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Title: Parboiled rice hull mulch in containers reduces liverwort and bittercress growth

item Altland, James
item Krause, Charles

Submitted to: Journal of Environmental Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2014
Publication Date: 6/30/2014
Publication URL:
Citation: Altland, J.E., Krause, C.R. 2014. Parboiled rice hull mulch in containers reduces liverwort and bittercress growth. Journal of Environmental Horticulture. 32(2):59-63.

Interpretive Summary: Preemergence herbicides are the primary tool for controlling weeds in containers. However, preemergence herbicides cannot be used on all crops, nor are they labeled for use in enclosed structures. Alternatives are needed for managing weeds where preemergence herbicides are either not labeled or cannot be used with a wide margin of safety. In particular, there are needs for weed control alternatives in propagation, hoophouses and other enclosed structures, and herbaceous perennials and other sensitive crops. Data herein demonstrate that parboiled rice hulls applied at a depth of 1.3 to 2.5 cm (0.5 to 1.0 in) over the substrate surface prevented establishment of bittercress and liverwort from seeds or gemmae, respectively. Parboiled rice hulls at 0.6 cm (0.25 in) provided only marginal control. Parboiled rice hulls did not affect rose growth and development. Parboiled rice hulls are commercially available for horticultural use.

Technical Abstract: Use of preemergence herbicides for weed control is not always possible; some crops and many enclosed production sites are not labeled for herbicide applications. The objective of this research was to determine the utility of parboiled rice hull mulch for controlling two of the most common weeds in nursery crop production: bittercress (Cardamine flexuosa) and liverwort (Marchantia polymorpha). Two experiments were conducted to determine control of bittercress and liverwort with 0, 0.6, 1.3, or 2.5 cm (0, 0.25, 0.5, or 1.0 in) rice hull mulch applied to the surface of 15 cm (6 in) diameter pots on a greenhouse bench. In both experiments, one group of containers were potted each with a single rose (Rosa ‘Radrazz’) and another group was not potted (only substrate and rice hull mulch). Bittercress seed and liverwort gemmae were applied to the surface of the substrate or mulch. Rose response and weed growth were monitored for 8 weeks in both experiments. Substrate pH, rose foliar color, and rose growth were not affected in either experiment. Bittercress and liverwort establishment and subsequent growth decreased with increasing rice hull depth. Containers with 1.3 or 2.5 cm (0.5 or 1.0 in) rice hulls provided nearly 100% weed control. Rice hulls provided effective bittercress and liverwort control for 8 weeks with no adverse effects on roses.