Abstract
Tolpyralate is a new HPPD-inhibiting herbicide that is efficacious on annual grass and broadleaf weed species in corn. For maximum herbicide performance of tolpyralate, it is recommended that atrazine is tank mixed with tolpyralate along with the adjuvants methylated seed oil concentrate (MSO) plus urea ammonia nitrate (UAN). A common use pattern of tolpyralate plus atrazine will be in a tank mix with Roundup WeatherMAX® due to the high proportion of corn acres that are seeded to Roundup Ready® hybrids in Eastern Canada. There is no information in the peer-reviewed literature if the adjuvant system in Roundup WeatherMAX® is adequate for optimal herbicide performance of tolpyralate plus atrazine, or if MSO and UAN are still required. Six field trials were conducted over two years near Ridgetown and Exeter, ON, Canada to determine if adjuvants are still required when tolpyralate plus atrazine is tank mixed with Roundup WeatherMAX® in corn. Tolpyralate plus atrazine plus MSO and Roundup WeatherMAX® plus tolpyralate plus atrazine provided excellent control of velvetleaf, pigweed spp, common ragweed, lambsquarters, ladysthumb, wild mustard, flower-of-an-hour, barnyardgrass and green foxtail in this study. Results of this study show that in the absence of Roundup WeatherMAX®, weed control with tolpyralate plus atrazine was improved substantially with the addition of MSO; however, there was little to no increase in weed control with the addition of UAN. When tolpyralate plus atrazine was co-applied with Roundup WeatherMAX®, there was no improvement in weed control with the addition of MSO and/or UAN.
Highlights
Weed interference during the early stages of corn development can cause physiological changes in the plant and lead to yield loss [1]
There is no information in the peer-reviewed literature if the adjuvant system in Roundup WeatherMAX® is adequate for optimal herbicide performance of tolpyralate plus atrazine, or if methylated seed oil concentrate (MSO) and urea ammonia nitrate (UAN) are still required
Results of this study show that in the absence of Roundup WeatherMAX®, weed control with tolpyralate plus atrazine was improved substantially with the addition of MSO; there was little to no increase in weed control with the addition of UAN
Summary
Weed interference during the early stages of corn development can cause physiological changes in the plant and lead to yield loss [1]. A study conducted across the corn producing regions of the United States and Canada found that in the absence of any weed management tactics, corn yield loss due to weed interference was 50% [2]. The critical weed free period (CWFP) in corn delineates the time period during which weed interference must be minimized to prevent corn yield loss. Hall et al 1992 [4] determined that the CWFP in Ontario for corn is from the 3 to 14 leaf-tip stage. Using the CWFP as a guideline to time POST herbicide applications can minimize corn yield and economic losses [3]
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