PERFORMANCE OF GRANULAR COLLECTORS FOR CONTAINER PLANTS AND A COMPARISON OF THE INFLUENCE OF CANOPY TYPE ON PREEMERGENT HERBICIDE DEPOSITS

Preemergent herbicides are commonly used to manage weeds in nurseries that produce container-grown plants. Granular products are applied over the top of a canopy and must pass through the canopy to reach the substrate where weed control is needed. Little guidance is available on methods for measuring the distribution of clay herbicide granules reaching the surface of a container pot substrate. A study was conducted to evaluate three different types of collectors. A glass bottle, sunken in the substrate, provided the most efficient collection of granules released from 76 cm above the substrate surface. The bottle collectors were used to evaluate differences in deposits produced by an air-boom spreader in different sizes of butterfly bush (Buddleja davidii 'Pink Delight') and hydrangea (H. macrophylla 'Niko Blue') canopies. Plant species did not contribute to significant differences in mean collector deposits but did contribute to differences in the variation of deposits under the canopies. Canopy size was a significant factor contributing to differences in mean collector deposits. The variability in granule deposits on the substrate increased with increasing plant size thus increasing the potential for more variability in weed control.