- Author: Luis Espino
- Editor: Consuelo B Baez Vega
- Editor: Taiyu Guan
Stem rot is a common disease of rice that can cause blanking and lodging. When the disease is severe, the presence and effects of the disease on yield can be obvious. However, at lower levels, the symptoms and effects of the disease may “fly under the radar”.
Stem rot affects the tillers at the water level. Mid season, small black lesions appear on lower leaf sheaths. As the disease progresses, the pathogen penetrates the tiller and can reach the culm, causing rot. These symptoms are most obvious when fields are drained for harvest. Once plants start to senesce, it can be difficult to identify stem rot symptoms because plants dry out.
The severity of stem rot is determined at drain time using a ranking that goes from 0 (no disease) to 4 (tillers rotted through). Several years of trials have shown that for each increase in severity level, there is a 3.2% yield loss. The table below shows the yield losses that can be expected under each severity level for three different yield potentials.
- 50% of tillers show stem rot symptoms = Severity level 1
- 100% of tillers show stem rot symptoms = Severity level 2 or higher
Yield losses at severity level 2 could be significant, so a manager should aim to be below this disease level. To determine incidence at drain time, cut a handful of tillers at the soil level and determine how many show symptoms of stem rot. Do this at several representative places in the field, avoiding nitrogen overlaps or skips, until you feel you have a good estimate.
The second challenge is that evaluating the severity of stem rot at drain time provides information that cannot be used to make any management actions the current year. However, the information can be used to plan management for the following year. Because stem rot inoculum survives in crop residue in the soil, disease severity levels tend to be uniform across years.
To manage stem rot, an integrated approach is needed. Managing straw after harvest is key. Burning or decomposing straw aids in reducing the amount of inoculum that survives from year to year. Excess nitrogen and potassium deficiency can significantly increase the severity of the disease. While there are no resistant varieties, very early varieties (CM-101, M-105) tend to develop more severe stem rot that varieties with longer cycles (M-209, M-211). Finally, fungicides can help manage the disease. Azoxystrobin applied at the early heading stage has been shown to reduce the severity of the disease by 30%.
Survey: Challenges and Opportunities for Organic Rice
In the next few weeks, you will receive an email with a link to a survey being conducted as part of a project looking at the attitudes of rice producers towards organic farming. This project is trying to understand what drives US rice producers to adopt organic farming and what factors limit adoption, and is a collaboration between University of Arkansas, Texas A&M University, and University of California Cooperative Extension. The information generated by the project can help the industry identify adoption barriers and try to address them through policy and extension, so that organic production can become a viable option for more producers. The survey should take 15-20 minutes to complete. You can learn more about this project at The Organic Center website (https://organic-center.org/site/challenges-and-opportunities-us-organic-rice)
- Author: Bruce A Linquist
- Author: Luis Espino
- Author: Whitney B Brim-Deforest
- Author: Michelle Leinfelder-Miles
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Every year, the University of California Cooperative Extension, in cooperation with the Rice Experiment Station (RES), conducts rice variety trials in several locations of the Sacramento Valley (fig. 1). The trials are conducted at the RES and eight farm locations across the Sacramento Valley, and one location in the San Joaquin Delta (not on the map) representing the main production areas of California. In 2023, the South Yolo trial was not conducted. Plots in the Sacramento Valley trials were 200 ft2 and hand seeded while in the San Joaquin Delta trial plots were 150 ft2 and drill seeded; seeding rate for all trials was of 150 lbs/a. Grower cooperators treated the trial in the same manner as the rest of the field. Parameters evaluated in the trials included seedling vigor, days to 50% heading, plant height, lodging at harvest, grain moisture at harvest, and grain yield at 14% moisture. Varieties are replicated four times. In this summary, only yields are presented. All other parameters are included in the complete report, which will be available on our website at the end of February (http://rice.ucanr.edu).
- Author: Bruce A Linquist
- Editor: Consuelo B Baez Vega
- Editor: Taiyu Guan
In California, most acreage is devoted to high quality medium grain varieties. In 2023, over 94% of the acreage was grown to medium grains. There are currently six medium grain varieties to choose from: very early (M-105), early (M206, M-209, M-210, and M-211), and late-maturing (M-401 – a premium medium grain). Here are some things to consider when making a choice.
M-105 is the earliest variety; although it is only 1-2 days earlier than M-206 in the northern part of the valley but it is 3-5 days earlier in the southern cooler parts of the valley. It also has excellent yield potential. Last year it had the highest yields in our yield contest with a yield of 132.5 cwt/ac. It also tends to yield the highest in our variety trials located in the southern portion of the valley (south of hwy 20). It is an excellent choice to plant at the start of the season in order to get an early start on harvest. The knock on M-105 is that it can lodge; however, in our variety trials (and other trials at the Rice Experiment Station), there is no indication that its lodging potential is different than M-206.
