Prohexadione calcium, a plant growth regulator, is commonly used on virginia market type peanut ( Arachis hypogaea L.) cultivars to manage excessive vine growth and improve digging efficiency.  However, use of prohexadione calcium on runner market type cultivars has been minimal.  The objective of this research was to evaluate prohexadione calcium on virginia and runner market type peanut cultivars at multiple rates in small-plot (17 site years) and on-farm (5 site years) experiments.  Applications of prohexadione calcium were at the manufacturer’s recommended use rate of 140 g/ha (1x), 105 g/ha (0.75x), and 70 g/ha (0.5x) rates.  A non-treated control was also included in all experiments.  Cultivar and treatment responses were evaluated based on mainstem height, yield, total sound mature kernels, and return on investment. Plants treated with prohexadione calcium had greater row visibility based on a 1-10 row visibility. Plant main stem heights were often shortened when prohexadione calcium was applied compared to the control, although response varied by location and by year.  Average mainstem heights were 26 cm for non-treated plots and 23 cm for prohexadione calcium treated plots across all virginia market type small plot experiments. Prohexadione calcium did not significantly increase yield at any rate in any small plot experiments regardless of rate. Reduced rates of prohexadione calcium significantly increased yield in all the large on-farm experiments compared to the control. Yield increases ranged from 453 to 731 kg/ha for all prohexadione calcium treatments compared to the control across all large plot on-farm experiments. The greatest return on investment was the 0.75x rate resulting in an increase in revenue of $210 ha -1 . With an increase in yield and return on investment in all large plot on-farm experiments and not in small plot experiments no matter the market type, it is assumed that the growth and yield response to prohexadione calcium may be more pronounced where soil variability is greater, affecting growth, digging, and yield potential.  Prohexadione calcium can be beneficial in virginia market type and runner market type peanut cultivars to decrease vine growth and increase yield.

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