- Author: Luis Espino
- Author: Michelle Leinfelder-Miles
Thankfully, 2022 was not a bad year for rice diseases, but it is worth mentioning a couple of observations. Overall, there was very little blast this year. In the Sacramento Valley, UCCE did not diagnose any blast in the field but did receive a couple reports of it after harvest.
Blast was identified in the San Joaquin Delta in a field of M-206. Blast in the Delta is a rare occurrence because of the cooler temperatures in the area. In fact, UCCE has only identified blast there once before. Back in 2010, one Delta field of variety M-104 was confirmed as infected with blast. Year 2010 was a bad blast year, with many fields affected across the Sacramento Valley.
Blast can infect seed, it can survive in crop residue, and its spores can move long distances. Additionally, weeds are suspected to be alternate hosts. All these factors can be sources of inoculum that can result in a blast epidemic. In seed, the mycelium of the blast fungus has been found colonizing the internal surfaces of the lemma and palea (the seed coat), the pericarp and endosperm. Unfortunately, treating the seed with bleach for bakanae does not help with the blast fungus. In general, seed is not considered a major source of blast inoculum in California. Until a few years ago, certified seed used to be tested for blast. The requirement for this test was stopped in 2018 because results were always negative. However, if during the certification inspection a seed field or a portion of a seed field is identified as infected with blast, that field or portion can be rejected. Research has shown that under water seeding, there is no seed to seedling blast transmission. Seedling transmission has been documented from infected seeds planted in soil or infected seeds that remain on the soil surface. Given that most of the acreage in California is water seeded, the risk of infected seed producing blast inoculum is low. However, in the Delta, where rice is drill seeded, the risk is higher.
While disease was low overall, we did come across another fungus that is relatively new to us. A report of possible blast in M-211 was received in late summer form a PCA in Butte County. Inspection of the field revealed only a few plants affected with symptoms that looked like collar blast (Fig. 1). Samples were submitted to the UC Davis Plant Pathology Lab, and the identification came back as Nigrospora oryzae, which causes “panicle branch rot”. Interestingly, this fungus was also identified in three Delta fields (Fig. 2), one of which also had blast. Prior to 2022, we identified this fungus from samples with symptoms similar to stem rot in 2017 and 2021, and in a field with heavy discoloration of rice panicles in 2021 (Fig. 3).
The Compendium of Rice Diseases and Pests (2018, APS Press) indicates that Nigrospora species are common and occur in senescing plant tissue, and may cause lesions in plants weakened by diseases, insects, or poor nutrition. This fungus is reported to cause an ear blight and blackening of rice kernels. These descriptions fit the symptoms mentioned above. Additionally, Nigrospora oryzae has recently been identified as the causal agent of panicle branch rot disease in China (Liu et al., 2021, Plant Disease 105 (9): 2724), a disease very similar to blast, with reported yield and quality losses.
It is not clear if this fungus is developing in tissues that are already affected by stem rot or blast, or if it is causing disease symptoms. In any case, given the information in the literature and the low frequency of observation, at this point the identification of Nigrospora oryzae from California rice samples is not cause for concern, but it does warrant vigilance from the industry. Please reach out to us in the future if you see symptoms similar to these so that we can gather more information about this fungus.
- 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: Michelle Leinfelder-Miles
I have been trapping armyworms in Delta rice since 2016, after the industry experienced an outbreak in 2015. Monitoring involves scouting for damage and deployment of pheromone bucket traps that catch the moths (Figure 1). I have traps at three Delta locations, and at each location, there are three traps that span adjacent fields. 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. UC IPM provides treatment guidelines, and a Section 18 emergency exemption of methoxyfenozide (Intrepid 2F) has been approved for the 2022 season. (For more information, please contact your county Agricultural Commissioner's office.)
We have begun our 2022 monitoring, and trap counts are higher than they were at this same time last year (Figure 2). (Overall, 2021 was a low-pressure year.) The counts we are observing are not extreme but are on par with what we saw in 2020. It's hard to pinpoint why populations fluctuate from year to year, but it could relate to higher minimum winter temperatures (i.e. better winter survival), and/or migratory patterns from other western states and Canada.
The monitoring that I do in the Delta is part of a larger effort that is spearheaded by my colleague, Luis Espino, rice advisor in Butte and Glenn counties. Luis writes a weekly blog to provide real-time information on trap counts to help growers and consultants with scouting and decision-making. In his blog announcements, he will link to an interactive mapping tool called Ag Pest Monitoring, where you can view counts across trapping locations. Please consider subscribing to Luis Espino's blog, but don't hesitate to reach out to me if you'd like to discuss what is happening in the Delta.
Good luck this season, and I hope to see you in the field!
Figure 1. Bucket traps are placed along field edges. Nine traps are deployed across three Delta locations and are checked weekly. The traps include a pheromone lure that selectively traps true armyworm moths. (Photo by M. Leinfelder-Miles)
Figure 2. 2016-2022 Delta armyworm trap counts. The trap counts represent the number of moths caught per day, averaged across three Delta locations (9 total traps). The 2022 counts are still moderately low, averaging about thirteen moths per day during the week of June 13th, but now is the time to intensify monitoring since peak populations tend to occur between now and early July.
- Author: Michelle Leinfelder-Miles
UC Cooperative Extension will host a Weedy Rice Meeting on Thursday, March 31, 2022 from 10:00am to 11:30am. The meeting location is the Cabral Agricultural Center in Stockton (2101 E. Earhart Ave., Stockton, CA 95206). A printable version of the agenda is attached at the bottom of this post. The agenda is as follows:
10:00am Weedy Rice Identification Refresher/Review, Luis Espino, Whitney Brim-DeForest, UCCE
10:15am Current Status of Weedy Rice – Acreage Surveys, Luis Espino, Whitney Brim-DeForest, Michelle Leinfelder-Miles, UCCE
10:30am Seed Certification Process/Rules and 2021 Observations, Timothy Blank, CA Crop Improvement Association
10:45am Best Management Practices, Luis Espino, Whitney Brim-DeForest, Michelle Leinfelder-Miles, UCCE
11:00am Research Updates, Whitney Brim-DeForest, UCCE
11:15am Open Discussion – Q & A
We have submitted applications for continuing education, including credits for pesticide licensing (1.5 of Other) and certified crop advisers (1.5 of PM). Refreshments will be provided. If you require special accommodations, please contact UCCE San Joaquin County at 209-953-6100. Thank you, and hope to see you at the meeting!
2022-3-31 Weedy Rice Meeting Agenda
- Author: Michelle Leinfelder-Miles
Statewide results will be available from the UC Rice webpage (https://rice.ucanr.edu/Reports-Publications/Agronomy_Papers/). Table 1 (below) shows the San Joaquin County results. Among the entries, M-206 is the most commonly planted variety in the Delta, followed by M-105. The average yield across all commercial varieties and advanced lines was 10,129 lb/ac. When interpreting the results, the CV, or coefficient of variation, is a measure of variability in the data in relation to the mean. The LSD (.05), or least significant difference at 95%, is used to compare means of different varieties. When the difference between two varieties exceeds the LSD value, we are 95% certain that the two varieties performed differently; the results are not due to random chance.
This trial helps to support the Delta rice industry, which has a different production system from the Sacramento Valley. We plan to continue trialing rice varieties in the Delta again in 2022. Please don't hesitate to reach out if you have questions about Delta rice production, and good luck this season!
Table 1. 2021 San Joaquin County very early rice variety test (advanced lines and varieties).