Early-season weed control

Controlling early-season weeds is critical to achieving high corn yields. It’s most important to preventing weed competition in corn three to six weeks after planting. This period begins the V2 to V3 growth stage of corn, or when corn plants are about 6 to 8 inches tall.

Early-season weed control

Controlling early-season weeds is critical to achieving high corn yields. It’s most important to preventing weed competition in corn three to six weeks after planting. This period begins the V2 to V3 growth stage of corn, or when corn plants are about 6 to 8 inches tall.

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 two-pass program, but they require careful management.

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

Throughout the growing season, take notes and photos of weeds and field conditions to aid in your herbicide management plan. If you are interested in taking pictures and notes via your smartphone, download the free Encirca app.

Be sure to use herbicides with multiple modes of action to prevent herbicide resistance, and to best manage postemergent weeds.

Reasons to control weeds early are:

It helps protect the yield potential of the crop.

Small weeds are easier to control than large ones.

Young weeds absorb and translocate herbicides better than older ones.

Herbicides can be less effective during times of heat and drought stress, which often occur at later application times.

Weeds can reduce corn yield as soon as the V2 stage. Control weeds before this stage and maintain control through at least V14 to help ensure maximum yield potential. Control weeds in soybeans within the first four weeks. Maintain control through canopy closure.

See the accompanying table for the difference early weed control makes in corn. 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 three times greater compared to when weeds were controlled when they were 2 to 6 inches tall.

If preplant or preemergence herbicides cannot be applied, apply postemergence herbicides as soon as possible. Include residual herbicides to extend control of weeds that are still germinating. Do not cut the use rate. Use the recommended rate for the weed size. Use high-quality adjuvants as directed on the product labels. Be prepared to apply follow-up treatments to control escapes and late-germinating weeds.

Ruhland is a field agronomist for DuPont Pioneer. He covers central and southern South Dakota. Contact him at [email protected] Follow local DuPont Pioneer agronomists on Twitter @PioneerNDakota and @PioneerSDakota.

02151246B.tif

Table 1: The effect of application timing
on weed control and corn yields

Application timing
(weed size)

Weed control

Corn yield loss
(early-season competition only)

Corn yield loss
(early- and late-season competition)

---------------------------------------------%------------------------------------------

2 inches

73

0

7

4 inches

83

3

6

6 inches

90

6

7

9 inches

93

14

11

12 inches

95

22

21

Source: Adapted from Grower et al. 2003 Weed Technol. 17:821-828

This article published in the February, 2015 edition of DAKOTA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2015.

Weed Control

Crop Management

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