St. Augustine Herbicide Damage in Hot Weather

Why Damage Occurred

Weed-and-feed products contain broadleaf herbicides (2,4-D, dicamba, MCPP) that volatilize above 85°F, becoming gaseous and drifting to non-target plants—including St. Augustine grass. The label warning exists because volatilization destroys the selectivity that normally protects grasses.

Damage Assessment

Yellowing at 4-5 days post-application, worsening at 16 days with more yellow than green, indicates severe herbicide injury. Recovery depends on crown survival.

Immediate Actions

1. Water frequently to flush residuals (don't overwater—just maintain moisture)
2. Mow at 2" to reduce transpiration demand on damaged foliage
3. No fertilizers, herbicides, or "recovery" products
4. Monitor for 4-6 weeks for new growth from crowns

Realistic Expectations

Only time reveals survival extent. If crowns die, renovation required. Consider this a costly lesson: never apply herbicides above labeled temperature limits. The 7-10 day chlorosis disclaimer assumes proper application conditions.