In case the bright spots are caused by sun being reflected by the grass blades, this is a physically correct phenomenon that you can also observe in real life (examples: waves on the water reflecting sun, "sparkling" snow).
Examples
Example of bright pixels visible in grass:
glossiness = 1.0
To decrease this effect, you can:
1. Lower glossiness value of the grass material:
Glossiness lowered from 1.0 to 0.5 in 3ds Max and Cinema 4D:
After lowering material's glossiness to 0.5, sun reflections became "softer" and more realistic:
...or...
...or...
2. Disable reflection visibility for Corona Sun in 3ds Max and Cinema 4D:
Result of disabling sun's reflection visibility:
There are no bright pixels but the grass looks less realistic. Using this option will globally disable sun reflections for all objects.
Other solutions
In post-1.3 versions of Corona, highlight clamping in 3ds Max / highlight clamping in Cinema 4D can be used to clamp the brightest parts of the image and thus get rid of fireflies and noise.