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Herbicide Application Layby; What does Layby Mean? How does it Work? (05/30/19)

I am writing about waterhemp control in sugarbeet today although we will attempt to expand the concept into soybean, too.

I am writing about waterhemp control in sugarbeet today although we will attempt to expand the concept into soybean, too. In sugarbeet, the idea is to use SOA 15 herbicides (chloroacetamide, S-metolachlor, Outlook and Warrant) postemergence to sugarbeet and preemergence to waterhemp. In the beginning, the concept was a single application of one of the three chloroacetamide herbicides applied between V2-V8. However, the concept has evolved into split applications, the first application usually timed to the V2 stage and the second application at V6-V8 stage. We call the concept layby. The term is not original, and it might be technically incorrect, but that what we call it in sugarbeet.

Let’s take a step back. What does the term ‘layby’ mean and how is the concept used in other parts of the country? I believe the term ‘layby’ originates from cotton country and refers to herbicides applied to maintain weed control until the cotton canopy is sufficiently developed to shade the furrow and bed top, thereby suppressing small weeds. The herbicides commonly used at layby have both preemergence and postemergence activity to control emerged weeds and to provide residual control for an extended duration of time. Layby herbicides complement weed control provided by other integrated weed management practices including cultural and mechanical weed control and use of other herbicides including preplant-preemergence and early season postemergence herbicides. Layby herbicides are primarily used to control broadleaf weeds in cotton.

Now back to sugarbeet. Layby application are usually timed to waterhemp emergence. In the southern part of the RRV and west central Minnesota, that means herbicide applied and activated by May 20th (note, 2019 is a unique season and application is later than normal since sugarbeet plant was later than normal).

Application is with a tank-mix of glyphosate plus ethofumesate and either S-metolachlor, Outlook or Warrant, with ammonium sulfate and an HSMOC class adjuvant. Water volume is a compromise between volume to provide good coverage for soil applied herbicides and volume to optimize glyphosate efficacy. Volume is usually 12-15 gpa. It is critical to combine herbicides with glyphosate that control emerged weeds. Ethofumesate applied at 4 fl oz/A is an effective mixture as it improves glyphosate penetration of cellular waxes, especially waxes on waterhemp. Chloroacetamide herbicide choice is at the discretion of the farmer. However, more recently, we have found split application of chloroacetamide herbicides improves sugarbeet safety and waterhemp control.

Now to soybean. We have observed the same benefit applying chloroactamide herbicides POST to soybean to control late emerging waterhemp. In soybean, waterhemp control is better when chloroacetamide herbicides are combined with a PRE with longer residual control such as sulfentrazone (sold under several brand names) or pyroxasulfone. Cultural practices including narrow rows and bumping soybean population density, also are effective ways to close soybean rows sooner, thus assisting with waterhemp control.

 

Tom Peters

Extension Sugarbeet Agronomist

NDSU & U of MN

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