EDITOR'S

RESEARCH PAPER 39 MARCH 1961

FILE COPY

CHEMICAL CONTROL o f BRUSH

WALTER %D!AHMS

PACIFIC NORTHMTEST FOREST AND RANGE EXPERIMENT STATION FOREST SERVICE

U. S. DEPT OF AGRICULTURE

.

R e s e a r c h P a p e r 39

CHEMICAL CONTROL O F BRUSH IN PONDEROSA PINE FORESTS O F CENTRAL OREGON

by Walter G. Dahms

M a r c h 1961

PACIFIC NORTHWEST FOREST AND RANGE EXPERIMENT STATION R. W. Cowlin, Director P o r t l a n d , Oregon FOREST SERVICE

U. S. DEPARTMENT O F AGRICULTURE

CONTENTS Page INTRODUCTION

. . . . . . . . . . . . . . . . . . . . . . . .

EARLY STUDIES

. . . . . . . . . . . . . . . . . . . . . .

R E C E N T STUDIES

:

1

.

. . . . . . . . . . . . . . . . . . . . . . .

Methods

. . . . . . . . . . . . . . . . . . . . . . . . . .

Results

. . . . . . . . . . . . . . . . . . . . . . . . . .

P i n e Manzanita

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Golden Chinkapin

. . . . . . . . . . . . . . . . . .

13

. . . . . . . . . . . . . . . . . . . .

13

Snowbrush Ceanothus Ponderosa Pine

APPLICATION O F RESULTS

. . . . . . . . . . . . . . . . . .

COMMON AND CHEMICAL NAMES O F HERBICIDES MENTIONED

16

. . . . .

INTRODUCTION The m a n y a c r e s of f o r e s t land that a r e occupied by b r u s h in c e n t r a l Oregon r e p r e s e n t a l a r g e - s c a l e waste of timber-growing capacity and a m a j o r economic l o s s to the a r e a . Although l a r g e brushfields devoid of t r e e growth p r e s e n t the m o s t spectacular examples of l o s s , l e s s obvious but equally important b r u s h probl e m s a r e common in established t i m b e r stands. B r u s h frequently overtops and s u p p r e s s e s young seedlings f o r long periods of time in s m a l l n a t u r a l f o r e s t openings and competes with t r e e s of a l l s i z e s f o r soil m o i s t u r e . The t h r e e m o s t common b r u s h s p e c i e s in c e n t r a l Oregon a r e pine m a n z a nita (Arctostaphylos parryana v a r . pinetorurn), snowbrush ceanothus (Ceanothus velutinus), and golden chinkapin (Castanopsis chrysophylla). Manzanita, the m o s t light demanding of the t h r e e , i s usually the m a j o r species in l a r g e brushfields. It a l s o o c c u r s frequently in s m a l l openings of i r r e g u l a r l y stocked f o r e s t s o r a s a n u n d e r s t o r y beneath s p a r s e l y stocked ponderosa pine (Pinus ponderosa) stands (fig. 1). Manzanita o f f e r s e s ecially s e v e r e comp e t i t i o n i to young pine seedlings (fig. 2) and m a y delay regeneration of s m a l l openings o r s p a r s e l y stocked stands f o r many y e a r s .

P

Figure 1. - Understocked old-growth pomderosa pine with manzanita understorg.

Dahms, Walter G. The effect of manzanita and snowbrush competition on ponderosa pine reproduction. U. S. F o r e s t Serv. P a c . NW. F o r e s t & Range Expt. Sta. Res. Note 65, 3 pp. 1950. ( P r o c e s s e d . )

Figure 2. - Suppressed ponde~osa pine growing very slowlly beneath manxanita. 2, 4, 5 - T can be used to release such seedlings from overtoppiing m n xanita without serious damage to trees.

Snowbrush, intermediate in shade tolerance between manzanita and chinkapin, i s often a s s o c i a t e d with manzanita in open situations but i s a l s o able to grow a s a n u n d e r s t o r y shrub beneath well-stocked pine stands. Consequently i t probably competes with the pines in a n important way f o r s o i l m o i s t u r e . In managed stands, i t m a y b e n e c e s s a r y to u s e d i r e c t b r u s h control if t r e e s a r e to be grown a t the low stand densities r e q u i r e d f o r f a s t individual t r e e growth. Chinkapin i s usually found in the m o r e m o i s t p a r t s of the ponderosa pine zone, especially on north slopes o r a t higher elevations. A high tolerance f o r shade and a n ability to grow in a n u n d e r s t o r y position indicate chinkapin probably i s a n a g g r e s s i v e competitor f o r s o i l m o i s t u r e . Manzanita does not sprout following death of a e r i a l p a r t s , but snowbrush and chinkapin do. Snowbrush s p r o u t s have overtaken and crowded out t r e e s planted following a burn. Chinkapin s p r o u t s a l s o grow rapidly and probably have the potential to overtake and crowd out planted t r e e s . C e n t r a l Oregon f o r e s t m a n a g e r s need b r u s h control to accomplish the following objectives : 1.

