Efficacy of new generation oomycete-specific fungicides on life stages of Phytophthora meadii and field evaluation through bunch spraying system

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Fruit rot disease (FRD) of arecanut, caused by Phytophthora meadii, is an important fruit disease of this palm tree that resulted in huge economic losses to the growers in India. In recent years, the control of this disease has become a prime factor in the management of arecanut plantations. Though prophylactic sprayings of Bordeaux mixture (1%) along with other older fungicides are useful in reducing the disease severity. Hence, there is an urgent need for new generation molecules to combat FRD under field conditions. The present investigation was aimed at evaluating newer oomycete-specific fungicides in in-vitro on different life stages of Phytophthora and in-vivo through a Bunch Spraying System (BSS) from ground level. The pathogen was isolated, identified, and characterized from varied regions and one virulent isolate from each region was used. Out of the 11 fungicides tested, EC50 for mycelial inhibition among isolates was lowest in Famoxadone + Cymoxanil. Similarly, the lowest EC50 for sporangial production was recorded in Iprovalicarb + Propineb, Famoxadone + Cymoxanil, and Kresoxymethyl ranging from 210.70 to 517.87 mg mL_1. The most effective fungicide for inhibition of zoospore release was Dimethomorph + Mancozeb which ranged from 406.81 to 565.80 mg mL_1. Bunch spraying of fungicides such as Bordeaux mixture (1%), mandipropamid (0.5%), fosetyl-Al (0.3%), and a combination of metalaxyl-mancozeb (0.2%) from ground level had a significant (P < 0.05) effect against FRD. These fungicides were found most effective in reducing the disease up to an extent of 65–70% and which in turn increased the dry nut yield by 75–95% when applied twice compared to untreated control. However, a semi-systemic fungicide mandipropamid could be a potential alternative to the Bordeaux mixture for effective control of FRD under field conditions.