In 2008, Mark VanGessel, University of Delaware, Roger Becker, University of Minnesota, and Ed Peachey, Oregon State University and I collaborated again to evaluate sweet corn hybrid tolerance to herbicides. In 2008, the herbicides tested were Accent Q, Status, and the experimental herbicide Kixor. In this article, I am only summarizing our results for Accent Q, which is expected to be labeled in 2009. The other herbicides are not currently labeled for use on sweet corn.

 

Dupont is launching Accent Q in 2009, which is a new formulation of Accent that contains the safener isoxadifen. This safener is also in the herbicides Laudis, Option, and Status and functions by increasing the rate that a corn plant can metabolize specific herbicides. As a consequence, the degree of injury is reduced under stressful conditions or when marginal tolerance exits.  

 

We know that sweet corn hybrids differ in their natural tolerance to Accent and that stressful weather conditions can further increase the risk of injury. Much of the natural difference in tolerance is controlled by a single gene, which is labeled NSF1. When a hybrid inherits a sensitive version of this gene from each inbred parent, the hybrid will be highly sensitive to Accent and will be killed. The hybrid Merit is a highly sensitive hybrid that we use as sensitive check in our trials. If a hybrid inherits a tolerant version of the gene from each parent, the hybrid usually has a good level of tolerance. If the hybrid has a both a tolerant and sensitive version, the hybrid may be injured by Accent to some degree. Because of the variation in tolerance among sweet corn hybrids, Accent has only been recommended on certain hybrids that are known to have acceptable levels of tolerance. 

 

The development of Accent Q may increase the opportunity of using Accent on sweet corn if the safener is effective. Therefore, we wanted to determine if Accent Q increased the tolerance of hybrids compared to Accent. To increase the potential of observing a safening effect with Accent Q, we selected 20 hybrids previously rated as sensitive, 9 hybrids rated as intermediate, and 10 hybrids rated as tolerant (Table 1). These 39 hybrids were planted in single rows in trials in each of our four states.  At the V3-growth stage, Accent and Accent Q were applied to their respective plots with a nontreated check plot in between so injury could easily be rated. The Accent was applied at 1.09 oz/a with 1% crop oil concentrate and 2 lb/a ammonium sulfate. The Accent Q rate was 1.5 oz/a, which had the same amount of Accent (1.09 oz/a) plus 0.41 oz/a of isoxadifen. This rate of Accent is higher than normal to increase the potential of obtaining injury. The anticipated standard rate of Accent Q is 0.9 oz/a, which would contain 0.66 oz/a of Accent. 

 

Table 1. Sweet corn hybrids evaluated for tolerance to Accent Q. Hybrids listed according to previous Accent tolerance ratings at 2x rates of application.
Sensitive	Sensitive	Intermediate	Tolerant
Argent	GSS 1477	Captivate	Ambrosia
Basin R	GSS 2914	Chase	Bliss
Celestial	Hollywood	Early Gold	Challenger
Coho	How Sweet It Is	Incredible	Enterprise
Colombus	Merit	Lancaster	HM 2390
Devotion	Mystique	Overland	Legacy
DMC 21-84	Punch	Passion	Prime Plus
DMC 21-85 (S?)	SS Jubilee Plus	Providence	Rocker
Dynamo	Suregold	Sentinel	Sugar Buns
GH 2042	Turbo		Temptation

 

On average, sweet corn hybrids had 50% less stunting when sprayed with Accent Q compared to Accent at 7 days after treatment (Table 2). (By 14 days after treatment, sweet corn typically starts to recover so the 7 day rating usually shows the greatest difference in injury). The safening effect of Accent Q also appeared to be effective at most locations (Table 3). Average stunting was reduced at Delaware, Oregon, and Wisconsin. Accent did not cause significant stunting to most hybrids at Minnesota, but safening was observed in individual hybrid comparisons (data not shown). Chlorosis was also noticeably reduced at Delaware and Wisconsin (Table 3) and is illustrated with photos of Punch (Figures 1 and 2). It should be noted that even though the safener isoxadifen increased the tolerance of these hybrids to Accent, the highly sensitive hybrid Merit was still killed by Accent Q (Figure 3). Apparently because Merit lacks even one functional version of the NSF1 gene, the safener cannot trigger this gene to become more active in metabolizing Accent. Fortunately, only a few of these highly sensitive hybrids exist and most are not grown commercially.  

 

The safening effect of Accent Q occurred across all trial locations and with most hybrids at the elevated rates tested (Table 4). This demonstrates a level of consistency for the safening effect. Although some of the more sensitive hybrids may have unacceptable injury under certain weather conditions or when over applied (e.g. overlaps), more hybrids should have acceptable tolerance to Accent Q than Accent. This reduced risk of injury should expand the options for using Accent Q for postemergence grass weed control in sweet corn. 

Table 2. Average stunting of sweet corn hybrids across four locations within each tolerance group at 7 days after treatment with Accent and Accent Q. The range among the hybrids is listed in parentheses. Merit had 48 to 49% stunting for both herbicides and is excluded from the range.
	Stunting (%)
Hybrid tolerance group	Accent	Accent Q
Sensitive	15 (4-22)	8 (3-16)
Intermediate	9 (5-16)	5 (0-9)
Tolerant	7 (2-16)	4 (0-9)
Grand average	12	6

Table 3. Average stunting and chlorosis of 39 sweet corn hybrids at 7 days after treatment with Accent and Accent Q.
	Stunting (%)		Chlorosis (%)
Location	Accent	Accent Q	Accent	Accent Q
Delaware	19	9	15	5
Minnesota	2	1	1	0
Oregon	7	0	-	-
Wisconsin	18	11	10	4

Table 4. Sweet corn hybrid stunting to Accent and Accent Q at 7 days after treatment when averaged across locations and sorted previous tolerance rating.
	Stunting (%)			Stunting (%)
Sensitive	Accent	Accent Q	Intermediate	Accent	Accent Q
Argent	20	5	Captivate	11	6
Basin R	12	4	Chase	5	0
Celestial	15	6	Early Gold	16	8
Coho	9	4	Incredible	7	3
Colombus	14	6	Lancaster	7	4
Devotion	11	4	Overland	10	9
DMC 21-84	8	3	Passion	10	8
DMC 21-85	9	4	Providence	10	3
Dynamo	22	16	Sentinel	10	3
GH 2042	14	9
GSS 1477	12	3	Tolerant	Accent	Accent Q
GSS 2914	10	9	Ambrosia	6	3
Hollywood	13	6	Bliss	10	9
How Sweet It Is	14	8	Challenger	16	5
Merit	49	48	Enterprise	8	5
Mystique	20	8	HM 2390	6	3
Punch	13	8	Legacy	8	3
SS Jubilee Plus	21	13	Prime Plus	5	3
Suregold	9	3	Rocker	2	4
Turbo	11	0	Sugar Buns	4	0
			Temptation	9	4

Figure 1. Punch sweet corn hybrid treated with 1.09 oz/a Accent shows stunting and chlorosis at 7 days after treatment. 

 

 

 

Figure 2. Punch sweet corn hybrid treated with 1.5 oz/a Accent Q has less stunting and minimal chlorosis at 7 days after treatment.

 

 

 

Figure 3. Merit sweet corn hybrid treated with 1.5 oz/a Accent Q at 7 days after treatment. This highly sensitive hybrid is still killed with Accent Q.