- Author: Mike Hsu
Supply-chain crisis forces some to pivot to mechanical, biocontrol measures
Driving through her vineyards on a chilly morning in December, Hortencia Alvarado is taking comfort – for now – that the weeds she sees are all yellow. But there remains a nagging worry that, like the pesky plants, is merely lying dormant for the season.
When March rolls around, and the first signs of new green growth appear on the vines, Alvarado and other vineyard managers will again have to confront the ongoing shockwaves of the global supply-chain crisis.
Growers of grapes – the third-highest valued agricultural commodity in California at $4.48 billion in 2020 – likely won't be able to access the herbicides that they usually apply.
“I definitely need to start thinking and considering it because I don't want to be in that situation where I don't have [the herbicide] when I need it,” said Alvarado, a vineyard manager in the San Joaquin Valley.
Imperfect alternatives
She first noticed the effects of the shortages this past August, during the application following the harvest of early varietals. Alvarado's agricultural pest control adviser had recommended a different product, instead of their usual standby, Rely – because none of the handful of suppliers in California could find it.
Then Alvarado's foreman started reporting that the substitute wasn't controlling the weeds.
“We were using some other stuff that wasn't as good, so basically we were wasting money on stuff that wasn't doing what we wanted it to do,” Alvarado explained.
The need for more machines or labor is just one result of the herbicide shortage, said George Zhuang, University of California Cooperative Extension viticulture farm advisor in Fresno County. Zhuang has received “a lot” of calls from growers about the chemical supply issues, which are also affecting fertilizers. He's been urging them to move away from traditional herbicides to mechanical means or biocontrol such as sheep or fowl – even though they might be more expensive.
Zhuang estimates that while a weed program comprises 5% to 10% of total production costs in a normal year with the usual herbicides, the use of nonchemical alternatives could hike that percentage up to 10% to 20%. In addition to their impact on the bottom line, effective herbicides are especially crucial to grape growers because vines – unlike tree crops – cannot naturally shade out weeds with expansive canopies.
“Right now, people can still scramble around and find some limited chemicals to make sure the crop is successful for the harvest, but if the situation goes for another year, I think there's going to be a panic in farming communities,” Zhuang said.
Herbicide challenges expected to linger
Unfortunately, the availability of certain products is likely going to be “challenged” into at least the middle of 2022, according to Andy Biancardi, a Salinas-based sales manager at Wilbur-Ellis, an international marketer and distributor of agricultural products and chemicals. Biancardi said that the suppliers he talks to are advising people to make preparations.
The supply of glyphosate, the key component in products such as RoundUp (used by many Midwestern farmers), appears to be most affected, Biancardi said. As a result, that shortage has put the squeeze on alternatives such as glufosinate, used in products like Rely – the herbicide favored by many California grape growers.
“The cost of glufosinate has definitely gone up because there just isn't enough, so everyone is obviously marking it up,” said Biancardi, who estimates that prices for both glyphosate and glufosinate are up 25% to 30% for growers.
Alvarado said that while large commercial operations are able to pay the premium prices or shift to other weed control measures, some smaller growers have essentially given up the fight – simply letting the weeds take over.
“They're just letting it go wild until the dormant season,” she said. “They're hoping that – by when they do start to spray [around March] – they'll hopefully have that Rely.”
Silver lining to supply crisis?
Large-scale growers and retailers are buying up those scarcer products when they can, in anticipation of future shortages during critical times. Biancardi said that while his company traditionally runs inventories down at the end of the season, they are instead stocking up on herbicides that customers will demand.
“Careful planning and forecasting is going to be more important than ever, that's really the key,” he said. “At this point we can't guarantee ‘business as usual,' based on what we're hearing.”
Shaking off old habits might actually bring some benefits to business, according to Alvarado, as a forced shift away from chemicals could prove to be a selling point for customers, from a sustainability and marketing standpoint.
“Out of this shortage, there might be some good, some wins,” she said, “but at the same time, we're going to need some answers – I think it's going to be a bumpy road.”
Calling the confluence of drought, record heat and a shortage of chemicals a “perfect storm,” Zhuang said that consumers could start feeling those jolts as well.
“Eventually, somebody is going to eat the costs – either the farming community or the consumer is going to eat the cost, I hate to say it,” he said.
