ibeebitioh o p r o o t e r plahts i h the strawberry iPRA&ARIA SPP. ) BY CHEMICAL TREATMSHT By Robert P. Carlson AH ABSTRACT Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OP PHILOSOPHY Department of Horticulture 1952 Approved INHIBITION OP HJNKER PLANTS IN THE STRAWBERRY (ERAGARIA s p p .) b y c h e m i c a l t r e a t m e n t Many of the horticultural strawberry varieties have a tendency to produce a super-abundance of runner plants creating a need for thinning and spacing by manual methods. Inhibiting runner formation by chemical treatment seemed logical for the elimination of excess runner plants. Several strawberry varieties were treated under greenhouse and field conditiona with certain chemicals including dichloral urea* phenoxyethyl trichloroacetate, sodium 2,4-Dichlorophenoxyethyl sulfate, isopropyl N-phenylcarbamate, maleic hydrazide and 2,h-Dichlorophenoxyacetic acid. These materials were applied to the plants by various methods; spraying, leaf-emersion, drop-method, pouring and by soil applications; and at different concentrations ranging from 5 to 25 milli­ grams per plant and equivalent amounts in pounds per acre in the field. The strawberry runners were inhibited most when a certain chemical was applied twice at the time of runner initiation. Dichloral urea, phenoxyethyl trichloroacetate and 2,4-Dichlorophenoxyacetic acid were most effective in re­ ducing runner formation, whereas, isopropyl N-phenylcarbamate and maleic hydrazide were less effective depending on the concentration used. 2,4-Dichlorophenoxyethyl sulfate did not significantly inhibit any runners from plants either in the greenhouse or in the field. The percentage inhibition under greenhouse conditions ranged from 10 to 80 per cent depending on variety and concentration. In the field the percentage inhibition was greater. The chemicals that were effective in inhibiting runner formation were also effective in killing many of the germinating weed seeds, thus serving a dual pur­ pose in the field* IN H IBITIO N O F R U N N E R P L A N T S IN TH E S T R A W B E R R Y (F R A G A R IA S P P .) BY C H E M IC A L T R E A T M E N T By ROBERT FRITZ A CARLSON THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY D e p a r t m e n t of Horticulture 1952 ProQuest Number: 10008273 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest, ProQuest 10008273 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106- 1346 ACKNOW LEDGM ENTS T h e author wishes to express his sincere appreciation to Dr. C. L. H a m m e r for his generous help and guidance, to Dr. H. B. T u k e y for his valuable suggestions and criticisms of the re­ search and the manuscript, and to Dr. J. E. Moulton for his ad­ vice and helpfulness in obtaining plant materials. T h e author also wishes to express his sincere thanks to Dr. L. W . Mericle of the D e p a r t m e n t of B o t a n y and to D e a n C. R. M e g e e for their valuable guidance. TA BLE OF CONTENTS Page I N T R O D U C T I O N ........................................ 1 NORMAL 3 FACTORS RUNNER INFLUENCING MATERIALS AND RESULTS D E V E L O P M E N T ................... RUNNERPRODUCTION ... M E T H O D S .......................... ............................................... R u n n e r Inhibition U n d e r G r e e n h o u s e Conditions .. 5 9 15 15 Effect of C h e m i c a l s on Flowering and Plant G r o w t h ............................................. 27 Effect of C h e m i c a l s Applied to Strawberry Plants in the F i e l d ............... 36 D I S C U S S I O N ............................................. 42 SUMMARY ....................... 47 .................................. 