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Title:   Author  item
                                            Altland, James
  Submitted to: Meeting Abstract
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 1/4/2016
                                    Publication  Date: 1/7/2016
                                    Citation: Altland, J.E. 2016. Horseweed control in field nursery crops[abstract]. Northeaster Plant, Pest and Soils Conference, January 3-7, 2016, Philadelphia, Pennsylvania. 1:101.Interpretive Summary:
                                Technical Abstract: Horseweed (Conyza canadensis) is one of the most problematic weeds across all crops in agriculture.  Its economic impact worsened when it developed resistance to glyphosate-containing herbicides.  Nursery growers in the Midwest have recently reported difficulty in controlling horseweed in field-nursery crops with glyphosate applications.  Considering this, the only practical method for controlling horseweed in nursery crops is through an effective preemergence program.  However, very few of the preemergence herbicides registered for use in nursery crops have been evaluated in the scientific literature for horseweed control.  The objective of this research was to evaluate preemergence herbicides for horseweed control in a field soil.

Herbicides were spray-applied to a Canfield silt loam soil on October 1, 2014, in plots 1.2 m wide and 3 m long.  Herbicides were applied with a CO2 backpack sprayer equipped with a two-nozzle boom and calibrated to deliver 374 L/ha.  The following herbicides were applied: isoxaben at 1.12 kg/ha ai, flumioxazin at 0.42 kg/ha ai, oxyfluorfen at 1.68 kg/ha ai, indaziflam at 0.084 kg/ha ai, simazine at 4.48 kg/ha ai, pendimethalin at 5.1 kg/ha ai, and dimethenamid at 1.68 kg/ha ai.  A non-treated control was also included.  The field in which the experiment was conducted has a history of heavy horseweed pressure.  Nonetheless, approximately 2000 horseweed seed collected from local populations were applied to each plot in a seed and sand mixture.  There were five replications per treatment arranged in a randomized complete block design.  Weed counts were conducted the following spring to assess control of horseweed and other weed species.  Weed counts were conducted by randomly tossing a 30-cm diameter copper ring (0.07 m2 area) into each plot three times, and counting the number of each species within the ring.

In addition to horseweed, the most prevalent weed species observed in plots included annual bluegrass (Poa annua), lambsquarter (Chenopodium album), and Pennsylvania smartweed (Polygonum pensylvanicum). Isoxaben, indaziflam, and flumioxazin provided the most effect horseweed control, each with less than 1 weed per 0.07 m2 compared to more than 11 horseweed per 0.07 m2 subplot in non-treated controls. Oxyfluorfen, pendimethalin, and simazine reduced horseweed numbers compared to non-treated controls, although not as effectively as the three aforementioned herbicides.  Dimethenamid application resulted in similar horseweed numbers to non-treated controls.  While isoxaben provided effective control of horseweed and other broadleaf weeds, it provided no control of grass weeds.  Indaziflam and flumioxazin provided nearly 100% control of all weed types.  Pendimethalin provided effective grass control, but moderate to poor control of horseweed and other broadleaf weeds.  

Results from this experiment suggest that flumioxazin and indaziflam would provide excellent broad-spectrum weed control, including horseweed, throughout spring and early summer when applied in a fall application.  A tank mix of isoxaben, which provided good horseweed and broadleaf weed control, and pendimethalin, which provided excellent grass control, might in combination provide effective broad spectrum weed control in sites where phytotoxicity is a concern with flumioxazin or indaziflam.


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