- Author: Giuliano Carneiro Galdi
- Posted by: Gale Perez
Roundup Ready technology incorporates genetic resistance to glyphosate into crops and it's an excellent tool for weed control. Initial screening in the early 2000s found good alfalfa crop safety, and many growers currently rely on glyphosate as the only herbicide. Although using the same herbicide over and over is not a good idea because it may accelerate herbicide resistance in weeds, Roundup Ready alfalfa has been successfully used with few to no concerns regarding crop safety. However, the combination of glyphosate and cold weather may cause crop injury, especially in certain regions.
The problem was first observed in 2014 by Steve Orloff, former UCCE farm advisor in Siskiyou County. A Roundup Ready alfalfa field showed injury after glyphosate application followed by a frost event. The main symptoms were plant stunting, chlorosis, and “shepherd's crook”, in which individual alfalfa stems curl over and die (Figures 1 and 2). Yield reductions were also observed for the first cutting. It was clear to Steve the injury was somehow related to the glyphosate application because a section of the field where the wheel line was sitting was not sprayed and it looked perfectly normal.
Interestingly, the injury seen was very similar to symptoms caused by frost and/or bacterial blight caused by Pseudomona syringae – a bacteria that is present everywhere. The bacteria can exacerbate frost damage due to its protein that mimics a crystalline structure and provides a starting point for ice formation, damaging the plant tissue and serving as an entrance port into the leaves and stems. Once into the plant tissue, colonization leads to infection and symptoms about 7-10 days after the frost event. Symptoms on stems start as water-soaked lesions that extend down one side. Leaves become water-soaked and often are twisted and deformed.
Steve was able to replicate the symptoms in field trials conducted in 2015, 2016, and 2017. The field trials showed yield reductions of up to 0.7 ton/acre in the first cutting in Scott Valley. Crop injury was not observed in a similar field trial conducted in 2014, probably because there was no frost event after glyphosate application. Similar impacts were observed in a trial in the intermountain region near Tulelake, CA; additional yield reductions were observed with higher glyphosate rates (Table 1).
Based on this work, a multi-year project started to investigate the effects of glyphosate rate and application timing during various seasons at 24 sites over five years, measuring the impact on alfalfa crop height and biomass yield. Results were published in the Agronomy Journal in 2023 (Loveland et al, 2023). All sites in this study were in the Intermountain West (California and Utah). Results showed that while summer glyphosate application did not injure alfalfa, spring applications reduced crop height at 76% of the sites and biomass at 62% of the sites. In sites where glyphosate application resulted in crop injury, low (22 oz/A) and high (44 oz/A) rates of glyphosate reduced yields by 0.24 ton/A and 0.47 ton/A, respectively. Data also show that the crop height at glyphosate application influenced the degree of injury (Figure 3), with greater yield reductions at 30 – 40 cm than at 5 to 10 cm height.
As alarming as the possibility of injury might sound, its occurrence and degree are widely variable, and most fields will resume normal growth and yields after first cutting. Figure 4 illustrates this complexity and variability throughout experimental sites where harvest yield and crop height were assessed. Note that the locations represented in the following graph are colder than the San Joaquin Valley and the injury happened after glyphosate applications in the spring.
As of 2024, this type of injury has only been reported in the intermountain west due to its high altitude and cooler weather. However, one field I visited in early February in Firebaugh brought my attention back to the issue. The field was planted in the fall of 2023 and had many of the symptoms described above: plant stunting, typical shepherd's crook, chlorosis, and dead stems. While all these symptoms could be exclusively due to bacterial blight infections or frost, parts of the field where glyphosate application was accidentally skipped looked better.
Current UC IPM weed management guidelines for RR alfalfa recommend rotating herbicides with different modes of action to reduce the development of herbicide resistant weeds and avoid glyphosate overuse during the colder winter months. Second, spray glyphosate when the alfalfa is short (< 2”) when using the higher rate (44oz/A) or 4” when spraying at the lower rate (22oz/A). Third, use the lowest glyphosate rate possible according to the weeds present and their stage of development. Finally, pay attention to the weather forecast. Applying glyphosate before frost events increases the likelihood of crop injury, especially in old stands.
Reference
Loveland, L.C., Orloff, S.B., Yost, M.A., Bohle, M., Galdi, G.C., Getts, T., Putnam, D.H., Ransom, C.V., Samac, D.A., Wilson, R., and Creech, J.E. (2023). Glyphosate-resistant alfalfa can exhibit injury after glyphosate application in the Intermountain West. Agronomy Journal, 115, 1827–1841. https://doi.org/10.1002/agj2.21352.
