July 15, 2010
By Pam Charbonneau
OMAFRA Turf Specialist

The broadleaf herbicide Fiesta (active ingredient iron in the form of FeHEDTA, 4.43 per cent) is very new to the marketplace. We continue to test its efficacy on broadleaf weeds, weed re-growth after treatment and safety on newly seeded turf.

It provides a very quick defoliation of dandelion and black medick in a mixed stand with turf at label rates. When applied as a broadcast application, it also results in the greening-up of the turf. Fiesta showed some re-growth of dandelions, regardless of the application rates used in the fall of 2009 (200 mL, 400 mL or 800 mL). By the following spring, the percentage of dandelion cover was back up to the same level as the beginning of the experiment for all of the Fiesta rates.  

The Fiesta label does state that you can “repeat once in four or more weeks.” In this experiment, Fiesta was not re-applied because the application in early October did not allow time for a re-application before the onset of winter.  We conducted tagged weed trials following individual dandelions treated once with Fiesta and treated twice with Fiesta, four weeks apart. So far, the results with the single application of Fiesta applied in the spring resulted in re-growth. The second application with Fiesta will be applied soon.

The re-growth of black medick was similar to dandelion in the fall of 2009 and spring, 2010. By the spring, only the 800 mL rate had a lower percentage of black medick cover than the weedy check. The label rate range (200 and 400 mL per 100m2 rates) had re-growth equal to the weedy check. Again, the second application that is allowed on the label at four or more weeks after the first was not applied, so this experiment does not shed any light on how well the Fiesta would work at controlling black medick with two applications, four weeks apart.  

The situation with the narrow-leaved plantain was a bit different than the dandelion or black medick. Fiesta did not result in a quick defoliation. Instead, the percentage of narrow-leaved plantain cover decreased at each rating date for all of the Fiesta rates and decreased more quickly than in the plots treated with Par III. By the spring, the percentage of narrow-leaved plantain was almost completely gone from all of the plots, including the weedy check. This indicates that the growth habit of the narrow-leaved plantain is such that it is slow to re-grow in the spring, regardless of whether it has been treated with a herbicide or not. Again, a second application was not applied and the results may be quite different with a second application.  

This spring we also tagged weed trials where we are following individual dandelions treated once with Fiesta and treated twice with Fiesta, four weeks apart. So far, as with the dandelions mentioned above, the narrow-leaved plantain has resulted in re-growth after two weeks.  

As I mentioned, more trials are underway at the Guelph Turfgrass Institute on Fiesta rates, timing (spring applied vs. fall applied) and with and without re-application. As also mentioned, there are  trials underway following tagged individual weeds (dandelions, narrow-leaved plantain, broad-leaved plantain and clover) that have been treated with Fiesta to evaluate re-growth. By the end of the 2010 season, we should have a much clearer idea of how well this product works. I will update the results later in the season. 
Pam Charbonneau may be contacted at 519-824-4120, ext. 52597, or by e-mail at pamela.charbonneau@ontario.ca.