Phosphorus influence on the critical period of weed control in sweet corn

Understanding the effect of phosphorus (P) fertilization on weed interference with sweet corn is important for deciding appropriate fertilization levels and weed control programs. Field experiments were conducted in 2020 and 2021 in Belle Glade, FL to determine the influence of P fertilization levels (0 or residual P, 62.5, and 120 kg P2O5 ha-1) on the critical period of weed control (CPWC) in sweet corn on organic soils. Experimental plots were subjected to increased duration of weed interference and weed-free period treatments for each P fertilization level. The beginning and end of the CPWC based on 5% and 10% acceptable yield loss levels were determined by fitting log-logistic and Gompertz models to represent the increasing duration of weed interference and duration of the weed-free period, respectively. The log-logistic curves did not estimate the beginning of the CPWC at 5% AYL for 0 and 125 kg P2O5 ha-1 because the estimated upper limits of the curves were lower than the 95% relative yield used for estimation of 5% AYL. Based on 10% AYL level, the length of the CPWC in sweet corn under optimum P fertilization level was estimated to be 27 days, from the six- to seven-leaf stage until the silking stage of growth. Reducing P fertilization by 50% increased the CPWC to 36 days, from the five-leaf stage until the silking to blister stage of growth. Lack of P fertilization increased the CPWC to 64 days, from sweet corn emergence until the blister to milk stage of growth. These results show that the beginning of CPWC in sweet corn is delayed and the end shortened as P fertilization level increases. Therefore, reduction in P fertilization will require a more intensive weed management program for sweet corn because of the prolonged duration of the CPWC.