Effect of fungicides, seaweed extracts, tea tree oil, and fungal agents on fruit rot and yield in strawberry

Abstract

Seven fungicides, 2 seaweed extracts (Maxicrop and Seasol), tea tree oil (Multicrop), and fungal agents including yeasts and an isolate of a Trichoderma sp., were compared for the control of fruit rots in strawberries in 5 field trials in Victoria, Australia. The fungicides tested were thiram, iprodione, dichlofluanid, chlorothalonil, fluazinam, phosphorous acid and fosetyl-aluminium. All treatments were applied as foliar sprays (at recommended rates) at weekly intervals, except for one of the Trichoderma treatments in which Trichoderma was cultured on rice and applied around plants at 1 and 5 weeks after the start of the trial. Rots were assessed after harvest by incubating fruit for 3 days at room temperature (15–25˚C). Between 55 and 71% of fruit developed rot in the unsprayed plots and consisted mainly of grey mould (Botrytis cinerea), leak (Rhizopus and Mucor spp.), anthracnose (Colletotrichum acutatum), leather rot (Phytophthora cactorum), and stem end rot (Gnomonia comari). All fungicides except fosetyl-aluminium and phosphorous acid significantly (P<0.05) reduced the total incidence of fruit rots by 27–72%. Thiram, dichlofluanid and chlorothalonil reduced grey mould by 61–94%, anthracnose by 63–100% and leather rot by 65–100%; iprodione reduced grey mould by 60–94% and leak by 74–96%. In one experiment each, fluazinam reduced grey mould by 85% and leather rot by 100%, and phosphorous acid reduced leather rot by 100%. Thiram, iprodione and phosphorous acid also reduced stem end rot by 55–100%. Of the biocontrols, seaweed extracts and oil, only tea tree oil in 1 trial of 3 reduced the total incidence of fruit rots significantly (by 31%), and in 2 trials significantly reduced anthracnose, and leather rot by 60–88% and 71–72% respectively. In 2 out of 3 trials, Trichoderma sp. reduced (P<0.05) grey mould by 29–63%. In one trial each, seaweed extract 1, and a yeast treatment amended with malt extract, both reduced grey mould by 40 or 54% respectively. The addition of sucrose to the yeast treatments significantly increased the incidence of anthracnose infection. Chlorothalonil, dichlofluanid, thiram and iprodione sprays increased the yield (weight) of healthy fruit significantly (P<0.05) compared with that from untreated plants by 43–114%. By contrast, none of the biocontrol treatments, the seaweed extracts or tea tree oil increased fruit yields.