Growers know the despair when a crop has a root disease or a virus infection. Some growers will use a chemical to try to control it, but this approach is often not effective. It may even worsen the situation. As with everything, prevention is better than cure. Prevention starts with understanding what causes root or virus diseases * and what steps can be implemented to avert difficulties in advance.

By Elly Nederhoff & Bert Houter, CropHouse, New Zealand, Elly@ CropHouse. co. nz with supplements added by Boris Del Mar, Enzymologist, HYGROZYME -  Sipco Industries Ltd.

Spores in growing system

Recirculation or the re-use of drain water brings the risk of spreading root diseases.

The start of a disease is when a pathogen, like a fungal spore, is released from a source and transmitted by a 'vector' into a crop. A vector is something that helps the spread of a pathogen. For instance, it is not unusual for the irrigation water to be contaminated with fungal spores. Through irrigation, spores are introduced into the growing system. If a fungal spore lands on a plant root, the spore germinates and produces 'mycelium' thread that penetrates the plant root. If the fungus grows inside the plant and establishes itself, the plant is infected. Millions of spores will be produced and released. The infected plant is host to the fungus, and it also becomes a source of fungal spores.

Then a vector, such as water, wind, insects or people spread the spores to other plants. There the spore germinates and infects the plant. Millions of spores spread from here. After some time all the plants are infected and the system is full of spores and fungal growth. Obviously the production will suffer.

There are ways to break this circle, namely by controlling the sources of the pathogen and/or the vectors.