• By Steve Li, Alabama Cooperative Extension Specialist and Assistant Professor,
Crop, Soil and Environmental Sciences •
[dropcap]Q [/dropcap]What is Zidua? How does it kill weeds?
A: Zidua (pyrosasulfone) is a Weed Science Society of America (WSSA) group 15 herbicide, which has similar mode of action to Dual Magnum (S-metolachlor), Warrant (acetochlor) and Outlook (S-dimethenamid). It controls weeds by inhibiting production of very long chain fatty acids in cells. Zidua and other group 15 herbicides target susceptible weeds during emergence; therefore, proper incorporation by irrigation or rainfall after application but before weed germination is required.
Similar to Dual Magnum, Outlook and Warrant, Zidua will not control large and established weeds because this group of herbicides are absorbed by cotyledon and hypocotyl of susceptible weeds during seedling emergence through treated soil layers.
[dropcap]Q[/dropcap] What weeds does Zidua control in peanut and what are the benefits?
A: Zidua provides control of many problematic weeds such as pigweed, nightshade, Florida pusley, carpetweed, prickly sida, common purslane, crabgrass, crowfootgrass, goosegrass, and barnyardgrass. It can also suppress horseweed (marestail), morningglory, common ragweed, Texas millet and yellow nutsedge, but tankmix or sequential applications are usually required to provide additional control on these species.
The greatest benefit is providing residual weed control and delaying the occurrence of new weed resistance, considering that the infestation of glyphosate- and ALS-inhibitor-resistant pigweed in Alabama is very high.
[dropcap]Q[/dropcap] When and how should Zidua be used?
A: According to the label, only early postemergence application at 1.5–2.1 oz./A is allowed. The application window is from first true leaf through beginning of pod development. Zidua up to 3 oz./A preemergence has been tested in research trials without unacceptable peanut injury.
However, due to low soil absorption, peanut injury can happen if excessive rainfall occurs during seedling emergence or if seed vigor is low. Therefore, preemergence application of Zidua is not recommended. Sequential applications can be made with a 14-day interval and a maximum combined rate for a year of 5 oz./A.
[dropcap]Q[/dropcap] Can I tankmix Zidua with other herbicides?
A: Absolutely. Zidua can be tankmixed with Basagran, Gramoxone, Storm, Cadre, Outlook, Poast, Select, Pursuit, Ultra Blazer, Aim, 2,4-DB and Cobra. In 2016 and 2017, tests showed good results on these tankmixes in dryland and irrigated peanut in Alabama: Gramoxone + Storm/Basagran + Zidua; Gramoxone + 2,4-DB + Zidua; Cadre + 2,4-DB + Zidua; Ultra Blazer + 2,4-DB + Zidua; Cobra + 2,4-DB + Zidua; Storm + 2,4-DB + Zidua.
Timely application of these treatments will be key to controlling weeds. Nothing can completely control pigweed, sicklepod and coffeeweed when they reach more than 6 inches tall.
[dropcap]Q[/dropcap] What about potential injury caused by Zidua?
A: No significant peanut injury (> 20%) in Zidua treatments have been observed in Alabama Extension trials. Avoid spraying Gramoxone + Zidua on thrips-damaged peanut, weak stand or peanut under intensive stress, such as from drought or disease.
[dropcap]Q[/dropcap] Is carryover a problem?
A: Follow label restrictions about rotational crops. Pyroxasulfone does not persist in soil for a long time (reported soil half-life of 16 to 34 days, as compared to S-metolachlor half-life of 11 to 30 days). At 2 oz./A rate, corn can be planted after two months, grain sorghum after six months, wheat after one month, cotton after two months, and soybean is tolerant to Zidua preemergence and has no restrictions.
Zidua is not expected to cause a similar level of carryover problems as Cadre on cotton and Strongarm on corn. However, planting canola, carinata, grass cover crops and winter vegetables into Zidua-treated fields may cause a negative impact on crop growth; therefore, caution is needed.
[dropcap]Q[/dropcap] How does Zidua work in dryland peanut?
A: Its soil persistence is not expected to be substantially different as compared to Dual Magnum, Warrant and Outlook. Field experiments are being conducted to evaluate the lowest amount of rainfall needed to activate this herbicide and its persistence in dryland as compared to other residual herbicides in peanut.