P r e p a r e brushfields f o r planting o r seeding.

2.

R e l e a s e existing t r e e s f r o m overtopping b r u s h .

3.

Eliminate understory b r u s h where i t competes with t r e e s f o r s o i l moisture.

P u r p o s e of this paper i s to b r i e f l y s u m m a r i z e r e s u l t s of e a r l i e r (1953 and 1954) chemical b r u s h control studies which have a l r e a d y been reported?/ and to m o r e completely d e s c r i b e findings f r o m m o r e r e c e n t (1955 and 1956) experiments.

EARLY STUDIES Chemical b r u s h control methods w e r e shown to be practical on c e n t r a l Oregon f o r e s t lands when a e r i a l spraying f i r s t proved to be successful in 1954. Manzanita was completely killed and a e r i a l p a r t s of snowbrush deadened. F u r t h e r m o r e , a few undamaged ponderosa pine t r e e s standing in 2,4-D-killed m a n z a nita a t the edge of a e r i a l s p r a y plots demonstrated that selective manzanita control (control without s e r i o u s damage to intermingled pine t r e e s ) was possible. Rates of 2 , 4 - ~ 3 /t r i e d f o r the initial a e r i a l application w e r e 1 , 2, and 3 per a c r e . The 1-pound r a t e proved to be completely effective on m a n zanita. Dead b r u s h in d r i f t a r e a s beyond plot boundaries suggested a l e s s e r r a t e probably would b e effective. A e r i a l p a r t s of snowbrush w e r e a l m o s t a l l killed by the 2-pound r a t e , but 1 pound killed only the tips of m o s t twigs and p a r t s of m o s t leaves. Spray volumes t r i e d in the 1954 a e r i a l s p r a y experiment included 3, 5, and 10 gallons p e r a c r e with a 2-pound-per-acre r a t e of 2 , 4 - D , and 10 gallons with the 1- and 3-pound r a t e . All t r e a t m e n t s w e r e completely effective on m a n zanita and no differences in effectiveness on snowbrush a s s o c i a t e d with s p r a y volume w e r e evident. The evidence suggests that a 3-gallon s p r a y volume would a l s o be s u c c e s s f u l on manzanita with a 1-pound r a t e but provides no conclusive proof. Small-scale t e s t s on chinkapin in 1953 and 1954 showed that a e r i a l p a r t s could be killed with either 2, 4-D o r 2, 4, 5- T applied a s a foliage s p r a y , but sprouting always followed. Rates t r i e d w e r e a s low a s 2 pounds p e r a c r e but no minimum effective r a t e was established. Because s p r a y was applied with a hand s p r a y e r , no minimum effective s p r a y volume f o r a e r i a l application was obtained.

Dahms, Walter G . Chemical b r u s h control on c e n t r a l Oregon pondero s a pine lands. U. S. F o r e s t Serv. P a c . NW. F o r e s t & Range Ekpt. Sta. R e s . Note 109, 5 pp. 1955. ( P r o c e s s e d . )

2/

Common and chemical n a m e s of herbicides mentioned in this r e p o r t a r e l i s t e d on the inside back c o v e r .

-41 Acid equivalent f o r the phenoxy herbicides 2,4-D, 2 , 4 , 5 - T , 2 - ( 2 , 4 - D P ) , and silvex.

d i s c u s s e d in this r e p o r t :

RECENT STUDIES

A new s e r i e s of experiments was installed in 1955 and 1956, with the f o l lowing objectives: 1.

To d e t e r m i n e i f manzanita, snowbrush, o r chinkapin could be controlled by b r o a d c a s t s p r a y applications without injury to intermingled ponderosa pine t r e e s (selective control) and to define suitable t r e a t ments.

2.

To determine if sprouting of snowbrush and chinkapin could either be eliminated o r g r e a t l y reduced by chemical t r e a t m e n t .

Studies to determine relative tolerance of ponde r o s a pine and manzanita to v a r i ous herbicides w e r e given special emphasis i n 1955 a s a n e s s e n t i a l s t e p in attaining objective 1. Methods 2 , 4 - D and 2 , 4 , 5-T w e r e the herbicides t e s t e d m o s t completely, but 2 - ( 2 , 4 - D P ) , silvex, a m i t r o l e , and trichlorobenzoic a c i d w e r e a l s o t r i e d . The phenoxy compounds ( 2 , 4 - D , 2 , 4 , 5- T, 2 - ( 2 , 4 - D P ) , and silvex) w e r e always used a s the P G B E ~e s~t e r s . The two c a r r i e r s t e s t e d w e r e water and oil-in-water emulsion. sion c a r r i e r contained 1 gallon of s u m m e r oi&l per a c r e .

