Spray early, spray less
We say it every year, repeatedly, to the point of getting eye rolls: focus on pre-emergence (PRE) herbicides! There’s no single easier way to improve weed control and save money than to get PRE herbicides overlapped and applied and activated early.
The earlier we plant, the longer residuals can stretch. But we still want to shoot for the overlap. Planting late March to early April, we can probably get 3-plus weeks out of our first residual (if conditions turn dry, this window shortens). The later we plant beyond that, the window in which residuals will last shortens as temperatures rise and conditions get drier. Suddenly, 2-plus weeks becomes the normal expectation.
In row rice, research has shown that getting PREs overlapped at two weeks is critical for barnyardgrass control. Waiting until three weeks to overlap results in major issues. Luckily, flushing for activation in row rice is pretty easy compared to levee rice.
A stale seedbed approach to planting has been an emphasis for me this year. Getting the ground slicked off, followed by a nice, packing rain works wonders for efficiency. We’ve got all these nice no-till drills. Let’s use them.
In a stale seedbed situation, not only does planting efficiency improve (better stands), but weed control also improves. When we plant into a stale situation and can include some burndown and our first PRE immediately following planting, we are way ahead of the game.
Now we’re working from a point where the opportunities for weed flushes are greatly reduced. So additional PRE applications will be more effective combatting reduced weed pressure. If we do end up needing a post-emergence application, we’ll be fighting lower densities.
Take the fight to weeds early to have the best 2022 season. It’s the best way to keep more money in your pocket.
Dry winter may impact early season weed control
Here in California, we’ve had one of the driest January-February periods ever recorded. While still possible, we are not likely to get a large amount of rain in March and April (based on historical weather patterns). What does this mean for early season weed control?
If you drill-seed your rice, some weed emergence may be impacted. The soil is going to be extremely dry, meaning that flushes of water may not increase soil moisture enough for weed seeds near the soil surface to imbibe enough water for germination. This will disproportionately impact small-seeded weeds, which cannot emerge from deep in the soil. Some of our smaller-seeded weeds are smallflower umbrellasedge, sprangletop and redstem.
Emergence of large-seeded weeds, such as our watergrass species, are likely not to be impacted, as they can emerge from deeper in the soil profile — where the soil moisture content is likely higher — with enough water to imbibe for emergence.
For continuously flooded fields, the dry winter will likely cause a slow flood-up. Last year, we saw it take more than a week in some cases, depending on the size of the field. The dryness of the soil, coupled with a lower water table in some areas, may have contributed to the slower-than-normal flooding, and this year will likely look similar.
Here are some things to be aware of (again, based on observations from last year). Slow flood-up may contribute to low rice germination rates. This can happen if the soil was saturated for a long time before the rice seed was planted.
Rice — like all plants — needs oxygen. If the soil remains saturated for a long period, the oxygen level in the soil and water will go down. This causes some of the seeds to die shortly after germination and not make it to the surface of the water.
» What you might notice: poor stand, patchiness through the field, gaps where rice is missing.
» What it may cause: poor weed control in areas where the rice stand is thin, leading to low yields in those areas.
Since a thick stand of rice can usually outcompete the rice, the thin stand allows for weeds to come through, even if herbicide applications are perfect.
» What you can do: If possible, make targeted herbicide applications to those areas of the field where the stand is thin. Also, you may want to avoid harvesting those areas — if the weeds have gone to seed and are particularly thick — to avoid spreading weed seeds around with the combine.
Note: High wind shortly after seeding may also contribute to low rice germination rates, as soil can be pushed over the rice seeds, creating the same anaerobic conditions as described above (no oxygen to the seed). High wind can blow seedlings to one edge of the field. In this case, employing a Leather’s Method (draining the field) is the best way to ensure the rice has enough oxygen and that the seedlings are not pushed to one edge of the field.
As always, please follow all herbicide water-holding periods, and do not pull boards if a water-hold is in place. Shutting off the water into the field may be effective to allow water to subside in some fields.
Even if the rice stand is good, there may still be poor weed control from a slow flood-up if the weeds are germinating ahead of the rice being planted. Many grasses germinate early and will likely be ahead of rice in this scenario, especially if temperatures are warm.
» What you might notice: grasses that are much larger than the rice, perhaps even after an early herbicide application.
» What it may cause: Since grasses are the biggest contributor to yield loss out of all of the weeds, fields with a particularly large grass infestation early on will likely suffer some yield loss … even if the field looks clean at the end of the season.
The largest decrease in yields from grass competition occurs during the first 30 days after planting.
» What you can do: Although it may not be possible to salvage yields due to early grass competition, it is still important to try to control the grasses before they go to seed, as leaving them in the field will contribute to the weed soil seedbank for many years to come.