51 AND LITERATURE CONCLUSIONS CITED IN T R O D U C T IO N T h e production of runners b y the strawberry plant (hybrids of Fra g a r i a virginiana, _F. chiloensis and IT. a n a n a s s a ) represents the vegetative phase of reproduction. The produc­ tion of too m a n y result in re­ runner plants by a variety m a y duced yield of fruit. Thus, the n u m b e r of runners m a y vary f r o m 2 or 3 to as m a n y as 20 or m o r e per plant, depending on the variety and on environmental conditions. It has been demonstrated with the Klondike and M i s s i o n ­ ary varieties that the m o t h e r plants will produce about 100 crates of fruit per acre m o r e than will the runner plants (18). M o r r o w has s h o w n that strawberry beds which are renovated m a y produce a large n u m b e r of runner plants, w hich are less productive than the m o t h e r plants (19). C o m m e r c i a l growers have indicated, also, that the m o t h e r plant m a y r e m a i n p r o d u c ­ tive for as long as 8 years. W a l d o observed that (1) allowing runner plants to develop reduces the fruit-producing capacity of the m o t h e r plants; (2) m o t h e r plants, if n o w c r o w d e d or devital­ ized by runner plants, are m o r e fruitful per plant than early- established runner plants; (3) the available water and m i n e r a l 2 nutrients in the soil are utilized m o r e effectively by relatively small n u m b e r s of plants per acre than b y larger n u m b e r s of plants; and (4) with fewer plants per acre there is less shading and greater photo synthetic activity per plant (27). Since the m o t h e r plants appear to be m o r e productive than runner plants, it would s e e m desirable to devise s o m e means for control of runner formation and plant set. In c o m ­ mer c i a l strawberry production, the n u m b e r of runner plants in a planting is often controlled by clipping of all runners except the first ones f o r m e d and by spacing these plants equidistant around the m o t h e r plant. This m e t h o d often results in an in­ crease in yield over the m a t t e d r o w s y s t e m of culture, in w h i c h plants are permitted to f o r m and establish themselves at ran­ dom. But the expense of clipping and spacing does not w arrant its use in m a n y cases. In w o r k with herbicides it had bee n observed that s o m e chemicals affected runner formation (4). With these factors in mind, the research p r o b l e m here reported w a s undertaken to test the influence of several chemical substances on the inhibi­ tion of runners. NORMAL The RUNNER DEVELOPMENT strawberry plant is capable of exogenously initiating buds w h i c h are modified b r a n c h structures of three types; r u nner— shoot, crown - s h o o t and flower-shoot. T h e s e buds occur in the axils of the leaves on the short s t e m of the well-developed plant, w h e r e a s leaf formation occurs at the ap e x of the s a m e stem. The sequence of occurrence of these different b r a n c h structures depends on the genetic constituion of the variety, and the environment. Accord­ ing to D a r r o w , the growing points of seedlings of horticultural va­ rieties first produce in that order (5). shoots, then runners, and then inflorescences, Spring-set strawberry plants in northern regions begin to produce runners in late M a y , or usually 3 to 4 w e e k s ter planting, following n e w leaf production and flowering. af­ Fruiting strawberry plants, on the other hand, usually produce runners af­ ter the fruit has b e e n harvested. duction varies m o r e T h e actual time of runner p r o ­ or less with the variety. New runners are p r o d u c e d over a considerable period f r o m late M a y into early September, depending o n the variety, w h e n the plants w e r e and the environment. set, T h e general growth cycle of strawberry plants in northern regions is s h o w n in the lower half of Figure 1. 4 U o CO UJ 1 - < 1 <0 z a : UJ X H X MATERIALS o z UJ X 1- z 1z < INHIBITING UJ _J CL >X X UJ X UJ RUNNER C S I 0> c 3 [2 £c v o £ < X H CO UJ X 1Ul o UJ UJ _l o U. o o 2E IZ H » < QC O Q X £ C o “3 J £. J '1 9--i ■- ;1 ' A f -: t- a ■> i Vj ■i- V 1 + * r *■ '■ t, + I JJL -r ■ ’ ** * r r 'I r*-- ■ . J--3 -r " £c. ■ C , V O. ;'i r K r <•> <* 4— - a. \ , f- -• "h < X '■.y\ * ■ 4~i; 0. 