Citation: Sharma, M.; Gaviyappanavar, R.; Tarafdar, A. Evaluation of Fungicides and Fungicide Application Methods to Manage Phytophthora Blight of Pigeonpea. Agriculture 2023, 13, 633. https:// doi.org/10.3390/agriculture13030633 Academic Editors: Biruta Bankina and Neringa Rasiukeviciute Received: 4 January 2023 Revised: 25 February 2023 Accepted: 28 February 2023 Published: 7 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). agriculture Article Evaluation of Fungicides and Fungicide Application Methods to Manage Phytophthora Blight of Pigeonpea Mamta Sharma * , Ramanagouda Gaviyappanavar and Avijit Tarafdar International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, India * Correspondence: mamta.sharma@icrisat.org Abstract: Phytophthora, a blight of pigeonpea caused by Phytophthora cajani, has been signifi- cantly increasing in major pigeonpea production regions of India. Limited information on infec- tion with this pathogen and its epidemiology, as well as a lack of adequate resistant cultivars, is hampering the management of Phytophthora blight significantly. Therefore, five fungicides, viz., metiram + dimethomorph, cymoxanil + mancozeb, famoxadone + cymoxanil, mancozeb, and metalaxyl-M + mancozeb, were evaluated against P. cajani under control conditions to control zoospore induction, as well as the infection of zoospores, at the seedling stage. The half-maximal effective concentration (EC50) of fungicides for mycelial inhibition was calculated. The lowest EC50 was recorded in metiram + dimethomorph (0.17 μg/mL), followed by the metalaxyl-M + man- cozeb (2.49 μg/mL) and cymoxanil + mancozeb (8.23 μg/mL) fungicides. The formation of the sporangium and zoospores was most significantly affected by metalaxyl-M + mancozeb, followed by metiram + dimethomorph and cymoxanil + mancozeb, in terms of sporangia viability and zoospore germination and encystment. Further, under glasshouse conditions, different fungicide application methods (e.g., seed-treatment; soil-drench; foliar-spray, either singly or in combinations) were evalu- ated with fungicides on susceptible (ICP 7119) moderately resistant pigeonpea (ICPL 99010, ICPL 20135 and ICPL 99048) cultivars. The seed-treatment + soil-drench, soil-drench + foliar-spray, and soil- drench of fungicide application methods were found to be effective in controlling the Phytophthora blight, at p < 0.001. A combination of the seed-treatment + soil-drench and soil-drench + foliar-spray methods, using metalaxyl-M + mancozeb or metiram + dimethomorph fungicides on moderately resistant cultivars (ICPL 99010), has a synergistic effect on the ability to control the Phytophthora blight at the seedling stage. Keywords: pigeonpea; Phytophthora cajani; sporangia; zoospores; fungicides 1. Introduction The pigeonpea (Cajanus cajan L.) is a perennial legume, widely cultivated as an annual crop in tropical and semitropical regions of South and Southeast Asia, Africa, and Latin America. It is highly nutritious, containing high levels of protein and several important free amino acids, e.g., tryptophan, methionine, and lysine. An estimated 4.49 million tons of pigeonpea are produced per year, and 63% of the total production occurs in India. In India, pigeonpea is cultivated in a 3.9-million-hectare area; this accounts for 72% of the total area used for pigeonpea cultivation across the world (FAOSTAT, 2021). Phytophthora blight caused by Phytophthora cajani is one of the most important emerg- ing pigeonpea diseases, after Fusarium wilt and sterility mosaic disease [1]. The disease was first observed in India [2] and subsequently addressed in other parts of the world [3,4]. The disease was initially classified as Phytophthora drechsleri f. sp. cajani, but later, it was amended to Phytophthora cajani [5]. Considering its distribution and severity, Phytophthora blight is an emerging threat to pigeonpea production across the world [6]. Under favorable conditions, P. cajani can infect pigeonpea plants at any growth stage and produce a variety of symptoms, including stem blight, stem rot, stem canker, and leaf Agriculture 2023, 13, 633. https://doi.org/10.3390/agriculture13030633 https://www.mdpi.com/journal/agriculture