I wrote in a previous Newsletter article about some new research we are doing testing no-till drill seeded rice production. Why are we doing this? It is one way to save considerable amounts of irrigation water. We estimate that up to 0.5 ac ft/ac of water could be saved. Water savings are due to using existing soil moisture (from the winter/spring rains) and limiting the evaporation of water during the first month of the season by not having the field flooded. Other potential benefits include reduced tillage costs, the ability to plant early, and avoiding tadpole shrimp and seed midge injury. If rotating with water-seeded systems, it is also a great way to use different modes of action to address herbicide resistant weed issues.
Briefly, to recap. This study was conducted at the Rice Experiment Station and was run by Mia Godbey (graduate student) and Ray Stogsdill, with Luis and Whitney looking at pests and weeds. We tested NT drill seeding into four different seedbeds.
- Fallow stale-seedbed (FSS): field was fallowed in 2022. It was disked and leveled then. It was not flooded during the winter. No tillage was done in 2023.
- No-till. We have three strict NT treatments. Rice was grown in 2022. After harvesting (harvested to limit ruts), the straw in the field was subjected to one of three treatments:
- Chopped (NT-Chop)
- Half removed to simulate baling (NT-Remove)
- Burned (NT-Burn)
The no-till fields were all winter flooded.
At time of planting, there were a lot of winter weeds in the NT-Burn and FSS treatments (with the wet spring we got more winter weeds than normal). While we tried to get rid of them by spraying glyphosate before drilling, many were tolerant. In the NT-Chop and NT-Remove treatments there were little to no weeds. On May 2 the fields were all planted with a Great Plains no-till drill seeder (see above) at a rate of 150 lb seed/ac. After seeding, all treatments received an initial irrigation flush on May 4 and the flush was drained on May 8. We did not apply any herbicide at planting before or after the flush.
We chose this year to have the same planting date for all treatments, but the FSS and NT-Burn treatments could have been planted in mid-April. However, the treatments with straw on the surface had too much soil moisture to be able to get equipment into the field and May 2 was the earliest we could get into these fields.
We did not apply any irrigation water after the initial flush at planting until June 2 when we applied the permanent flood. The rice was at the 4-leaf stage by this time. We got a good stand in all treatments. The stand was lowest in the NT-Chop treatment but still good. The soil moisture in the NT-Burn and FSS was starting to dry out but we did not see any moisture stress. In the NT-Chop treatment, there was still a lot of moisture beneath the straw mat. The winter weeds were still present but we saw very few other weeds coming up. Just before permanent flood, we applied urea and herbicides (Prowl, Clincher and Propanil).
After the permanent flood, the plants almost doubled in height in the first few days and were well above the water line. The winter weeds persisted into the permanent flood. However, they did not appear to affect the stand of rice.
Compared to 2022, 2023 had higher relative humidity during the season (fig. 1). According to the Williams CIMIS weather station, the average maximum relative humidity for the month of July for 2022 and 2023 was 77 and 96%, respectively, while the minimums were 19 and 44%. Higher relative humidity, combined with lower wind speeds during the months of July and August probably, may have resulted in longer periods of free moisture on plant surfaces during mornings, which allows for germination of blast spores and infection of leaves and panicles. These plots were harvested with a small plot combine on September 28. Grain yields responded to various rates of N application. Yields were highest (8640 lb/ac) in rice after fallow (FSS) followed by NT-Burn and then the NT-Remove and NT-Chopped. Yields in all treatments were highest at the 175 lb N/ac N rate. While these yields were no super high, they were comparable to the maximum yields we observed in water-seeded conventional rice at the RES which was 8490 lb/ac.
We are very encouraged by these results and will be providing greater detail in our upcoming winter grower meetings. In future years we will be looking at optimizing herbicide and fertility practices as well as quantifying water savings.
Certified seed production returned to normal levels in 2023. The CA Crop Improvement Assn. passed 27,818 acres for seed. Field inspections were initiated in early August and the last inspections took place in early October.
107 acres (1 field) were rejected due to the presence of weedy red rice, and those rejected acres were within the Quality Assurance program that oversees specialty varieties that are not eligible for certification. Included in the total acres passed for seed production are 1297 acres approved within the Quality Assurance program, of which 978 seed acres were Koshihikari production.
M-206 remains the variety with the most acres of seed production, followed by M-211, M-209, M-105, and M-210. Looking at all seed production by grain size, 87% of the approved production was medium grain varieties, 11% short grain varieties, and 2% long grain varieties.
Rice production in the Sacramento-San Joaquin Delta region has been steadily increasing in recent years (Table 1). While Delta acreage is only a fraction of that in the Sacramento Valley, Delta yields are consistent with statewide averages. I estimate that in 2023, the Delta had around 10,000 acres of rice. In this seasonal recap, I'll overview UCCE research in Delta rice, as well as provide some observations about the 2023 season.
