Dandelions don’t seem like they should be one of the more problematic weeds in field crops, but they certainly are in Wisconsin. With an abundant seed supply, wind dispersal, and limited dormancy, dandelions can start an infestation in spring, summer or fall. The perennial nature of dandelion then leads to management challenges in no-till and alfalfa fields. Unfortunately, established dandelions are not consistently controlled with burndown applications of glyphosate or 2,4-D in the spring. However, we can control dandelions quite well with fall applications. As we approach this fall, we wanted to summarize a recent dandelion trial to generate thoughts and plans on management options.  

 

This dandelion trial was established after corn stalks were chopped off in the fall of 2006. The herbicide treatments were applied on November 14. The weather during that week (3 days before and after the 14^th) was relatively cold with an average of 38F as the daily high temperature and 27F for the daily low temperature. The dandelions ranged in size, but were not extremely large and appeared to have some frost damage from earlier in the month (Figure 1).  

 
Figure 1. Dandelions and crop residue on November 14, 2006, the day of treatment.

Despite the weather conditions that did not seem to be highly favorable for herbicide activity, several treatments provided excellent dandelion control into the spring (Table 1). The first seven herbicide treatments in the table were applied as single herbicide products to provide a basis for understanding their relative contribution to the subsequent tank mixtures. All of the sulfonylurea herbicides provided excellent initial control of dandelions in April, but some of the dandelions started to recover by mid-May and control dropped below 90% except for Classic. Roundup Original Max and 1 qt/a 2,4-D were not as effective as the sulfonylureas, which may be related to their generally less consistent control of dandelion and the cold temperatures when they were applied.

Almost all of the herbicide tank mixtures provided excellent control in April and three of the treatments controlled the dandelions almost completely through mid-May. While many of the single herbicide products were not able to control dandelions into May, combinations of some herbicides increased the control noticeably.  For instance, Synchrony + Express + 2,4-D controlled dandelions better than any of the single herbicides.  Figures 2 through 5 illustrate the range of dandelion control observed in the trial in early May.  

 

This trial supports previous UW research in showing that there are several effective fall herbicide treatments that can be used to control dandelions. This trial also re-affirms that the sulfonylurea herbicides can be applied late into the fall under cold weather conditions and maintain effective dandelion control. This trial certainly suggests that fall herbicide treatments may be a worthy option to consider for dandelion control. 

 

Remember that certain herbicides limit the crop that can be planted the following spring.

Basis and Princep can only be followed by corn in the spring and Classic, Canopy EX, and Synchrony can only be followed by soybeans in the spring.  Autumn, Express, glyphosate, and 2,4-D can be followed by either crop.

 

Some herbicides have geographical use restrictions. Classic at the 1 oz/a rate and Canopy EX at 1.1 oz/a (contains 1 oz/a of Classic) can only be used south of I-90 west of Madison and I-94 east of Madison.

 

Some herbicides provided residual activity into the spring, which reduced the need for a spring burndown herbicide application at this site. The residual activity may have been more apparent in this trial because of the late fall application date. Treatments containing Classic, Canopy EX, Synchrony, and Autumn had notable annual grass and broadleaf residual activity.

 

Table 1. Dandelion control in spring 2007 after fall herbicide applications at Arlington, WI.

		Dandelion control
Treatment	Rate	April 19	May 18
		(%)
Nontreated		0	0
Autumn + COC	0.3 oz/a + 1%	97	84
Basis + COC	0.5 oz/a + 1%	99	84
Classic + COC	1 oz/a + 1%	100	93
Express + COC	0.25 oz/a + 1%	97	73
Synchrony + COC	0.375 oz/a + 1%	100	80
Rdp Original Max + AMS	22 oz/a + 3.4 lb/a	89	59
2,4-D ester + COC	1 qt/a + 1%	87	67
Basis + Express	0.33 oz/a + 0.19 oz/a	100	96
+ 2,4-D ester + COC	+ 1 pt/a + 1%
Basis + Princep	0.4 oz/a + 1 qt/a	99	82
+ 2,4-D ester + COC	+ 1 pt/a + 1%
Express + Rdp Orig. Max	0.25 oz/a + 22 oz/a	99	81
+ 2,4-D ester + NIS + AMS	+ 1 pt/a + 0.25% + 3.4 lb/a
Express + 2,4-D ester + COC	0.25 oz/a + 1 pt/a + 1%	99	79
Synchrony + Express	0.375 oz/a + 0.19 oz/a	100	96
+ 2,4-D ester + COC	+ 1 pt/a + 1%
Canopy EX + 2,4-D ester + COC	1.1 oz/a + 1 pt/a + 1%	100	99
Autumn + Sencor + COC + 28%	0.3 oz/a + 10 oz/a + 1% + 1.5 qt/a	88	65
Autumn + 2,4-D ester + COC + 28%	0.3 oz/a + 1.5 pt/a + 1% + 1.5 qt/a	94	78
Autumn + Rdp Orig. Max + AMS	0.3 oz/a + 11 oz/a + 3.4 lb/a	97	82
LSD (0.10)		4	8

Abbreviations: COC = crop oil concentrate, NIS = nonionic surfactant, AMS = ammonium sulfate.

 

 
Figure 3. Autumn treated dandelions in early May.

 

 
Figure 4. 2,4-D ester treated dandelions in early May.

 

Figure 5. Synchrony + Express + 2,4-D treated dandelions in early May.