Plant growth regulator herbicides such as dicamba are used for selective control of many broadleaf weed species. The introduction of dicamba-tolerant (DT) soybean ( Glycine max ) and cotton ( Gossypium hirsutum ) in 2016 and the increase in
Dicamba is commonly used as a postemergence herbicide in corn ( Zea mays ), small grains, and pastures. Recent advances have led to the development of dicamba-resistant soybean and cotton ( Gossypium hirsutum ) cultivars to combat glyphosate
genetically modified crops, including cotton, field corn, soybean, and canola with resistance to dicamba and 2,4-D herbicides has been developed to address the problem of glyphosate-resistant weeds ( Behrens et al., 2007 ; Wright et al., 2010 ). In the few
) salt of dicamba (3,6-dichloro-2-methoxybenzoic acid) (alone or in combination with glyphosate) over the top of crops that were previously intolerant to these two herbicides. Soybean ( Glycine max ), cotton ( Gossypium hirsutum ), and corn ( Zea mays
combat herbicide-resistant weeds, agrochemical companies have developed soybean and cotton that are resistant to 2,4-dichlorophenoxyacetic acid (2,4-D) and dicamba ( Behrens et al., 2007 ; Wright et al., 2010 ). Recent deregulation of dicamba and 2,4-D
Abstract
Symptoms of apparent growth regulator injury (curling, resetting and yellowing of new growth, blackening, death, and dropping of needles) were observed in plantings of Taxus sp. These symptoms were produced also in container grown plants (Taxus cuspidata, Sieb. and Zucc. and Taxus media ‘Brownii’, Hort.) with 3,6-dichloro-o-anisic acid (dicamba). Injury symptoms appeared at the 0.13 kg/ha rate and a marked reduction in growth occurred at all higher rates. The injury at 0.3 kg/ha was severe and plants failed to recover after 18 months; death resulted at 1.1 kg/ha and above.
and dicamba, were created to decrease their volatility in the environment ( Sosnoskie et al., 2015 ). The diglycolamine salt of dicamba and choline salt of 2,4-D choline are two formulations that have been used on genetically modified soybeans and
herbicide chemistry. For example, Panke et al. (2012) report that labeled rates of dicamba or picloram can provide control of creeping bellflower, but Moechnig et al. (2007) report that commercially available synthetic auxin herbicides only provide
Greenhouse experiments were conducted to compare visible injury from sublethal rates of 2,4-D, dicamba, and a premixed product of 2,4-D + mecoprop + dicamba for eight annual flowers and to describe herbicide injury symptoms for these annual species. Herbicides were applied at rates 0.05×, 0.1×, and 0.2× of their highest labeled rate for turfgrass to simulate spray drift conditions. Visible injury varied between species, herbicide rate, and time after herbicide application. Alyssum (Lobularia maritima Desv.) showed the greatest initial injury and ageratum (Ageratum houstonianum Mill.) showed the greatest injury at 4 weeks after treatment. Symptom severity increased as herbicide rate increased, with the greatest injury from the premixed product, followed by 2,4-D, and then dicamba. The eight species varied in their degree of visible injury and flower production to dicamba, 2,4-D, and the premixed product. Reduced flowering was most obvious for prolific flowering species such as alyssum. Impatiens (Impatiens wallerana L.), salvia (Salvia splendens Sello), and snapdragon (Antirrhinum majus L.) produced more flowers in response to sublethal dicamba rates compared to the untreated plant. All rates of 2,4-D generally reduced flowering compared to untreated plants, except the lowest rate of 2,4-D for geranium (Pelargonium xhortorum Bailey) and snapdragon. Dahlia (Dahlia hortensis Cav.) sprayed with dicamba at the highest rate produced three times as many stems as plants untreated or those sprayed with 2,4-D. Overall order of species susceptibility to sublethal rates of dicamba, 2,4-D, or the premixed product from most susceptible to least susceptible was ageratum > alyssum > marigold (Tagetes erecta L.) > dahlia > geranium = salvia = snapdragon = impatiens. Differences in overall susceptibility to the plant growth regulator herbicides evaluated should provide useful information to horticulturalists designing annual flower beds and borders and lawn care applicators.
·ha −1 acid equivalent) or Myrothecium verucaria alone controlled trumpetcreeper 45% and 30%, respectively ( Boyette et al., 2008 ). Bradley et al. (2003) reported that reduced rates of two mimics of indole-3-acetic acid, dicamba (280 g·ha −1 ) and 2