The 2011 ASHS Annual Conference

Weedy spurges (Euphorbia hyssopifolia, E. maculata, E. nutans and E. prostrata) are among the most difficult to control weeds in nursery containers in the desert southwest. Nursery managers complain that available granular herbicides are ineffective.  Dithiopyr,  trifluralin + isoxaben and trifluralin + isoxaben + oxyfluorfen were topdressed into one gallon nursery containers without a crop on 07 September 2010 at 150 and 200 lbs granular product./A; dimethanamid + pendimethalin was applied on the same date at 150 lbs. granular product/A only.  Chemical treatments were compared to an untreated control (UTC). Spurge control was compared in containers with a regular planting medium composed of 2 parts fine mulch, 2 parts volcanic cinder and one part coarse mulch to containers with regular planting medium plus a two inch coarse mulch topdress. Weekly spurge germinations were counted and percent of the container covered by spurge mat was calculated at 30 days after treatment (DAT) and 60 DAT. Data was analyzed using JMP 8.0.2. There was no improvement in spurge control applying the higher rate of dithiopyr, trifluralin + isoxaben or  trifluralin + isoxaben + oxyfluorfen. The addition of the coarse mulch topdress improved spurge control in trifluralin + isoxaben and trifluralin + isoxaben + oxyfluorfen. At 60 DAT, greatest control was achieved using dimethanamid + pendimethalin, although trifluralin + isoxaben + oxyfluorfen and dithopyr performed better than the UTC.