Armillaria is a soil-borne pathogen that damages a range of plant species.
Armillaria root rot remains a major limitation to establishment of crops on land where forest trees were planted, then removed and are not totally removed thoroughly during land preparation. The root and stump remnants are essential food bases for ensuring the longevity of Armillaria. Symptoms of Armillaria infection in kiwifruit include poor growth, small leaves, yellowing of the foliage, premature leaf drop, cane die-back, and ultimate vine death. Further to the above, vines affected by Armillaria exhibit sudden wilt and collapse during the summer as crop loads, nutrient deficiencies and water stress increase.
Chemical control and how it failed.
Armillaria root rot is notoriously difficult to control. Traditional orchard management of Armillaria through the removal of tree / vine stumps is virtually impossible, therefore chemical controls were tested for the eradication of this pathogen. Systemic and non-systemic fungicides were trialed for the control of Armillaria and subsequent field experiments showed that the chemicals failed to fully eradicate the rhizomorphs (shoe-string growth of Armillaria around the roots by which the pathogen can spread) in soil even with as high as 10,000mg/L (West).
Because the currently available chemicals for controlling Armillaria were either ineffective or phytotoxic, there was a need for an alternative approach to the problem (Baker and Snyder).
Biological control using Trichoderma species
Perhaps the most thoroughly studied antagonist of Armillaria are Trichoderma species. There is a lot of research being undertaken in New Zealand at present about the biological control methods for Armillaria using Trichoderma species.
Research has been undertaken on an intensive level overseas since 1914 using Trichoderma as an antagonist to Armillaria, however significant findings were made by Dumas and Boyonoski in 1992 with regards to the mode of action of Trichoderma species. They found using electron microscopes that certain Trichoderma species attacked, penetrated and destroyed outer tissue of the Armillaria rhizomorphs and, once inside, they killed Armillaria hyphae by coiling and direct penetration. After one week, the rhizomorphs infected with each of these Trichoderma species were devoid of hyphae.