The effects of selected pre-emergence herbicides on the germination, survival, health and germinant morphology of Sitka spruce (Picea sitchensis (Bong.) Carr.).

Abstract

The effects of five pre-emergence herbicides, diphenamid, oxyfluorfen, napropamide, isoxaben and oxadiazon, on the germination of Sitka spruce (Picea sitchensis (Bong.) Carr.) seeds over a 6 week period when sown under grit or soil were investigated. The main objective was to find a herbicide that could be used as an alternative to diphenamid, the principal pre-emergence herbicide used in Irish nurseries. The number of surviving seedlings was determined at the end of the test, 2 weeks later, after all germination was complete. The results under soil and grit were consistent, although as expected, seeds germinated more slowly and final germination was lower under soil. Only the results from the grits are reported. Diphenamid and oxyfluorfen had little detrimental effect on the speed of germination and final (cumulative) germination of seeds, and the survival of germinants. Final germination (approximately 80%) and survival (approximately 90%) were almost the same as in the control. Morphological development and health scores, seedling height, root length and seedling dry weights also differed little from the control. Germination and survival were a little lower in those treated with napropamide (74% and 80% respectively), and the seedlings were healthy. Shoot growth, and to a greater extent, root growth, were however adversely affected by this treatment. Germinants in this treatment also had lower dry weights than in those from the control, diphenamid and oxyfluorfen treatments. Germination and all other variables were very poor in those treated with isoxaben and oxadiazon. In all cases, the herbicides tested had no effect on mycorrhizal associations in germinants.