by Rodrigo Werle

Editor’s note: Precision spraying that targets just weeds and not the crops is a technology that many farmers are eyeing as part of their future technology plans. The following article details discussions that Rodrigo Werle, a University of Wisconsin Extension cropping systems weed scientist, had with two Wisconsin farmers (and their crop consultants) who recently acquired the John Deere See & Spray Premium precision system. Werle stresses the article’s goal is not to promote a specific technology nor specific herbicide products. Instead, it is to provoke discussions and thoughts about these novel technologies. If widely adopted, he says, it will change the status quo of herbicide applications in corn and soybean systems in Wisconsin and into states such as Iowa. (This article has been edited for style.)

With the John Deere See & Spray Premium precision upgrade system (one tank, one boom system), a grower can either target-spray established weeds or broadcast-spray entire fields. With this system, growers cannot simultaneously target-spray foliar herbicides and broadcast-apply soil residual herbicides during the same trip, as they could if they had purchased a brand-new sprayer with the See & Spray Ultimate system (two tank, two boom system, also known as a dual-tank system).

This is from the John Deere See & Spray Premium webpage: "We’ve taken the advanced camera detection and artificial intelligence system from the revolutionary See & Spray platform and now offer them as a factory install on MY25 and newer Hagie, 400 and 600 Series sprayers, or as a Precision Upgrade on MY18+ and newer R-series and 400/600 series sprayers."

My first take is that the See & Spray Premium and the See & Spray Ultimate systems differ on what they can deliver. The See & Spray Premium can be retrofitted to certain sprayers, whereas the See & Spray Ultimate is a factory-installed system only and isn’t available as a precision upgrade. The latter also requires a larger financial investment.

Where it can fit

Early preemergence soil residual herbicide applications at planting time or shortly after are highly recommended for corn and soybean weed management. This is particularly true for growers dealing with waterhemp.

In this case, the targeted application modality of the See & Spray Premium system is no use unless a grower is willing to make two trips on the same field. One would target established weeds with a burndown program. (In this case, the See & Spray modality would be on in a green-on-brown — weeds in fallow — application.) The second immediate trip would deliver the residual herbicide program through a regular broadcast application (See & Spray modality would be off).

This discussion becomes important in no-till fields where established weeds need to be controlled at planting time. This is less important in conventional tilled fields, where cultivation eliminates preplant-established weeds.

During postemergence applications (in-season weeds in crop, or green-on-green applications) is where this particular system can shine, in my opinion. It delivers foliar herbicides only where weeds are, resulting in product savings for growers and the agricultural environment.

Through our research conducted with a different equipment brand but similar technology, we are learning that early postemergence applications are more likely to yield better results compared with late postemergence applications. Less crop canopy is present during early postemergence applications when compared with late postemergence applications. (For example, V2-V3 compared with V5-V6.) This allows for more precise weed detection and higher foliar herbicide savings.

What about layered residual programs?

One question concerns a soil residual herbicide that a grower may want to deliver postemergence as part of a layered residual herbicide program to control waterhemp. That's a difficult question to answer.

A grower can make two postemergence trips, one to deliver the foliar herbicides with the See & Spray modality on and a second, broadcast postemergence pass that delivers the soil residual herbicide with the See & Spray modality off. (I am not sure growers will be willing to do that, however.)

In my opinion, a good alternative would be to alter the overall herbicide program by moving the in-season soil residual herbicide to the preemergence herbicide application. This would allow for a stronger early-season weed control program, which should lead to reduced weed infestation in season. This would optimize the use of the See & Spray technology postemergence (e.g., fewer weeds and more savings of foliar herbicides).

For this plan to work, enough early-season precipitation is necessary to activate the soil residual herbicides, which all should be applied at appropriate rates (labeled rates based on soil conditions). I would not cut rates.

System comparison

Below is the outcome of one of our discussions that will be implemented this year in one of the Wisconsin farms that recently has purchased the See & Spray Premium system. It uses the E3 soybean system and conventional tillage with preplant field cultivation to eliminate established weeds. Waterhemp is the target weed species.

Scenario A was the original plan before the grower upgraded to the See & Spray Premium system. Scenario B is the herbicide program now that the See & Spray Premium system is available in the operation.

Scenario A: Preemergence followed by postemergence broadcast herbicide application program

Scenario B: Broadcast preemergence followed by See & Spray postemergence herbicide application*

*Note that the Zidua that was part of the layered residual program postemergence in scenario A was moved to the preemergence program in scenario B. This is where postemergence herbicides will be target-applied only where the See & Spray Premium system detects the weeds. The grower and agronomist could have decided to remove Zidua from the herbicide program to potentially save more (further reduce herbicide costs). However, this could be a risky decision in my opinion (e.g., more weeds to be controlled postemergence).

Summing up

Balancing savings and effective management of troublesome weed species will be a major challenge with these novel precision application systems. In my opinion, postemergence foliar herbicide savings can be achieved if we don't cut corners on our soil residual herbicide programs and continue to incorporate nonchemical approaches to weed management in our cropping systems.

Werle is a University of Wisconsin Extension cropping systems weed scientist.