Status and Best Management Practices of Potato Early Dying Disease in New Brunswick, Canada

Potato early dying (PED) disease complex is often called the <i>Verticillium</i> wilt of potato and is considered one of the most economically devastating diseases of potato worldwide. The severity of the disease greatly increases with the association of the soil-borne pathogens <i>Verticillium dahliae</i> and <i>V. albo-atrum</i> and the root lesion nematode (<i>Pratylenchus</i> sp.). Recently, an increase in wilt disease symptoms and a sharp decline in marketable tuber yield were observed in New Brunswick (NB), Canada. A survey of 71 fields, along with eight fumigated and eight non-fumigated fields, was carried out to determine and quantify nematodes and <i>Verticillium</i> in the soil. Techniques used included plate counts for <i>Verticillium</i> (CFU/g soil), real-time qPCR (RT-qPCR) for <i>V. dahliae</i> (cell/g soil), and nematode identification and counts (# of nematodes/kg of soil). The survey results of the 71 fields revealed that 55 fields had <i>Verticillium</i> sp. ranging from 2 to 66 CFU/g of soil by the plate method, and 68 fields had high <i>V. dahliae</i> ranging from 261 to 27,471 cell/g of soil by RT-qPCR method. All fields had high numbers of root lesion nematodes ranging from 560 to 14,240 nematodes/kg of soil. There was an uneven distribution of PED incidence in potato fields at various locations of NB. Fumigation with Chloropicrin significantly reduced the numbers of root lesion nematodes by 34.1-99.0%, <i>Verticillium</i> sp. CFU/g of soil by 50-100%, and <i>V. dahliae</i> cell/g soil by 38-91% in the eight fumigated fields. The management of the PED complex with various disease management products under field conditions was also studied in a field plot trial setup. The nematicide Velum applied in-furrow at the recommended label rate decreased the numbers of root lesion nematodes by up to 66% compared to other products. The combination of both Velum + Aprovia and the application of ammonium-lignosulfonate significantly reduced <i>V. dahliae</i> by 190.55% and 274.24%, respectively, compared to other products. The fungicide Aprovia applied in-furrow at the recommended rate for the management of <i>Verticillium</i> wilt significantly reduced <i>Verticillium</i> sp. CFU/g of soil in treated soil by 73.3% compared to Velum, Mustgrow, Senator PSPT, Vapam, ammonium-lignosulfonate, Nimitz, and the untreated control. Disease management products increased potato marketable yield by 27.38-97.74%. The results of this study suggest that the root lesion nematode and <i>V. dahliae</i> have a ubiquitous distribution in the fields cultivated with potatoes in NB. The co-infection of potato by both <i>V. dahliae</i> and the root lesion nematode can greatly increase the severity of PED. Fumigation with Chloropicrin significantly reduced the levels of root lesion nematodes and <i>Verticillium</i> in all fumigated fields. Management practices of PED using the fungicide Aprovia, the nematicide Velum, and a combination of both Velum + Aprovia had the greatest effect in reducing the population density of the root lesion nematode and <i>Verticillium dahliae</i> in soils of commercial potato fields in New Brunswick.