Researchers studied how different fungi can help control a plant disease called crown rot in cereals by competing with a harmful fungus called Fusarium pseudograminearum. They found that the availability of nitrogen, not carbon, is crucial for the effectiveness of these helpful fungi in displacing the harmful fungus from plant residues. Adding nitrogen in the form of urea or nitrate increased the displacement of the harmful fungus, while sugars reduced the inhibitory effect of the helpful fungi. This research suggests that the way nitrogen is applied can impact how well these beneficial fungi can control the plant disease.