Surveys of Mississippi rice growers indicate that nearly 40 percent believe they have herbicide-resistant barnyardgrass in their fields, says Jason Bond.
In screening of barnyardgrass samples from 2007-2009, “we found 45 percent were resistant to propanil, 20 percent to Facet, and 15 percent with multiple resistance to propanil and Facet,” he said at the annual Delta Ag Expo at Cleveland, Miss.
“This does not mean that 45 percent of barnyardgrass in the Mississippi Delta is propanil resistant — it just means that these are the percentages we’ve observed in the samples we’ve collected, all of which came from problem fields.”
Bond, who is associate research professor at the Delta Research and Extension Center, Stoneville, Miss., says control of barnyardgrass with Clincher herbicide is “variable, from 58 percent to 97 percent in greenouse studies,” and that resistance is suspected for Newpath, Beyond, and Grasp.
“About seven to eight years after a new herbicide comes out, we usually find resistance somewhere.”
Over the years, Bond says, as growers have widely adopted Roundup Ready and Clearfield production systems, many have paid less attention to timing of herbicide applications.
“Timing is important; herbicides work better on small weeds than large ones every time. In one study at Stoneville last year, for each day herbicide application was delayed beyond optimum the yield loss was 2.4 bushels.”
For best results with barnyardgrass, Bond says, growers should start with clean fields, and “treat early and often,” using Command, Facet, Prowl H20, RiceBeaux, along with Newpath in Clearfield rice.
Vary herbicides for best results
“Well-timed early season applications, using multiple pre-and postemergence herbicides with different modes of action, provide the most consistent weed control.”
Rice flatsedge “blew up on us” in several areas last year, Bond says, with ALS resistance in Tallahatchie County and suspected in Bolivar, and Leflore Counties.
With this weed, he says, “scout often and spray early. Tank mixes of propanil and Basagran or RiceBeaux are effective, if applied early.” But, he cautions, don’t tank mix Basagran with Clincher or RiceStar.
Pigweed (Palmer amaranth) is now the No.1 weed problem in Mississippi row crops, Bond says, with resistance to glyphosate herbicide increasing. This leads to problems when those fields are rotated to rice.
“A full rate of propanil plus Grandstand has provided the most consistent pigweed control,” he says. “The earlier you spray, the better chance you have for control.”
And he advises growers to control pigweed plants on levees and field borders. “Any plants not controlled in these areas will mature and produce seeds that can cause problems for years to come.”
Water conditioners, in some situations, may facilitate herbicide effectiveness. “Rice herbicides can sometimes be finicky as to water pH. If the pH is more than two units away from 7, you may want to add a water conditioner.”
Controlling rice water weevils
Rice water weevils infest almost every acre of rice in Mississippi to some extent, says Jeff Gore, assistant research professor, Delta Research and Extension Center.
Just one weevil per core can reduce yield by as much as 1 bushel per acre, he told producers attending the Delta Ag Expo.
Planting date can affect density of the pest, he says, “but it varies from year to year and there’s no way to predict it.”
Managing the pest with foliar-applied insecticides can be “highly variable,” Gore notes, but seed treatments do a good job of reducing weevil numbers and are more consistent.
Two new seed treatments, granted full labels in 2010 — Dermacor X-100 from DuPont and CruiserMaxx from Syngenta — do a good job of reducing the number of weevils, he says.
In three-year studies at the research center and on grower farms, percentage of control has varied widely, depending on initial larval densities.
In general, Gore notes, little benefit is obtained with either material if rice water weevil densities are low (1 to 2 weevils per core). Benefit increases as the insect density increases.
Both seed treatments produced “significant benefits” in terms of yield, he says. Over the three years of the studies, Dermacor X-100 provided an 11.8 bushel increase, with a 72 percent probability of a net return over costs, and CruiserMaxx gave an 8.3 bushel increase, with a 79 percent probability of a net return over costs.
A product expected to be available in the near future, Nipsit Inside from Valent, will offer growers another product for rice water weevil control, Gore says.
In 2009-10 studies, Nipsit did not provide a benefit when insect densities were low, but at moderate to high densities, it gave control similar to CruiserMaxx, with an average yield benefit of 9 bushels per acre.
Since the product price is not known, no economic benefit analysis could be done, but Gore says the probability of a net economic return will likely be similar to CruiserMaxx and Dermacor X-100.
Last year was “one of the worst in a long time” for fall armyworms in rice, Gore says. “We had a lot of calls from growers about lack of control with pyrethroids in later rice. Because there’s a lot more plant mass late season, it’s a good idea to bump up the rate of the pyrethroid for better control.”
Tailor nitrogen rate to variety
Many growers may need to rethink their rice fertilization strategy, says Tim Walker, associate research professor at the Delta Research and Extension Center.
“We’ve tended to get into the mindset that rice nitrogen response is linear,” he said at the Delta Ag Expo. “But that’s not so — it’s actually curvilinear.”
Researchers are finding, he says, that reducing N rates can, in many cases, reduce production costs without yield loss. And applying excess N can reduce, rather than boost, rice yield; with some varieties, too much N can also increase lodging.
While some varieties can tolerate N rates as high as 240 lbs. per acre without lodging, he says, others will have lodging at rates over 135 pounds.
“We need a more precise way to prescribe N rates,” Walker says, “so we don’t over- or under-fertilize rice. The N-ST*R test, developed by the University of Arkansas, shows tremendous promise in providing the accuracy and precision we need.”
The test allows growers to make fertilizer decisions based on knowledge of how much N is supplied by soils on their farm. The results may be greater or less than current state average rates.
Although N-ST*R is not yet commercially available, Walker says work is continuing to validate the models.
Commenting on nitrogen stabilizers, he says, “There are a lot of these products, but the only one we’ve found that will stabilize nitrogen from volatility losses is Agrotain.”
With Agrotain, he notes, urea loses only about 7 percent of its effectiveness to volatility, compared to as much as 40 percent for urea alone.
“With urea at $400-plus per ton, unless you can flood quickly, I would suggest using Agrotain.”