Large grasses respond well to tank mixes, top-of-label rates, and multiple herbicide applications in close succession. However, it is important to weigh the economic cost of the herbicide applications against the potential yield losses.
If possible, targeted applications in the worst-infested areas of the field may be a good option.
Reach out to your pest control advisor or local Extension advisor if you need additional assistance in planning your herbicide program.
Start clean, stay clean
If you’ve ever been to an Extension meeting, you’ve likely heard the saying “start clean, stay clean.” If you’re tired of hearing that expression, you’ve come to the wrong place.
“Growing up” the last four years in the rice industry, 95% of my work focused on furrow-irrigated rice. Coming from that mentality, you really must keep the grass from ever emerging. However, I believe that’s a mindset we all ought to have regardless of production system.
With resistance issues ever increasing, if we see grass, it may indeed be too late.
We didn’t have a ton of chemistry to begin with, but post options are very limited. There aren’t a ton of new products lined up at the door. Better yielding Provisia and Max-Ace cultivars — along with Rogue herbicide receiving full approval — will help us on some acres. But many of us will continue to rely on old chemistries and even heavier on the pre-emerges.
The vast majority of successful rice systems start with clomazone up front. Barnyardgrass, signalgrass and sprangletop are all controlled well by clomazone, with very little resistance to this point. The only major scenario I would not want to apply clomazone directly behind the planter is on cut ground. Even a reduced rate can cause issues on deep cuts!
Our second application should fall no later than two-to-three leaf rice and can include pendimethalin (Prowl) for barnyard and crabgrass control. Quinclorac (Facet) can be used for barnyard, signalgrass and fall panicum control, and thiobencarb (Bolero) can be used for barnyard, crabgrass, fall panicum and sprangletop control.
We’ve been very successful with mixing quinclorac with either pendimethalin or thiobencarb at the two-leaf stage. Quinclorac does a great job at filling in the gaps of pendimethalin (sprangletop) and thiobencarb (signalgrass).
While broadleaves and sedges are a little easier to clean up, we do have some pre options for those as well. Imazosulfuron (League) is a great pre on hemp sesbania (coffeebean), both jointvetches (indigo), flatsedge, yellow nutsedge and pretty good on smartweed.
Quinclorac + thiobencarb also does well on coffeebean and indigo. Saflufenacil is a player as well in controlling palmer amaranth, flatsedge and umbrella sedge. If we start clean and get timely rains on top of these pre-emerge options, we’ll set ourselves up for a good and happy September!
If you have any questions, feel free to contact me or Jim Heiser, weed scientist in the Bootheel. As always, eat Missouri rice!
Weedy rice — or red rice — is the same species as cultivated rice and is competing with the crop for resources throughout the growing season, robbing the crop of nutrients, water and space. Rice is self-pollinating, which slows the rate of cross-pollination, especially since the reproductive window of individual varieties is relatively narrow.
Fields where hybrids have been growing for many years can increase outcrossing, resulting in numerous offspring that have varying maturity dates. This leads to an increased window for cross-pollination, which results in more varieties of weedy rice.
Rice that shatters is left in the field and will produce volunteer plants in following years. Volunteers increase potential for outcrossing. Hybrid rice is more compatible with red rice and can have a higher outcrossing rate. The outcrossing rate in hybrids is double that of conventional rice varieties.
Some herbicide resistance has also passed along to weedy rice. Persistence is key to managing weedy rice over the long-term, and many strategies may need to be used to reduce populations. Don’t forget dormancy issues and think there is a quick fix. Crop rotation is recommended as it allows for the use of herbicide modes of action, which are not available in rice.
Herbicide technology such as Clearfield and FullPage have been used and can still be used where there is no resistance. New herbicide technology such as Provisia and Max-Ace will also allow weedy rice and red rice to be controlled but should be used with good stewardship practices.
Water management has been used for many years in Louisiana to control red rice and can also be used to control weedy rice. While there are increased seed costs because of higher seeding rates needed for water planting, water management using a pinpoint flooding system can effectively control weedy rice populations.
Planting early and flooding early can also help reduce weedy rice germination. Remember red rice- and weedy rice-free seed should be a must when planting.
The variability in maturity also affects harvest. Weedy rice may be overly mature or under-mature at harvest. Grains from overly mature weedy rice shatter in the field, leaving seed that will increase the weedy rice seed bank and reduce overall yield. Over-mature grains can also break during the milling process, lowering the crop’s milling quality. Grain that is not mature at harvest means moisture content will be high, delaying harvest and increasing rice-drying cost.
Variety selection is an important decision for weedy rice control. Regardless of planting method or herbicide-tolerant technology utilized, research has shown that early control is the link to successful weedy rice control. Choosing the right variety and planting method for weedy rice should be tailored to each field.