Is it OK to use desiccants on mown ryegrass seed crops? Find out what the research says.
In years of wet weather during harvest, ryegrass will often re-grow through the swath reducing harvest efficiency and potentially increasing seed losses. The question ‘can re-growth be desiccated’ has been asked multiple times in the last week as rainfall approached.
Previous work in the United Kingdom has evaluated diquat and glyphosate as a pre-harvest desiccant for direct heading. In perennial ryegrass with two cultivars, Roberts & Griffiths (1973) reported a high percentage of abnormal and low germination rates when diquat was applied and the crop harvested two to nine days later. Similar results have been reported from the United Kingdom during wet harvests within the last five years, thus products containing diquat and glyphosate remain risky when used prior to cutting. More specifically prior to physiological maturity. At physiological maturity (approx. 37% seed moisture content) the seed stops feeding and therefore cannot translocate products into the developing seed. However, the seed is still vulnerable to direct chemical uptake while it remains green.
In the 2009/10 season, a trial was conducted utilising; Reglone® (MOA group 22) diquat 200 g ai/l, glyphosate (MOA group 9) 360 g ai/l, and Buster® (MOA group 10) glufosinate-ammonium 200 g ai/l, all applied at 2.5 l/ha to a ryegrass seed crop that had been in the swath for over four weeks. This trial showed no treatment effect on final machine dressed seed yield but harvest efficiency was greatly improved with desiccation. There was no difference in seed quality six months after harvest including germination, emergence and viable endophyte transmission into seed. At 10 months after harvest (medium term storage) there was no difference in germination between any of the treatments.
Thus, Reglone®, glyphosate and Buster® were safe on seed germination after the seed had changed to a brown colour (following swathing) as all products require green tissue to activate.