ARS | Publication request: Post-emergence herbicides useful in calendula

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: September 14, 2011
Publication Date: September 14, 2011
Citation: Forcella, F., Papiernik, S.K., Gesch, R.W. 2011. Post-emergence herbicides useful in calendula [abstract]. The Association for the Advancement of Industrial Crops. Available: http://www.aaic.org/11program.htm.

Technical Abstract: Easy and effective weed control is required by growers who are considering new industrial crops. Post-emergence herbicides typically are the products of choice by today’s growers. Unfortunately, post-emergence herbicides with proven safety margins are not known for calendula (Calendula officinalis), whose seed oil has applications as a replacement for volatile organic compounds used in paints and other finishes. Our immediate objective was to examine the tolerance of calendula to a number of post-emergence herbicides commonly used for broadleaf weed control in other crops. The longer-term objective was to include calendula on the label of at least some of these products. Fifteen postemergence herbicides were tested under greenhouse conditions and six of these were tested further under field conditions. In all cases a dilution series of concentrations were examined. The concentrations ranged from 1% to 1000% of the normal label rate in greenhouse tests, and 25% to 100% of the normal label rate in field tests. Plants were at the 2- to 4-leaf pair stage at the time of treatment. Plants were scored for damage and weighed about two weeks after treatment in the greenhouse. Field-grown plants were scored for damage while immature and, subsequently, harvested for yield at seed maturity. Only three post-emergence herbicides appeared to be tolerated by calendula. These were desmediphan + phenmedipham, imazamethabenz, and MCPB. These herbicides are the active ingredients in commercial products such as Betamix, Assert, and Thistrol, respectively. Calendula seedlings exhibited no damage symptoms with imazamethabenz treatments, slight deformity with MCPB, and substantial but ephermeral leaf damage with desmediphan + phenmedipham. Plants treated with these herbicides appeared normal at seed maturity. Seed yields of plants treated with desmediphan + phenmedipham, imazamethabenz, or MCPB did not differ appreciably from those of non-treated control plants. At present desmediphan + phenmedipham, imazamethabenz and MCPB are three post-emergence herbicides that appear to be tolerated sufficiently by calendula to merit further testing. If tolerance is confirmed, the activity spectra regarding susceptible weed species is complementary among the three herbicides. For instance, of locally important broadleaf weed species, imazamethabenz controls only kochia (Kochia scoparia), wild mustard (Sinapis arvensis), and wild buckwheat (Polygonum convolvulus). Desmediphan + phenmedipham control the three latter weeds as well as buffalo bur (Solanum rostratum), cocklebur (Xanthium strumarium), common lambsquarters (Chenopodium album), common ragweed (Ambrosia artemisiifolia), eastern blacknightshade (Solanum ptycanthum), and various pigweeds (Amaranthus spp.). MCPB adds control of thistles (Cirsium spp.), field bindweed (Convolvulus arvensis), and sowthistles (Sonchus spp.). Although many other broadleaf weed species exist in the Upper Midwest of the USA, where calendula is expected to be commercialized, control of the above species by desmediphan + phenmedipham, imazamethabenz and triflusulfuron methyl may facilitate the commercialization process.