Over the last several years, we have conducted trials to evaluate the efficacy of a new herbicide product, Loyant (florpyrauxifen-benzyl; Corteva Agriscience), on grasses and sedges in the Delta drill-seeded system. Loyant is now registered and was available for the 2023 season. Over the last two years, I have been working with Deniz Inci (UC Davis graduate student) and Kassim Al-Khatib (UC Extension Specialist) to evaluate Loyant for efficacy on cattails. In the the Delta's drill-seeded system, cattails may emerge ahead of the rice crop and outcompete the rice. In both years, we found that the label rate of Loyant had efficacy on cattails that were less than three feet tall (Fig. 1). When treated by that size, we were later able to pull up dessicated plants, including the rhizomes. Growers will need to be cautious of drift issues, however, because pistachio and grape are highly-susceptible to drift damage by Loyant, with almond, walnut, and peach being only minorly damaged, if at all.
I have been monitoring armyworm populations in the Delta since 2016, in collaboration with my UCCE colleague, Luis Espino. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths. We can use trap counts and Growing Degree Day modelling (i.e. a temperature measure of time) to determine whether and when to treat fields. In 2023, we were thinking we might get away with minimal pressure because the population stayed low through early July. Then, the population spiked in mid-July, later than we had ever observed (Fig. 2). We surmise this was due to the cool, wet spring and later planting season. This year, Methoxyfenozide (Intrepid 2F) was available for use under full registration.
We have identified diseases like stem rot, aggregate sheath spot, and rice blast on some Delta farms. It is important to scout for these diseases at late-tillering and early-heading because treatment timing is critical for management. Fungicide treatments are most effective when applied at early-heading. Rice blast may be exacerbated by too much nitrogen, and stem rot and aggregate sheath spot by low potassium (K). K can be limiting in some Delta soils, especially where the straw is baled. There is a loss of approximately 28 lb K/ac for every ton of straw removed. Consider leaf tissue sampling for K between tillering and panicle initiation. The Y-leaf should have a K concentration of at least 1.5%. At heading, the flag leaf should have a K concentration of at least 1.2%. On-farm consultations are a service provided by UCCE. Please reach out if I can help identify pests and provide management guidelines.
We should continue to keep weedy rice on our radars because we have observed it in the Delta. In-season management includes rogueing or spot spraying before viable seed is produced. The organic herbicide Suppress is registered for spot spraying. Post-harvest management should include straw chopping but not incorporation and winter flooding. This will keep seed on the soil surface, where it can potentially deteriorate over the winter.
UCCE collaborates with the California Rice Experiment Station to evaluate commercial varieties and advanced breeding lines. The San Joaquin County Delta location was one of ten locations in the 2023 statewide trial. The Delta is a test site for very-early maturing varieties because it has cooler growing conditions than other rice growing regions of the state. Variety trial results will be made available in the February 2024 newsletter.
With funding from the CDFA Healthy Soils Program and CA Rice Research Board, I am collaborating with Sara Rosenburg (UC Davis graduate student) and Whitney Brim-DeForest (UCCE rice advisor) to evaluate winter cover crops. We are interested to learn whether cover cropping improves soil carbon and nitrogen dynamics in the rice system. Since rice may be grown over multiple seasons without rotation, cover crops may provide an opportunity to introduce plant diversity, including nitrogen-fixing legumes. Trials will occur from 2022-2025, and the Delta site is one of three (also in Butte and Colusa counties). The 2022-2023 winter season presented several challenges for cover cropping. At the Delta location, seasonal rainfall exceeded 25 inches, and in the ten days after planting, the site received nearly 3.5 inches of rain. In addition to saturated soils, bird predation was severe. This fall, our aim is to plant earlier, if conditions allow.
Thank you to all the growers who collaborated with us on these projects. I wish everyone a good end to the year and a great 2024.
Michelle Leinfelder-Miles, Delta and Agronomic Crops Farm Advisor
*Rice acreage and yield according to the San Joaquin County (SJC) Agricultural Commissioner's Crop Reports. Rice acreage in SJC is primarily in the Delta region. Delta acreage in other counties is not included in these statistics. At the time of publishing, 2022 CDFA statewide data were not yet available (N/A).
Figure 1. The herbicide, Loyant, was trialed on cattails in the Delta in 2022 and 2023. We observed good control when cattails were less.
Figure 2. Delta true armyworm trap counts, 2016-2023. In 2023, the population was late to peak, likely due to the cool, wet spring and late planting season.
PCAs and growers were very creative and timely in planning and applying products this year, and control was good in many fields. The two most widespread weed control problems that I noticed this year were the watergrass complex and sprangletop. We have widespread resistance, but control issues this year were likely also related to the wet spring, as well as colder temperatures which resulted in different emergence timings and weed growth patterns as compared to other years.
Propanil Usage and Over-Reliance as a Tool
Propanil is a powerful tool in our herbicide arsenal in California rice. It has wide-spectrum control, controlling many grass, sedge, and broadleaf species.
