- Author: Ben Faber
There has been a good overall discussion of herbicide resistance found in plants and how they can affect orchard management. Check out this presentation by UC Cooperative Extension Weedologist, Brad Hanson, in the "past Webinars" section:
https://ucanr.edu/sites/ucexpertstalk/
And read more about glyphosate resistance in orchards:
- Author: Ben Faber
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
- Author: Ben Faber
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.
- Author: Travis Bean
Although the main objective of herbicide use in avocado orchards (and all crops) is to manage weed populations, sometimes unintentional injury of the crop itself can occur when herbicides are incorrectly applied. Herbicide injury in avocado can reduce yield, decrease fruit, reduce plant vigor, increase susceptibility to diseases and pests, and sometimes result in plant death. Common situations resulting in injury include spray drift, tank contamination, application of the wrong herbicide or rates, and herbicide carryover from a previous crop. The extent of herbicide damage on avocado can vary widely according to factors such as herbicide mechanism of action (MOA) and application rate, route of exposure, plant size and growth stage, soil properties, and weather.
Herbicide injury can be difficult to diagnose properly and is often confused with disease, insect damage, nutrient deficiencies, and other environmental stresses. It is recommended that trained researchers or Pest Control Advisers, who may utilize plant tissue, make diagnoses or soil samples along with plant symptoms, injury progression, and other plant species affected, orchard herbicide use history, weather conditions, and other factors to confirm or rule out injury from herbicides or other causes.
Where the injury occurs can also be an indication of herbicide injury. For example, if injury is on just one side of a tree or trees near another field, it may be an indication of spray drift. If it occurs only along the edge of the skirts, it may be a hint that an uneven ground spray was applied.
The majority of herbicides for use in avocado orchards in California fall into eight MOAs as defined by the Weed Science Society of America. MOAs describe the specific biological processes that are disrupted by a group of herbicides. These processes control the growth and development of plants and when interfered with, can result in plant injury or death.
Table 1: Common herbicides used in avocado, their mechanism of action, and possible injury symptoms
|
WSSA Group |
Mechanism of Action |
MOA description1 |
Example herbicides |
Possible injury symptoms1 |
|
1 |
Acetyl CoA Carboxylase (ACCase) Inhibitors |
Inhibits lipid creation in grasses, preventing production of plant cell membranes |
Fluazifop-P-Butyl (Fusilade DX), Sethoxydim (Poast) |
Chlorosis, necrotic spots, leaf crinkling, leaf distortion |
|
3 |
Mitosis Inhibitors |
Inhibits cell division in germinating seedlings and lateral roots |
Oryzalin (Surflan) |
Thickened, shortened lower stems and small, crinkled leaves |
|
5 |
Photosystem II Inhibitors |
Prevents the transfer of energy generated during photosynthesis, causing a buildup of reactive molecules that damage chlorophyll and cell membranes |
Simazine (Princep 4L) |
Chlorosis, necrosis progressing from leaf margins toward the center of the leaves, foliar applications will appear as leaf burn |
|
9 |
Enolpyruvyl Shikimate-3-Phosphate (EPSP) Synthase Inhibitors |
Inhibits the production of three aromatic amino acids and the enzymes and proteins built from them |
Glyphosate (Roundup) |
Leaves of trees and vines become chlorotic 3 to 7 days after exposure, and margins of new leaves become necrotic |
|
12 |
Carotenoid Biosynthesis Inhibitors |
Inhibits production of carotenoid pigments, which harvest light and protect chlorophyll from reactive molecules |
Norflurazon (Solicam DF) |
Plant foliage turns white and appears bleached
|
|
14 |
Protoporphyrinogen Oxidase (PPO) Inhibitors |
Blocks the production of chlorophyll and causes a buildup of reactive molecules that damage existing chlorophyll, carotenoids, and cell membranes |
Oxyfluorfen (Goal 2XL), Carfentrazone (Shark EW), Flumioxazin (Chateau) |
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. |
|
21 |
Cellulose Inhibitors |
Inhibit cell wall synthesis and plant growth |
Isoxaben (Gallery 75 DF) |
Chlorosis, necrosis, leaf crinkling, leaf distortion, purpling of the leaf, and stunting |
|
22 |
Photosystem I Inhibitors |
Disrupts photosynthesis, forming reactive molecules that destroy cell membranes |
Paraquat (Gramoxone SL) |
Drift injury will appear as speckling or necrotic spots on leaf tissue |
1Not a complete list. Symptoms listed are likely for established orchards. For detailed descriptions of MOAs and injury symptoms, as well as a searchable database of specific injury images (e.g., “chlorosis, necrosis, stem swelling, etc.” visit http://herbicidesymptoms.ipm.ucanr.edu.
References:
Al-Khatib, K. 2015. University of California Integrated Pest Management Herbicide Symptoms. http://herbicidesymptoms.ipm.ucanr.edu (accessed 09/05/18)
Faber, B.A., C.A. Wilen, B.D. Hanson. 2016. Weeds. Pages 107-124 in University of California Integrated Pest Management Guidelines for Avocado. http://ipm.ucanr.edu/PMG/selectnewpest.avocado.html (accessed 09/05/2018)
Sosnoskie, L.M., B.D. Hanson. 2013. Understanding herbicide mechanisms (modes) of action and how they apply to resistance management in orchards and vineyards. UC Weed Science Blog Post. http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9383 (accessed 09/05/2018)
Weed Science Society of America. Summary of Herbicide Mechanism of Action
According to the Weed Science Society of America. https://wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf (accessed 09/05/2018)
Photo: Sometimes weeds are tasty, like amaranth and purslane
- Author: Ben Faber
With the rains, and in those area where fire took out the competition, weeds are coming back in their glory. Mustard has painted the hills yellow. The question comes up, what to do about all that wild growth. Mechanical control, such as discing or whipping can work great. Sometimes chemical control is the only answer. A recent request for an alternative to glyphosate (Round-up) control of marestail (horseweed, Conyza canadensis) which is similar to hairy fleabane (Conyza bonariensis), came to the office from a lemon grower. Glyphosate just wasn't controlling it. And it's been a problem for a while, even in tank mixes with paraguat and old-line weed killer. The alternative might be a newer material, such as saflufenacil (Treevix) which has been recently added to the herbicides that can be used on citrus.
As always before doing "vegetation management" it's best to identify the plant that is the problem
Identify the problem plant (weed)
http://wric.ucdavis.edu/information/weedid.htm
or if you know what the plant is, go directly to a listing of the weeds
Listing of weeds, their biology and control
http://wric.ucdavis.edu/information/info_spec_weed.htm
- Susceptibility of Winter Weeds to Herbicide Control (9/08)
- Susceptibility of Spring/Summer Weeds to Herbicide Control (9/08)
Or you can go in reverse order and look at your tree crop and see what herbicides are listed
Listing of herbicides by tree crops, including avocado and citrus
http://wric.ucdavis.edu/PDFs/T&V_herbicide_registration_chart.pdf
