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Journal American Rhododendron Society

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Volume 32, Number 2
Spring 1978

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Controlling Mosses and Liverworts
G. F. Ryan
Washington State University
Western Washington Research and Extension Center, Puyallup, Washington
From a paper given at the 1977 Breeders Roundtable in Eugene, Oregon

        Mosses and liverworts growing over the surface of pots, cans or seed flats are unsightly. They probably compete for nutrients and may exclude or limit light reaching small seedlings.
        Much of the research on control of moss in ornamentals involves one-year-old or older potted plants rather than very young seedlings in seed flats, which is the primary concern of rhododendron breeders. The published research reviewed here and the report of our work at Puyallup should be regarded only as a basis for trials with small seedlings, which may be more sensitive to chemical treatments than older container grown plants.
        Several fungicides have been used for controlling liverworts (Marchantia polymorpha in most cases). Thiram (trade names include Thiram, Tersan and Thylate) killed liverwort thalli at concentrations approximately five times as high as required for inhibition of spore germination (9, 10, 16). A second application to control surviving gemmae usually was necessary. Dodine acetate (Melprex, Cyprex) is another fungicide that was reported to be effective against Marchantia (6).
        A combination of the fungicide Manzeb (Dithane M45, Fore, Manzate 200) and the mitacide binapacryl (Morocide, Acricid) controlled the liverwort Sphaeocarpus terrestris in trials with various pot plants (20). In another test, binapacryl controlled Marchantia, but plant tolerance was poor (13). Azaleas, Camellias and Ericas were among the container grown plants involved.
Dichlorophen (Panacide, Preventol) is an algicide that killed liverworts without injury to the woody ornamentals on which it was used (2).
        Herbicides that have shown promise for liverwort control in containers include simazine (Princep), diuron (Karmex), chloroxuron (Tenoran) and chlorbromuron (Maloran) (4, 5, 7, 14, 16, 17). Some of these were reported to control mosses also (1, 17, 18). Plant injury varied with the species or cultivar tested, the rate and method of application, and the formulation used. Spraying down with water immediately after treatment reduced injury (5). Tenoran was better tolerated than Karmex or Maloran (5). Several herbaceous plants, including Aubretia, Iberis, Pachysandra and Phlox, were not seriously injured in one test with Tenoran at 1.8 and 3.6 Ib/A (14). A seedbed of Mollis azaleas was treated successfully with Tenoran in October in another case (17).
        Another chemical recently reported in Germany to be effective against algae, certain mosses, and liverworts is quinomid (Quinonamide) (8, 15). Ornamentals in the tests were tolerant except for some leaf flecking.
        Other chemicals that have been used for moss control with limited success include copper sulfate and potassium permanganate. Mercurous chloride (Calomel) was reported to be slow acting but persistent for moss control in bentgrass turf (19). Ferrous sulfate and ferrous ammonium sulfate are sold for moss control in turf, either as a separate treatment or as an additive in fertilizer. Most of these chemicals are reported to be ineffective against liver worts (10).
        Maneb (Manzate, Dithane M22), a fungicide related to Manzeb but without the zinc component, gave good control of silver moss (Bryum argenteum) and funaria (Funaria sp.) (3).
        Delegol (chlorinated a-phenyl p-cresol) is an antiseptic preparation that gave the best control of mosses in a trial of various antiseptic and fungicidal chemicals (11).
        Experiments were started at Puyallup in 1973 with some of the previously reported chemicals, and with herbicides available or potentially available for use in ornamentals. Chemicals screened in 1973 and 1974 included diphenamid (Dymid at 6 lb/A'; simazine at 1.5 and 3.0 lb/A; chloroxuron at 3 and 6 lb/A; ferrous ammonium sulfate at 2 and 4 lb/A; and pronamide (Kerb), alachlor (Lasso), nitralin (Planavin) and oxadiazon (Ronstar), all at 4 lb/A. The best control of moss with minimum plant injury in these tests was from Ronstar or Tenoran in combination with ferrous ammonium sulfate.
        An experiment to compare these treatments was started March 15, 1974, using four kinds of plants in a 50-50 peat-sand mix in 4-inch pots. The two herbicides were applied as granular formulations and ferrous ammonium sulfate also was applied dry. The rate of Tenoran was reduced to 2 lb/A because of some indication of slight injury in the preliminary tests. Three additional treatments were three rates of copper sulfate applied as drenches. One set of plants was fertilized with ammonium sulfate at a rate that would supply the same amount of nitrogen as the ferrous ammonium sulfate treatments. Another set was left with no treatment. Final evaluation of moss control was made the first week of June, and plant tops were cut off and weighed at that time to determine effects of treatments on growth as measured by fresh weight.
        Control of the established moss was 80 percent or better from Ronstar, combinations of ferrous ammonium sulfate with Ronstar or Tenoran, and from the highest rate of copper sulfate (Table 1). All treatments except ferrous ammonium sulfate prevented new growth of moss on most of the soil surface. No information was obtained on control of particular moss species. Leptobryum pyriforme, Polytrichum juniperum, and Funaria hygrometrica were species observed in the pots. Liverworts were not present in sufficient quantity to evaluate control.
        None of the treated plants made significantly less growth than the untreated plants (Table 2). No treatment that included ferrous ammonium sulfate resulted in significantly less growth than fertilizing with ammonium sulfate. However, the Ronstar plus ferrous ammonium sulfate treatment on Rosebud azalea did greatly increase growth, even though the fertilizer or ferrous ammonium sulfate alone did not. This suggested that the ferrous ammonium sulfate was having some effect other than acting as a source of nitrogen. Its effect did not appear to be from enhanced moss control (Table 1).

