- Author: Luis Espino
Arthropods have not been very problematic in California in the past few years. However, do not let your guard down and let the bugs catch you unprepared. The tadpole shrimp is our key pest. Shrimp tend to be a problem in the same fields year after year because their eggs remain in the soil from one season to the next. Make sure to scout fields soon after seeding, maybe even before seeding, especially fields that take more than a few days to flood. Tadpole shrimp eggs hatch very soon after the field is flooded and the young shrimp grow quickly. Seeding into a field with shrimp present, even small shrimp, is asking for trouble. Small shrimp (about ½ an inch or less) can injure rice, just not as much as larger shrimp. Also, do not just rely on the muddiness of the water. When they are small, shrimp do not disturb the soil much, and therefore you might not see muddy water even though shrimp are present.
Another arthropod that can be problematic in California is the armyworm. Many fields had significant yield losses during the outbreak of 2015. We have not seen a similar outbreak since, but in some years worm numbers have been high. I have been monitoring armyworm moth populations with pheromone traps across the rice area since 2018. Last year we had the highest moth numbers we have ever seen but that did not translate into high worm numbers in the field. In fact, the worm pressure was very low. While the traps do not predict worm numbers, they can help us improve the timing of scouting. We know that we will see the highest worm numbers two weeks after the moth numbers peak. With Intrepid now fully registered for use in rice, we have a good tool that we can use to control armyworm populations if they get out of hand. You can sign up for my armyworm updates on the UC rice website.
The last pest that can be of concern is rice seed midge. The past three years we have seen some fields suffer stand reduction due to midge. This is a difficult pest to manage given its sporadic nature. Ian Grettenberger, UC Davis Extension Entomologist, has been doing insecticide trials for midge control. His work shows that pyrethroids are not very effective against midge, but at this point they are the only tool we have. Like tadpole shrimp, rice seed midge can be worse in fields that take a long time to flood. Also, late planted fields are at more at risk. Scout your field right at seeding and for the next few days, looking for the silken tubes rice seed midge form on the soil surface and inspect seed looking for injury. If there is enough injury to reduce the stand significantly, use an insecticide. A brief drain will also work; however, take into consideration any effects the drain may have in weed control and fertility.
- Author: Whitney B Brim-Deforest
This year brings several new chemical tools to California rice. With many herbicide resistant species as well as emerging problematic weed species, the new chemistries are a welcome tool for managing resistance and preventing the selection of resistant biotypes.
Last year, we had use of Loyant® CA Rinskor™ active (florpyrauxifen-benzyl) for the full season (registered late in 2022). Loyant®, which is an auxin mimic, is applied as a foliar product. It gives additional options for early-season control of sedges and broadleaf weeds, and although not strong on watergrasses when applied alone, provides added control when tank-mixed with other herbicides for grass control. Based on data collected in 2022-2023, two good tank-mix options for watergrass control are SuperWham®/Stam® (propanil) and Regiment (bispyribac-sodium). It does not control sprangletop.
Cliffhanger™ (benzobicyclon) was just registered in 2024, and is a new formulation of a previously-registered granular product already widely in use in California rice. Since it can be applied as a foliar product, it expands the timing that benzobicyclon can be applied in the flooded system. It can also be applied as a direct-stream application into the water. It is an HPPD-inhibitor, providing a good option for rotation. It controls sprangletop, ricefield bulrush and smallflower umbrella sedge. Additional tank-mix testing will be occurring this season to determine if it might be a good partner in combination with other herbicides for added late-season watergrass control.
The last product recently registered is Zembu™ (pyraclonil). Zembu™ is a granular formulation of pyraclonil, applied pre-emergence or at day-of-seeding into a flooded field. It provides control of smallflower umbrella sedge and broadleaf weeds, and provides suppression of watergrass. As a PPO-inhibitor, it is a new mode of action for watergrass, as the only other PPO-inhibitor registered in California rice only has activity on sedges. It will provide a great rotational option for growers at the beginning of the season, as well as a great partner product (for added control) with other granular into-the-water products.
As always, the label is the law, so make sure to read and follow the current labels for each of these herbicides (found on the manufacturers website or at the Department of Pesticide Regulation's website). Also check in locally with your Agricultural Commissioner's office for training information and any other county-specific requirements.
With these three new options, as well as the currently-registered products, rice growers in California should have a great suite of tools available this year, both for resistance management as well as to prevent the selection of future resistance. For help planning a weed management program, please reach out to your local Rice Farm Advisor.
- 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)
