7/12/2021 - By Syngenta

As we approach nearly 30 years following the introduction of Primo Maxx® Plant Growth Regulator (PGR) into the turf market, it’s still important to review the basic guidelines for Primo Maxx® applications. Primo Maxx® remains the most popular PGR for use on turfgrasses. It’s the only PGR developed specifically for use on turfgrasses and provides growth regulation and plant safety across all turf species.

Water Quality

Primo Maxx® is stable and effective in a broad range of water conditions and is not substantially affected by water hardness. However, water hardness may affect the stability of the Primo Maxx® formulation when tank mixed with multiple fertilizer components, resulting in high salt levels. (See tank mix recommendations below). The active ingredient is stable in water with pH ranging from 5 to 8, but optimal plant absorption occurs when applied in neutral to slightly acidic water. Measure the pH of spray water and any new tank-mix combinations and, if necessary, buffer pH to 6-7 for best results with Primo Maxx®.

Tank Mix Partner

Primo Maxx® is compatible with a broad range of commonly used turf products, including fertilizers and plant protectants. Although, you should avoid mixtures with post emergence herbicides that may cause foliar discoloration, as adding Primo Maxx® to the mix may increase level of discoloration. Applications can be separated by 5 to 7 days. Primo Maxx® should be allowed to dry on the foliage for best results, so it is not advised to tank-mix with products that require immediate irrigation. Before applying any new tank-mix combination, read all product labels carefully and perform a jar test to confirm physical compatibility. Tank mixtures with Trimmit® 2SC Plant Growth Regulator can increase the intensity and residual of regulation on certain applications.

For recommendations on mixing Primo with Trimmit® 2SC, refer to:
Recommended Turf Sites and Applications Rates for Primo Maxx® and Trimmit® 2SC

Recommendations to Minimize Bronzing or Discoloration

Applications of Primo Maxx® can cause turf discoloration under some conditions, particularly with the first application of the season or on sensitive species like ultra-dwarf bermudagrass. To mitigate the risk of bronzing, Primo Maxx® can be tank-mixed with iron or nitrogen fertilizer as recommended on the product label. Iron sulfate or chelated iron sources help to prevent bronzing without negatively impacting product performance or make the first application at 2/3 to 1/2 of the desired rate and increase the rate with subsequent applications.

Effects of Primo Maxx on Water Use and Drought Tolerance of Bentgrass Species, Dr. Bingru Huang, Rutgers University, 2007

Spray Volume

Primo Maxx® performs well in spray volumes ranging from 20 to 80 gallons of water per acre, with 40 gallons (the most common fairway rate) and 80 gallon per acre (more common on greens). The active ingredient is absorbed by above-ground tissues, including crowns, leaf sheath, and leaf tissue. It is a common misconception that absorption only occurs through leaf tissue. In fact, absorption by the crown and leaf sheaths is more rapid and efficient than leaf tissue absorption.

Nozzle Selection

Proper nozzle selection is perhaps a more important consideration than spray volume. Coverage of the plant is important. Primo Maxx® moves upwards readily but downward movement is limited. Flat fan nozzles that produce medium to coarse droplets are commonly recommended. Larger droplets (very coarse to extremely coarse) do not provide uniform coverage, especially when delivering low spray volumes. Finer droplets (fine to very fine) are prone to drift and much of the active ingredient may not reach the turf surface in windy conditions.

Air induction nozzles provide excellent turf coverage with reduced potential for drift by producing larger droplets, which shatter into many small droplets upon contacting the turf. Air induction nozzles that produce coarse to extremely coarse droplets are recommended for applications of Primo Maxx®.

Refer to TeeJet® or Hypro catalogs for details on droplet size as influenced by orifice size and air pressure.

Application Interval

Primo Maxx® must be re-applied on regular intervals to maintain consistent growth regulation over time. Many factors, including turf species, mowing height, fertility levels, and growing conditions can influence the intensity of regulation provided by Primo Maxx®. Increased rates can deliver extended periods of regulation; the Primo Maxx® label allows for up to 2X rates to be applied for extended regulation. Alternatively, reduced rates can be applied more frequently to achieve more consistent regulation over time. This is especially important on golf course putting greens, where applications on 7-day intervals have become standard.

Relative Clipping Production Based on Application Rate & Frequency

Creeping bentgrass fairway, Iowa State, 2012

Growing degree days are a tool that can assist with re-application intervals of Primo Maxx®. Growing degree day (GDD) thresholds vary by grass species, variety, and growing conditions and can be regionally specific. You can use the GDD tool on Greencast to monitor growing degree day accumulation in your location and receive an alert when the target threshold is reached.

#Time4PrimoMaxx®

© 2021 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties and/or may have state-specific use requirements. Please check with your local extension service to ensure registration and proper use. GreenCast®, Primo Maxx®, and Trimmit® are trademarks or service marks of a Syngenta Group Company. All other trademarks are the property of their respective owners.

Authors

Dean K. Mosdell, Ph.D.

Dean serves as the Western Technical Manager for the Professional Solutions business unit of Syngenta.  His responsibilities include product stewardship, field testing and technical support of Syngenta products in turf, landscape and ornamental markets for the Western United States. Dean have over 30 years’ experience in developing plant growth regulating products for application on turfgrasses, including the introduction of the first PGR for fine turf.  He received both BS and MS degrees in Agronomy (Turfgrass Specialty), from Virginia Tech, Blacksburg, VA., and a Ph.D from Purdue University, West Lafayette, IN. Dean’s Professional Organizations include Crop Science Society of America, Weed Science Society of America, California Weed Science Society, and International Turfgrass Society.

Lane Tredway, Ph.D.

Lane serves as the Southeastern Technical Manager for Syngenta Professional Solutions. In this role he works with turf managers, sales representatives, and university specialists to develop effective pest management programs. Dr. Tredway received a doctorate in plant pathology from the University of Georgia, a master's degree in plant biology from Rutgers, and a bachelor's degree in agronomic science from Penn State University. Prior to joining Syngenta, he was an Associate Professor and Extension Specialist in the Department of Plant Pathology at North Carolina State University. In this role he published extensively on the biology and management of turf diseases in the transition zone.