1All rates are given in terms of active ingredient.
Table 1. Moss control, 1974.
  
  Percent moss control
Treatment Established New
  
None 0c2 0 c
Ammonium sulfate1 0 c 77 a
Ferrous ammonium sulfate1 17 bc 33 b
Ronstar 4 lb/A + Fe ammonium sulfate 87 a 93 a
Ronstar 4 lb/A 90 a 93 a
Ronstar 6 lb/A 83 a 100 a
Tenoran 2 lb/A + Fe ammonium sulfate 80 a 90 a
Tenoran 2 lb/A 33 b 83 a
Copper sulfate 0.26 lb/ 100 sq ft 33 b 90 a
Copper sulfate 0.53 lb/ 100 sq ft 17 bc 100 a
Copper sulfate 1.06 lb/ 100 sq ft 83 a 100 a
1Ammonium sulfate at 0.67 1 b per 100 sq ft; ferrous ammonium sulfate at 2 lb per 100 sq ft.
2Means followed by the same letter are not significantly different at the 5% level. Data are from 3 replications.
  
      
Table 2. Effects of moss control treatments on plant growth, 1974.
Fresh weight of tops as percent of untreated plants
  
  Azalea Azalea Rhododendron Arborvitae
  Hinodegiri Rosebud Blue  
Treatment     Diamond  
  
None 100 bc2 100 b 100 e 100 bcd
Ammonium sulfate1 147 a 95 b 200 b 120 ab
Ferrous ammonium sulfate1 147 a 88 b 240 a 105 abcd
Ronstar 4 lb/A + Fe ammonium sulfate 126 ab 44 a 205 ab 115 abc
Ronstar 4 lb/A 97 bc 80 b 115 cde 95 cd
Ronstar 6 lb/A 85 c 78 b 145 c 100 bcd
Tenoran 2 Ib/A + Fe ammonium sulfate 150 a 84 b 220 ab 123 a
Tenoran 2 lb/A 118 ab 78 b 135 cd 95 cd
Copper sulfate 0.26 lb/ 100 sq ft 104 bc 84 b 120 cde 95 cd
Copper sulfate 0.53 lb/ 100 sq ft 106 bc 72 b 120 cde 88d
Copper sulfate 1.06 lb/ 100 sq ft 106 bc 86 b 105 de 98 cd
1Ammonium sulfate at 0.67 lb per 100 sq ft; ferrous ammonium sulfate at 2 lb per 100 sq ft.
2Means followed by the same letter are not significantly different at the 5% level. Data are from 3 replications of 4 plants of each species.