The emul-

Herbicides w e r e applied to the b r u s h and t r e e s a s a foliage s p r a y with a hand s p r a y e r . T r e e s w e r e understory saplings growing in dense stands (fig. 3 ) . In m o s t c a s e s , a l l vegetation within a 1 / 1 0 0 - a c r e rectangular plot was s p r a y e d with a volume of 100 gallons per a c r e . Each t r e a t m e n t was repeated on two plots a t each date of application. A slightly different procedure was used on one snowbrush study because the plants w e r e too f a r a p a r t to cover a n e n t i r e 11100a c r e plot. In this c a s e , individual bushes w e r e sprayed a f t e r the a r e a occupied by each bush was m e a s u r e d and the amount of s p r a y adjusted according to a r e a occupied. Where individual plants w e r e t r e a t e d , s p r a y volume was r a i s e d to 150 gallons per a c r e . Percentage of b r u s h cover dead was the c r i t e r i o n used to r a t e effectiven e s s of b r u s h t r e a t m e n t s . It was estimated by m e a n s of 100 systematically located points on each plot. A plumb bob was dropped a t each of the 100 points,

Propylene glycol butyl e t h e r .

6'

A petroleum product of low toxicity to plants that readily goes into a n oil-in-water emulsion.

Figure 3. - A dense understory of ponderosa pine saplings typical of trees used to determine toleranae of ponderosa pine to herbicides.

and a t those locations where b r u s h was encountered i t was r a t e d a s dead o r live. Before percentage of b r u s h cover dead was adopted a s the c r i t e r i o n to be used, percentage of plants dead on each plot was t r i e d on manzanita plots. Results w e r e n e a r l y the s a m e r e g a r d l e s s of the c r i t e r i o n used. The standard used to r a t e tolerance of ponderosa pine to herbicide t r e a t m e n t s was percentage of t e r m i n a l buds o r l e a d e r s dead. Growth r a t e of ponderosa pine before and a f t e r t r e a t m e n t and number of y e a r s of growth killed w e r e m e a s u r e d on 19 t r e e s growing on two a e r i a l s p r a y plots that had received approximately 1 pound p e r a c r e of 2 , 4 - D in a n emulsion c a r r i e r . These plots w e r e t r e a t e d in 1954. Examinations w e r e generally made in the s u m m e r of the y e a r following t r e a t m e n t . Where t r e a t m e n t s had been applied in l a t e s u m m e r o r e a r l y fall, examinations w e r e delayed until the second s u m m e r a f t e r t r e a t m e n t . However, amount of sprout growth that would eventually develop could not always be gaged a t the end of the 1 - to 2-year period a f t e r t r e a t m e n t . The various t r e a t m e n t s applied to manzanita, chinkapin, snowbrush, and ponderosa pine a r e shown in tables 1 to 4.

Table 1.--Herbicide

t r e a t m e n t s a p p l i e d a s f o l i a g e sprays t o

p i n e manzanita, by d a t e of a p p l i c a t i o n , 1955

Date of a p p l i c a t i o n z l Chemical and carrier.L/

' :

May 6

:

May 27

:

July 5

:

Sept. 22

2,4-D: Water do do Emulsion do do 2,4,5-T: Water do do Emulsion do do

!I. Propylene g l y c o l b u t y l e t h e r e s t e r s of both chemicals were used; r a t e of a p p l i c a t i o n i s i n pounds ( a c i d e q u i v a l e n t ) p e r a c r e . The emulsion c a r r i e r cont a i n e d 1 g a l l o n of summer o i l p e r a c r e .

21

S t a g e of p l a n t development by d a t e :

May 6.

Few blossoms s t a r t i n g on manzanita; no o t h e r v i s i b l e s i g n of growth a c t i v i t y ; l a s t of snow had melted only a few days b e f o r e .

May 27. Manzanita blossoming n e a r l y over; ponderosa p i n e buds beginning t o e l o n g a t e ; b i t t e r b r u s h s t a r t i n g t o l e a f o u t ; no v i s i b l e snowbrush activity. J u l y 5. Manzanita blossoming complete and new f r u i t s formed; twig growth w e l l under way on most brush s p e c i e s ; ponderosa p i n e h e i g h t growth c o n t i n u i n g ; snowbrush s t i l l blossoming. Sept. 22. No v i s i b l e s i g n s o f growth on e i t h e r t r e e s o r shrubs; f i r s t l i g h t f a l l r a i n s had f a l l e n b u t t h e s o i l was s t i l l dry.

T a b l e 2.--Herbicide

treatments applied a s foliage sprays t o

g o l d e n c h i n k a p i n , by d a t e o f a p p l i c a t i o n , 1955 and 1956

Date o f a p p l i c a t i o & / Chemical and c a r r i e d . /

j

:

1955 J u n e 16

:

J u l y 15

:

S e p t . 29

:

.

