Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 7/29/2006
Publication Date: 8/5/2006
Citation: Rayamajhi, M.B., Pratt, P.D., Center, T.C. 2006. Additive impacts of plant pathogen-insect enhances pest-plant control efficacy: experimental evidence from the rust-insect-melaleuca system.. Phytopathology. 96:S96 Interpretive Summary: Melaleuca trees have invaded ecologically sensitive landscapes in south Florida. The trees cut in an effort to control mechanically coppice vigorously from cut-stumps. Natural enemies, namely, a leaf rust fungus (accidentally introduced) and two kinds of insect (weevils and psyllid, introduced following vigorous evaluation) are causing substantial damage to this invasive tree in Florida. Herein, we determined the impact of the rust and insects on performance of melaleuca coppices. At least 5-times (60%) more coppicing stumps died in rust-insect combination treatment than in no treatment (18%) within 2-year period. Overall health of coppices on surviving cut-stump was also drastically reduced (at least by 50%) in rust-insect treatments compared to insect or rust alone treatments as measured in terms of biomass and stem to leaf ratio. Thus, weakened coppices are expected to continue to die over years after the initial treatments. This indicated that combination of disease and herbivore attack provides more effective control of melaleuca regrowth compared to disease or insects alone.
Technical Abstract: Plant pathogen-insect integration is becoming popular in pest plant control programs. Herein, we tested the impacts of pathogen-herbivorous insect integration in the biological control of a pest tree, Melaleuca quinquenervia (melaleuca). Melaleuca trees were cut at 25-cm above ground, allowed to coppice for 6-wk, and the coppicing stumps were divided into four groups. Each group received one of the treatments: rust Puccinia psidii, insects (weevil), Oxyops vitiosa plus psyllid, Boreioglycaspis melaleucae, rust-insect combination, or none of the above (control). Treatments were replicated at three sites and the whole experiment was temporally repeated. The stump attributes in treatments were assessed for 2-year. Coppicing stump-mortality in 2-year was 60, 52, 32, and 18% for rust-insect, rust, insect, and control treatments, respectively. Both coppice height and twig-tip numbers in rust-insect combination treatments were less (P=0.05) compared to rust or insect alone and control. Three and 1.5-fold coppice-biomass reduction occurred in rust-insect and only rust or insect treatments, respectively. Leaf ratio in total coppice-biomass declined (P=0.05) by 52% in rust-insect compared to ca 27% in rust or insect treatments. These results show additive impacts of rust-insect combination treatment in melaleuca biocontrol activities.