/h3>/h3>/h3>/h2>- Author: Marie Jasieniuk
- Author: Maor Matzrafi
Italian ryegrass is a major weed in orchards, vineyards, field crops and fallow fields of California (Figure 1). Several different herbicides are used to control ryegrass and had been effective in reducing infestations until resistance evolved in many populations following repeated use of the herbicides. To date, resistance to glyphosate, paraquat, and some ACCase and ALS inhibitors has been confirmed in ryegrass infestations across the agricultural landscape of California. To make matters worse, resistance to multiple postemergence herbicides with different modes of action has been confirmed within the same orchard, vineyard, or field in some areas. Consequently, management of Italian ryegrass in California annual and perennial cropping systems has become a major challenge.
Glufosinate is an alternative non-selective postemergence herbicide that can still be used to control herbicide-susceptible and most herbicide-resistant Italian ryegrass in California, as only two populations with resistance to glufosinate have been documented to date. However, the higher cost of glufosinate relative to other herbicides may drive farmers to apply glufosinate at reduced rates, as has occurred in other cropping systems, such as the Australian wheat belt, with other herbicides. The lower rates and other drivers such as herbicide applications at non-optimal weed size, inappropriate weather conditions, and insufficient spray coverage may result in sublethal rate selection of ryegrass by glufosinate.
To evaluate the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and to determine if selected populations are cross-resistant to herbicides with other modes of action as has been observed in a few studies, we conducted a greenhouse study using a herbicide-susceptible parent population originally collected from a vineyard in Sonoma County. Plants were grown in the greenhouse to the 3-4 leaf stage and treated with low glufosinate rates for three generations. For the first round of selection, plants were treated with glufosinate at 1/8X, 1/4X, and 1/2X of the labelled field rate (984 g ai ha-1). Surviving plants were grown to reproductive maturity and allowed to cross-pollinate. Seeds were harvested from all plants, pooled, germinated, and plants grown in the greenhouse for the next round of selection at slightly higher rates (1/2X, 3/4X, and 1X). For the third round of selection, plants were treated at 3/4X, 1X, and 1.25X of the labelled field rate.
Results showed that susceptibility to glufosinate was reduced in offspring in comparison with the susceptible parent population following only three generations of selection (Figure 2). Comparing the susceptible parent population with the offspring from the second and third selection cycle, the percentage of surviving plants increased to values of LD50 (1.31 and 1.16, respectively) and LD90 (1.36 and 1.26, respectively).
Figure 2. Dose-response of the Italian ryegrass susceptible parent population (P0) and three successive generations (P1, P2, P3) of offspring following selection with low glufosinate rates in the greenhouse. Lines are the predicted values for percent survival. Red arrow indicates the labelled field rate (984 g ai h-1). Adapted from Matzrafi et al., 2020 (https://www.biorxiv.org/content/10.1101/2020.07.04.182733v1).
When treated with alternative postemergence herbicides (glyphosate, paraquat, or sethoxydim), no plants of either the parental or successive offspring populations survived treatment with 0.75X or higher rates of these herbicides (see Matzrafi et al., 2020 (https://www.biorxiv.org/content/10.1101/2020.07.04.182733v1).
The magnitude of increases in resistance levels over three generations of recurrent low-rate glufosinate selection observed is relatively low compared with higher levels of resistance observed in response to low-rate selection with other herbicides (three-fold and greater). However, under field conditions, even low levels of resistance within weed populations may reduce control. This study shows that repeated selection with glufosinate at low rates can reduce the susceptibility of Italian ryegrass populations to glufosinate, and points to the importance of incorporating a diversity of approaches, both chemical and non-chemical, in the management of ryegrass in annual and perennial cropping systems of California.
This article was originally published in the Weed Science blog.
- Author: Marie Jasieniuk
- Author: Maor Matzrafi
- Posted by: Gale Perez
Italian ryegrass is a major weed in orchards, vineyards, field crops, and fallow fields of California (Figure 1). Several different herbicides are used to control ryegrass and had been effective in reducing infestations until resistance evolved in many populations following repeated use of the herbicides. To date, resistance to glyphosate, paraquat, and some ACCase and ALS inhibitors has been confirmed in ryegrass infestations across the agricultural landscape of California. To make matters worse, resistance to multiple postemergence herbicides with different modes of action has been confirmed within the same orchard, vineyard, or field in some areas. Consequently, management of Italian ryegrass in California annual and perennial cropping systems has become a major challenge.