1t + A- " ^ J, t, > 4- o ^ s • > 4- o ■ K ,i ,r. X -Q 3 Li ^ ) vi 1' < X UJ z UJ o 4V4 \1 f-' F A C T O R S IN F L U E N C IN G R U N N E R P R O D U C T IO N R u n n e r s are p r o d u c e d in the sequence of the annual g r o w t h cycle of the strawberry plant, progressing in order f r o m to spring as follows: (1) leaf growth, flowering and fruiting; (2) runner initiation and runner development; tion and development; (Fig. 1). spring (3) crown - s h o o t f o r m a ­ (4) flower initiation; and (5) d o r m a n t phase T h e s e phases are not clear cut, and tend to overlap and v a r y a m o n g the horticultural varieties, an d with location of culture. This is the general situation with the strawberry plant, irrespective of age. H o w e v e r , if flowers are r e m o v e d f r o m plants the first year they are set, as is usually done in c o m ­ mercial plantings, runners are p r o d u c e d earlier. It has b e e n demonstrated that the roots of strawberry plants have a cyclic development, m o s t of t h e m showing m a x i m u m summer growth in late and fall, wh i c h bears a relationship to runner p r o d u c ­ tion (17). T h e general grow t h cycle m a y be modified by ex­ ternal conditions, such as daylength, temperature, moisture, and nutrient levels, and internal factors. The strawberry plant is classified as a short-day plant, the flowers initiating during S e p t e m b e r and October in the northern 6 latitude (22 and 26). Runners, on the other hand, are initiated during long days, as in July and August, in m o s t varieties (5). F o r example, a 20-hour photoperiodic cycle (10 hours light and 10 hours darkness) does not produce runners, but a 28-hour photoperiodic cycle (14 hours light and 14 hours darkness) will produce runners (10). T h e relation of daylength to runner production is affected b y temperature, especially at the extremes, w h i c h interfere with the metabolic activity of the plant (10). runners w e r e p r o d u c e d at 60 o In greenhouse tests, F. on a 14-hour and 16-hour light period, w h e r e a s at 55°, fewer runners w e r e f o r m e d under the same daylength (6). U n d e r controlled environmental conditions, H a r t m a n n found that flowers w e r e initiated under a long photoperiod (15 hours) at 60 o F., and that no runners w e r e f o r m e d under the s a m e photoperiod at 70° F. (11). T h e nutrient level also has an effect on runner p r o d u c ­ tion. Spring applications of nitrogen, alone or in combination with phosphoric acid or phosphoric acid and potash will increase runner production (15), depending on the condition of the plants at the time of the application. showing deficiency s y m p t o m s F o r example, a strawberry b e d may respond m o r e readily than 7 one exhibiting a vigorous condition. T h e use of irstarter solu­ tions11 with analysis of 0-52-34, 6-25-15 or 10-52-17 applied near the plant at the time of planting has b e e n found b y Re a t h (21) to produce earlier plant grow t h and earlier runner f o r m a ­ tion under both greenhouse and field conditions. Other workers, however, w e r e unable to increase the n u m b e r of runners with the addition of nitrogen alone, or with complete fertilizer, whereas stable m a n u r e alone, at the rate of 32 tons per acre, gave an increase in the n u m b e r of runners (15, 25). Moisture also has an effect on the n u m b e r of runners f o r m e d during a growing season. In studying the effects of ir­ rigation on runner production, it w a s found that with no irriga­ tion there w e r e f ewer plants per acre than with three irrigations (27). T h e limited soil moisture evidently w e a k e n e d the m o t h e r plants to the extent that they lost the p o w e r to produce as m a n y runners as the plants w h i c h received a m p l e moisture. Varieties of strawberries vary greatly in their ability to produce runners. Varieties such as Fairfax, Catskill, and Midland produce comparatively f e w runners, w h e r e a s varieties like Robinson, Dunlap, and B l a k e m o r e are active runner p r o ­ ducers. Differences in runner production are easily o b s e r v e d 8 in a planting of seedling strawberries w h e r e each plant is dif­ ferent genetically. M A T E R IA L S A N D M ETH O D S Since the introduction of a 2,4-Dichlorophenoxyacetic acid (2,4-D) in 1944 (9) as a herbicide and in 1947 as a material for control of w e