195 6 ( J u l y 13)

2,4-D: Water do Emulsion do 2,4,5-T: Water do Emulsion do 2- ( 2 $4-DP) : Water do Emulsion do Silvex: Water do Emulsion do 2,3,6-TBA (suspended a c i d ) : Water do

---

3.0 15.0

---

2,3,6-TBA (sodium s a l t ) : Water do Ami t r o l e : Water

L/ P r o p y l e n e g l y c o l b u t y l e t h e r e s t e r s o f t h e phenoxy h e r b i c i d e s 2 $4-D, 2 , 4 , 5 - T , 2-(2,4-DP) , and s i l v e x were used. Rate o f a p p l i c a t i o n o f a l l c h e m i c a l s i s i n pounds p e r a c r e ( a c i d e q u i v a l e n t f o r t h e phenoxy h e r b i c i d e s ) . The emulsion c a r r i e r c o n t a i n e d 1 g a l l o n o f summer o i l p e r a c r e .

-

3 /

L

I

S t a g e o f p l a n t development by d a t e :

J u n e 1 6 , 1955.

No a c t i v e growth e v i d e n t .

J u l y 1 5 , 1955.

New growth a b o u t h a l f complete on c h i n k a p i n and p r o c e e d i n g r a p i d l y ; snowbrush i n f u l l blossom and growing r a p i d l y .

S e p t . 29, 1955.

No v i s i b l e i n d i c a t i o n s o f a c t i v e growth.

J u l y 1 3 , 1956.

New c h i n k a p i n twig growth a b o u t h a l f complete; flower s t a l k s a p p r o a c h i n g f u l l l e n g t h b u t f l o w e r s n o t y e t open.

T a b l e 3.--Herbicide

treatments applied a s foliage sprays t o

snowbrush c e a n o t h u s , by d a t e o f a p p l i c a t i o n , 1955 and 1956

Date o f a p p l i c a t i o n z l Chemical and c a r r i e r -11

1955

:

J u n e 14

:

Aug. 2

:

S e p t . 28

: :

1956 ( J u l y 18)

2,4-D: Water do Emulsion do 2,4,5-T: Water do Emulsion do 2-(2,4-DP) : Emulsion L ' ~ r o p y l e n e g l y c o l b u t y l e t h e r e s t e r s o f a l l chemicals were used; r a t e o f a p p l i c a t i o n i s i n pounds ( a c i d e q u i v a l e n t ) p e r a c r e . The emulsion c a r r i e r cont a i n e d 1 g a l l o n of summer o i l p e r a c r e . 2 1 ~ t a g e o f p l a n t development, by d a t e : J u n e 1 4 , 1955.

F i r s t snowbrush twig growth s t a r t i n g .

August 2 , 1955.

A c t i v e growth n e a r l y complete.

S e p t . 28, 1955.

A l l v i s i b l e s i g n s of a c t i v e growth gone.

J u l y 1 8 , 1956.

Twig growth a c t i v e .

Table 4.--Herbicide treatments applied as foliage sprays to ponderosa pine, by date of application, 1955 and 1956 Date of applicatio& 1955

Chemical and carrierll

: May 5 : May

26

July 1 : Aug. 2

Sept. 29

: 1956 : (July 18)

.

2,4-D: Water do do Emulsion do do 2,4,5-T: Water do do Emulsion do do Silvex: Water do Emulsion 2-(2,4-DP) : Water do Emulsion do L/propylene glycol butyl ether esters of all chemicals were used; rate of application is in pounds (acid equivalent) per acre. The emulsion carrier contained 1 gallon of summer oil per acre. 2/stage of plant development, by date: May 5, 1955. Few blossoms starting on manzanita; no other visible sign of growth activity; last of snow melted only a few days before. May 26, 1955. Manzanita blossoming nearly over; ponderosa pine buds beginning to elongate; bitterbrush starting to leaf out; no visible snowbrush activity. July 1, 1955. Manzanita blossoming complete and new fruits formed; twig growth very active on most brush species; ponderosa pine height growth continuing; snowbrush still blossoming. Aug. 2, 1955. Height growth of ponderosa pine complete, Sept. 26, 1955. No visible signs of growth on either trees or shrubs; first light fall rains had fallen but the soil was still dry. July 18, 1956. Slow height growth continuing on ponderosa pine; manzanita and snowbrush still actively growing.

