Management of Phytophthora cinnamomi Using Fungicides and Host Plant Defense Inducers Under Drought Conditions: A Case Study of Flowering Dogwood

Phytophthora cinnamomi is considered one of the most destructive pathogens of ornamental crops. Different fungicides and host plant defense inducers were tested for their efficacy in managing Phytophthora root rot in drought conditions. In this study, the drought conditions were maintained by evaluating the moisture-holding capacity of the pine bark in a 10.2-cm nursery container. Four controls and nine different treatments were used in two trials for this greenhouse study. All treatments were drench-applied as a preventative or curative treatment. Seedlings were artificially inoculated with P. cinnamomi. Regular irrigation was carried out using overhead irrigation for 1 month after inoculation. Irrigation was regulated by drip irrigation after the first month. A moisture level of 15% to 18% of total moisture-holding capacity was maintained using the gravimetric method throughout the drought period. Physiological parameters of the seedlings were recorded a week after seedlings were drought stressed. In both trials of preventative and curative treatments, all treatments were able to suppress the disease significantly except Orkestra Intrinsic. Orkestra Intrinsic had a disease severity statistically similar to the inoculated and stressed control in trial 1 of the curative treatment. Net photosynthesis, stomatal conductance, and leaf moisture potential were significantly greater in seedlings treated with Subdue MAXX, Signature Xtra, and Empress Intrinsic in both trials of preventative and curative treatments. Effective quantum yield of Photosystem II was significantly lower in the inoculated stressed control in both trials of preventative and curative treatments. Net chlorophyll content through the SPAD meter showed higher values for Subdue MAXX treated seedlings compared with the noninoculated nonstressed controls in trial 1 as both a curative and preventative application. In trial 2, Subdue MAXX and Signature Xtra were the best curative treatments, whereas Empress Intrinsic, Interface, and Subdue MAXX were the best preventative treatments for higher chlorophyll content. This case study will help growers perform successful management of Phytophthora root rot in woody ornamental crops during drought or water deficit conditions.