- Author: Konrad Mathesius
Summary note: This is a belated research update from herbicide trials (targeting Italian ryegrass) carried out in the winter of 2021-2022 in wheat fields in the Esparto area. The southern Sacramento Valley saw a record number of consecutive days without rain in that year, which severely limited the efficacy of post-emergent systemic herbicides. Growers should prioritize scheduling post-emergent herbicide applications early in the weed's growth stages and when weeds are actively growing to avoid the severe reduction of herbicide efficacy that can occur as a result of unexpected droughty conditions. This is particularly important given that the weather systems in our area are unpredictable between December and February and will often dissipate as they approach the Sacramento Valley.
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Hot days would seem to indicate that we are nowhere near wheat season, but unpredictable weather patterns as early as October can make weed management difficult. As we approach winter, it's worth taking a minute to reiterate some of the interactions between herbicide efficacy and drought conditions that we witnessed in what was a very dry winter (2021-2022).
Italian ryegrass: a widespread weed with a track record of herbicide resistance
Italian ryegrass (IR), like Palmer amaranth and horseweed, is known for its capacity to develop herbicide resistance. In order to address resistance issues in IR, the University of California Cooperative Extension (UCCE) has been looking into the various ways in which growers can reduce IR populations through the use of available herbicides as well as mechanical cultivation techniques. Some of these lessons are valuable not only in winter rotations, but also in summer cropping systems.
2022 Herbicide Trials: a perfect storm
If there's one thing we learned in the spring of 2022, it was how severely drought conditions can reduce the efficacy of herbicides. In short: drought-stressed weeds are much harder to control with postemergence herbicides.
Figure 1. Cumulative rainfall from 2022. Flat parts of the curve are indicative of drought periods.The season was characterized by feast/ famine rainfall patterns. Heavy rainfall followed by long periods of drought stress produced conditions that dramatically reduced herbicide efficacy.
Substantial early rains in October of 2021 led to early germination of IR in the trial. Burndown applications were delayed due to wet field conditions throughout most of November and December and wheat was planted during a brief window of time in December.
The herbicides for the post-emergent trial were sprayed in late-January when wheat was at the tillering growth stage (Feekes 2) and ryegrass had 2-3 tillers and was about 6” tall.The ryegrass was still within the size recommendation on the herbicide labels; however, drought conditions had begun to set in three weeks prior to treatment.
The area where the trial was located saw no rainfall for 70 days after the herbicide application. The dry spell lasted 92 days in total, the longest in the region since the 1920s.
Results / Discussion:
The absence of a burndown application allowed for competitive weed growth that stunted the crop
The fact that the planned December burndown spray had to be canceled meant that the early-emerging weeds continued to grow alongside wheat. By January, the impact of the weed competition on the crop stand was severe. Although in-season herbicides suppressed the ryegrass and other weeds, much of the damage from competition had already been done. Most wheat plants were severely stunted and had only one or two reproductive tillers, the wheat spikes were shortened and had far fewer seeds per tiller at harvest than you would expect with an average crop stand.
Drought conditions reduced herbicide efficacy dramatically
It took more than 30 days before the IR in the trials began showing a significant amount of damage in response to the herbicide application. When damage assessments were taken on March 7th (38 days after application), where 0 indicated ‘no damage' and 6 indicated ‘total control', the highest rating was a 4.5 via a tank mix of Simplicity and Osprey. In other words, none of the plots had been controlled after more than 5 weeks.
After a few light showers in late March, the IR resumed growth and rapidly declined as herbicides began to finally take effect. Despite the increased impact of the herbicides, overall control was still sub-optimal, with the highest control ratings being between 71 and 87 percent. Axial, which had performed well in this exact field two years prior ended up with very low levels of control (14%). The reduced efficacy was likely due to drought stress, weeds hardening off, or simply because the herbicide was affected by some amount of decay in the field before it could be fully taken up by the plant itself. This was a good reminder that researchers and growers should consider other externalities before they throw their hands up and say the “R” word (resistance).
