Feasibility study of effect of ultrasound on water chestnuts

Water chestnut (Trapa natans L.), an annual aquatic plant with floating leaves was first introduced into North America in 1874. Since then, wild populations have quickly become established in many locations within Northeastern USA. Due to its detrimental effects on the overall health of aquatic ecosystems, millions of dollars have been spent to control the water chestnut infestations in the North America through mechanical harvesting and manual removal, with limited success. The potential for continued expansion of the infestations demonstrates an urgent need for an effective control method. This study examined the potential of ultrasound application as an alternative control strategy for water chestnut management. Various frequencies and amplitudes of ultrasound generated by submerged transducers were applied directly to water chestnuts harvested from Lake Champlain. Substantial damages on water chestnut cells as well as penetrated petitoles were observed at the following tested frequencies of ultrasound, 20 kHz, 187 kHz, 469 kHz, 519 kHz and 2.34 MHz. Among them, 20 kHz ultrasound of 1.9 MPa acoustic pressure amplitude demonstrated the most significant damages within 10 s of ultrasound exposure. The treated plants started to die within 72 h and the mortality rate of water chestnut plants treated with the ultrasound application was 100%.