Reduced Input Corn Weed Control: The Effects of Planting Date, Early Season Weed Control, and Row-Crop Cultivar Selection

Concerns of pesticide detection in ground and surface water and the desire to lower external or off-farm inputs have renewed interest in mechanical weeding to reduce herbicide use and weed control costs. Field research was conducted to evaluate weed control using S-tine, minimum-till, rolling, and C-shank rowcrop cultivators in corn (Zea mays L.) planted 25 April, 5 May, and 15 May. Rotary hoeings or a 10-in. band of atrazine plus metolachlor PRE herbicide were used for early season in-row weed control. The field had a silt loam soil and high annual weed pressure and the previous crop was corn. Weed control was excellent with banded herbicide at all planting dates. Weed control with the rotary hoe was less than that of the banded herbicide but improved as planting was delayed. Banded herbicide resulted in better weed control, higher corn yield, and less corn population reduction than rotary hoeing. Weed control, corn population reduction, and corn yield were similar for all row-crop cultivators. Early planted corn treated with banded herbicide and cultivated twice gave the highest economic return. Research QuestionCorn producers seek weed control methods that reduce herbicide use to minimize potential surface and groundwater contamination. Mechanical weed control is not new, but has received little attention following the advent of highly selective and effective herbicides. The objective of this study was to compare two early season weed control strategies (banded herbicide and rotary hoeing), followed by two cultivations with four row-crop cultivator models, over a range of corn planting dates in a reduced tillage system. Literature SummaryMechanical weeding was a standard practice in corn production until recently. Even when weeds are controlled with herbicides, cultivation often improves corn yield. Planting date and soil tillage affect cropweed interactions. Delayed planting allows corn to germinate after the peak germination period of some weed species and also enhances corn's competitiveness because seeds are planted in a warmer soil. Rotary hoeing and band-applied herbicides try to control early emerging in-row weeds, which is the row-crop cultivator's main weakness. Iowa data show that banded herbicides, complemented with cultivation, reduce chemical inputs by two-thirds without decreasing corn yields. Relatively little research on row-crop cultivation has been done in recent years. Study DescriptionThe study was conducted in 1990 and 1991 at the University of Wisconsin Arlington Research Station on a Plano silt loam soil. Corn was planted in 30-in. rows and cultivated twice. The study was set up as a complete factorial with three factors. Factor 1. Early season in-row weed control Banded herbicide (applied preemerge in 10-in. bands) Rotary hoeing (twice) Factor 2. Planting date 25 April 5 May 15 May Factor 3. Row-crop cultivator design S-tine Minimum-till Rolling C-shank Applied QuestionsHow do banded herbicide and rotary hoeing compare as methods to lower corn weed control inputs and does date of planting affect these strategies? Two years of field research show that preemergence herbicide applied in a 10-in. band and complemented with two timely cultivations controls more than 90% of the in-row weeds in corn planted from late April to mid May (Table 1). If rotary hoeing without herbicides is the only early season weed control method, corn planting should be delayed until at least late April to avoid earlier emerging weeds. Rotary hoe weed control may be improved by delaying planting from early to mid May, however, maximum yields are attained if corn is planted before 15 May in Wisconsin. Are row-crop cultivators equal in effectiveness or is one design better suited than another to a particular weed control system? When properly adjusted, all row-crop cultivators tested controlled weeds similarly in a chisel plowed silt loam soil when corn was cultivated at 5- and 20-in. heights. What are important considerations if shifting to a lower input weed control system? Corn population may be reduced 2 to 3% for each mechanical weeding operation. Producers using systems based on two rotary hoeings and two cultivations should increase corn seeding rates 8 to 10% above those based on a single cultivation. A 10-in. herbicide band is adequate to achieve efficient weed control with cultivation. Costs of rotary hoeing plus two cultivations are comparable with those of a banded herbicide and two cultivations. Both reduced input systems have lower costs than a broadcast application of the recommended rates of most corn herbicides. Table 1Average visual weed control and corn yield for two methods of early weed control and three planting dates.† In-row weed control‡Corn yieldEarly weed controlBandedherbicideRotaryhoeingBandedherbicideRotaryhoeing------- % -------------- bu/acre ------Planting date 25 April9569189176 5 May9887186177 15 May9889162157†Data averaged over 2 yr and four between-row cultivators. ‡Visual evaluation taken 90 d after planting.