Temperature and herbicide impacts on germination of water chestnut seeds

Water chestnut (Trapa natans L.) is a nonnative, annual invasive species that has infested fresh water bodies in the eastern United States (US). Management techniques intended to control or eradicate water chestnut include mechanical or physical removal and herbicide treatments. Information is limited regarding the impact of lake drawdowns on the viability of water chestnut seeds as a complement to other control measures. Experiments were conducted to determine the influence of freezing and simulated drawdowns on the viability of fruit from water chestnut plants growing in herbicide-treated and non-treated areas. In a laboratory experiment, water chestnut fruit frozen in water for 35 d did not germinate. In 2 yr of mesocosm studies, simulated drawdowns did not have a significant influence on water chestnut seed germination, whereas fruit collected from areas treated with herbicide had a significantly different germination rate than those collected from untreated areas. In these studies, the mass of fruit collected from plants in areas treated with herbicide(s) (2,4-D, and/or glyphosate) was significantly less than fruit collected from plants growing in untreated areas. These data suggest that herbicide applications may have a greater or more consistent impact on water chestnut seed viability than lake drawdowns.