- Author: Daniel K Macon
Barb goatgrass (Aegilops triuncialis L.) is a winter annual grass native to the Mediterranean region and western Asia. According to a UCANR publication, it was introduced to Sacramento and El Dorado Counties via the importation of cattle from Mexico. And it is a growing problem on annual rangelands here in the Sierra Foothills. In some ways, I think of this invasive grass as "medusahead on steroids" - barb goatgrass spikes and joints (seedheads) disperse by attaching to animals, humans, and equipment. I often see new infestations along roads or walkways. Barb goatgrass forms dense stands with a rapidly establishing root system, making it extremely competitive with other annual grasses and forbs. In some areas, barb goatgrass reduces forage quality and quantity by as much as 75 percent - and because livestock tend to avoid the plant (and graze more desirable forages), it can spread rapidly.
Carol and Andy Kramer, who operate a sheep and cattle ranch in Nevada County, have been fighting barb goatgrass for several years. Most recently, they've been working with the Natural Resource Conservation Service (NRCS) through an Environmental Quality Incentives Program contract focused on goatgrass control. Over the course of the last 9 months, Carol and Andy have been working with the Placer Resource Conservation District (RCD) and UCCE to experiment with using prescribed fire to reduce goatgrass and re-invigorate native grasses.
Research suggests that burning goatgrass for two consecutive years offers "excellent control." Sounds pretty straightforward, right?! Not so fast! Fire is an effective control method when most of the fine fuel has dried sufficiently to carry the fire, but when the goatgrass seedheads are still attached to the stem - in other words, in late spring or early summer, when everyone is starting to get nervous about fire in the foothills!
A quick aside about using prescribed fire as a range improvement tool. When I started working with ranchers in California in the early 1990s (when I was just out of college, working for the California Cattlemen's Association), prescribed fire had largely gone out of vogue. This was partly a result of increasing worries about liability, and partly, as I recall, a shift in focus and attitude within the California Department of Forestry and Fire Protection (which became officially known as CalFire in the early 2000s). Today, after a decade of increasingly catastrophic wildfires (and the accelerating spread of invasive weeds like barb goatgrass), prescribed fire is making a comeback - thanks to efforts of many of my UCCE colleagues, RCD staffers and contractors like Cordi Craig and Chris Paulus (who led this effort), and especially of landowners like Carol and Andy!
Obviously, with something as complicated as prescribed burning, you don't simply wake up one June morning and say, "Hey, this would be a great day to light the back pasture on fire!" Carol and Andy (along withCordi and Chris, andUCCE) began planning for this burn last winter. As fire professionals,Cordi and Chris recommended putting a "black line" around the 1.5 acres ofgoatgrass during the winter months, whenCALFIRE burn permits are not required. Carol and Andy invested in water tanks and other equipment, and spent much of the winter and early spring pile burning and creating fire lines. Working together, we also burned several adjacent units to remove ground and ladder fuels in the areas surrounding thegoatgrass site.
Then we all waited! We needed the underlying fuel to be dry enough to burn, but we also needed the goatgrass to hold onto its seedheads. And we needed the right weather conditions. With the wet, cool spring we had in 2023, these conditions didn't arrive until July - well into fire season. This meant that we also needed a permit from CalFire. I've lived and worked in CalFire's NEU unit (which covers Placer, Nevada, and Yuba Counties) - and worked with and around ranchers - for nearly 30 years. I wasn't aware of CalFire ever allowing a rancher to do a prescribed fire for range improvement (or any other reason) in July. But thanks to the Kramer's persistence and Cordi and Chris's experience and knowledge, we received permission to do the burn on July 13.
Carol and Andy started the fire around 9am that morning - temperatures were hovering around 80F, and the relative humidity was just over 50%. Amazingly, we had difficulty getting the vegetation to burn - even as temperatures rose and humidity dropped over the course of the morning. By midday, we'd burned all we could burn, and began mopping up (making sure the fire was completely out).
Walking through the burn, I was amazed by the variability in burn intensity. Some of the goatgrass seedheads were completely consumed; others looked like they had not been exposed to fire at all. Carol collected seedheads from before the burn, as well as singed and apparently unsinged seedheads, to see if there will be any difference in germination (we'll keep you posted). We also started thinking about next year's burn.
