Pre transplant herbicide application and cultivation to manage weeds in southeastern broccoli production

Authors: CUTULLE, MATTHEW - Clemson University; CAMPBELL, HARRISON - Clemson University; Couillard, David; WARD, BRIAN - Clemson University; Farnham, Mark

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2019
Publication Date: 9/15/2019
Citation: Cutulle, M., Campbell, H., Couillard, D.M., Ward, B., Farnham, M.W. 2019. Pre transplant herbicide application and cultivation to manage weeds in southeastern broccoli production. Crop Protection. 124:104862. https://doi.org/10.1016/j.cropro.2019.104862.
DOI: https://doi.org/10.1016/j.cropro.2019.104862

Interpretive Summary: Broccoli production is increasing along the eastern seaboard of the United States from northern Florida to Maine. These increases have taken advantage of the increased popularity of the crop, interest by consumers in purchasing and eating a relatively local or regional vegetable, and the lower costs associated with shipping the commodity shorter distances along the eastern seaboard. Many weeds thrive in conditions of high soil moisture and controlling weeds is more difficult along the east coast where annual rainfall is typically much higher than in the primary broccoli growing regions of California and Arizona. In light of this fact, eastern growers must establish effective practices to control weeds using cultivation and a limited number of relatively broad spectrum herbicides available for use in this crop. To help develop good weed control practices for eastern producers, ARS scientists at Charleston cooperated with Clemson University scientists in research studies to test the effectiveness of herbicides labeled for broccoli to control weeds when applied pre-transplant, to examine the possibility that the different herbicides might cause crop injury, and to evaluate the potential benefit of a timely cultivation used in combination with each herbicide. All tested herbicides provided significant control of most problem weeds in fall and spring trials; however, none of the herbicides had a significant effect on yellow nutsedge, a weed that was prevalent in the fall. The best treatments for overall weed control included a combination of herbicide and a timely cultivation. The herbicides napropamide and pyroxysulfone caused temporary crop injury in the spring that was not evident by the time plants reached maturity. There were few effects of the different treatments on yield or quality characteristics of harvested heads. These results are of great interest to eastern broccoli growers working to improve weed control in their broccoli productions and who are uncertain of their options. This work also provides useful information to state extension personnel advising growers who are producing broccoli.

Technical Abstract: The East Coast broccoli industry is growing and optimizing weed control strategies in a southeastern environment is important for the expansion of commercial broccoli in the region. Research was conducted at the Clemson Coastal Research and Education Center in Charleston, SC to evaluate the impact of four herbicides (pyroxasulfone, napropamide, S-metolachlor, and oxyflurofen) applied pre-transplant and two cultivation practices (cultivation after transplanting or no cultivation) on weed control, broccoli safety, broccoli quality characteristics and yield characteristics for two broccoli hybrids Emerald Crown and Lieutenant. The trials were conducted during the fall of 2017 and the spring of 2018. No injury was observed during the fall trial, though significant injury occurred from napropamide and pyroxysulfone application in the spring. Generally, it appeared weed competition did not influence quality ratings at all. Stem diameter of broccoli generally increased with cultivation, though likely more from aeration of broccoli roots than the added weed control. Based on the results of these studies it appears cultivation is essential for maximizing broccoli yield characteristics in coastal South Carolina but herbicide application may not be.