Control Early Season Weeds in Corn

Controlling early season weeds is critical to achieving high corn yields. The critical period for preventing weed competition in corn is 3 to 6 weeks after planting. This period begins in the V2 to V3 growth stage or when corn is roughly 6 to 8 inches tall.

Soil-applied herbicides require light incorporation or rainfall within 5 to 7 days of application. Lack of rainfall, uneven incorporation or excess rainfall can dramatically reduce herbicide performance and yield.

A preemergent herbicide followed by a postemergence herbicide program is the most reliable and effective weed control program. Preemergence or postemergence only herbicide programs can protect yield equally to a 2-pass program but they require careful management.

The study below compares weed competition in a total post-herbicide program. The highest level of weed control was achieved by delaying the postemergence herbicide application until weeds were 12 inches tall. However, yield loss due to weed competition was nearly 3 times greater compared to when weeds were controlled when they were 2 to 6 inches tall.

Table 1: The Effect of Application Timing on Weed Control and Corn Yields
Application Timing
(Weed Size)
Corn Yield Loss
(Early Season Competition Only)
Corn Yield Loss
(Early & Late Season Competition)
2" 73 0 7
4" 83 3 6
6" 90 6 7
9" 93 14 11
12" 95 22 21
Adapted from Grower et al. 2003 Weed Technol. 17:821-828

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