One of the biggest challenges in burning for a second consecutive year, I expect, will be whether there is enough fine fuel (other grasses, pine needles, dry leaves, etc.) to carry the fire through the goatgrass. Visiting the site two weeks ago, I was impressed to see native blue wildrye starting to grow in the blackened burn unit (even with very little precipitation since the fire) - we'll be anxious to see what happens once we've had a germinating rain. Even so, we are considering broadcasting a quick-growing, early maturing annual grass (like soft chess (Bromus hordeaceus) this fall so that we have more receptive fuel next spring.
I think we all learned a great deal about the logistics of using fire to manage goatgrass (thanks to Cordi and Chris) - and about the challenges of using prescribed fire during fire season. One of the side benefits, from my perspective, is the demystification of fire generally. This was not a scary burn, even though it happened in the middle of July! While this was partly due to the conditions on the day of the burn, the work that Carol and Andy did to prepare (with Cordi and Chris's guidance) over the many months leading up to July 13 made it successful and safe. We're all looking forward to next year's fire!
- Author: Clebson G Goncalves Ph.D.
- Posted by: Gale Perez
In California, Italian ryegrass [Lolium perenne L. spp. multiflorum (Lam.) Husnot] has been around for a long time and is a major weed in orchards, vineyards, field crops, fallow fields, and so on. It grows vigorously in winter and early spring. Italian ryegrass is a short, rhizomatous, that grows from 11 to 35 inches tall, often with erect stems exhibiting purple coloration at the base. That species can be identified by its dark green, glossy, and hairless leaves that are rolled in the bud. Auricles are well-developed and the shape can vary from clasping to blunt, and the ligules are long and membranous. Once flowering occurs, Italian ryegrass is easily distinguishable by alternating spikelets that run along the length of the main seed head stem. The seed heads range from 3 to 12 inches and consist of solitary small stalkless spikelets (Fig. 1). Additional details regarding identification can be found on the UC IPM website.
Also called annual ryegrass, Italian ryegrass herbicide resistance and management strategies have been the topic of discussion among growers, PCAs, UC Cooperative Extension farm advisors, and UC weed science specialists. Because Italian ryegrass has been controlled in crop production systems mainly with herbicides for decades, since 1998, populations of Italian ryegrass have been documented to be resistant to herbicides (Fig. 2). In California, the first report of Italian ryegrass glyphosate-resistant was in 2008 in almond orchards and vineyards, and the evolution and spread of these populations in the state made alternative postemergence herbicides an important management strategy against this troublesome species (published by Jasieniuk et al. 2008, Weed Sci. 2008).
Repeated herbicide use has selected Italian ryegrass populations resistant to multiple of herbicide mode of actions. A recent Weed Science publication by Dr. Brad Hanson's lab confirmed multiple Italian ryegrass resistance to the herbicides paraquat (Gramoxone® 2.0 SL), clethodim (Envoy Plus®), and glyphosate (Roundup PowerMax®). A second study conducted in Dr. Hanson's lab also confirmed that another Italian ryegrass biotype population collected in Hamilton City, CA is resistant to paraquat (Gramoxone® 2.0 SL), clethodim (Envoy Plus®), glyphosate (Roundup PowerMax®), and Mesosulfuron-Methyl (Osprey®). It should be noted that ryegrass populations resistant to fluazifop-butyl (Fusilade® DX), glufosinate-ammonium (Rely® 280), and sethoxydim (Poast®) also have been reported in other cropping systems elsewhere in California.
Worldwide Italian ryegrass has been identified as resistant to 29 herbicides, from 8 different groups of classification with multiple resistance to 1, 2, 3, or 4 sites of action (WeedScience.org, 2022). The most recent Italian ryegrass biotype was identified in a soybean and winter wheat field in North Carolina with multiple resistance to 4 sites of action (clethodim, glyphosate, nicosulfuron, and paraquat).
Management Strategies
For efficient management of Italian ryegrass, integrated weed management (IWM) practices must be adopted that allow the combination of various control strategies, including preventive, cultural, mechanical, physical, biological, and chemical control.
Prevention Control: Avoiding dispersion and introduction of Italian ryegrass into the property and ensuring that seeds and equipment are free of Italian ryegrass contaminants is one of the main strategies in the IWM programs.
Physical Control: Soil tillage may be used as one strategy to be added to the IWM toolbox. Italian ryegrass seeds buried in the soil die quickly and must be close to the surface to emerge. So, this practice can help suppress the population and provide long-term control.
