Soil fertilization as a control strategy against Quercus root rot in agroforestry systems

Abstract: We studied the effect of various calcium (CaO, CaCO3 and CaSO4) and potassiumproducts (KIO3 and KOH) on the inoculum density in the soil and infectivity of Phytophthoracinnamomi, the main biological agent causing root rot on Quercus species in oak-rangelandsecosystems in southern Spain. Products were chosen by their known effectiveness on inhibitionof P. cinnamomi sporangial production. The chemicals were added separately to soil infestedwith P. cinnamomi at the usual doses used in rangelands. Two weeks after chemicals addition,only potassium products produced a significant decrease on inoculum densities. At that time,soils were transferred to plastic pots and holm oak seedlings were planted. Eight weeks later,plants growing in infested and untreated soil showed high levels of foliar and root symptoms,whereas plants growing in soil treated with fertilizers (exception made with KIO3) showed asignificant reduction of symptom severities. These results suggest that, together with othercontrol strategies, the regular application of Ca and K fertilization in oak rangelands should beconsidered for reduction of the incidence of this severe disease.