The goal of the thesis was to find out whether it is possible to slow down or prevent the symptoms and propagation of red stele (Phytophthora fragariae var. fragariae) in strawberry seedlings with the soil improvement products of Humuspehtoori ltd. Strawberry red stele has spread to Finland in recent years although it has been common for a long time in rest of Europe. It is hard to prevent because its oospores can hibernate in the ground for long periods. Therefore scientists and farmers are considering various means of prevention.

A diverse population of microbes in the soil offers potential means for prevention in a natural way. By raising the biodiversity of microorganisms in the fields, the red stele fungus is put in a competitive position which weakens its chances of infecting its host.

An incubator experiment was conducted for this thesis in which the seedlings were potted in different substrates. There were seven different substrates which were assembled from soil which was infected with red stele, sterilized soil and two different soil improvement products. The experiment was a split-plot design with four repetitions. The seedlings were grown little over 8 weeks in temperature of 15C and a relative humidity of 90 % so that the conditions would be favorable for red stele. At the end of the experiment fresh and dry weights were measured from the above ground parts of the plants. The measurements were applied to a spreadsheet and were processed with a statistics program and analyzed.

The results were inconclusive as to whether or not the soil improvement products affected strawberry growth positively. It was clear that the seedlings grew better in the sterilized substrates that had soil improvement product #1 added. Though this distinction wasn’t visible in the infected samples. The fresh and dry weights of the seedlings grown in the substrates containing soil improvement product #1 didn’t differ from peat that was used as a control for the experiment.