Alternative methods to control Phytophthora cactorum in strawberry cultivated in soilless growing media

Phytophthora cactorum is an important threat in strawberry propagation and production. No reliable non-chemical control measures are available. Therefore different control strategies were tested. Spread of pathogen infection can be reduced by disinfection of the irrigation water. Slow sand filtration effectively removed P. cactorum from drain water, i.e., disease severity in strawberry plants was reduced with 45 to 65% and rhododendron baits showed a 95-100% reduction of P. cactorum after the drain water had passed the sand filter. However, upstream movement of P. cactorum was detected within the unit. A complementary strategy to reduce the damage caused by P. cactorum is to enhance disease suppressive properties of the soilless substrate. Pasteurization of the substrate mixtures showed increased levels of disease, indicating that biological factors might play a role in disease suppression. Antagonistic bacteria inhibiting growth of P. cactorum were present in roots, rhizosphere as well as in the crown. However, compost amendment or other additions did not elevate suppressiveness. Further experiments were performed where different beneficial microorganisms and/or elicitors were added. The most promising treatments were salicylic acid, followed by inoculation with the endophytic fungus Acremonium strictum and growing Lepidium sativum previous to the crop