In both summer and winter crops, if plants are healthy and actively growing, herbicides will be much more effective and should work within the weed growth stage ranges specified on the label. However, because weather patterns can be unpredictable, the windows for herbicide labels should be seen as somewhat optimistic (written for ideal conditions).
Yields in the trial area ended up being one quarter of what they normally would be in this field due to a combination of early weed competition from the missed burndown treatment and the effects of a persistent drought period which both stressed the crop and reduced the efficacy of the applied herbicides.
Takeaways:
Spray windows on herbicide labels are often somewhat optimistic and assume that plants are actively growing (labels for systemic herbicides will typically specify that applications be made to actively growing weeds). Because drought can't always be predicted, growers should prioritize herbicide applications early in the weed growth stages and should apply herbicides when weeds are actively growing. In cases where irrigation is an option, growers should consider an irrigation event if conditions are excessively dry as it can greatly improve the efficacy of an herbicide (not to mention the fact that a small grain crop will likely be able to utilize the soil moisture as it enters the rapid growth phase in late winter).
The trial results are a strong example of how herbicide efficacy is tied to a number of factors. It is also an example of how researchers can serve their clientele by demonstrating how much things can go wrong when environmental conditions collide with their own optimism and the idealized ranges of herbicide labels.
Figure 2. Percent control of Italian ryegrass in a wheat field experiment in 2022 near Esparto, CA. Treatments were applied in January and these ratings were made on April 15th (80 days after herbicide applications, and following a few small showers in March that provided enough moisture for plants to continue growing). Note that Axial, which had worked well at this location in the previous years was largely ineffective under these conditions. It is highly unlikely that this is due to resistance, but rather is an example of how drought conditions can impact herbicide efficacy.
Figure 3. Plots in Esparto trial area in April (80 days after herbicide treatments). By the time herbicides began to impact Italian ryegrass, wheat was already severely stunted. This is an example of how critical early weed control and burndowns can be. Note again that Axial, which has worked well in this field two years prior, was dramatically less effective due to drought conditions. As an ACCase inhibitor, Axial is a valuable tool for growers looking to diversity their herbicide program, but this is an example of why it is important to prioritize early applications of herbicides on actively-growing weeds.
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- Author: Konrad Mathesius
- Editor: Mark Lundy
Half the battle in learning and development is knowing what you don't know. I have been collecting a running list of different ag-related tools and technologies that I think growers, managers, and crop consultants could benefit from. Below are some notable tools:
Using Google Sheets to Manage Tasks Among Ag Teams:
https://www.google.com/sheets/about/
Google sheets is an incredibly simple and flexible tool, basically an excel spreadsheet that is housed in the cloud (online). This means that multiple people can be given access to it for organizational purposes to create a live project board that can guide field operations.
Greenbook (or Agrian):
https://agrian.com/labelcenter/results.cfm (label lookup)
Greenbook is basically a searchable a collection of herbicide labels. Agrian is similar. They provide an easy way to look up an herbicide's group and active ingredient. This is valuable for multiple purposes, including when PCAs or growers are trying to diversify herbicide programs to reduce herbicide-resistant weed populations. The fact that it's digitized also makes it easy to navigate labels using a ‘find in page' or ‘search' function in mobile browsers. Greenbook saves me a lot of time and energy digging around through different herbicide labels and straining my eyes in the process.
Crop Manage:
If you haven't heard of Crop Manage, it's a crop management tool (go figure) that leverages crop models and local weather data to predict growth curves, manage irrigation, and help growers keep track of what's happened in their various fields. The software is based online and you can sign up for free access here: https://cropmanage.ucanr.edu/. A good introductory tutorial can be found here: https://www.youtube.com/watch?v=6Nu8D3uaE4o&ab_channel=UCANR. Crop Manage is particularly useful in that it streamlines operations and can be a one-stop-shop for managing critical operations.
Small Grains N-management Webtool:
https://smallgrain-n-management.plantsciences.ucdavis.edu/
I've mentioned this one before, but anyone with wheat in their rotation will find this tool worthwhile. Given that the price of fertilizer is relatively high these days, now is a good time to take a moment and see where you might be able to optimize your inputs. This tool is based on a collection of statewide data and uses in-season measurements provided by the grower and local weather to produce a fertilizer recommendation for small grain acreage.