Glufosinate is an alternative non-selective postemergence herbicide that can still be used to control herbicide-susceptible and most herbicide-resistant Italian ryegrass in California as only two populations with resistance to glufosinate have been documented to date. However, the higher cost of glufosinate relative to other herbicides may drive farmers to apply glufosinate at reduced rates as has occurred in other cropping systems, such as the Australian wheat belt, with other herbicides. The lower rates and other drivers such as herbicide applications at non-optimal weed size, inappropriate weather conditions, and insufficient spray coverage may result in sublethal rate selection of ryegrass by glufosinate.
To evaluate the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and to determine if selected populations are cross-resistant to herbicides with other modes of action as has been observed in a few studies, we conducted a greenhouse study using a herbicide-susceptible parent population originally collected from a vineyard in Sonoma County. Plants were grown in the greenhouse to the 3-4 leaf stage and treated with low glufosinate rates for three generations. For the first round of selection, plants were treated with glufosinate at 1/8X, 1/4X, and 1/2X of the labelled field rate (984 g ai ha-1). Surviving plants were grown to reproductive maturity and allowed to cross-pollinate. Seeds were harvested from all plants, pooled, germinated, and plants grown in the greenhouse for the next round of selection at slightly higher rates (1/2X, 3/4X, and 1X). For the third round of selection, plants were treated at 3/4X, 1X, and 1.25X of the labelled field rate.
Results showed that susceptibility to glufosinate was reduced in offspring in comparison with the susceptible parent population following only three generations of selection (Figure 2). Comparing the susceptible parent population with the offspring from the second and third selection cycle, the percentage of surviving plants increased to values of LD50 (1.31 and 1.16, respectively) and LD90 (1.36 and 1.26, respectively).
Figure 2. Dose-response of the Italian ryegrass susceptible parent population (P0) and three successive generations (P1, P2, P3) of offspring following selection with low glufosinate rates in the greenhouse. Lines are the predicted values for percent survival. Red arrow indicates the labelled field rate (984 g ai h-1). Adapted from Matzrafi et al., 2020 (https://www.biorxiv.org/content/10.1101/2020.07.04.182733v1).
When treated with alternative postemergence herbicides (glyphosate, paraquat, or sethoxydim), no plants of either the parental or successive offspring populations survived treatment with 0.75X or higher rates of these herbicides (see Matzrafi et al., 2020 (https://www.biorxiv.org/content/10.1101/2020.07.04.182733v1).
The magnitude of increases in resistance levels over three generations of recurrent low-rate glufosinate selection observed is relatively low compared with higher levels of resistance observed in response to low-rate selection with other herbicides (three-fold and greater). However, under field conditions, even low levels of resistance within weed populations may reduce control. This study shows that repeated selection with glufosinate at low rates can reduce the susceptibility of Italian ryegrass populations to glufosinate, and points to the importance of incorporating a diversity of approaches, both chemical and non-chemical, in the management of ryegrass in annual and perennial cropping systems of California.
/span>
- Author: Drew A Wolter
- Author: Dani Lightle
- Posted by: Gale Perez
Introduction
In order to prevent herbicide damage in young trees, especially from postemergence herbicide, standard pomological practice is to apply white latex paint to the bottom 2 to 3 feet of trunk of newly planted trees, before applying herbicides. While this may provide some level of protection, research to support this practice is lacking. In order to assess the efficacy of white latex paint in mitigating herbicide damage, a field experiment was conducted in Arbuckle, CA to evaluate the impacts of latex paint on herbicide injury in young almond trees.
Methods
To conduct this experiment, second-leaf almond trees were grouped into three categories: old paint (9-week old), new paint (2-day old), no paint (hardened-off for 9 weeks), and cartons. On June 20th, 2019 treatment combinations of different rates (see treatment table below) of glyphosate (Roundup PowerMAX), glufosinate (Rely 280), or a tank mix of both were applied. Each treatment combination had 4 replicates.
Herbicide applications
Herbicide applications were made using a CO2 backpack sprayer at 35 psi, and a spray volume of 20 gallons/acre. A single nozzle was held 18 inches from the trunk, moving vertically (from top to bottom) for one second on both the eastern and western side of the trees.