e d s in strawberries (1), a great deal of data has b e e n reported on the influence of this material on the strawberry plant in general, but no specific data on its effects on runner formation (8, 20, 25). Accordingly, since 2,4-D is n o w widely used in strawberries, a study w a s m a d e material o n runner production. of the effect of this In the greenhouse 2,4— D w a s used at a range of concentrations of 2.5, 5.0, 7.5, 10.0 and 12.5 milligrams per plant, and in the field at 0.5, 1.0, and 2.0 pounds per a c r e / In the greenhouse each plant w a s plotted in 1-gallon tin cans. All rates of the chemical materials reported in this paper are based on the active ingredients in the c o m p ound: 2,4-D, a m i n e salt containing 40 per cent 2,4-Dichlorophenoxy— acetic acid equivalent; IPC, a wettable p o w d e r containing 50 per cent isopropyl N-phenylcarbamate; E H — 1, s o d i u m salt containing 92 per cent 2,4-Dichlorophenoyethyl sulfate; D C U containing 73 per cent dichloral urea and 24 per cent clay diluent and 3 per cent wetting agent; P E - T C A , containing 60 per cent phenoxyethyl trichloroacetate and the remaining percentage a carrier and wetting agent and M H , diethanolamine salt containing 30 per cent maleic hydrazide. Isopropyl N - p h e n y l c a r b a m a t e (IPC) w a s first reported in 1949 as being effective in controlling c o m m o n chickweed (Stellaria media) in strawberry plantings without any serious effe on either the plant or the yield (2, 3). In detailed studies with ethyl p h e n y l c a r b a m a t e , it has bee n s h o w n that the growth of the apical m e r i s t e m s of plants is inhibited, and that nuclei in the metaphase, anaphase and telophase are affected (12). A later report in 1951 gave s o m e indications that repeated appli­ cation of I P C affected runner production (4). This material w a s used at the rates of 5, 10, 15, 20 and 25 milligrams per plant in the greenhouse, and 5, 10 and 15 pounds per acre in the field. T h e material, 2,4-Dichlorophenoxyethyl sulfate (EH-1), which is n o w r e c o m m e n d e d as a herbicide in strawberries, w a s used in s o m e of the detailed studies (4, 13 and 14). This m a ­ terial is not active chemically to a great extent on green plant foliage, but w h e n in contact with the soil solution, it is con­ verted into a f o r m which b e c o m e s active. This material w a s used at 5.0, 10.0, 15.0, 20.0 and 25.0 milligrams per plant in the greenhouse, and 2, 3 and 4 pounds per acre in the field. 11 Dichloral urea ( D C U ) w a s found in preliminary studies to have p r o m i s e both as a herbicide a nd as a runner inhibitor (4, 13). This substance w a s used at 5.0, 10.0, 15.0, 20.0 and 25.0 milligrams per plant in greenhouse tests, and 3, 6, and 9 pounds per acre in field experiments. Phenoxyethyl trichloroacetate ( P E - T C A ) w a s also found in preliminary tests to have effects similar to D C U (4, 13). This material w a s applied at 5.0, 10.0, 15.0, 20.0 and 25..0 milligrams per plant in the greenhouse tests, and 1, 2, and 3 pounds per acre in the field. Maleic hydrazide ( M H ) w a s used in s o m e of the g reen­ house tests at 48.0, 96.0, 144.0, 192 and 240 milligrams per plant, and in the field at 1,500 and 2,000 p p m . This material has be e n used to inhibit sprouting of onions and potatoes (23, 28). T h e materials w e r e applied to the strawberry plants in various ways. in s o m e In the greenhouse tests the solutions (emulsions cases) w e r e (l) poured over the soil surface only, (2) poured over the plant only, (3) pour e d over both the plant and the soil surface, and (4) sprayed over the plant and the soil surface. Usually 10 ml. of the solution w a s applied to each 12 plant so as to insure wetting of the leaves and contacting of the growing points in the leaf axils. Various other m e t h o d s of a p ­ plication such as lanoline paste, d r o p - m e t h o d and leaf-emersion w e r e tried, but these did not prove as effective as spray and pouring applications. Since difficulty is often experienced in growing straw­ berry plants under greenhouse