Effect of grass species and sowing methods on Pyronota species (P. setosa and P. festiva: Scarabaeidae) in a traditional farm system

Abstract

Manuka beetles (Pyronota festiva and P. setosa) have become a serious and persistent pest on developed land on the West Coast of New Zealand. The broad spectrum insecticide diazinon has failed to adequately control this complex of insect pests and the resulting pest pressure is costing West Coast farmers about 15-20% in lost production on developed ground. High larval populations in pastures cause loss of seasonal production and deterioration of the pasture stand. Feeding activity on grass roots not only reduces dry matter production (affecting stocking rates and milk yields), but allows ingress of weeds, so that pastures require renewal much sooner than expected. Recent fieldwork has suggested that tall fescue (Festuca arundinacea) and chicory (Cichorium intybus) may have better ability to grow under the challenge of manuka beetle feeding, in comparison to perennial ryegrass (Lolium perenne) which is decimated by feeding pressure. The purpose of this research was to determine whether tall fescue and/ or chicory can tolerate manuka beetle feeding, establish well and persist in pastures. Several questions relating to the use of grass species, diazinon insecticide treatment and the effect of different sowing rates and methods were addressed in this project. Perennial ryegrass had a greater annual yield (15.2 t DM/ha), than tall fescue (12.6 t DM/ha) and chicory (12.5 t DM/ha) in 2011, from destructive cut measurements, although the difference in yield was not statistically significant in the first year of the trial. The 2012 season showed a significant difference between total dry matter production of the pasture species. The average total production yield for tall fescue was 15.2 t DM/ha, which was 15% greater than the average yield for perennial ryegrass, at 12.8 t DM/ha. These yields differed significantly from the 2011 destructive cuts, where perennial ryegrass yielded 17% more dry matter than tall fescue. The total dry matter production by destructive cut for chicory in 2012 (4.7 t DM/ha), was dramatically lower than the total production by destructive cut for chicory in the 2011 season (12.5 t DM/ha), total yield had reduced by 62%. In 2011 sowing method by cross drilling always averaged a significantly greater total dry matter yield (14.6 t DM/ha) than direct drilling (13.9 t DM/ha) for tall fescue and perennial ryegrass pastures. This was expected, because cross drilled pastures were sown with 14 kilograms of extra seed. In comparison, the 2012 destructive cuts of tall fescue and perennial ryegrass did not show any significant difference in dry matter yield between sowing methods. All pasture species and treatment of diazinon insecticide significantly affected manuka beetle larval numbers in both the 2011 and 2012 trials seasons. Tall fescue had an average of 281 larvae /m² and perennial ryegrass an average of 436 larvae /m² in 2011. In 2012 tall fescue averaged 276 larvae /m², chicory averaged 338 larvae /m² and perennial ryegrass averaged 445 larvae /m². Perennial ryegrass pastures exhibited the largest response to diazinon insecticide with larval numbers decreasing by an average of 350 larvae /m² in 2011 and 2012. Tall fescue is slow establishing, but the dry matter production yield increases in year 2. Careful grazing management is required for tall fescue in year 1. Perennial ryegrass is quick to establish, but yield decreases significantly in year 2 due to larval feeding pressure. Chicory is not recommended: chicory’s almost nil growth patterns over winter is also the time manuka beetle larvae are doing the most damage whilst feeding on plant roots.