Herbicide Treatments | |
Top Label Rate | 3x Label Rate |
Glufosinate- 1.5lbs/ac | Glufosinate - 4.5lbs/ac |
Glyphosate- 2.75lbs/ac | Glyphosate - 8.25lbs/ac |
Glufosinate + glyphosate- 1.5 + 2.75lbs/ac | Glufosinate + glyphosate- 4.5 + 8.25lbs/ac |
Trunk protection
In 2017, the block used to conduct this experiment was planted with greenhouse-grown trees. Each tree came with preinstalled cartons. Nine weeks before the herbicide applications for this experiment took place, the cartons for the “no paint” and “old paint” treatments were removed for the first time, exposing green bark. Valspar interior latex paint diluted 50:50 with water was then applied using a painter's mitt to the group of trees in the old paint treatment. This also allowed for the no paint treatment to harden off for nine weeks prior to the herbicide application. Two days prior to the herbicide application, the cartons for the new paint treatments were removed for the first time (again, exposing green bark) and painted. The cartoned treatments in this experiment never had their cartons removed.
Trunk Protection |
Old Paint (9-week old paint) |
No Paint (hardened-off for 9 weeks) |
New Paint (2-day old paint) |
Carton |
Evaluations
Evaluations across three categories of tree stress were taken on a weekly basis, starting three weeks after treatment (WAT) to allow symptoms to develop.
- Trunk damage: Assessments made from 3WAT-5WAT quantified the number of individual gumming sites on each trunk (see Figure 1). No further trunk gummosis was observed starting five weeks after the herbicide applications.
Rating scale--Trunk Damage | |
1 | 0 – 10 Individual sites |
2 | 11 – 20 Individual sites |
3 | 21+ Individual sites |
- Canopy stress: Evaluations were taken from 5-8WATassessingthedegreeofinterveinalchlorosis,mottledchlorosis, spotting,stackedinternodes, necrosis and stem die back.
Rating scale--Canopy Stress 1 Coming out of stress, exhibiting new growth. 2 Damage, new growth may be present but injured. 3 Leaf drop and further necrosis; no new growth present.
- Defoliation: Ratings were taken from 5-8 WAT assessing the degree of defoliation for each tree (see Figure 2).
Rating scale--Defoliation | |
1 | Less than 25% |
2 | 25-50% |
3 | Greater than 50% |
4 | Complete defoliation |
Results
Preliminary results indicate that paint as a trunk protection method may not provide significant protection from glyphosate or glufosinate. Tree stress caused by trunk-applied herbicides was lowest in most treatments with no paint at all, which suggest that hardening of the bark is key to mitigating herbicide damage in young trees. Examples of treatment combination results shown in images and graphs below.
Trunk damage:
Five weeks after herbicide treatments, data from the top-of-label-rate tank-mix application showed a 22% increase in trunk damage in trees with old paint, and a 4% increase in damage in trees with new paint, when compared to trees with no paint.
Canopy stress:
Eight weeks after treatment, the label rate tank-mix applications showed a 29% increase in canopy stress in trees with old paint, and a 14% increase in damage was observed in trees with new paint, when compared to trees with no paint.
Defoliation:
Eight weeks after treatment, the high rate (3x) tank-mix applications showed a 40% increase in defoliation in trees with new paint, and a 20% increase in defoliation was observed in trees with old paint, when compared to trees without paint that were allowed to harden-off for 9 weeks.
Figure 2. These three images demonstrate the level of defoliation observed 5 weeks after the high rate tank-mix applications were made. Arranged in order of stress response severity: new paint (2a, above) exhibiting the highest level of defoliation, old paint (2b, above), and no paint (2c, below).
Conclusion:
Preliminary results indicate that in most treatment combinations, old and new paint as trunk protection methods did not reduce tree stress caused by trunk-applied herbicides. Allowing the bark of young almond trees to harden off for at least nine weeks reduced herbicide damage. The most efficacious trunk protection option for young almonds trees is to install a carton, though remember when cartons are eventually removed green bark may be present and susceptible to herbicide injury. Therefore, as the trees mature and cartons are removed, allow the bark on trunks of trees to harden off to minimize herbicide damage.
/h3>/h3>/h3>
- 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.