Sweet Corn Weed Control Study (2001)

Sweet corn growers have limited options available to them to control weeds. Many traditional products like Bladex will no longer be available. Other products that were initially only available for use on field corn (e.g. Permit) are now available for sweet corn. Growers need information on strengths and weaknesses of these particular products, and the effect of application timing on yield and sweet corn marketability.

Study Objectives:

• Assess the effect of various sweet corn herbicides on yield and marketability

• Evaluate some potential herbicides that may be approved for sweet corn

 Data collected

• Plant heights and leaf chlorophyll at 4 LS

• Weed ratings at 2 and 5 leaf stage and at canopy closure

• Weed biomass at silking

• Sweet corn yield and marketable yield

Results

Environmental conditions were not particularly favorable to get optimum activation from the preemergence herbicides used in the study this year. Although at this point in time, many of these herbicide combinations have performed quite well (examples include the Princep + Dual, ZA1296 + Dual, and Python and Dual) appears to have provided adequate control.  Note, that Python and Callisto (ZA1296) are not currently approved for sweet corn. Please see Table 1 for 5 leaf stage weed ratings. 

Table 1.  Pre and Postemergence Weed Control at the 5^th Leaf Stage of Development 

*  indicate postemergence weed control applications

Two other indicators of weed control and crop herbicide tolerance is plant height and leaf chlorophyll. Plants having to compete with thick annual grass stands for water and nutrients on such a dry year can cause real injury. Our 4 leaf stage measurements of leaf chlorophyll and plant height are listed below:

Table 2.  Plant height and leaf chlorophyll as influenced by herbicide combination

*  indicate postemergence weed control applications 

The final weed rating presented in Table 3 gives a good indication of the overall weed control in the study. The stunting estimate is due to weed pressure not herbicide injury. It should correlate negatively with yield.  Annual grass in this study is intense. The combination of witchgrass and barnyard grass competed well with the corn for water and nutrients in this very dry sandy field. Lambsquarters and pigweed also were capable of significantly competing with sweet corn as seen by the stunting found in the Dual only plot. 

Table 3.  Pre and Postemergence Weed Control at Canopy Closure

*  indicate postemergence weed control applications

These data show the effect that the lack of early annual grass control has on sweet corn growth and development. Although some N was applied at planting, the competition for N between the corn and weeds is evident in plant height and leaf chlorophyll. All plots that provided over 85% weed control were significantly taller and deeper green (as indicated by the leaf chlorophyll values). Plants struggling to compete with weeds were shorter and paler. There appears to be no significant injury caused by the Callisto on sweet corn (either in 2000 or 2001). 

Weed Biomass

Weed biomass measurements were collected in early August. We found significant treatment differences in small seeded broadleaf and annual grass biomass (Table 5). Broadleaf control with all Callisto combinations was excellent. In the ZA 3oz/ac with atrazine treatment, one replicate was found to have a high broadleaf density causing the overall mean to be higher than expected, and this could be an outlier.  Overall broadleaf weed control was excellent with Callisto and equal to the standard higher rate products.   The most striking effect found in the biomass data is how much annual grass control is improved with Callisto when combined with Dual. Even at the 6 oz/ac rate of Callisto, annual grass control was no better than the control. The addition of the 0.5 lb/ac rate of atrazine with Callisto applied postemergence significantly improved annual grass control.

Table 5.  Broadleaf and annual grass biomass as influenced by herbicide combinations

*  indicate postemergence weed control applications

**  possible outlier

Yield

Sweet corn yields were very low and spotty due to the drought and intense weed pressure in particular plots (Table 4). Sweet corn receiving only Callisto performed very poorly primarily due to intense annual grass (witchgrass and barnyard grass) pressure. Conversely, if Callisto was mixed with an annual grass herbicide and applied preemergence, total ear number, marketable ear number and total weight was significantly increased. Only marketable ear weight was not significantly affected. We found no injury at any application rate or timing with Callisto. In fact, the highest rate of Callisto combined with Dual II-Magnum provided excellent weed control and the best sweet corn production in the experiment. This treatment combination appears to provide excellent weed control despite the dry weather following application. The 6 oz/ac rate appears to be needed to provide sufficient season-long weed control particularly under dry conditions like we found this year. 

 Table 4.  Sweet Corn Yield