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Diggin' In When herbicides are applied is as important as the what or how Good Timing Diggin' In HERBICIDES | By Pamela J.S. Hutchinson, University of Idaho From potato planting to row closure is a busy time for growers. It's also a busy time for weeds. Getting the herbicides on at the right time and linking up with tillage operations between planting and row closure is the key for weed control from start to finish. Time from planting to emergence can be three to four weeks. From emergence to row closure, when the potato crop finally starts to help control the weeds with shading and competition, can be another four to five weeks. Here's why timing matters: University of Idaho research shows that when hairy nightshade is at a density of 2 per meter-row, it must be controlled, or a yield loss of U.S. No. 1s of 5 percent or great will occur. This time is from a few days after potato emergence to 22 days later. If only 1 per meter-row competes all season long, as much as 21 percent U.S. No. 1 yield is lost. Using an integrated weed management strategy will provide the best weed control in potatoes. Such an approach includes cultural, mechanical, chemical and biological tools available for weed control, rather than relying on any single tool. There are different approaches to tillage-timing out there. This article will concentrate on two: Method 1: "Drag-off" before potato emergence and a hilling-reservoir tillage operation (often referred to by the brand name Dammer Diker) after potato emergence. Post-emergence herbicides are applied after that tillage. Drag-off occurs with a harrow or similar equipment to knock down the moderate hill that was built at planting so that the seed piece is closer to surface. If the field is leveled, however, the final hilling-reservoir tillage cannot occur until after potato emergence when the rows can be seen—unless a precision planter with GPS features is used Method 2: Hilling-reservoir tillage conducted after planting but before potato emergence. Herbicides are applied after that tillage but before potato emergence. For both scenarios, the reservoir tillage equipment is set up to hill at the same time, and that is the last tillage operation to be performed until harvest. In both scenarios, another herbicide application after potatoes emerge may be needed. Tank-mix herbicides with different mechanisms of action in order to achieve broad-spectrum weed control and prevent or delay the development of herbicide-resistant weed populations. Design herbicide tank mixes to target the weeds present in a given Drag-off before potato emergence and hilling-reservoir tillage after potato emergence. Herbicides are applied after hilling post- emergence to the potatoes. A second post-emergence spray may be necessary. Only hilling-reservoir tillage after potato emergence. Herbicides are applied after hilling but pre-emergence to the potatoes. A post-emergence spray may be necessary. Reservoir tillage creates divots in the furrow, which can slow irrigation water's infiltration rate slow for more efficient irrigation. 30 POTATO GROWER | APRIL 2019