Submitted to: Potato Country USA
Publication Type: Popular Publication
Publication Acceptance Date: February 1, 2006
Publication Date: June 1, 2006
Citation: Boydston, R.A. 2006. Strengths and Weaknesses of Two New Potato Herbicides. Potato Country USA. July-August pp 4-5. Technical Abstract: Outlook (dimethenamid-p) and Chateau (flumioxazin) are two new preemergence herbicides labeled for use in potatoes. Both herbicides are restricted to preemergence applications only and improve nightshade control when tank mixed with other potato herbicides. Dimethenamid-p is particularly strong on annual grass weeds (foxtail sp., barnyardgrass, fall panicum, crabgrass sp., pigweed, and nightshade species (hairy, black, and cutleaf nightshade). Dimethenamid-p is fair on common lambsquarters, Russian thistle, and kochia, but improves common lambsquarters control as a tank mix partner. Waiting to apply dimethenamid-p until just prior to potato emergence will extend the weed control until about row closure. Fall-seeded crops (grass seed, small grains) may be planted four months or more after an dimethenamid-p application. Flumioxazin is taken up primarily through roots weed seedlings and should be also applied prior to weed and potato emergence. Flumioxazin inhibits an enzyme important in the synthesis of chlorophyll and susceptible plants accumulate porphyrins that lead to membrane disruption. Flumioxazin is particularly strong on nightshade species (hairy, black, and cutleaf nightshade). At the low use rates labeled in potato, flumioxazin is most useful as a tank mix partner for nightshade control. Flumioxazin will also help suppress common lambsquarters and pigweed species, but will not control grass weeds at the rates labeled in potato. Flumioxazin may injure potato shoots near the soil surface and should be applied when there is still 2 inches or more of soil above emerging potato shoots, well ahead of potato emergence. Mechanical incorporation may reduce weed control and may place the herbicide in proximity of emerging potato shoots, increasing the chance of injury. Flumioxazin is not persistent in soils and field corn, sorghum, sunflower, soybean, and wheat can be planted 30 days or more after an application. Dimethenamid-p and flumioxazin have shown good potato tolerance on seven major potato varieties grown in the PNW; Russet Burbank, Ranger Russet, Russet Norkotah, Shepody, Umatilla, Bannock Russet, and Alturas.