Root-mat disease appeared in hydroponic tomato crops recently and, with a lack of effective control measures (chemical "disinfection" has proved ineffective), it posed a significant risk to economic production of tomatoes. HDC project PC 241 was initiated as an alternative "biological" strategy to investigate alternative non-chemical strategies to minimise or eliminate the risk of root-mat.
Previous studies have shown the greatest infection risk occurs about four weeks post-sowing. Increasing the microbial diversity within the rockwool led to a suppression of root-mat symptoms in hydroponic cucumbers. Observations on organic tomato and soil-grown cucumber nurseries supported the suggestion that increasing the population of naturally occurring microbial antagonists might suppress or prevent the disease.
The potential of different filtration techniques based on the principle of slow sand filtration but incorporating organic substrates such as soil to mimic the disease-suppressive effects seen in organic tomatoes were evaluated. The project also looked at the impact of microbial preparations to increase microbial diversity. The potential for using alternative rootstocks was tried but the graft combination reduced yield by 80 per cent. Progress with other treatments was hampered by a drop in the severity and occurrence of root-mat. There may be a decline in the disease as was seen in cucumbers, or recent cool summers may have affected the pathogen.