Effects of Seed Treatment Fungicides on Ascochyta pinodes of Field Pea Under Controlled and Field Conditions

Abstract

                Nine fungicides namely thiram, chlorothalonil, metalaxyl, benomyl, thiabendazole, carbendazim, thiophanate-methyl, benalaxyl and iprodione at the rate of 0.001, 0.01, 0.1, 1.0, 10 g/L medium ai were tested in vitro against Ascochyta pinodes (teleomorph = Mycosphaerella pinodes) from field pea for inhibition of mycelial growth. Tests were also conducted on the effect of these fungicides on seed mycoflora at the rate of 2g ai/kg seed. Further studies were carried out on the effects of selected fungicides on seedling infection in growth chamber and field conditions.

                 Radial growth of A. pinodes culture was completely inhibited by carbendazim and thiabendazole at the lowest concentration tested (0.001 g/L), benomyl at 0.01 g/L, thiram, thiophanate-methyl and iprodione at 0.1 g/L. Other fungicides affected the growth at various degrees. Seed treatment with carbendazim, chlorothalonil and iprodione completely inhibited the recovery of A. pinodes from treated seeds while 2 to 3% incidence was obtained for thiram, benomyl and thiabendazole. Untreated seeds showed 16% incidence while benalaxyl and metalaxyl gave 15 and 12% incidence, respectively. Seedling infection in growth chamber was completely controlled by carbendazim and iprodione and a reduction of 4.6% by chlorothalonil.

                  In field trial, seed treatment with fungicides didn’t affect emergence date while there was significant difference (p = 0.05) due to variety. However, carbendazim and iprodione had high emergence on all the three varieties and significantly (p < 0.05) reduced the incidence of Ascochyta infection at both locations at early development period of the crop. Infection appeared in late July and a mean incidence of was 0.03, 3.6, 7.6 and 97.1% on 28 July, 5 August, 12 August and 19August at Denbi, respectively. But at Holetta, the incidence was 0.04, 4.0 and 96.9% on 28 July, 5 August and 12 August, respectively. At both locations, a fast increase from about 10 to 100% of incidence was observed within a week time, but at different weeks. Blight severity was slightly affected at the beginning of the season and became similar soon as the season progressed. A mean seed yield of 2.15 t/ha was obtained at Holetta while it was only 0.80 t/ha at Denbi that were significantly (p < 0.05) different. This was due to difference in blight pressure. Generally, treating seeds with carbendazim improved seed yield by 13.2% and with iprodione by 12.5% over the untreated control. Seed treatment with fungicides could be used as a component of integrated blight management in field pea production.