However, there are several weed species that are already resistant to propanil, including smallflower umbrella sedge and ricefield bulrush (roughseed). As a reminder, resistance is likely to occur when we apply the same mode of action or same herbicide, more than once in a season, or over consecutive years, over more than one season. In both smallflower and bulrush, we have populations that are multiple-resistant to propanil and another herbicide mode of action (mostly ALS-inhibitors, like Granite GR/SC,Londax, and Halomax). This occurs because propanil is typically used as the season's last clean-up spray. If a weed is sprayed with an herbicide early in the season, but is resistant to that herbicide, and then is sprayed later in the season with propanil, there is a possibility that the weed may be resistant to propanil as well (naturally occurs in the population). When we always use propanil as the cleanup spray, we increase the chances of having weed species that are resistant to multiple herbicides, with resistance to propanil being “stacked” onto resistance to the first herbicide.
While we know we already have populations that are multiple herbicide resistant in both bulrush and smallflower, it is very likely that we may soon see this in watergrass populations. In fact, it is increasingly likely, as we are seeing double-propanil applications in many parts of the rice-growing region.
The propanil label lists several products that should not be applied with propanil, namely certain insecticides. The reason that these are put on the label is because in combination with propanil, they can overcome the rice plant's ability to metabolize propanil. When we utilize these products in combination with, or closely following propanil, there is a high risk of significant injury to the rice, including death of rice plants. Please make sure to follow the label, and do not apply these insecticides either as a tank-mix with propanil or soon after (refer to the label).
Alternative Cleanup Sprays (Instead of Double Propanil)
Some alternative cleanup sprays (instead of the double-propanil spray) are suggested below. Keep in mind that these are not endorsements of these products, and not all combinations have not been tested on all weed populations, so efficacy is not guaranteed.
• Abolish + Regiment (watergrass and smallflower umbrella sedge control) • Propanil + Loyant (watergrass, broadleaf and sedge control)
• Propanil + Shark (watergrass control). Worked very well in 2022 at one site—I am conducting further research this year. It caused significant phytotoxicity, but the rice recovered.
• Regiment followed by Propanil applied about 7 days apart (watergrass control). This caused significant phytotoxicity and grass control was not as good as some of the other treatments, but it is a good alternative treatment to double propanil.
Further research is being conducted at multiple sites this year, and results will be forthcoming later this year.
Other Management Methods
As weeds get tougher to control due to resistance, there are some things to keep in mind to maximize efficacy (including some Integrated Weed Management strategies).
Some tips include:
• Using tank mixes of multiple products, as early as possible in the season.
• Utilizing a stale seedbed on badly infested fields (Suppress or glyphosate).
• Applying multiple granular products early in the season (at the same time or in close succession).
• Utilizing pre-plant herbicides (Prowl or Abolish) to suppress early-germinating weeds.
• Deep water at the beginning of the season will help to suppress grasses (watergrass, barnyardgrass, and sprangletop). The deeper, the better (at least 6 inches, but up to 10-12 inches will suppress more plants).
• Winter flooding with no fall tillage: this is a great way to reduce watergrass populations, as seeds are predated upon and will rot if left on the soil surface.
For assistance in implementing an alternative program, contact Whitney (firstname.lastname@example.org).
Herbicide Resistance Testing
If you have large populations of weeds that survive until the end of the season, please get them tested, to ensure that you are using the most effective herbicides for your particular weed populations.
The UCCE Rice Weeds Program tests grower submitted seed samples of potentially herbicide-resistant watergrass species, sprangletop, smallflower umbrella sedge and bulrush. However, we encourage you to submit ANY species that you suspect to be resistant. We keep individual grower information confidential and any reporting of results will not identify individual growers.
Please fill out the form (under the “Weeds” section at https://agronomy-rice.ucdavis.edu/) for each weed seed sample (each field and/or species).
The following tips will ensure that you receive the best possible results:
• The best timing of collection is when the seed easily falls off the seed head by gentle agitation in a paper bag. Collecting seeds that don't easily fall off will make it difficult to germinate the seeds, resulting in poor or no results.
• For watergrass species, collection timing should be close to rice harvest (seeds should be brownish in color).
• For sprangletop, timing will be earlier, in August or September (seeds will appear greenish).
• For the sedges, timing may be as early as July, all the way through early September.
• Smallflower umbrella sedge seed is yellow, with brown hulls (looks like dust).
• Bulrush (roughseed) seeds are black and have small hairs
Seed should be collected from areas that you know have been sprayed with the suspected herbicide.
Collect seeds from multiple plants, and the amount should be at least a few handfuls of seed, to ensure sufficient quantity for testing.
Please do not collect seed from around field margins.
Allow seed to dry in the paper bag to prevent molding.
Bring the sample and form to your local UCCE Farm Advisor (Whitney, Luis, or Michelle) or send or drop off samples at the Rice Experiment Station (RES) in Biggs. If you need assistance in collection, please contact your Farm Advisor or PCA. Results should be emailed to you in March of 2024.
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