To provide a summary of pre emergent herbicide performance. (i. the rainfall timing and amount, ii. impact of tillage on pre emergent herbicides and iii. herbicide resistance)

• A major factor influencing pre-emergent herbicide activity from year to year is the timing and quantity of received rainfall.
• Rainfall within ten days of herbicide application is desired. Most pre-emergent herbicides are relatively stable in dry soils, however, warm conditions and dew on the soil surface can begin breakdown of herbicides.
• Lighter soil types are more likely to have herbicide leaching, particularly if dry sown and is a problem for the more soluble herbicides, such as Tenet® and Luximax®.
• Weed control by pre-emergent herbicides needs the herbicide near the seed. Leaching, breakdown and tillage are all factors that reduce weed control when resistance is not present.