Results P i n e Manzanita Foliage s p r a y s of 2 , 4-D and 2, 4, 5- T w e r e found t o be highly and equally effective on manzanita when applied during the period f r o m e a r l y May to e a r l y July (fig. 4). R a t e s of application f o r both c h e m i c a l s a s low a s 0. 5 pound p e r a c r e i n a n emulsion c a r r i e r o r 0. 75 pound in a w a t e r c a r r i e r r e s u l t e d in a n aver-, a g e kill close to 80 p e r c e n t . Thus, approximately two-thirds a s m u c h c h e m i c a l i s r e q u i r e d with a n emulsion c a r r i e r a s with a w a t e r c a r r i e r to achieve a s p e c i f i e d d e g r e e of control. COVER DEAD 100 Percent

1

Figure 4 - Average percentage of manzanita cover killed b y 2, 4 - D and 4, 5 - T applied during the growing season (combined results fov M a y 6, May 27, and July 5 , 1955basis, 7 2 plots). The emulsion c a ~ r i e rcontairted 1 gallon of summer oil per acre.

.50

,75

RATE LEGEND:

1.00

.50 .75

( Pounds per acre

1.00

1

Water carrier Emulsion carrier

Susceptibility of manzanita t o both 2, 4 - D and 2 , 4, 5 - T r o s e gradually f r o m e a r l y May and r e a c h e d a high point in e a r l y July. By l a t e S e p t e m b e r , effectiven e s s of both c h e m i c a l s had fallen off g r e a t l y (fig. 5). Results f r o m a 1953 e x p e r i m e n t l / a t P r i n g l e F a l l s E x p e r i m e n t a l F o r e s t indicate that effectiveness of both

L1

Dahms, Walter G. Chemical b r u s h control on c e n t r a l Oregon pondero s a pine lands. U.S. F o r e s t S e r v . P a c . NW. F o r e s t & Range E x p t . Sta. R e s . Note 109, 5 pp. 1955. ( P r o c e s s e d . )

COVER DEAD

27 TH

6 TH

MAY

5 TH

JUNE

22 ND

JULY

AUGUST

SEPTEMBER

Figure 5 . - Percentage of manzanita cover killed by 2, 4 - D and 2, 4, 5 - T applied a t four d i f f e r e n t dates (basis: 64 plots). Results from 0.5- and 1-pound-per-acre r a t e s w m e averaged for each date. The emulsion carrier cowtained 1 gallon of m m m e r oil per a w e . herbicides had a l r e a d y begun t o fall off by July 31. Effectiveness of 2 , 4 , 5- T f e l l off even m o r e rapidly than did that of 2, 4-D a s the season advanced. The late September application of 2 , 4 , 5-T a t the 1-pound r a t e in emulsion c a r r i e r killed only 3 3 percent of the manzanita cover, compared with 66 percent killed by 2: 4-D. Differences in percentage of manzanita cover killed between the two c a r r i e r s and between the four dates of application w e r e statistically significant a t the 1 - p e r c e n t probabilitylevel. Differences between chemicals w e r e significant only f o r the l a t e September application, a t the 1 -percent level. Golden Chinkapin T e s t s on chinkapin showed that 2,4, 5- T was the m o s t effective chemical, that a n emulsion c a r r i e r was definitely s u p e r i o r to a water c a r r i e r , and that midJune t r e a t m e n t s produced a b e t t e r kill of a e r i a l p a r t s than late September applications (fig. 6)- The m i d - July 1956 t e s t f u r t h e r showed that the 0. 5-pound-pera c r e r a t e of 2 , 4 , 5 - T in a n emulsion c a r r i e r produced a complete top kill. Amit r o l e and trichlorobenzoic a c i d w e r e not effective. Differences between effectiveness of 2 , 4 , 5 - T , 2, 4-D, silvex, and 2 - ( 2 , 4 - D P ) a t the mid-June application w e r e significant a t the 1 - p e r c e n t Level. Difference in effectiveness between emulsion and water c a r r i e r s was significant a t the 5-percent level.

COVER DEAD

Emulsion carrier

Herbicide :

2,4,5-T

2,4-D SILVEX 2-(2,4-DP) June 16 treatments

2,4,5-T 2,4-D SILVEX September 29 treatments

Figure 6. - Average percentage of chinkapin cover killed b y four herbicides applied June 16 and September 29 a t the r a t e of 1.5 pounds per acre (basis: 24 plots). T h e emulsion carrier contained 1 gallon of summer oil per acre. T h e 2, 4 - D and silvex in water carrier8 and t h e 2- (2, 4 D P ) in either a water or a n emulsion carrier did v e r y little damage in t h e S e p t e m b m 29 treatments and conseqztently are not represented o n the chart.

