Been getting a few questions about planting grain sorghum following watermelons that were previously treated with Reflex. Here are a few things to think about:
1. The “official and legal” rotation restriction for grain sorghum after an application of Reflex is 10 months. Watermelons are roughly a 90 day (3 month crop).
2. I have heard that some test strips (i.e. not for sale or entry into the market) of grain sorghum have been planted after Reflex with no problems and others have seen some major problems.
Herbicide carryover is a complicated issue that depends upon many factors including rate, soil type, moisture, temperature, tillage, and where the Reflex was applied (bare-ground, on/over plastic much, under plastic mulch). In general, carryover potential to rotational crops would be greater when Reflex was applied under plastic mulch.
3) I have a test in the field right now at the UGA Ponder Farm where I applied Reflex at various rates to bare-ground 90 days before planting (DBP) grain sorghum. The typical use rate of Reflex in watermelons is 12 oz/A. In these plots, 12 oz/A of Reflex has caused significant injury and reduced sorghum height/biomass.
If I can keep the birds out of these plots, I might be able to get some good yield data as well (but I have not been able to do that with sorghum in 20 years though). See pics below: