Effects of Bifenox, DCPA, and 

 Napropamide on 

 Ectomycorrhizal Development 

 of Conifer Seedlings in Central 

 and Northern Rocky Mountain 

 Nurseries 



Alan E. Harvey 

 Russell A. Ryker 

 Martin F. Jurgensen 



INTRODUCTION 



Herbaceous weeds are a major problem in Central and 

 Northern Rocky Mountain forest tree nurseries. Weed 

 competition, when uncontrolled, seriously reduces 

 survival and growth of tree seedlings. Weed control 

 practices most often used are fumigation and costly 

 hand or mechanical removal. Hand or mechanical weed- 

 ing is slow, often unsatisfactory, and increasingly expen- 

 sive. Soil fumigation is highly effective in reducing the 

 number of viable seeds in the soil but does not prevent 

 reinvasion from neeirby areas. Thus, herbicides are 

 attractive as an economical means of reducing weed 

 competition. 



Several years of testing pregermination and early post- 

 germination herbicides have shown that several may be 

 useful for weed control in Central and Northern Rocky 

 Mountain nurseries (Ryker 1981). Among these, the 

 herbicides Bifenox (Mobil trade name Modown) [methyl 

 5-(2,4-dichlorophenoxy)-2-nitrobenzoate], DCPA (Diamond 

 Shamrock trade name Dacthal) [dimethyltetrachloro- 

 terepthalate], and Napropamide (Stauffer trade name 

 Devrinol) [2-(Q:-naphthoxyl)-N, N-diethylpropionamide] 

 have the potential to reduce hand weeding time by 75 to 

 95 percent, depending on weed density (Ryker 1981). 



Good ectomycorrhizal development is closely related to 

 the ability of conifer seedlings to grow in nursery soils 

 (Trappe and Strand 1969), to survive on harsh sites 

 (Marx 1976), and to successfully afforest or reforest soils 

 lacking in ectomycorrhizal inoculum (Meyer 1973). Some 

 herbicides are reported to reduce growth or development 

 of ectomycorrhizal fungi (Iloba 1974, 1976; Dasilva and 

 others 1977) and to reduce populations of other soil 

 microorganisms (Greaves and others 1976; Ogawa and 

 Yambe 1980). It is possible that herbicides may reduce 

 ectomycorrhizal development on seedhngs in treated 

 nurseries, thereby reducing seedling quality. Information 

 on the effects of the above-named three herbicides on 



ectomycorrhizal development of seedlings in nurseries is 

 lacking and is needed before the herbicides can be 

 approved. This report documents these effects in major 

 forest nurseries of the Central and Northern Rocky 

 Mountains. 



MATERIALS AND METHODS 

 Nursery Locations 



The nursery locations represented major conifer- 

 producing nurseries in the Central and Northern Rocky 

 Mountains. These included the U.S. Forest Service nurs- 

 eries at Coeur d'Alene, ID; Boise, ID (Lucky Peak); 

 Albuquerque, NM; Carbondale, CO (Mt. Sopris); the 

 Montana State Nursery at Missoula, MT; and the pri- 

 vately owned Mountain Home Nursery at DeBorgia, MT. 



Experimental Design 



The basic experimental design was a randomized block 

 that included the herbicide treatments listed in table 1, 

 and the following seedling species: Austrian pine {Pinus 

 nigra Arnold) (AP), blue spruce (Picea pungens Engelm.) 

 (BS), Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) 

 (DF), Engelmann spruce (Picea engelmannii Parry ex 

 Engelm.) (ES), grand fir (Abies grandis [Dougl. ex D. 

 Don] Lindl.) (GF), lodgepole pine (Pinus contorta Dougl. 

 ex Loud.) (LPP), ponderosa pine (Pinus ponderosa Dougl. 

 ex Laws.) (PP), and western larch (Larix occidentalis 

 Nutt.) (WL). Not all species were tested in all locations, 

 but only those normally produced at the respective nurs- 

 ery. The herbicide treatment/species combinations tested 

 at the respective nurseries are shown in tables 3, 4, and 

 5 in the results section. Each combination, including the 

 untreated control, was represented by three rephcate 

 plots. Statistical analysis included ANOVA and 

 Duncan's Multiple Range tests, considering treatment 

 effects and interactions only. 



1 