-

Sprouts have developed on chinkapin plants t r e a t e d a t a n y time f r o m m i d June to-late September; e a r l i e r t r e a t m e n t s w e r e not t r i e d . Sprouts on chinkapin plots t r e a t e d in 1953 f o r m e d a solid cover and a v e r a g e d about 18 inches t a l l by the f a l l of 1960. F a l l t r e a t m e n t of chinkapin with 2, 4, 5-T in a n emulsion c a r r i e r m a y delay sprouting. No sprouts a p p e a r e d f o r 2 y e a r s following t r e a t m e n t in the f a l l of 1955, but numerous s m a l l s p r o u t s had appeared by the end of 1960. Effect of herbicides on c e n t r a l Oregon chinkapin i s quite different f r o m that on chinkapin found in southwestern Oregon. ~ r a t k o w s k i 8 1found that southw e s t e r n Oregon chinkapin was r e s i s t a n t to a l l herbicide t r e a t m e n t s tested. The r e a s o n f o r this difference i s not known.

8'

Gratkowski, H. Effects of herbicides on s o m e important b r u s h species in southwestern Oregon. U. S. F o r e s t Serv. P a c . N W . F o r e s t & Range Expt. Sta. Res. P a p e r 3 1 , 33 pp., i l l u s . 1959. ( P r o c e s s e d . )

Snowbrush

C eanothus

Information on effectiveness of h e r b i c i d e s applied to snowbrush i s l e s s complete than f o r the o t h e r two b r u s h s p e c i e s b e c a u s e a s e v e r e f r e e z e in Novemb e r 1955 d e s t r o y e d a n e x p e r i m e n t b e f o r e r e s u l t s could be fully evaluated. Availa b l e f a c t s come f r o m a 1954 a e r i a l spraying e x p e r i m e n t , f r o m intermingled snowb r u s h plants growing on the manzanita plots, and f r o m incomplete observations on the snowbrush e x p e r i m e n t p r i o r t o the f r e e z e . 2, 4, 5 - T was the m o s t effective c h e m i c a l t r i e d on snowbrush. 2 , 4 - D and 2-(2, 4-DP) w e r e a l s o effective but g r e a t e r amounts w e r e r e q u i r e d . Rates of 1 pound p e r a c r e of 2 , 4 , 5 - T and 1 . 5 pounds of 2 , 4 - D a r e adequate in a n emulsion c a r r i e r , but 1 . 5 pounds of 2, 4, 5 - T a r e r e q u i r e d i n a w a t e r c a r r i e r . The e f f e c tive r a t e f o r 2 , 4 - D i n w a t e r was not reached. One a n d one-half pounds of 2 - ( 2 , 4 - D P ) in a n emulsion c a r r i e r m a y a l s o be effective. T h e s e r a t e s a r e f o r foliage s p r a y s applied during the a c t i v e growing season. Snowbrush h a s s p r o u t e d vigorously following a l l chemical t r e a t m e n t s t r i e d s o f a r . Rate of s p r o u t growth i s i l l u s t r a t e d by data f r o m the 1954 a e r i a l s p r a y plots. B e f o r e the a r e a was s p r a y e d , snowbrush c o v e r e d 1 6 . 5 p e r c e n t of the ground. By the fall of 1956, snowbrush s p r o u t s covered 6 . 3 p e r c e n t of the a r e a and plants not killed back by spraying covered 1 . 0 p e r c e n t , Thus two a n d a half growing s e a s o n s a f t e r spraying, snowbrush covered n e a r l y half of the a r e a i t occupied b e f o r e spraying. Ponderosa Pine P o n d e r o s a pine can t o l e r a t e about twice a s m u c h 2 , 4 , 5 - T a s 2 , 4 - D a n d about twice a s m u c h of e i t h e r c h e m i c a l in a w a t e r c a r r i e r a s in a n emulsion c a r r i e r . T h e s e relationships a r e i l l u s t r a t e d b y t h e s i m i l a r amount of d a m a g e c a u s e d by 0.75 pound of 2, 4-D i n w a t e r , 0.75 pound of 2 , 4 , 5 - T i n a n emulsion c a r r i e r , a n d 1. 5 pounds of 2, 4, 5 - T i n w a t e r (fig. 7). T o l e r a n c e of ponderosa pine t o 2 , 4 - D and 2 , 4 , 5 - T v a r i e s with the s e a s o n . Of d a t e s t e s t e d , t r e e s w e r e m o s t damaged by e a r l y July t r e a t m e n t s a n d l e a s t damaged b y l a t e S e p t e m b e r t r e a t m e n t s (fig. 8). T e r m i n a l buds w e r e killed on only a few t r e e s following l a t e S e p t e m b e r application of 2, 4-D in a n emulsion c a r r i e r a t the r a t e of 1 pound p e r a c r e . No t e r m i n a l l e a d e r s w e r e killed by o t h e r treatments. Relative t o l e r a n c e of ponderosa pine t o f o u r common h e r b i c i d e s i s shown graphically i n f i g u r e 9. P o n d e r o s a pine i s m o s t susceptible to 2, 4-D and m o s t t o l e r a n t of 2-(2, 4-DP). T o l e r a n c e t o 2, 4, 5 - T a n d silvex i s i n t e r m e d i a t e . Differences i n percentage of t e r m i n a l buds killed between w a t e r a n d emulsion c a r r i e r s , between different t r e a t m e n t d a t e s , a n d between 2, 4-D a n d 2 , 4 , 5-T w e r e significant a t the 1 - p e r c e n t probability level. Differences i n n u m b e r of t e r m i n a l buds killed by 2, 4, 5 - T a n d silvex a n d by silvex a n d 2-(2, 4 - D P ) w e r e s i g nificant a t the 5 - p e r c e n t level.

