Submitted to: International Plant Propagators Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/15/2005
Publication Date: 2/1/2006
Citation: Richardson, B.M., Gilliam, C.H., Wehtje, G.R., Fain, G.B. 2006. Pinebark mini-nuggets provide effective weed control in nursery crops grown in large containers. International Plant Propagators Proceedings 55:561-566. Interpretive Summary: The market for large plants is increasing steadily; however, weed control in large containers present new production problems for growers. Preemergence herbicides are inefficient in large containers due to non-target loss and hand weeding is expensive. Mulches can provide an alternative. Experiments were conducted to evaluate fresh pine bark nuggets for weed control in 7 gallon containers. Gardenia were seeded with oxalis and crapemyrtle with bittercress. Treatments consisted of mulch applied at 0, 1.5, 3.0 inches and seeded before or after mulch. A separate group of treatments were included similar to the above except that a granular preemergence herbicide was applied after mulch application. Growth of gardenia and crapemyrtle were similar regardless of mulch depth. Season long weed control was obtained in all treatments when mulch was applied at 3 inch depth.
Technical Abstract: The objective of this study was to evaluate fresh pine bark mini nuggets as a long term weed control in large container nursery crops. Crapemyrtle (Lagerstroemia x ‘Acoma’) were transplanted from trade gallon containers into 7 gallon containers September 27, 2004 and treated on October 8, 2004. All plants were potted to equal depths, approximately 3 inches below the top of the container. Three treatments consisted of broadcasting 25 bittercress (Cardamine) seed on each container substrate surface followed by application of pine bark mini-nugget mulch which was hand applied at 0, 1.5 and 3 inches deep respectively. Two other treatments consisted of first applying mulch at 1.5 and 3 inches, then broadcasting the bittercress seeds on top of the mulch. These same treatments were repeated except that a granular preemergence herbicide (Broadstar 0.25G at 150 lb product/A) was applied after all mulch and seed were present. In a similar study, gardenia (Gardenia jasminoides) were transplanted from trade gallon containers into 7 gallon containers on September 27, 2004. On September 30, 2004 the same treatments were applied to the gardenia except 25 oxalis (Oxalis stricta) seed were used per container. At 90 DAT and 180 DAT bittercress was growing vigorously in the no mulch, no herbicide containers. These containers averaged 48% and 100% coverage of container surface, respectively and 59.6 g of bittercress dry weight per container at 180 DAT. In comparison, no herbicide, 1.5 inches of mulch treatment with seeding after mulching, averaged 5% coverage at 90 DAT and increased to 44% coverage of container surface and 33.7 g per container at 180 DAT. All other treatments provided excellent bittercress control at 90 and 180 DAT. There were no weeds in the 3 inches of mulch at 300 DAT. At 90 and 180 DAT, oxalis coverage in the no mulch, no herbicide treatment averaged 18.5 and 35 % coverage of container surface, respectively. At 180 DAT shoot dry weight was 12.9 g per container. All other treatments resulted in minimal oxalis growth at 90 and 180 DAT. The combination of mulch plus herbicide provided complete oxalis control 180 DAT. General weed coverage at 300 DAT averaged 71% coverage per container for the no mulch, no herbicide, 56% coverage for no mulch, with herbicide and 24% for 1.5 inches of mulch, seeded before mulch with no herbicide. Results are similar for gardenia compared to crapemyrtle in that 3 inches of mulch provided excellent weed control. Crop growth for crapemyrtle and gardenia were not significantly different among treatments at 180 DAT. The process of applying this type of mulch could easily be mechanized by growers at potting. Fresh pine bark mini-nuggets mulch could virtually eliminate the use of herbicides and handweeding in production of nursery crops grown in large containers.