Date: January 2002

Liverwort and Pearlwort Management

Many of you have growers who are trying to control the primitive plant called Liverwort . . . what you have is probably Marchantia polymorpha. In regularly moist areas, particularly in propagation, this weed can become a real problem.

(Please note that I referred to this plant as a weed. Joe Neal is the weed management specialist and all I am doing is providing you with some information . . . I do not have definitive answers on this one. If there is an expert in NC for this problem, it is Joe.)

There is a website for Liverwort and Pearlwort management that has been very active recently. A lot of experience sharing has taken place. If you would like to be part of this listerserve, contact Sven Svenson at Oregon State.

Sven's Svenson is at Oregon State University. He posted information that read: most recent (1/10/02) posting said that "The thallus of the Marchantia has started growing again here at the NWREC (January 10, 2002). This growth response may be in response to the daylengths starting to get longer.

As a rule, use only products with proper labels for your crops, and follow and comply with all label instructions.

For deciduous perennials and container-grown shade trees, this is a good time of year to use products like CinnaMite, CinnaCure, Safers insecticidal Soap, TerraCyte, Timsen, Physan, Phyton-27, nearly any sanitizing product, and the various home-brews that folks use like acetic acid (vinegar - there are products with correct labels). With no green leaves on the plants, there is very little to no risk of phytotoxicity from the use of these products at label rates. At this time of year, the higher rates can be very effective on Marchantia populations. We have had good success with bacterial hand soaps containing the active ingredient Triclosan at this time of year. There can be a certain satisfaction in seeing the green thallus turn black! Perhaps your deciduous crop needs a soapy bath?

It is VERY IMPORTANT to get rid of all the Marchantia before April. In May and June, the Marchantia will start to produce its fruiting bodies (call them flowers if you like...but they are more like mushrooms than flowers). Once the Marchantia is in the fruiting stage, it seems to be more resistant to chemical controls. Thus, it is important to get eradication completed before 'flowering.' This strategy is the same for many other weeds. Also, the 'sporocarps' or flowers release more spores that will simply re-infect your crops, so it is important to eradicate the weed before it can propagate itself by air-borne spores. Finally, there are fewer gemmae cups on the plant at this time of it is less likely to be spreading itself by splashed gemmae. If your plants are under solid cover for the winter, there should be little or no raindrops or irrigation water drops available to splash gemmae around. Thus, this is the time of year when the Marchantia life cycle is most susceptible to control.

Don't forget to cruise your driveways, walkways, landscaped areas and property perimeters. Eradicate the Marchantia when and where you see it.

To help eradicate Marchantia from your crops, be very persistent about control from January through April. Then, the only way you will get infested is by the wind blowing-in more spores, or if you purchase-in plants that are infested.

Consider the growing media and fertilization practices you will be using as you pot-up plants this spring. Can you make any adjustments to help discourage Marchantia growth? What preemergent herbicides can you use on your plants? Do any of these have any activity on Marchantia? How soon after potting can you apply the herbicide?

Its 'hunting season' for Marchantia polymorpha. Enjoy!"

Sven is in Oregon. Conditions differ there. Labelling of chemicals may differ here. Please be sure to read the label before making any recommendations.

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