        An experiment was established in 1975 to further evaluate and elucidate the effects of Ronstar and Tenoran plus ferrous ammonium sulfate treatments. Treatments were applied February 24 to three kinds of one-year-old plants in 4-inch pots in the same peat-sand mix. As in 1974, all chemicals were applied in dry form except copper sulfate, which was applied as a drench.
        A chelated form of iron (Na Fe) was included in one treatment with Ronstar plus ammonium sulfate to supply the same amount of iron as in ferrous ammonium sulfate. Moss control was excellent from the Ronstar treatments (Table 3). Response of the ornamentals was similar to the previous year, except that Rosebud azalea did not show increased growth from Ronstar plus ferrous ammonium sulfate (Table 4). Growth of arborvitae was reduced by the combination of Ronstar, ammonium sulfate and Na Fe.

Table3. Moss control, 1975
Treatment Percent moss control2
  
Ammonium sulfate1 0 e3
Ferrous ammonium sulfate1 25 de
Ronstar 4 lb/A + ammonium sulfate 94 ab
Ronstar 4 lb/A + Fe ammonium sulfate 89 ab
Ronstar 4 lb/A + ammonium sulfate + NaFe 100 a
Tenoran 2 lb/A + ammonium sulfate 47 cd
Tenoran 2 lb/A + Fe ammonium sulfate 72 bc
Cu sulfate 0.53 lb/ 100 sq ft + Fe ammonium sulfate 83 ab
1Ammonium sulfate at 0.33 lb per 100 sq ft; ferrous ammonium sulfate at 1 lb per 100 sq ft. treatment
2Percent control based on amount of moss in ammonium sulfate expressed as zero control
3Means followed by the same letter are not significantly different at the 5% level. Data are based on 3 replications of 12 pots.
  
Table 4. Effects of moss control treatments on growth of plants, 1975
Fresh weight of tops as percent of ammonium sulfate treatment
  
  Rhododendron Azalea  
Treatment Bowbells Rosebud Arborvitae
Ammonium sulfate1 100 a2 100 a 100 ab
Ferrous ammonium sulfate1 108 a 100 a 99 ab
Ronstar 4 lb/A + ammonium sulfate 102 a 89 a 104 a
Ronstar 4 lb/A + Fe ammonium sulfate 107 a 93 a 101 ab
Ronstar 4 lb/A + ammonium sulfate + NaFe 87 a 88 a 84 c
Tenoran 2 lb/A + ammonium sulfate 107 a 88 a 97 ab
Tenoran 2 lb/A + Fe ammonium sulfate 98 a 85 a 91 bc
Cu sulfate 0.53 lb/ 100 sl ft + Fe ammonium sulfate 99 a 93 a 92 abc
1Ammonium sulfate at 0.33 lb per 100 sq. ft; ferrous ammonium sulfate at 1 lb per 100 sq ft
2Means followed by the same letter are not significantly different at the 5% level. Data based on 3 applications of 4 plants of each kind.

        Ronstar alone gave good moss control in 1974. Results in 1975 showed that when fertilized with ammonium sulfate, Ronstar treated plants grew as well as plants fertilized only. This treatment should be evaluated on small seedlings at a series of rates. A rate of 4 lb of active ingredient per acre would be 208 grams (7.3 oz) Ronstar 2113 (2% granule) per 100 sq ft. Ronstar is a relatively new herbicide that has shown much promise for weed control in container and field grown ornamentals, and its registration for that purpose is anticipated. Tenoran did not adversely affect plant growth, but moss control was not good at the 2 lb/A rate.
        The copper sulfate treatments at high rates were nearly as good as Ronstar, and may be worth further evaluating. Effects on small plants from repeated use of such large amounts of copper should be considered. The lowest rate used in 1974 (0.26 lb/ 100 sq ft) did not kill established moss but fairly well prevented new growth. Repeated use of low rates starting before moss appears might be effective.

