Control of Ink disease by trunk injection of potassium phosphite

Potassium phosphite was applied to 4-year-old chestnut plants either in the form of a foliar spray or by xylem injection (prophylactic or curative) to control the development of ink disease, following inoculation with Phytophthora cinnamomi. Foliar spraying reduced symptom expression by ~90% within 30 days, and later served to inhibit fungal colonisation of the stem. The prophylactic injection treatment fully prevented infection, but the efficacy of the curative treatment depended on the initial level of disease severity. Potassium phosphite was injected annually into the trunks of a set of old chestnut and young walnut trees, naturally infected by, respectively, P. cambivora and P. cinnamomi. The treatment was ineffective on heavily diseased trees, but acted curatively on less infected ones. Two fungicidal applications on chestnut (one on walnut) were sufficient to promote plant recovery, as observed by improved vigour of the sprouts, larger size and deeper colour of the leaves, normal fruit development and ripening, a halt in the flux of ink, and the dehydration and compartmentalization of disease lesions.