Managing Phymatotrichopsis Root Rot in Arizona Alfalfa.

Abstract

Alfalfa stands is a critical components of profitable alfalfa production. Number of important diseases can reduce alfalfa stand vigorous and yields, and limit production in many parts of southwestern Untied States. Phymatotrichopsis root rot (PRR) caused by Phymatotrichopsis omnivora is one of the most destructive fungal diseases of alfalfa that causes significant yield losses in Arizona. PRR reduces the productivity and persistence of alfalfa fields causing heavily affected sites to be taken out of production. Recent field trials in Arizona indicated that Topguard® (a.i. flutriafol) fungicide is effective in managing PRR in cotton production system. There is, however, no known research for this disease in Arizona’s alfalfa production system. The present study was conducted to evaluate the efficacy of flutriafol for PRR management in alfalfa. Multiyear (2015, 2016, 2017) and multilocation on-farm replicated trials were conducted in known PRR infested alfalfa production areas of Arizona (Arlington, Marana, Pierpoint, Parker). A week after first cut of the year and just before irrigation, flutriafol was applied at different rates (0.56, 1.12 and 2.24 kg ha^–1 in 2015; 0.28, 0.53, 1.05 kg ha^–1 in 2016 & 2017) using a backpack CO₂ sprayer. Four to five hay cuts were taken in each year. Data analysis showed that all application rates provided visible disease symptoms reduction with increased yield in all locations and years. In 2015, the higher two rates (1.12 and 2.24 kg ha^–1) resulted in significantly higher yield compared to untreated control. In 2016, the highest yield was recorded from plot treated at the lowest rates (0.28 kg ha^–1) of application. In 2017, the highest hay yield obtained from plots treated twice at 0.28 kg ha^–1 application rate. The results obtained from the four locations and three growing years suggest positive benefit of flutriafol use to reduce PRR induced yield losses and support the need for continued applied research in Arizona.