In the last several years we've demonstrated that growers can increase their net by an average of about $40 per acre through reduced input costs, increased yields, or a combination of both. Additionally, there are resources available in the Small Grains section of the UCANR Agronomy Research and Information Center that can help growers with some of the more technical aspects of N-management (N-rich reference zones, soil nitrate quick tests, soil sampling, etc. https://smallgrains.ucanr.edu/Nutrient_Management/ ).
- Author: Konrad Mathesius
Join us from 9 a.m.- 10 a.m. on Wednesday, September 29th for a short online demonstration/webinar on several powerful nitrogen management webtools that have been developed by UC researchers, including case studies from this year in the Sacramento Valley.
This webinar is free of charge and open to the public.
Click here for the full agenda and Zoom link
Please register by clicking the link below (required for CE units).
CE Units: CURES (1.0)
Other topics will include a brief overview of some of the research being conducted by Sacramento, Solano, and Yolo County UCCE Agronomist, Konrad Mathesius.
Presentations will be followed by Q&A and further discussion on research details as needed.
- Author: Gerry L Hernandez
The Saturday Sacramento Bee's Garden section talks about 7 insects that are relatively new to our area. Read about 2 of them here.
- Asian Citrus Psyllid - This insect can carry a devastating disease. The disease can kill your trees and has devastated citrus orchards in Florida. It is working it's way up the San Joaquin and Sacramento valley. The ACP has been found as far north as San Joaquin County. The ACP has two distinguishing features. The adult sticks it's "hinny" in the air when feeding. The nymphs produce a curly waxy substance. If you think you have this pest please bring it in an air tight container to the Ag Commissioner's office or the UCCE Master Gardener office.
- Brown Marmorated Stink Bug - This insect is an agricultural, garden and household pest. It is a large stink but at 5/8's of an inch. It has been found in all counties surrounding Colusa County. There is a good chance it will be here in 2015. The distinguishing features are white segments on it's antenna and legs. Also, it STINKS and it STINKS! Currently no household insecticides work on this insect. If you find it please bring it in an airtight container to the Ag Commissioner's office or the UC Master Gardener office.
- Author: Amy Brasch
The estimated population size of Sacramento Valley (SV) red foxes is very small, indicating possible conservation concerns. In addition, SV red foxes occur in a highly modified landscape used for intensive agriculture. In particular, while preliminary analyses indicate that the current distribution of SV red foxes in the northern part of the Central Valley overlaps a floodplain once characterized by native grasslands and riparian forests, these habitats have been heavily modified to meet agricultural needs. The continuous modification of habitats for agriculture in the SV may be impeding on the limited habitats available to foxes, particularly since these foxes only live at low elevations.
Based on their unique natural history and their close proximity and dependency on human modified landscapes, SV red foxes face multiple threats. Direct threats include deaths attributed to a variety of causes: residents protecting their poultry, vehicle collisions, exposure to pathogens from domestic animals, and ingestion of poison bait meant for rodent control or eating rodents killed by poison. Additional threats for the viability of SV red foxes are the species’ limited range and distribution. Species isolated in a single region with a small population, like the SV red fox, experience minimal genetic variation in their gene flow, and could potentially face genetic introgression from adjacent non-native populations. These threats, which are likely increasing over time, may warrant placing the SV red fox on the threatened species list in the near future.
In 2007, an online reporting system was launched by the University of California, Davis, with goals of involving the public in documenting any potential fox sightings. The goal of this website was to involve the local community with locating SV red foxes so that samples could be obtained for genetic testing and surveillance could be set up for behavior monitoring.
Now, master's student Amy Brasch of Victoria University of Wellington is assessing how effective public input was on locating the foxes and how the website can be improved for future conservation efforts.
You are invited to share your opinions regarding red foxes and the fox sighting website in a 5-minute survey located on the fox sighting website: http://foxsurvey.ucdavis.edu/
The results of this survey will enhance the website as well as develop a better understanding of how effective public input is on locating Sacramento Valley red foxes.