Postemergence Liverwort Control in Greenhouse and Nursery Crops

This report describes research on postemergence control of liverwort. For more information on preemergence liverwort control, see another page on this site that addresses that issue (click here).

Liverwort (Marchantia polymorpha) is one of the most difficult to control weeds in nursery production. Liverwort thrive in low light, high humidity, high nutrition, and moist substrates. Liverwort are primitive plants that lack a vascular system. They are more closely related to ferns and mosses than more common seed-bearing plants. Liverwort spread sexually by spores and asexually by splashing gemmae. Spores are microscopic and airborne, and thus are impossible to exclude from propagation areas. Gemmae are small asexually produced clonal fragments that accumulate in specialized structures on liverwort thalli (leaves) called gemmae cups. Gemmae allow liverwort colonies to spread quickly from a single plant.

This research evaluated three products for postemergence liverwort control including quinoclamine (Mogeton), TerraCyte, and flumioxazin (Broadstar).

Quinoclamine is an algaecide used for algae and moss control in rice paddies (in Japan). The Crompton Uniroyal Company is evaluating the market potential of labeling the product for indoor greenhouse and nursery production in the U.S. and Canada.

TerraCyte is a granular form of sodium carbonate peroxyhydrate. Upon contact with water, it breaks down into sodium carbonate and hydrogen peroxide. Hydrogen peroxide oxidizes cell membranes of some organisms, thus killing them. It is currently labeled for greenhouse and nursery crops as an algaecide and fungicide. It helps prevent liverwort, moss, and algae infestations by killing spores of these organisms. It has demonstrated postemergence activity on liverwort in several pilot studies (data not published).

Flumioxazin is a new herbicide labeled for field and container nursery crops (not in closed structures) under the names Broadstar and SureGuard. It is similar to Goal in its activity, mode of action, and crop tolerances. However, unlike Goal, it is available as a granular herbicide. Although Goal is a component of several granular herbicides, the concentration in those products was not high enough to provide postemergence liverwort control in pilot studies (data not presented). Preemergence herbicides are not labeled for indoor use, and are thus flumioxazin is not an option for liverwort control in hoop-houses, poly-covered houses, greenhouses, etc.

The objective of this research was to compare efficacy of quinoclamine, Terracyte, and flumioxazin for postemergence liverwort control.


THE EXPERIMENTS

Three experiments were conducted at the Oregon State University North Willamette Research and Extension Center. Sprayable herbicides were applied with a CO2 backpack sprayer at a pressure of 35 psi and calibrated to deliver 100 gal/A. Granular herbicides were applied with a hand-held shaker. In all experiments, plants were grown under a retractable roof greenhouse, with the roof open at all times. Plants were irrigated overhead with ½ inch of irrigation daily, split in two equal cycles.

View the results of each individual experiment by clicking on the link below.

Experiment 1. Phytotoxicity of herbicides on ornamental plants.

Experiment 2. Efficacy of herbicides on minor liverwort infestations.

Experiment 3. Efficacy of herbicides on heavy liverwort infestations.


DISCUSSION

Liverwort control with quinoclamine is more effective when the level of infestation is still small. As evident by the results of Experiment 2 and 3, smaller liverwort populations are controlled more effectively and for a longer period of time with lower rates.

Control of mature liverwort (from left to right) using quinoclamine at 1, 2, or 4 oz./gal, then a non-treated control.
Currently, it is speculated that Crompton Uniroyal will label the product for rates between 1 and 2 oz./gal. The 4 oz. rate used in these studies was only to be sure the product is safe (even if over-applied) when sprayed on ornamentals.

Quinoclamine provides excellent postemergence liverwort control with no detrimental effects on the ornamentals tested. Further studies are necessary to determine tolerance of cuttings without roots, plants from tissue culture, and lower plant types (ferns, for example). It is also not certain if the product provides residual or preemergence liverwort control.

Traditional weed control in container production relies heavily on preemergence herbicides applied prior to weed emergence. Preemergence herbicides are not likely to be labeled for use in closed structures. However, periodic applications of quinoclamine can be used to kill liverwort as they reach a level of minor infestation.

Integrated pest management (IPM) uses the concept of economic thresholds to govern pesticide applications. That is, under an IPM system, growers wait until a pest reaches a certain level before treating. Because preemergence herbicides have to be applied prior to weed emergence, and postemergence herbicides cannot be used in containers, IPM has limited application in container weed control programs. Killing liverwort with spray-applied quinoclamine once it reaches an economic threshold will be a powerful tool for container managers.

Cropmton Uniroyal is currently seeking a label for quinoclamine to be used in closed structures, sprayed directly over the top of actively growing ornamental plants.


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