WATER STRESS AND ROOT INJURY FROM SIMULATED FLOODING AND DIAPREPES ABBREVIATUS ROOT WEEVIL LARVAL FEEDING IN CITRUS.

Environmental stress from flooding can occur simultaneously with root weevil infestation to damage plant root systems. We conducted two factorial studies of flooding duration and Diaprepes abbreviatus (L.) root weevil larval feeding injury on citrus in the greenhouse in 2002 and 2003. Our objectives were to investigate the effect of soil anoxia by simulated flooding on plant water stress and the impact of prior flooding on root susceptibility to subsequent larval weevil feeding. The treatments consisted of two rootstock varieties, Swingle citrumelo [SWI; Citrus paradisi Macfad x Poncirus trifoliata (L.) Raf.] and Smooth Flat Seville (SFS; Citrus aurantium L.), flooding durations of 0, 10, 20, 30, or 40 days, and Diaprepes larval infestations of 0 and 5 neonates per seedling for 40 days. We used a Candler sand with 8 replicates in Experiment I and a Floridana loam with 15 replicates in Experiment II. Treatments were arranged in a completely ramdomized design. Plants were flooded, drained for a week, and then 1-day-old neonate larvae were introduced onto the soil surface of each seedling. Flooding significantly reduced soil redox potential (Eh), leaf stomatal conductance (gs), and shoot growth (P < 0.05). Soil Eh decreased from +220 to -0;100 mV within 1-3 days after flooding, and leaf gs declined from 260 to 80 mmol m-2 s-1 within 20 days of flooding. Flood-injured and larval-injured roots had little growth. With equal previous flooding durations (20 days), the larval survival was on average 25% higher in sandy soil than in loamy soil. Twenty-day prior flooded roots were more water stressed and also more susceptible to Diaprepes larval feeding injury. It is suggested that limited soil waterlogging and early root weevil larval control would be useful for plant protection.