- Author: Bruce A Linquist
As I write this in early April, the weather is shifting back and forth between being warm and cold and there is the occasional rainfall. Many of you have started or are thinking about starting ground work in preparation for planting. With all this going on, I ask you to imagine what it would be like for your farming operations if you could plant a rice field in mid-April. Later this week, we are planning to plant our first research plots on a summer stale-seedbed (fallowed last year and worked in the summer into a seedbed) using a no-till planter. The ground is firm enough to support equipment, we have taken care of our winter weeds and the seed will be planted into moisture. On top of that, we have rain in the forecast for the weekend. Once planted, these rainfall events are helpful.
If the soil is dry, how early one can plant really depends on temperature. Daily average temperature (average of daily minimum and maximum) should be 60oF. Historically, this average falls between April 10 and 15 in the Sacramento Valley. The other consideration if you are planting early is the availability of water. The seeds need to have water to germinate. You cannot always rely on rainfall. Sometimes it may be hard to plant to moisture. In these cases, you need irrigation water. If you have an irrigation pump, you are free to decide when to plant and irrigate your field. If you have to rely on district water, you will be more restricted in your planning.
- Author: Michelle Leinfelder-Miles
With funding from the CDFA Healthy Soils Program and CA Rice Research Board, we are evaluating how well different cover crop species establish, provide soil coverage, affect soil carbon and nitrogen dynamics, and/or impact rice yield in subsequent growing seasons. Since rice may be grown over multiple seasons without rotation, cover crops may provide an opportunity to introduce plant diversity, including nitrogen-fixing legumes. Other potential benefits include increasing soil organic matter, reducing nitrogen loss in the winter, reducing nitrogen inputs during the rice season, and improving rice straw decomposition. While evaluating winter cover crops in the rice system is the primary purpose of the trial, the project has relevance for other annual systems where winter cover cropping may be employed.
This article describes one of the three trial locations, which was on Staten Island in the San Joaquin Delta Region. We planted the cover crops on November 13th by hand-broadcasting seed over 200-ft2 plots and then gently raking it in. We planted 10 single species and two mixes (Tables 1-2). Each treatment was replicated four times, and the graphs below illustrate cover crop stands over the season (Figs. 1-4).
Table 1. Cover crop species and seeding rates. Table 2. Cover crop mixes and seeding rates.
- Timing of operations is critical. Growers should strive to plant winter cover crops as early as conditions allow (e.g. early to mid-November). Drill seeding is more effective (i.e. better stand establishment) than flying on and harrowing in seed.
- Stand establishment is impacted by conditions outside the control of the manager (i.e. weather, herbivory). If neighboring fields will be winter-flooded, having drainage ditches between fields will help cover crop growth.
- Author: Sarah Marsh
A system of permanently flooded rice and a lack of diverse weed management techniques have selected for flood-tolerant weed populations in California water-seeded rice fields. Rising herbicide resistance results in increased costs of weed management, as well as increases the difficulty of growing rice in California. One technique to delay further expansion of herbicide resistance is to develop new herbicides to assist in managing current herbicide-resistant weed biotypes.
From 2019-2022, greenhouse and field experiments were conducted to characterize Zembu (active ingredient pyraclonil) activity on common California rice weeds alone and in combination with currently available herbicides.
Zembu, a novel protoporphyrinogen oxidase (protox) inhibiting active ingredient developed for California rice, was applied alone and in combination with other herbicides to determine grass, sedge, and broadleaf control and crop safety.
These experiments indicated that Zembu applied alone is insufficient for broad-spectrum weed control (Table 1), but, when applied in combination with currently available herbicides (SuperWHAM!, Cerano, Butte, Bolero, Granite, Regiment, Loyant) can provide consistently greater control of watergrass species, bearded sprangletop, ricefield bulrush, smallflower umbrella sedge, ducksalad, and redstem (Table 2). Yields from plots treated with Zembu, alone and in combination with other herbicides, were significantly higher than untreated control plots. There was no significant difference in yield among any plots treated with Zembu (Figure 1). There was evidence of temporary plant phytotoxicity in some plots treated with Zembu, Bolero, and SuperWham (Figure 2), but no plots demonstrated lasting injury that affected rice yields. Zembu was effective as a base treatment herbicide for incorporation into water-seeded rice weed management programs.
Table 1. Sedge and broadleaf control from Zembu at different application timings in water-seeded rice and at three assessment dates as a repeated measure pooled across 2019, 2020, and 2023ab
- 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.