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<div>The agricultural sector consumes the highest percentage of available fresh water and, with climate change driving increased in water insecurity, agricultural demands are becoming unsustainable. Sensor-driven deficit irrigation networks use less water by allowing a mild crop stress, but may pose disease risks. The objectives of this study were to evaluate (i) effects of deficit irrigation (DI) on <i>Phytophthora</i> root disease in tomato and (ii) effects of DI on root disease in commercial greenhouse crops. When tomatoes inoculated with <i>Phytophthora</i> <i>capsici</i> were placed under saturated, mild deficit and severe deficit irrigation treatments, disease severity was significantly lower under the saturated and mild deficit treatment compared to severe deficit (<i>P</i> = 0.025). The mild deficit deployed 18% less water than the saturated treatment; irrigation treatment did not affect growth of non-inoculated plants. There was no effect of minor deficit on Pythium root rot in commercially grown poinsettias. When poinsettias were inoculated with<i> Pythium aphanidermatum</i>, disease<i> </i>incidence was significantly lower under saturated and mild deficit conditions, compared to the severe deficit treatment (<i>P </i>= 0.05). These studies indicate that, although severe deficit increases risk of disease losses and should be avoided, minor deficit may not increase root disease risk and can reduce water usage, improving water security in agricultural systems.</div>