For vegetable growers, sweet corn is a good rotational crop because there are a number of products that can be used in corn that also help break the weed cycle. However, weed control in early plantings can still be challenging as the weather can limit the number of opportunities to enter the field prior to planting. In turn, the use of floating row covers also increases the amount of work required when applying post emergent herbicides and strong pre-emergent herbicides should be used within these fields to reduce weed build up early in the season.
Take care when applying herbicides within any given field, as the plant back intervals (and danger of herbicide carry over and injury to following crops) may impact what crops can be planted within the field in following seasons (as corn fields are usually not double cropped in the Fraser Valley).
While there are a number of products available for pre-emergent weed control within corn plantings, the 2 primary options for broadleaf weed control are either Integrity or Aatrex plus Dual II Magnum applied shortly after planting. Prior to tilling apply glyphosate to control tough perennial weeds, as required. After 7 to 14 days plow and prepare the field, then wait 4 to 7 days before planting so that weed seeds at the soil surface can germinate. Plant the field without any further tilling, and either just before planting apply glyphosate again or after planting apply Desica (diquat) herbicide. These applications can potentially be combined with pre-emergent herbicide application.
Research work in Ontario found that weed competition during the 3 to 8 leaf over stages of growth (V1 to V6) within corn plantings significantly reduced yield; later weed competition did not impact plant growth; however, it can impact picking operations, certain weeds may also serve as an alternate host for pests.
As sidedressing (and potentially cultivation) does not usually occur until roughly 8 leaves over (v-6), weeds must be controlled well in advance of sidedressing or the harvest will be significantly reduced. Note that many herbicides labels recommend waiting at least 1 week between herbicide applications and cultivation, so the latest post emergent herbicides should be applied is roughly 6 to 7 leaves over (V-5), if significant weed problems are present, then weeds should be controlled even earlier than this timing.
Monitor for weed emergence after planting, most post emergent herbicides are best used on small, 1 inch high, weeds, and production will be impacted well before heavy weed infestations are noticeable. Prior to applying herbicides, determine which weeds are present in the field as different products are more effective on different weeds. Again double check the plant back restrictions prior to applying any herbicides, along with the Pre-Harvest Interval (PHI). See the labels and additional information on the herbicides to determine the best options. For broadleaf weed control Pardner and Basagran can be used with little concern about herbicide carry over. Accent can be used on some sweet corn varieties when grass control is required but some varieties of sweet corn can be injured by Accent.
Compared to most field vegetable crops there is a fairly broad list of herbicides available for use in sweet corn and a number of different timings. If you wish to know more about other herbicide choices, ask our Sales Desk.