S.E. Holmes and C. Anderson
SERG Project #1995/01 (1999)
The yellowheaded spruce sawfly, Pikonema alaskensis (Roh.) (YHSS), is considered to be the most serious insect threat to black spruce, Picea mariana (Mill.) BSP., plantations in central Newfoundland at this time. The YHSS is a defoliator of open-growing black spruce, and severe infestations have been found for a number of years, resulting in severely reduced growth. Registered control products available for use on the YHSS are limited in number, and no biological materials are registered for this insect. An experimental ground spray field trial was conducted to determine the efficacy of Neemix® 4.5, a botanical insecticide, on the YHSS at doses of 25 and 50 g/ha at a study area located in central Newfoundland approximately 27 km southeast of Grand Falls. Five plots with five trees each were established in each block. Sample times were established as before treatment (prespray sample) and after treatment (2, 5, 7, and 10 days). The defoliation assessment of branches in the field was based on a ranking scheme of 1 to 5. In order to test the accuracy of this five-point scheme, a ten-point scheme was devised to be used on photographs of the same branches. This study showed that Neemix® 4.5 is a systemic material that must be eaten to have an insecticidal effect on the YHSS. The effect on the insects was expressed between 2 and 5 days following application, making evidence of effectiveness difficult to interpret. For reasons of logistics and timing, no single traditional measure of efficacy showed dramatic control of the insect. A discernible effect was found using population reduction as a standard. A minor effect on current foliage for a short period only was found using defoliation as a measure. However, a non-traditional and inferential field measure of efficacy, frass production, as Neemix® acts primarily as an antifeedant, proved to be a valuable method of estimating product effectiveness. The use of sequential photographs of all sample branches proved valuable as a permanent record of insect damage. Differences in effectiveness normally related to dose levels were not evident in this field trial, although it can be cautiously concluded that the 25 g/ha dose in a ground application would reduce defoliation satisfactorily when applied at early instars of the YHSS. Neemix® 4.5 is an effective control agent for use against the YHSS and should be registered for application on spruce plantations.