Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2000
Publication Date: N/A
Interpretive Summary: A rotary hoe usually never provides adequate weed control by itself. However, if coupled with reduced herbicide rates it can be a very effective tool to manage weeds. A two-year study examined the control of foxtail (pigeon grass) in corn by timely rotary hoeing superimposed upon a series of 'Surpass' (acetochlor) application rates. Timely rotary hoeing was defined as that conducted at 15% and 30% foxtail emergence, as weed emergence is a much better indicator of when to rotary hoe than other rules-of-thumb such as "days after planting" or "white-threads in soil." Somewhat greater than 90% weed control was achieved with the full label rate of Surpass with or without a rotary hoe. With two timely passes of a rotary hoe, however, this same level of control could be achieved with only 1/3 the label rate of Surpass, and adequate control could be achieved with 1/10 the label rate of Surpass. Importantly, the often-noticed annual variability in the effectiveness of rotary hoeing was eliminated by basing the use of the implement on weed emergence percentage rather than other indices. This information is valuable to farmers, crop advisors, and extension specialists who desire to reduce variable costs, as well as to extension specialists and agri-chemical industry personnel who seek integrated weed management strategies to lessen selection pressure for herbicide resistance in weeds.
Technical Abstract: Dose-response curves for acetochlor, with and without timely rotary hoeing (two passes), were derived for corn fields over two years. The fields were dominated by green foxtail, which constituted 73-86% of the weed population, but also contained minor amounts of common lambsquarters, Pennsylvania smartweed, and redroot pigweed. In the absence of rotary hoeing, weed control averaged 92% at the full label rate of acetochlor, which is 3 kg ai ha**-1 on clay loam soil. With two timely rotary hoeings, however, this same level of control was achieved with only 1 kg ai ha**-1 acetochlor. Given the suite of weed species present in these experiments, timely rotary hoeing substituted for 67% of the label rate of acetochlor.