If you have fields with a history of hydrogen sulfide toxicity which led to a condition called autumn decline as in Figure 1 and 2, you need to begin scouting two weeks after establishing permanent flood. Healthy roots appear clean or even reddish, but not black. Black roots can indicate a potential problem.
Although root blackening alone may not be alarming at the beginning, considerable crop loss can follow due to rotting of root crowns by opportunistic fungi that invade the weakened crop due to hydrogen sulfide toxicity. The solution is simple yet complicated: “Drain and Dry”. This strategy is costly, and also may be difficult and risky when field sizes are big, water resources are limited or pumping capacities are low.
Fields with a known history can be protected by “drain and dry” before the mid-season, just like the way it is done for straighthead. However, rescue action in fields of unknown history should be carried out with care depending on the growth stage of rice. Please read the below references or contact us for us to help.