TERMINAL BUDS DEAD 1

100 Percent

Figure 7. - Average percentage o f ponderosa pine t e r m i n a l bwls killed b y 2, 4 D and 2, 4, 5 - T applied during t h e growing season (combined results for M a y 5, M a y 26, and J u l y 1, 1955 basis, 72 plots). T h e emulsion carrier contained 1 gallon o f s u m m e r oil per acre.

-

R AT E LEGEND:

( Pounds per acre

1

Water carrier Emulsion carrier

TERMINAL BUDS DEAD

Emulsion carrier

Figure 8. - Combined average percentage of ponderosa pine terminal buds killed by 2, 4 - D and 2, 4, 5 - T applied a t t h e r a t e of 1 pound per acre a t four different dates (basis: 32 plots). T h e emulsion carrier contained 1 gallon o f s u m m e r oil per acre. September 29 treatments w i t h t h e w a t e r carrier killed n o terminal buds.

TERMINAL BUDS DEAD 100

Figure 9. - Percentage o f p n d e r o s a pine terminal buds killed by four herbicides applied July 1 in a w a t e r carrier (basis: 16 plots). R e s d t s f r o m 1- and 1.5pound-per-acre rates w e r e averaged.

-

80

60

~ r e n & / r e p o r t e d a s h a r p d r o p in susceptibility of Lake States conifers to 2 , 4 - D and 2 , 4 , 5 - T a s soon a s height growth ceased. Ponderosa pine t r e e s i n c e n t r a l Oregon apparently develop tolerance m o r e gradually. F o r example, 2, 4, 5-T a t the r a t e of 1 pound per a c r e in a n emulsion c a r r i e r killed the follofving percentages of t e r m i n a l buds a t each of five d a t e s : Date .of application

T e r m i n a l buds killed ( P e r cent)

May 5 May 26 June 30 August 2 September 26 T h e r e i s s o m e evidence that effective control of b r u s h without injury t o intermingled c o n i f e r s m a y a l s o depend on the particular formulation of 2, 4-D o r 2,4, 5-T used. ~ r ~ ~ i e r f,oE r example, / found that the butoxy ethanol e s t e r s of

9/

Arend, John L. Tolerance of conifers to foliage s p r a y s of 2 , 4 - D and 2, 4, 5-T in lower Michigan. U. S. F o r e s t Serv. Lake States F o r e s t Expt. Sta. Tech. Note 437, 2 pp. 1955. ( P r o c e s s e d . )

10'

Krygier, J a m e s T. Effect of herbicides on salrnonberry and on Sitka s p r u c e and w e s t e r n hemlock seedlings. 1960, (In preparation f o r publication. )

2 , 4 , 5 - T damaged s p r u c e and hemlock seedlings m o r e than the propylene glycol butyl e t h e r e s t e r s . Because the butoxy ethanol e s t e r s w e r e not m o r e effective on s a l m o n b e r r y , t h e r e was a l o s s in selectivity. Observations on 19 ponderosa pine t r e e s a e r i a l l y sprayed in 1954 demons t r a t e that this species h a s the ability to r e c o v e r rapidly following s e v e r e t e m p o r a r y damage f r o m 2 , 4 - D s p r a y s . In this c a s e , 2 , 4 - D had been applied in a n emulsion c a r r i e r a t the r a t e of 1 pound per a c r e during e a r l y July when ponderosa pine i s m o s t susceptible to herbicides. T e r m i n a l l e a d e r s w e r e killed by the s p r a y on 10 of the 19 t r e e s and some damage was done to a t l e a s t one side of the crown on 1 5 t r e e s . L e a d e r kill-back on those t r e e s that suffered this type of damage ranged f r o m 1 to 5 y e a r s ' g r o w t h a n d averaged 2 y e a r s 1 . Length of m a i n s t e m killed back ranged f r o m 0 . 5 to 1 . 8 feet and a v e r a g e d 0. 79 foot. Growth was a c c e l e r a t e d r a t h e r than reduced following 2, 4-D injury. Height growth of a l l 19 t r e e s a v e r a g e d 0.47 foot annually during the 2 y e a r s p r e ceding t r e a t m e n t and 0. 52 foot y e a r l y during the 2 y e a r s following t r e a t m e n t . Similarly, d i a m e t e r growth of 11 t r e e s (those l a r g e enough to be b o r e d ) averaged 0 . 1 8 inch per y e a r during the 2 y e a r s b e f o r e spraying and 0 . 2 4 inch per y e a r during the 2 y e a r s a f t e r spraying. I n c r e a s e d growth s e e m s attributable to i n c r e a s e d soil m o i s t u r e and possibly to i n c r e a s e d s o i l nutrients m a d e available by elimination of b r u s h competition. ~ a r r a n t z has l shown that live b r u s h u s e s up available soil moisture dur ing the e a r l y p a r t of the growing season.

