Cecil Tharp, MSU Extension Pesticide Education Specialist

By planning a pesticide application ahead of time pesticide applicators may minimize future issues including non-target impacts and pesticide exposure while lowering costs and maximizing the effectiveness of their pesticide application. Pesticide application planning includes researching the best pesticide to meet your pest needs while purchasing personal protective equipment and recommended adjuvants well ahead of time. In addition, an applicator should prepare their pesticide equipment, test water quality, and conduct a site assessment to ensure the pesticide works as intended, while minimizing non-target impacts.   

Pesticide application equipment.     

Pesticide application equipment (M.J. Weaver, 1999)                                         

Purchasing Pesticide Products and Equipment

Various pesticide products do not act equally in managing select pests. For that reason, the best product should be purchased for any predicted pest to be managed. Contact your local MSU Extension Agricultural Agent for more information on the best products to purchase for selective pests.

Once the proper pesticide(s) are determined they should be purchased as soon as possible to allow time to prepare for the pesticide application. Supply chain issues have been reported with significant delays and increased prices on glyphosate, glufosinate and many other chemistries. Once pesticides are purchased an applicator should read the pesticide product label for information on required personal protective equipment (PPE) or adjuvants recommended to boost efficacy. Product labels are available at CDMS.NET.

Purchasing Personal Protective Equipment 

Pesticide applicators often report not wearing PPE due to not having PPE available at the time of application. By following the PPE requirements under the “Precautionary Statements” on the product label applicators can determine and purchase required PPE well ahead of time. This can be through a local hardware or agricultural distributor, or through many online outlets (i.e., airgas.com, gemplers.com, etc.).

Purchasing Adjuvants

Chemicals added to enhance the original pesticide products in any way are termed “adjuvants”. There are many adjuvants including surfactants, spreader stickers, crop oils, anti-foaming materials, buffering agents, and compatibility agents. Surfactants are adjuvants that reduce surface tension within the external surface layers of water to facilitate optimal absorption by increasing coverage. Surfactants are often recommended on the pesticide product label and should be used to optimize performance. Non-ionic surfactants (no charge) can often be used to increase efficacy if not prohibited on the pesticide product label. 

Other common adjuvants recommended on product labels include acidifiers if your water’s pH is alkaline (pH>7), or the use of liquid or granular ammonium sulphate at 8.5 – 17 lb/100 gal to reduce hardness. Other less common adjuvants include emulsifiers for tank mixing certain formulations or anti-foaming agents. By reading and following the pesticide product label an applicator can quickly understand the adjuvants to purchase well ahead of the application.

Testing Water Quality

Water quality can significantly lower pesticide performance of many pesticide products. Vast areas of Montana harbor ground water with less-than-ideal pH or hardness for spraying common pesticides.


The pH value describes the acidity and alkalinity of a solution and is related to the concentration of hydrogen ions (H+) and hydroxide ions (OH-). The pH ranges from 0 – 14 where:

  • pH of 7 = neutral (H+ equals OH-),
  • pH > 7 = alkaline (more OH-), and
  • pH < 7 = acid (more H+).

Some common weak acid pesticides susceptible to pH levels over 7.0 are glyphosate, glufosinate ammonium, ammonium salt of imazethapyr, some fungicides, and a wide range of carbamates and organophosphates insecticides. Weak alkaline pesticides such as the sulfonyl-urea pesticides (i.e. Ally, Escort, Amber, Harmony Extra, Accent, etc.) are less absorbable when mixed in an acid solution (pH < 7). Either can reduce the efficacy of an applicator’s pesticide application. Applicators should test their water prior to a spray application using a pH meter or pH litmus strips. If pH is a problem, then applicators should consider alternative water sources or adding a buffering agent (or acidifier) to adjust pH. Contact your pesticide manufacturer for ideal buffers compatible with each pesticide product and always read the product label for more information as to whether the product is susceptible, ideal ranges, etc.

Hard Water

Water hardness refers to the presence of minerals with a positive charge (cation) such as calcium (Ca++), magnesium (Mg++), and iron (Fe++). Total hardness can be measured in parts per million. These cationic minerals will bind with many weak acid pesticides significantly reducing the pesticides efficacy prior to application. This depends on the pesticide’s vulnerability to hardness, time within the hard water solution, and the concentration of hardness in the water. Follow these guidelines regarding hardwater:

  1. Always read and follow precautions regarding hardness on the pesticide product label.
  2. Weak acid pesticides such as clopyralid, 2,4-D amine, glyphosate and dicamba may lose efficacy if hardness exceeds 150 ppm.
  3. Some 2,4-D amine formulations can be totally deactivated if hardness > 600 ppm.
  4. Many other herbicides will lose efficacy if hardness > 400 ppm.