Literature Cited
1. Anon., 1964, Netherlands, Jversl. Proefstn Bloem., Aalsmeer, 159 pp. Weed Abst. 14:1426.
2. Anon., 1974, Container grown nursery stock: liverwort control, Rept. Efford Exp. Hort. Sta., 1973, 165-167, Weed Abst. 25:1256.
3. Anon., 1975, German Federal Republic, Biologische Bundesanstalt fur Land - and Forstwirtschaft, 1974, 266 pp. Weed Abst. 25:2298.
4. Bovre, 0., and G. Noye, 1974, [Seedling weeds and Marchantia polymorpha in container crops.] Gartner Tidende, 90(24):359, Weed Abst. 25:167.
5. Caron, J. E. A. and J. Rijswijk, 1972, [Control of mosses in pot culture.] Jaar. Proefstn Boomkwek., Boskoop, 1971, 115-116.
6. Carter, A. R., 1969, Weeds and weed killers, (b) Chemical control of weeds in hardy nursery stock. [Paper at] Seminar: Conf. Paps. natn. Fmrs' Union natn. Conf. Exhib., Eastbourne. Weed Abst., 18:2641.
7. Carter, A. R., 1972, Weed control for container-grown ornamentals, Proc. 11 th Brit. Weed Cont. Conf., 635-640.
8. Hartz, P., and H. Schumacher, 1975, [Quinonamide - use against algae and moss in the glasshouse and field.] Mitteilungen aus der Biologischen Bundesanstalt fur Land - and Forstwirtschaft No. 165, 224, Weed Abst., 25:2718.
9. Henson, I. E., 1968, The liverwort, Marchantia polymorpha L., as a weed problem in horticulture; its extent and control, Tech. Rept. Agric. Res. Coun. Weed Res. Org. 10, 21 pp. Weed Abst. 17:2698.
10. Henson, I. E., 1972, The liverwort problem, Gardeners Chron., 171(21): 28-29, 31. Weed Abst. 21:2921.
11. Jansen, W., 1970, [The control of algae and mosses in ornamental plantings.] Erwerbsgartner 24:1429-31. Hort. Abst. 41:1650.
12. Kemperman, J. H. L., 1971, [Control of mosses in pot culture at Bratant.] Jaarb. Proefstn Boomkwek., Boskoop, 1970, 100-101.
13. Leiber, E., and F. Hahn, 1975, [The problem of controlling bryophytes in ornamental plant growing.] Gesund Pflanzen, 27(7):129132, Hort. Abst., 46:3452.
14. Rijswijk, R., and J. G. A. Caron, 1974, [Control of mosses in potted herbaceous plants.] Jaarb. Proefstn Boomkwek., Boskoop, 1971, 102.
15. Schietinger, R., 1975, [Algae and mosses - a report on their control.] Gesunde Pflanzen, 27(11): 231-234. Weed Abst. 25:2297. 
16. Van de Laar, H. J., 1964, [Chemical weed control]. Jaarb. Proefstn Boomkwek., Boskoop, 1963, 93-110.
17. Van de Laar, H. J., 1970, [Moss and grass control in Ericaceae.] Jaarb. Proefstn Boomkwek., Boskoop, 1969, 91-92.
18. Van de Laar, H. J., 1971, [Control of mosses in pot culture.] Jaarb. Proefstn Boomkwek., Boskoop, 1970, 97-98.
19. Woolhouse, A. R., 1973, Moss eradication trials. Jour. Sports Turf Res. Inst., 1972, 48:102-107. Weed Abst. 22:1653.
20. Zittlau, W., 1975, [Liverwort can be controlled.] Deutsche Gartnerborse 75(22):421433. Weed Abst. 25:3338.


Volume 32, Number 2
Spring 1978

DLA Ejournal Home | QBARS Home | Table of Contents for this issue | Search JARS and other ejournals