figure 1. Dirt on field bindweed (Convolvulus arvensis) leaves

 

The detrimental effects of dust on glyphosate performance have been described by Zhou et al. (2006) and Boerboom et al. 2006). Results from Zhou et al. (2006) showed that dust applied to the surface of eastern black (Solanum ptychanthum) and hairy (Solanum sarrachoides) nightshades reduced weed control, with greater amounts of dust resulting in greater reductions in herbicide efficacy (Figure 2). In a study conducted by Boerboom et al. (2006), dust was deposited over the tops of plots of common lambsquarters (Chenopodium album); water was then used to remove the dust treatment from ½ of the plots prior to a glyphosate application. Similar to the results achieved by Zhou et al. (2006), the occurrence of dust visually reduced common lambsquarters control (relative to the plots where the dust had been washed away). Results from both sets of studies show that dust generation has the potential to significantly impact glyphosate performance'

Figure 2. Percent reduction in weed control by glyphosate as affected by the rate of a silty clay dust applied to the leaves of two nightshade species. Greater numbers on the Y-axis indicated greater reductions in control.

Adapted from Zhou et al. (2006) Weed Science 54:1132-1136.

 

A few closing thoughts about dust and it's impact on weed control:

  • Be mindful of how soil disturbance (cultivation, farm traffic, etc...) affects dust production.
  • Make glyphosate applications in advance of crop production events that are likely to generate substantial amounts of dust.
  • Sprinkler irrigation may be able to remove dust from the leaves of weeds under some situations. Glyphosate applications should be made after the leaves have dried but before more dust can be deposited.
  • Soil particles in spray water can also bind to glyphosate and reduce herbicide efficacy; only clean water should be used to fill spray tanks. (Not actually dust related, but a good practice to remember)

 

Citations:

Boerboom, C. et al. (2006) Factors affecting glyphosate control of common lambsquarters. Proceedings of the North Central Weed Science Society 61:54.

Miller, T. et al. (2013) Glyphosate stewardship: Maintaining the effectiveness of a widely used herbicide. ANR Publication 8492. https://anrcatalog.ucanr.edu/pdf/8492.pdf

Zhou, J. et al. (2006) Soil dust reduces glyphosate efficacy. Weed Science 54:1132-1136.

 

Note: An earlier version of this post is available at the following website: http://treefruit.wsu.edu/dust-can-affect-weed-control-with-glyphosate/

Posted on Monday, July 2, 2018 at 6:38 AM
  • Author: Lynn M. Sosnoskie
Tags: efficacy (1), glyphosate (5), herbicide (10), pesticide (9)

Seguridad de Pesticidas/Pesticide Training

Posted on Tuesday, August 15, 2017 at 3:48 PM

Horseweed Resistance

Researchers have now confirmed that six glyphosate-resistant weed species have been identified in California. Four have been known to exist for some time; they are horseweed (marestail, Conyza sp.), hairy fleabane, rigid ryegrass and annual ryegrass. To that list, junglerice and Palmer amaranth in the Central Valley have been recently added to the list. Additional weeds that have become more of a challenge to control and are on the suspect list are goosegrass and, in the central San Joaquin Valley, the summer grasses sprangletop and witchgrass.

There have never been a lot of herbicides registered for avocado, largely because once they are mature, they self-mulch with their leaves. It's really young orchards that have a weed problem. Growers for the most part have not used pre-emergent herbicides and relied on the many glyphosate products that originally started with Roundup. Sethoxydim (Poast) is registered for non-bearing orchards, but then what can be used as post-emergence herbicides when there is still large open spaces between trees when they are young and bearing? There are still some formulations of paraguat and diquat available for use on avocado, but horseweed is also showing resistance to these materials. Paraquat is also a restricted use material so limits who can apply it. That leaves some of the pre-emergents, such as norfluazon (Solicam), oxyfluorfen (Goal), oryzalen (Surgflan) and simazine (Pricep). These all require water to activate them, and in years with low rainfall efficacy can be erratic. 

From a postemergence standpoint for glyphosate-resistant horseweed the options are pretty slim in avocado. 

  • Paraquat is registered and likely to be pretty effective but has regulatory and safety baggage.

  • Diquat is registered in nonbearing orchards and likely to be effective.

  • Carfentrazone is registered but not very effective on Conyza.

Oxyfluorfen will help glyphosate performance to some extent on Conzya, but not likely to be fully satisfactory. 

From a preemergence standpoint:

  • Simazine should be really effective on Conzya.  It would have groundwater and runoff concerns in some areas.

  • A combination of oxyfluorfen plus pendimethalin or oryzalin would probably be the best available bet for broad spectrum PRE control with decent crop safety.

  • Isoxaben is registered on non-bearing avocado with reasonable Conzya control and good crop safety

Flumioxazin has a non-bearing label and should be pretty good on Conzya.

There has always been concern about the effect on shallow rooted avocado using pre-emergents. This has not been documented, but based on grower experience.

There have never been a lot of herbicides registered for avocado, largely because once they are mature, they self-mulch with their leaves.  It's really young orchards that have a weed problem.  Growers for the most part have not used pre-emergent herbicides and relied on the many glyphosate products that originally started with Roundup.  Sethoxydim (Poast) is registered for non-bearing orchards, but then what can be used as post-emergence herbicides when there is still large open spaces between trees when they are young and bearing?  There are still some formulations of paraguat and diquat available for use on avocado, but horseweed is also showing resistance to these materials.  Paraquat is also a restricted use material so limits who can apply it.  That leaves some of the pre-emergents, such as norfluazon (Solicam), oxyfluorfen (Goal), oryzalen (Surgflan) and simazine (Pricep).  These all require water to activate them, and in years with low rainfall efficacy can be erratic.

We are currently working on getting registration the post-emergence herbicide glufosinate (Rely) registered for avocado.  It's used extensively in other tree crops with success to control many weeds including the Conyza weeds. The registration is being sought through the IR-4 Project (Interregional Research Project Number 4) since 1963 has been the major resource for supplying pest management tools for specialty crop growers by developing research data to support new EPA tolerances and labeled product uses.

 

Photos of young and maturing Conyza

Horseweed
Horseweed

horseweed mature
horseweed mature

Posted on Wednesday, June 15, 2016 at 1:14 PM
Tags: Conyza (1), glyphosate (5), hairy fleabane (3), herbicide (10), horseweed (5), mare''s tail (2), marestail (4), marestail (4), resistance (12)
 
E-mail
 
Webmaster Email: rkrason@ucdavis.edu