Hardness can be reduced with addition of dry ammonium sulfate (NH4)2SO4 at 8.5 to 17.5 lb per 100 gallons of water, or liquid fertilizers (such as 28%N, 32%N, or 10-34-0) at a rate of 1.25 – 2.5 percent per 100 gallons. For more information on water quality see the MontGuide titled ‘Pesticide Performance and Water Quality’

Preparing Spray Equipment

Many applicators focus on purchasing pesticide products while neglecting to calibrate their spray equipment. A finely tuned ground sprayer in the fall may deliver a vastly different spray output in the spring. Rusted nozzles, ruptured seals, or rust in the lines may eventually lead to uneven spray patterns or a significant departure from desired target rates. This often leads to loss of revenue, and/or limited efficacy towards targeted pests. Applicators can avoid costly application errors by following a few simple steps in the spring.  

Inspect Spray Equipment 

It is not uncommon for a leaking backpack sprayer to saturate unwary applicators with pesticide product while spraying, or for a hose on a boom sprayer to leak from loose fittings. These dangerous situations can be alleviated if an applicator takes a few minutes to inspect their equipment. Check pumps, lines, hose clamps and fittings for leaks while assessing entire sprayer for rust, wear, and breakage. Spray nozzle pattern should be assessed for uniformity by activating nozzles over gravel or concrete. Nozzles should be replaced or cleaned if the spray pattern seems uneven. Likely suspects include rust, sand particulates, or simply a worn nozzle. Select nozzle tips and screens rated for your application. 

Table 1. Common backpack sprayer nozzles, uses and swath width
Nozzle Type
Variable. Spot spray, gardens, or tree spraying. Less accurate. 
Wide or narrow
Flat Fan Spray
Most common. Paths, gardens, and rangeland spot spray.
Hollow Cone
Spot spray, complete penetration, brush, and small trees.
Jet Stream
Tree or crevice applications.
High output nozzles, fertilizers.
Wide swath

Calibrate Spray Equipment

The goal of calibration is to ensure the output of a sprayer equals the output which is recommended on the pesticide product label. Output is often expressed in gallons per acre (GPA). An applicator can then understand exactly how much solution and product to add to a spray tank to meet a target product label required rate. The shortcut method can be used for calibrating backpack sprayers, boom sprayers and broad-jet sprayers without pesky mathematical formulas if the label or is expressed in GPA. See the MontGuide titled “Calibrating Ground Sprayers Using Shortcut Methods” or the calibration Pocket Guides at www.pesticides.montana.edu by selecting ‘Publications and Resources’. For techniques used for pesticides around the home and garden see “Calibrating Home and Garden Sprayers” or for all other products see the publication “Calibrating Pesticide Application Equipment”.

Site Assessment

The location of a pesticide application should be carefully considered prior to an application. Sensitive sites, harvest timing, and future plantings should be considered as part of an assessment. Sensitive sites such as shelterbelts, aquatic areas, pollinators, live-stock, and humans should be identified prior to application. Once identified, a mitigation strategy should be planned. This may include buffer zones or by reducing drift. Drift can be reduced with drift reducing nozzles, spraying in the morning, spraying when temperatures are <80°F, or by reducing spray pressure. In rangeland, applicators should follow grazing intervals on the label to understand when to safely introduce livestock, and in cropland, applicators should follow the pre-harvest interval (PHI) requirements on the pesticide product label prior to understand how long they must wait until harvest.

Many chemistries persist for years in the soil and can cause carryover damage to future susceptible crops. Applicators must understand the future of that site in upcoming months and years. Pesticide applicators should read and follow the rotation interval requirements (i.e., cropping intervals, planting intervals) on the label if they plan on planting a susceptible crop in future seasons. This is the amount of time an applicator must wait to plant a future susceptible crop.

For More Information

For more information regarding this article contact Cecil Tharp (406-994-5067; [email protected]) or see the MSU Pesticide Education website for more information. You may also see the Webinar titled “Preparing for Pesticide Applications”.

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