conditions, it is important to consider s o m e of the factors responsible for good growth. Va­ rieties differ; for example, the P r e m i e r variety produces only a limited n u m b e r of flowers and runners under greenhouse c on­ ditions, w h e r e a s the Robinson variety produces flowers and runners typical of field— g r o w n plants. T h e growth of m o s t varieties in the greenhouse approaches typical growth in the field if the plants have been properly p r e ­ conditioned and if they are provided with favorable growing con­ ditions, including soil, moisture, temperature and light. For o p t i m u m growth in the greenhouse, the plants should be allowed to r e m a i n in the field until they have reached a d o r m a n t stage (usually the latter part of October, depending on the season), and then dug and stored for at least two m o n t h s in a m o i s t m e d i u m at 35° F. After they are transplanted into containers and placed 13 in the greenhouse, supplemental light is required so as to p r o ­ vide about 10 hours for flower initiation, 14 hours for runner initiation, and 10 to 12 hours for general growth and fruiting. It has, however, been s h o w n by D a r r o w and H a r t m a n n that low temperature m a y induce flower initiation on a long day (7, 11). T h e P r e m i e r and Robinson varieties and certain seedling selections w e r e used extensively. T h e plants usually w e r e dug the last part of October, or after they appeared dormant, a nd then stored at 3 5° F. for 6 to 8 weeks. T h e y w e r e then trans­ planted into one-gallon tin cans filled with a soil mixture of loam, peat a nd sand. T h e plants w e r e treated at various stages of development to determine the m o s t sensitive runner-inhibiting period. Supplementary light w a s given f r o m 4:00 p.m. to 11:00 p.m., w hich produced about a 14—hour o p t i m u m ph.otoper.iod for runner production during D e c e m b e r , January and February. In the field, the materials w e r e applied by a conventional knapsack sprayer at a v o l u m e of 40 gallons per acre. single and double applications w e r e m a d e Both on different plants in the field to determine the influence on runner inhibition of each application. A b o u t one-half acre of the P r e m i e r variety w a s planted M a y 25 on a Hillsdale sandy loam. T h e materials w e r e 14 applied June 4 and July 18. A second-year planting of Sparkle, R e d Star, Fairpeake and P r e m i e r w a s treated July 29, and again A u g u s t 16, 1951, to see the effect of the materials on older plants. R u n n e r counts w e r e m a d e at regular intervals during the r e m a i n d e r of the growing season. R E SU LTS R u n n e r Inhibition U n d e r G r e e n h o u s e Conditions During three years, over 4,000 strawberry plants w e r e individually treated in the greenhouse* E a c h treatment with a certain concentration of a certain chemical w a s duplicates and repeated several times.. set up in Only the m o s t signifi­ cant data are presented. In one test, twenty plants each of the P r e m i e r , Robinson and N Y 23 502 w e r e treated with phenoxyethyl trichloroacetate at 4.0 and 8.0 milligrams per plant, a s a m e n u m b e r with di­ chloral urea at 6.0 and 12.0 milligrams per plant and similarly with 2,4-D at 1.0 and 2.0 milligrams per plant (Table I). The plants received a second application at these rates 15 days af­ ter the first. E a c h plant received these a m o u n t s of the c h e m ­ ical in 10 ml. of solution poured over the individual plants. this m a n n e r In s o m e of the liquid seeped into axils of the leaves and d o w n over the c r o w n and onto the soil. T h e plants w e r e runner plants f r o m the field that had been dug October 20 and stored at 3 5° F. for two months. At that time they w e r e planted Table I. of 20 plants rates indi­ These are average results twice, 15 days apart at the shoot-crowns of three strawberry varieties. of each treatment. The plants were treated cated. The effects of P E - T C A , DCU and 2,4-D on runner production, shoot-root ratio, and 16 cl o o rCj I d o O ^ o u +* ^ N xfl H vO ^ co cO co co oO cO O 03 CO 03 CO CO LO p—i ID r-H Ti —• 10 n L? hj Ci Ci CD U CD P. Q I —i d o O Ci O ^ T3 (U cd cd Ci H —* d CO o o 00 03 03 03 03 SH o 03 O 03 oo CO r-H rH CO O CO r-H 03 CO o - oo “H i— H 03 03 r d o to d •H rQ o co i— H 03 N • cd d o O- vO lT) Ci co r* o ^ »—c IsrO rO cO " Ifl • H o • « sO NO lO Lfl 03 O' 00 O H O ^ co ^ ^ m to CO CO CO o o o o o o ^ 'f-vO N H (M o o o o o o < < £ I * 0 o H H 1 q q iId |d i | W H U O t t 0 , C l| Q rv i Q o i CO 'O H Eh I t N H (V] Q tD ;=) i M W O U On 0. Q Q 03 03 17 -t-s U o CM r •-1 CO lo CM vo CM —I CD R cO O • • t f • CO ^ 00 • CO O • CO • CT' (M Shoot-root Ratio H i ' —I 5 O o ju o o ro o 00 O i—1 r'- rH c o r— o r-t CM CM CM tH t-H T3 CD ■+J cd Pi o •rH o r - co o n co CM ix £ CM CM CO CO O CM CO CM CM CM CO cO rd cd cd cd R H 00 00 O' N o o o o o o o o o o o o H p—H Pt Oh < . ■+J _J M * to ft, g , 00 R rj M 4 00 CM ■— < CM I to —i cd ■H R cd < < u u Eh H Q Q i i w W U U ^ 't. Ph P-* P Q (M CM I i 18 in the greenhouse and allowed to flower and fruit. Supplementary light w a s supplied to induce runner formation. T h e first treat­ ment was made This w a s done by careful daily observations of s o m e w h e n the first sign of runner formation appeared. in the leaf axils. of the buds If n e w flower branches occu r r e d they w e r e r e m o v e d , to encourage runner formation. Since runners w e r e still being p r o d u c e d on control plants and a f e w on treated plants a second application at the s a m e rate w a s made 15 days after the first treatment. Phenoxyethyl trichloroacetate ( P E - T C A ) reduced the n u m ­ ber of runners b y over one-third in the Robinson and P r e m i e r varieties, and b y 90 per cent with the N Y tion (Table I). 23502 seedling selec­ T h e differences b etween concentrations w e r e not great; however, the higher concentration p r o d u c e d m o r e injury to the plants, as w a s obs e r v e d in increased marginal ‘'burning11 of the leaves and degree of stunting of the plant. T h e plants soon o u t g r e w the burning and stunting effects, as w a s deter­ m i n e d at first b y visual observation and later b y m e a s u r e m e n t of the shoot-root ratio. The shoot-root ratio indicates that there w a s a reduction in foliage or a possible increase in roots, the f o r m e r being the m o s t likely condition, since the material 19 s h o w e d contact foliar injury. The material P E — T C A also p r o ­ duced a condition w h i c h caused m o r e shoot-crowns to be formed. T h e r e w e r e nearly 50 per cent m o r e shoot-crowns p r o d u c e d in the Robinson variety and about 30 per cent m o r e in both the P r e m i e r variety and the N Y 23502 seedling as c o m p a r e d with untreated plants (Table I and Fig. 2). Dichloral urea (DCU) caused a decrease in n u m b e r of runners and an increase in shoot-crowns similar to P E — T C A with all the three varieties tested in this experiment (Table I). The effect of D C U on the plants w a s not as pronou n c e d as that of P E — T C A , but s o m e bronzing of the leaves occurred about 10 days after each treatment. At the higher concentration, m g m s . p er plant, there appeared to be s o m e root injury since the shoot-root ratio w a s higher in these treatments. cations at the s a m e 12.0 Spray appli­ rate of either one of these materials w e r e as effective as w h e n the materials w e r e p o u r e d onto the plants. Spray sufficient to we t the foliage, appeared to produce inhibitory effects (Fig. 3). Differentiated runner "tips" appearing in the axils of the leaves w e r e checked in their further development b y P E - T C A and D C U . T here w a s a noticeable blackening and withering of J?ig, 2 The effect of two applications of 8 milligrams each of PE=TCA three weeks apart on Eobinson strawberry plant* The treated plant (right) produced six crown-shoots and two "dwarfM runners* whereas* the untreated plant (left) produced no ehoct-crowns and five runners* 20 It Q) •rn ft iH ft P« P, e o p o •p tfj ft >> ft *3 (0 ft a t 4> o p ft o p Pt P fl ft Q t>i (6 P «p a3 P P +> >» o u 