Spraying Herbicides for Weed Control
Use of herbicide sprays is the predominant method used to manage weeds in crops. However, technology to reduce the amount of herbicides used for weed control in crops is developing rapidly. The following factors are important to consider when spraying herbicides for weed control.
Precision Spraying Technology. This concept [“Smart Spray” is a term often used to describe this class of spray equipment] has been developed to reduce the amount of herbicide applied to a field in post-emergence [PE] applications. The intent is to lower the cost of PE weed control by allowing applicators to spray only emerged weeds where they occur in a field [spot spraying] vs. a broadcast application of a herbicide over an entire field regardless of weed presence or density. Sprayers used in this system are equipped with cameras that are capable of differentiating weeds from the surrounding crop. Precision spray technology systems likely will also require technology that will 1) maintain a consistent boom height, 2) maintain a constant ground speed that is within the range of that allowed for maximum sprayer effectiveness, 3) control individual nozzles on the spray boom, and 4) allow boom recirculation of the herbicide. Several companies [click One Smart Spray, See and Spray, Greeneye, IntelliSense, and Sense Apply for examples] have brought precision spraying technologies to market.
Spot Spraying/Targeted Spraying. Sprayers equipped with the technology described above will be used for “spot spraying”, or the spraying of targeted weeds only where they occur in a crop field. There are several factors that can/will affect the efficiency of spot spraying. They include:
• Weed pressure–spot spraying technology will likely work best following a PRE herbicide application that should result in lower weed pressure;
• Cover crops–this technology should work best where a cover crop was used to suppress weeds;
• Sensitivity of the spot spraying system to the presence of targeted weed(s);
• Nozzle type, spacing, and angle, and how many nozzles are activated when a weed is detected;
• Buffers that determine which nozzles turn on and how long they stay on;
• Travel speed, field topography [can affect boom sway], dust conditions [can affect camera detection of weeds], and wind speed;
• Location of cameras in relation to equipment wheels that will raise dust that could impede camera detection of target weeds.
• A potentially less expensive option for spot spraying weeds is to use drone technology to map weeds in a field and then retrofitting an already on-hand conventional sprayer to control individual nozzles. Several companies offer kits that can be used to adapt a conventional sprayer to one that is capable of targeted spraying without cameras. Results from preliminary research indicate that this less expensive targeted spraying system will result in herbicide cost savings and soybean yields that are comparable to those from using targeted sprayers with cameras.
Of course, the effectiveness of any chosen smart spraying system will only be acceptable if it is operated correctly and in acceptable weather conditions. Data from myriad sources indicate that the use of “Smart Sprayers” to spot-spray herbicides only where targeted weeds occur will save money. Also, when possible and if economical, upgrade an on-hand sprayer so that it can use the latest technology to control pesticide applications.
Spray Drift. The potential for drift of an applied herbicide spray away from its area of application is always a concern. Following are points to consider to reduce drift potential.
• Spray during low wind, which usually occurs early in the morning or late in the evening. Read the herbicide label for other factors that should be considered for a particular herbicide.
• Use lower spray pressures to allow for larger droplet sizes that may be less susceptible to drift.
• Use as much carrier volume as possible, usually 20 gal. or more per acre.
• Select nozzles that are designed to give adequate coverage with less drift.
• Use a low spray boom height coupled with nozzles that have a high spray angle.
• Match the ground speed with the field topography to lessen boom bouncing.
• Use drift retardants recommended on the herbicide label.
• Avoid spraying when the wind is blowing in the direction of sensitive areas.
• Include a buffer zone where possible to reduce or avoid drift into sensitive areas.
• Be mindful of label restrictions that must be followed in order to adhere to the Endangered Species Act drift mitigation requirements.
• Invest in or use “spot sprayers” to reduce the amount of herbicide being applied to a given field.
Click here for an article that provides information about other innovations for weed control in crops.
Composed by Larry G. Heatherly, Mar. 2025, larryh91746@gmail.com