Why GDD matters for Primo Maxx
Cornell Turfgrass Program explains that temperature affects the length of the suppression phase after Primo Maxx applications. As air temperatures increase, turf breaks down PGRs faster, which makes fixed calendar intervals less efficient during the growing season.
Base temperature depends on your grass type
Cornell's GDD research for trinexapac-ethyl was conducted on cool-season grasses (creeping bentgrass) using base 32°F — approximately 200 GDD at that base. For warm-season grasses like bermuda, Reasor et al. 2018 (Crop Science) used base 50°F and found reapplication intervals of approximately 216–230 GDD. Use the base temperature that matches your grass type. Neither threshold replaces the product label, turf species sensitivity, mowing height, rate, weather stress, or local regulations. Treat GDD as a tracking model, not a universal prescription.
Research sources
- Cornell Turfgrass Program: base 32°F, ~200 GDD for cool-season grasses
- Reasor et al. 2018, Crop Science: base 50°F, ~216–230 GDD for ultradwarf bermuda
How to track it
- Open the GDD Calculator.
- Use the from-date calculator starting on your last PGR application date.
- Log the product, rate, weather, mowing response, and next target in the Lawn Dominator app.