Harvest Aid Defoliation and Regrowth Suppression in Castor (Ricinus communis L.) in a Semi-Arid Environment.

Historically, U.S. castor production up to the early 1970s simply allowed a killing freeze to terminate the crop then castor was mechanically harvested 10 to 14 days later.  This practice, however, often allowed for substantial shattering loss of castor capsules which matured many weeks before the freeze.  With the routine use of harvest aids in cotton, whether for defoliation or regrowth suppression or both, harvest aid use in castor could help manage the end of the cropping season so as to minimize shattering losses and reduce weather risks.  The objective was to evaluate nine common harvest aids, defoliants, and herbicides in castor to evaluate defoliation and suppression of regrowth of castor.  Chemicals were applied to reduced-ricin ‘Brigham’ castor in mid-October 2009-2011 approximately two weeks before the first historical 32 F freeze.   These chemicals were sodium chlorate, glyphosate, thidiazuron/diuron, diquat, paraquat, glufosinate-ammonium, carfentrazone-ethyl, and ethaphon.  Defoliation ratings were initiated 4 days after application, and regrowth ratings began 10 days after application.  Among potential harvest aids, paraquat and diquat provided the highest degree of rapid defoliation, and carfentrazone-ethyl also was effective at defoliation.  Other chemicals, to some extent, left remaining green leaf matter on the plants.  Suppression of regrowth was significantly better from paraquat and glyphosate, and carfentrazone-ethyl also performed well.  Although diquat was highly effective at defoliation the regrowth potential in castor was not acceptable, which would interfere with harvest.  Further harvest aid work appears to best focus on rates, timing, and application method for paraquat, carfentrazone-ethyl, and glyphosate.