Silverleaf nightshade (Solanum elaeagnifolium) in the Jordan Valley: field survey and chemical control.
A field survey was conducted to assess the occurrence of Solanum elaeagnifolium Cav. in the Jordan Valley during 2011 and 2012. S. elaeagnifolium was found in field crops, on roadsides, on fallow land, in pastures, and around water sources. Different vegetable and fruit tree crops were infested and had suffered from this invasive weed species throughout the region. Weed densities ranged from 10-60 plants m-2, and populations extended along the whole of the Jordan Valley. Pepper (Capsicum annuum) was the most heavily-infested crop, and the weed severely affected the growth of Citrus spp. and olive (Olea europaea) trees at some locations. Individual weeds exhibited morphological variations and phenotypic plasticity. A field plot experiment was conducted to assess potential chemical control measures for this weed species. Apart from metribuzin (at 0.875 kg a.i. ha-1), all of the other ten herbicides tested inhibited weed growth and reduced weed fruit and seed production compared with the untreated controls. Shoot dry weights (SDWs) were reduced by 12-78% compared to the controls. 2,4-D-iso-octyl ester (at 0.93 l a.i. ha-1), triclopyr (at 1.38 l a.i. ha-1), and glyphosate (at 2.88 l a.i. ha-1) were most effective herbicides and reduced the DWs of weed shoots by 78%, 67%, and 57%, respectively. However, none of the eleven herbicides tested prevented regrowth of the weed. One additional herbicide treatment of regrown weeds significantly reduced weed density and growth 1 year after application. Triclopyr (at 1.38 l a.i. ha-1) almost eliminated all silverleaf nightshade plants 3 years after its first application.