M-206 and M-210 are nearly identical except that M-210 has blast resistance. They are both early varieties and stable across environments. In areas with blast, or if dry seeding, M-210 is an excellent choice. In 2023, blast was wider spread than normal. For growers that have only used M-206, try using M-210 on a field and see how it compares. You should have very similar results.
In terms of yield potential, M-209 and M-211 have the highest yield potential. M-211 regularly out yields other medium grains by 1-3 cwt/ac in our variety trials in the northern part of the valley (north of hwy 20). Both M-209 and M-211 are longer in duration than M-206 and neither are well suited to cooler areas (M-209 being the least suited). Duration is also important when thinking about water limitations as they require more water to irrigate. Achieving good milling quality is one issue with these varieties. Milling quality drops rapidly when harvest grain moisture drops below 20%. Given this, it may not be wise to plant these varieties on a large number of acres where a timely harvest may be difficult. On a positive note, these varieties are less prone to lodging. This is partly due to thicker tillers. Some growers indicate that managing the rice straw in M-211 is harder than for other varieties. Finally, where kernel smut is an issue, M-209 is one of the more susceptible medium grains.
Finally, California's first herbicide resistant variety M-521 has been approved for release. However, seed production for this variety will not proceed until the herbicide is approved.
- Author: Whitney B Brim-Deforest
- Editor: Consuelo B Baez Vega
- Editor: Taiyu Guan
Background
White water fire (Bergia capensis) was found in September of 2023, by the Butte County Agricultural Commissioner's office in a rice field in Butte County. The weed was identified by the California Department of Food and Agriculture. It is the first find of this weed in California, and possibly in the United States. It is native to Africa, southern China, and tropical Asia, and it is known to be in rice fields in Europe, Central and South America, as well as the Caribbean. It was likely transported in seed to rice-growing areas and has been established in those locations for many years.
In Butte County, the weed was only found in one rice field, and the Agricultural Commissioner's office surveyed surrounding rice fields but found no additional infestations. The method of introduction in California is unknown at this point.
It currently has a “Q” rating by CDFA: “An organism or disorder suspected to be of economic or environmental detriment, but whose status is uncertain because of incomplete identification or inadequate information”. At this point, it is not considered a quarantinable pest so if it is found, there is no penalty or restriction for finding it in a field.
Identification
White water fire looks similar to another common rice field weed, redstem (Ammania spp). However, the two species are not from the same plant family and are therefore not closely related. Due to the similarity, white water fire is quite difficult to identify in the field. One of the key distinctions is the thickness of the leaves, which are much broader in white water fire than in redstem. Another key distinction is flower color. The flower color of white water fire is white, whereas redstem can have either purple or red flowers.
- Author: Whitney B Brim-Deforest
- Author: Roberta Firoved
- Editor: Consuelo B Baez Vega
- Editor: Taiyu Guan
California rice growers will have a new herbicide available this year: Cliffhanger™, manufactured by Gowan Co. The active ingredient is benzobicyclon, which is the same as one of the two active ingredients in the currently registered herbicide, Butte®. Cliffhanger™ is a soluble liquid formulation (SC) which can be applied by ground-rig or airplane, including as a direct-stream application into the water. In contrast, Butte® is a granular formulation, as a pre-formulated mixture of benzobicyclon and halosulfuron. To use either product, applicators must attend a training and be certified.
Dates for the training are posted on the California Rice Commission calendar https://calricenews.org/events/, as well as the UC Rice website.
Controlled weeds are sprangletop, ricefield bulrush, and smallflower umbrella sedge. The application timing begins from day of seeding up to 82 days before harvest. Recommended timing for sedges is pre-emergent up to the 5-leaf stage, and for sprangletop, pre-emergent up to the 2.5 leaf stage as well as at tillering.
Flood water should be a minimum of 4 inches when the product is applied. The active ingredient, benzobicyclon, is a proherbicide, meaning that it is not active until it comes into contact with water. Therefore, for maximum efficacy, water should be held in the field for at least 5 days. Longer periods of flooding will result in better efficacy, whereas a drain soon after application will both reduce efficacy as well as encourage a new flush of weeds. The recommended waterhold is 10-14 days for maximum efficacy.
Cliffhanger™ should only be applied once per season. It is not recommended that it be applied in the same season as any other HPPD-inhibitor product (Butte®). Applying both in the same season can select for herbicide resistance and may cause significant phytotoxicity to the rice. Repeated applications, both during the same season, or season after season, can select for resistance, particularly in sprangletop, ricefield bulrush, and smallflower umbrella sedge.
Remember to always follow all label instructions when applying any pesticide, as the label is the law. Make sure to pay particular attention to the Use Precautions and Restrictions. Consult your local Agricultural Commissioner's Office regarding buffer zones and aerial restrictions, before making any applications. Label and SDS: https://www.gowanco.com/products/cliffhanger-sc-herbicide