ABSTRACT:

1. Shading from canopy closure is a proven way to help manage weed pressure.

2. Residuals need to last until canopy closure, which may not occur on wider rows. Narrower rows equal faster canopy closure.

3. The control increased when a pre-emerge herbicide with three SOAs was used, making multiple SOAs critical for 30 in. rows.

THE IMPORTANCE OF CANOPY CLOSURE

Canopy closure is one of the best defenses to prevent the germination of weeds. The competition from canopy closure will reduce the amount of light, making it much harder for weeds to germinate. When applying a pre-emerge herbicide, followed by an in-season residual, the goal is for the blanket of protection to last until canopy closure. Therefore, it is critical for the residual herbicide to last until canopy closure, which may not occur on wider rows. Beck’s Practical Farm Research (PFR)® data shows narrow rows can help reduce waterhemp pressure in the untreated check. This study showed that a 15 in. row width averaged 31% fewer waterhemp compared to a 30 in. row width. The narrower rows allow for faster canopy closure, making the herbicide program more successful.

THE INFLUENCE OF ROW SPACING ON SOAs AND RESIDUAL CONTROL

In general, a pre-emerge herbicide with three SOAs is better than one, and the same concept applies to row spacing.

ONE SOA: The 7.5 in. and 15 in. rows resulted in less waterhemp pressure because the soybean rows closed before the one SOA pre-emerge herbicide broke. In 30 in. rows, one SOA pre-emerge herbicide broke before canopy closure, resulting in flushes of waterhemp.

THREE SOAs: It’s crucial to use a pre-emerge herbicide with multiple SOAs in 30 in. rows. Though it took longer for the 30 in. rows to close, when a pre-emerge herbicide with three effective SOAs was used, canopy closure was reached before the product began to break.

When a pre-emerge herbicide with three effective SOAs is used, we saw waterhemp control across all row spacings and populations, greater control and less variability across a wide range of management decisions, and fewer weeds at the post-emergence application timing. 

CONCLUSION:

Canopy closure is one of the best defenses to prevent the germination of weeds. Reducing the amount of light will make it much harder for weeds to germinate. In regards to row width and a successful herbicide program, the residual needs to last until canopy closure, which may not occur with wider rows. Narrower rows allow faster canopy closure. It’s crucial to make a multiple SOAs pre-emerge herbicide application with 30 in. rows so that canopy closure can be reached before the products begin to break.