Turning Down the Heat

June 18, 1999
Contact herbicides generally cause more crop injury when temperatures and relative humidity levels are high during and shortly after application. BASF (with Blazer) was one of the first to average temperature and relative humidity to indicate the "heat" of contact herbicides. The current Blazer label states that "if the temperature and relative humidity exceed 150 (add temperature + relative humidity) then use the lower additive rates." PPG/Ortho/Valent (Cobra) went one step farther and made adjuvant recommendations (NIS vs. COC) based on temperature and relative humidity to minimize crop injury/maintain weed control.

The Buctril (bromoxynil) label indicates NIS or COC is allowed if you can stand the injury. The Aim (carfentrazone) label allows the use of NIS only (no oil) to minimize crop injury. Pinnacle recommends adding oil when conditions are dry or cool. Reflex allowed NIS or COC, while Flexstar actively promotes the use of COC or MSO.

Translocated herbicides are more likely to cause crop injury when crops are growing rapidly and leaf cuticles are thin, particularly if "hotter" additives are used. Adjuvant ratings for heat are MSO > COC > NIS > AMS = UAN.--Marshal McGlamery, Aaron Hager

Author: Aaron Hager Marshall McGlamery