Chemical Control: Italian ryegrass control using PRE and POST herbicide management programs continues to be the most effective. A well-designed herbicide application program with a combination of PRE- and POST-emergent herbicides (e.g., fluazifop-butyl (Fusilade® DX), glufosinate-ammonium (Rely® 280), pyroxsulam (SimplicityMT), rimsulfuron (Matrix®SG), sethoxydim (Poast®), flumioxazin (Chateau®), oxyfluorfen (GoalTender®), pendimethalin (Prowl H2O), and so on are possible options) still been quite effective in controlling Italian ryegrass. Growers should always consult a PCA and a local UCCE farm advisor to help design herbicide application programs and application rates appropriate for their unique growing system. Growers should also keep in mind that they need to avoid repeated herbicide use to prevent resistance in Italian ryegrass populations. Herbicides with different modes of action on a rotational basis should be encouraged to suppress the Italian ryegrass population and provide long-term control.
The growers also may adopt non-synthetic herbicide products for Italian ryegrass control. Among those available commercial products, the active ingredients, including acetic acid (Weed Pharm®), citric acid + Clove oil (BurnOut®), caprylic acid + capric acid (Suppress®), pelargonic acid + related fatty acids (Scythe®), D-limonene (AvengerAG®), ammonium nonanoate (Axxe®) and others, have been used for the non-selective control of that weed. Usually, organic herbicides are recommended for grass and broadleaf weeds in the early stages of growth. For Italian ryegrass already established, organic herbicides have shown poor effectiveness, and recovery approximately two weeks after treatment application (Fig. 3). Studies have shown that organic herbicides applied to control Italian ryegrass may require late sequential application due to the non-systemic characteristics of these products (ongoing trials by Clebson Gonçalves, 2023).
Even with the increase in herbicide-resistant weeds, herbicide control options continue to be the most effective and used option for producers because of time and money. However, diversified management practices should be encouraged as they are crucial for crop productivity, efficiency, saving cost, and sustainability of the systems.
Clebson Gonçalves is the UC Cooperative Extension Diversified Agriculture Advisor in Lake and Mendocino counties.
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- Author: Michelle Leinfelder-Miles
In 2022, I estimate rice acreage in the Delta, south of the Yolo Bypass, was at least 8,000 acres. Most Delta rice is grown in San Joaquin County, but there is some acreage in Sacramento County. While Delta rice acreage is relatively small compared to that in the Sacramento Valley, it has been steadily increasing over the last several years (Table 1).
Table 1. Rice acreage and yield according to the San Joaquin County Agricultural Commissioner's crop reports. County rice production is predominantly in the Delta region.
Given the increasing interest in rice production among Delta growers, and the differences in production practices from the Sacramento Valley, UC Cooperative Extension and UC Davis will be releasing a cost of production report specifically for Delta rice later this year or in early 2023. A Delta rice cost study was last produced in 2007, so updating the study was long-overdue. I want to thank all the growers who participated in a focus group to update the study.
Cool temperatures can make the Delta a challenging place to grow rice. Low night-time temperatures can cause blanking, which results in empty grains. Growers are limited to using only very-early and early maturing varieties. Most of the Delta acreage was planted with variety M-206, but some growers also planted a portion of their acreage with M-105. In 2022, we continued the UCCE Delta variety trial, which will help to identify and advance cold-tolerant varieties. The Delta trial is part of a statewide network of trials, led by UC Rice Extension Specialist, Bruce Linquist, and coordinated by Staff Researcher, Ray Stogsdill. I anticipate that the statewide results will be ready in early 2023.
This year, I worked with growers and consultants on a handful of pests. Weed management is always top-of-mind for rice growers. There are limited practices and products that can control problematic weeds, and in some circumstances, the weeds may develop resistance to the herbicides that are available. If herbicide resistance is suspected, please contact me so that we can submit weed seeds for testing. We would collect the seeds in the late summer or early fall when they have matured but have not shattered. Resistance testing is overseen by UC Weed Science Extension Specialist, Kassim Al-Khatib, and takes place in greenhouses during the winter. By the following spring, we provide the grower with information on which herbicides are still working and which are not.
I have been trapping armyworms in the Delta since 2016, in collaboration with fellow farm advisor, Luis Espino. The traps catch true armyworm moths. They were deployed on three ranches and monitored weekly. In 2022, we recovered the highest moth counts since 2017, and the peak flight occurred about one week earlier than in 2017. This is important information for management because, based on the armyworm life cycle, we know that peak worm populations occur approximately two weeks after peak moth flight. In other words, growers can make informed decisions based on the monitoring data and adapt their management to the field conditions. Trap monitoring is one part of an integrated pest management program for armyworms, which also includes scouting for feeding damage and the worms themselves. Over the years, I have observed armyworms in riparian and wetland vegetation that neighbor rice fields, so it is important to scout those areas, too.
We should continue to keep weedy rice on our radars because we have seen it in the Delta in the past. Where we have observed light infestations, it appears that keen management – including in-season rogueing, post-harvest management that includes straw chopping but not incorporation, and winter flooding – can reduce, if not eliminate the pest. These are our management tools until a herbicide is approved for spot-spraying. Growers should also pay attention to equipment sanitation – harvesting weedy rice fields last (if possible) and thoroughly cleaning out equipment after harvesting fields where weedy rice has been observed.
Finally, I will be starting new projects this winter, in collaboration with fellow farm advisor, Whitney Brim-DeForest, and graduate student, Sara Rosenberg, to evaluate winter cover cropping between rice crops. Our objectives are to evaluate carbon and nitrogen cycling and variety survivability during the cool, wet (we hope!) winter conditions. These projects are supported by the CDFA Healthy Soils Program and the CA Rice Research Board. I look forward to sharing results in the years to come.
I am grateful to work with a great team of UC colleagues on these rice projects. I am also grateful for all the growers who have collaborated with us. I wish everyone a good end to the year, and I look forward to working with you again in 2023.
- Author: Jim Catalano
- Posted by: Gale Perez
From the Cornell Chronicle--June 22, 2022
Farmers can tailor their efforts to control weeds more effectively by pinpointing when a particular weed will emerge, according to a new Cornell study.
Researchers in the College of Agriculture and Life Sciences reviewed past studies on the peak timing of emergence for 15 troublesome weed species in the Northeast, as well as potential ways to use this knowledge, in their study, “Improving Weed Management Based on the Timing of Emergence Peaks: A Case Study of Problematic Weeds in Northeast USA,” published June 21 in the journal Frontiers in Agronomy.
“There are lot of different weed management tactics out there, and most of them can be improved with some consideration of what weed species you have and when they emerge,” said lead author Bryan Brown, integrated weed management specialist for New York State Integrated Pest Management and adjunct assistant Professor in the School of Integrative Plant Science's Horticulture Section, in the College of Agriculture and Life Sciences. “In this paper, we provided a framework starting with those tactics that are easiest to tailor or adjust – all the way up to revamping a cropping system – based on avoidance of certain weed species.”
As an example, Brown pointed to common ragweed. “We found that in most of the literature, common ragweed had finished up its emergence by June 1,” he said. “So, if you're able to wait to till and plant your field until after June 1, then you've effectively avoided common ragweed for the season.” Conversely, if a field is riddled with mid or late-season weeds, planting earlier can help give crops a head start to outcompete them.
When it comes to controlling weed seedlings using herbicides or shallow tilling, control is most effective soon after weeds emerge, so knowing when different weed species grow can help farmers plan ahead.
Farms with flexible crop rotations can leave the ground bare, or perhaps cover cropped, during the period when their most problematic weed emerges. By controlling that species, they essentially remove its weed seeds from the soil so it will be less of a problem in the future.
The researchers found that the timing of weed emergence varied among previous studies due to factors such as weather, soil temperature and moisture.
“Naturally, that's going to vary from year to year and from study to study,” Brown said. “But the big surprise to me was that among previous studies that modeled weed emergence, when we input identical weather data weather data, there was still variation in when they expected weeds to emerge. That highlights the regional differences in soils and weed genetics.”
As the models improve by incorporating regional differences, the researchers hope work with the Network for Environment and Weather Applications to give farmers direct access to weather-based weed emergence predictions.
“As weed management becomes more challenging, I think that this type of planning is going to become more important,” Brown said. “Hopefully, as those emergence models become more accurate we'll be able to use these tactics to even better use and really fine-tune the timing of our weed management.”
This work was partially supported by a joint research and extension grant the Cornell University Agricultural Experiment Station and Cornell Cooperative Extension received from the U.S. Department of Agriculture's National Institute for Food and Agriculture.
Jim Catalano is a freelance writer for the College of Agriculture and Life Sciences. Cornell University.
Original source: Cornell Chronicle--June 22, 2022