APPLICATION OF RESULTS Pine manzanita can be effectively controlled with either 2, 4 - D o r 2, 4, 5-T a t the r a t e of 0 . 5 to 0.75 pound p e r a c r e in a n emulsion c a r r i e r o r 0 . 7 5 to 1 pound in a water c a r r i e r . Where manzanita brushfields do not contain i n t e r mingled ponderosa pines that need to be saved, 2 , 4 - D in a n emulsion c a r r i e r i s the cheapest effective t r e a t m e n t . Where intermingled pine t r e e s a r e p r e s e n t and should be saved, 2, 4, 5-T in water is the s a f e s t t r e a t m e n t . However, 2, 4, 5 - T in a n emulsion c a r r i e r a t a r a t e of 0. 5 pound per a c r e will cause only a s m a l l amount of t e m p o r a r y damage to ponderosa pine t r e e s and i s probably the b e s t treatment. Seasonal t r e n d s of susceptibility to herbicides a r e about the s a m e f o r both manzanita and ponderosa pine. F r o m l a t e May until m i d - July i s t h e r e f o r e

g l ~ a r r a n t ,Robert F. Soil m o i s t u r e conditions a f t e r chemically killing manzanita b r u s h i n c e n t r a l Oregon. U. S. F o r e s t Serv. P a c . NW. F o r e s t & Range Expt. Sta. R e s . Note 156, 4 pp. , i l l u s . 1957. ( P r o c e s s e d . )

recommended a s the b e s t t i m e f o r t r e a t m e n t because the m o s t effective b r u s h cont r o l i s obtained during this period. F o r golden chinkapin and snowbrush ceanothus the recommendations that follow should be considered tentative. F o r both s p e c i e s , 2, 4, 5- T i s the m o s t effective chemical tested. A e r i a l p a r t s of chinkapin can be killed with 2 , 4 , 5-T a t r a t e s a s low a s 0. 5 pound per a c r e in a n emulsion c a r r i e r during the active growing season, a r a t e ponderosa pine t r e e s can t o l e r a t e . Late-season applications a t a r a t e of 1 . 5 pounds per a c r e in a n emulsion c a r r i e r m a y delay sprouting. F u r t h e r m o r e , l a t e - s e a s o n t r e a t m e n t o f f e r s a g r e a t e r m a r g i n of safety f o r intermingled t r e e s . However, because of the limited experience with f a l l t r e a t m e n t s on this species t h e r e i s no certainty that a good kill of b r u s h will always r e s u l t . A e r i a l p a r t s of snowbrush can be killed with 2, 4,5-T a t the r a t e of 1 pound per a c r e in a n emulsion c a r r i e r o r 1 . 5 pounds p e r a c r e in a water c a r r i e r . The emulsion c a x r i e r i s the m o s t economical where t h e r e a r e no t r e e s to protect. Vigorous sprouting has followed a l l t r e a t m e n t s . B e s t prospects f o r treating snowb r u s h without s e r i o u s damage to intermingled pine t r e e s a p p e a r to be (1) u s e of 2, 4, 5-T with a w a t e r c a r r i e r o r ( 2 ) u s e of 2-(2, 4-DP) with a n emulsion c a r r i e r .

A total s p r a y volume of 5 gallons per a c r e f o r a e r i a l spraying with a n emulsion c a r r i e r a p p e a r s to be a safe amount f o r a v e r a g e c e n t r a l Oregon conditions. F u r t h e r t r i a l s m a y show that considerably l e s s e r s p r a y volumes will b e s u c c e s s f u l , especially on manzanita, a v e r y sensitive s p e c i e s .

C o m m o n and Chamic~liPTAnnnrr of Hcrbicidar Mentioned

2, 4 - D

2,4-dicklorophenax)rrrceMckcid

2 , 4 , 5-T

2 , 4 , 5 - t r i c h l o r ~ p h e n w ~ c d bacid ic

2-(2,4-DP)

2 - [ 2 , A-dichloropksnoxy) propionic acid

Silvex

2- [ 2 , 4 , 5 - trichlorophenoxy) propionic acid

Amitrole

3-amino-l,2,4-trknole

2,3,6-TBA

A mixture of 6 i n o m e r a

af txickdox&nnxaic a c i d