No. 2/April 4, 1997
Early Preplant Application of Herbicides
Several herbicides are cleared for early preplant (EPP) application. These applications provide several benefits but have some limitations as well. EPP applications often minimize existing vegetation at planting in no-till programs, which can eliminate the need for a burndown application. Application several weeks prior to planting also increases the probability that sufficient precipitation will be received to move the herbicide into the soil. However, predicting several weeks ahead of time when planting will actually take place is more of a shot in the dark than an exact science. Herbicides applied when planting is expected within 3 to 4 weeks may actually be on the ground for several additional weeks if soil conditions are not conducive for planting. The earlier in the spring a herbicide is applied, the earlier in the growing season the level of weed control may decline below acceptable levels.
Several preplant herbicides allow for split applications (Table 3) of 60 to 67% early preplant and 33 to 40% preemergence, to extend the application and weed control interval. Soil-applied "grass" herbicides have no foliar activity, so these herbicides must be applied before weed germination to be effective, unless they are applied with atrazine or cyanazine, which have foliar activity. Authority Broadleaf or Canopy XL, Canopy, Sencor, and Turbo are soybean herbicides that have foliar activity as well as soil residual activity.
Table 3. Corn and soybean herbicides that can be applied early preplant.
| Alone|| W/atrazine|| EPP|| EPP/PRE|| EPP|| EPP/PRE|
|Dual II||Bicep II||30||30-45||Dual, Frontier||30||30-45|
|Frontier||Guardsman||30||30-45||Prowl + Scepter or Pursuit||45|| |
|Harness||Harness Xtra||30||30-45||Pursuit, Pursuit Plus||45|
|Atrazine|| ||45|| ||Scepter, Squadron||45|
|Surpass||Surpass 100||30||Canopy XL||30|
| ||Sencor + Lasso or Dual||14||15-30|
*Use IMI-designated (IR or IT) corn hybrids.
2,4-D ester can be added with most corn and soybean preplant herbicides to improve knockdown of broadleaf weeds. Use 2,4-D ester at 1 pint per acre, 7 days before planting no-till soybeans; or 2 pints, 30 days before planting no-till soybeans. Gramoxone Extra, Roundup Ultra, or Touchdown can be added to most no-till preplant or preemergence herbicides to provide added knockdown of emerged weeds.
Marshal McGlamery and Aaron Hager, Department of Crop Sciences, (217)333-4424