3 p 0) ft OCi P s* •HI ft Jp pi 03 8 ft •H o ft fl!t vji ft f P u P •>5 ft < © w •cH o> ft to ft >* p 3 p CD o W) ft O ca ft o ft ft a> tj •c» & =3 p ft ►H s 9 22 the terminal growing points of the runners (Fig. 4). and D C U p r o d u c e d these effects; however, P E - T C A tent in that it p r o d u c e d withering of runner in length (Fig. 5). Runner Both P E - T C A was m o r e po­ 1^tips1-1 up to one inch shoots which h ad developed to a length of over 2 inches at the time of treatment exhibited a b r owning on the sides about 10 days later; however, they continued to grow. M a n y of the runner shoots w h i c h w e r e over one inch in length at the time of application w e r e only checked in their de v e l o p m e nt and later g r e w apparently into n o r m a l runner plants. Apparently, the m o s t effective time to inhibit further growth and development of the runner shoot is w h e n the b u d first appears in the leaf axis. T h e chance of inhibition is decreased f r o m the b ud stage up to the time the runner shoot is one inch in length. B e y o n d the one-inch stage, the chemicals p r o d u c e d only a delay in runner formation. Since this one-inch growth often w a s p r o d u c e d within one day, it w a s necessary to time the applications so as to con­ tact as m a n y of the young buds and shoots as possible. applications w e r e more Two effective than one. T h e material, 2,4-D, p r o d u c e d effects, as far as runner production is concerned, w h i c h w e r e and D C U (Fig. 6). similar to those f r o m P E - T C A T h e average reductions in runners w e r e about 23 RUNNER'BUD RUNNER CROWN SHOOT PETIOLES Pig, Strawberry crowns showing a ronner-bud inhibited from tv/o treatments of 12 milligrams each, of S5CU (left) and untreated (right)* Note some darkening also of the stipule® Pig. Brnmer-shoot (right) inhibited in its early development with two applications of 8 milligrams of PE-TCA, and runner from untreated plant (ieft)B pig* 6 Robinson plant (right) treated with two applications of 2 milli­ grams of and untreated plant (left)* 26 40 per cent with the R o binson and P r e m i e r varieties, and about 80 per cent with the N Y 23502 selection (Table I). T h e increase in shoot-crowns c o m p a r e d favorably to that f r o m P E - T C A DCU. and T h e r e appeared s o m e loss in foliage vigor a f e w days after treatments; however, the plants soon recovered. The shoot- root ratio indicates that no serious effects due to treatments w e r e found in either leaves or roots; however, newly f o r m e d roots showed s o m e From swelling. the greenhouse studies, there is an indication that each variety responded differently to the materials tested. was This especially true for varieties that ordinarily produce f e w runners such as the N Y 23502. Naturally, the m o r e shoots present in a variety, the m o r e young shoots with the spray. No runner— difficult to contact the appreciable difference occurred, however, b e t w e e n the R o binson and the P r e m i e r varieties in this respect. T h e materials, 2,4-Dichlorophenoxyethyl sulfate (EH-1), isopropyl N - p h e n y l c a r b a m a t e (IPC) and maleic hydrazide (MH), included in succeeding experiments did not inhibit runner f o r m a ­ tion as m u c h as the c o m p o u n d s previously mentioned. it is important to note that E H - 1 First, and I P C w e r e not effective in 27 controlling runner production (Table II). EH-1 p r oduced no ill effects o n the strawberry plants at the low concentrations used, whereas at the higher concentrations considerable wilting w a s very noticeable for six to eight days after application. T he plants soon recovered, however, and g r e w normally as c o m p a r e d to untreated plants. some IPC, at the higher rates used, p r oduced chlorotic s y m p t o m s on the n e w strawberry leaves that unfolded about 15 days after the applications. T h e lower concen­ trations induced no visible effects on plant growth (Table II). Maleic hydrazide (MH) inhibited runner formation to a limited extent but the material also slowed d o w n growth and n o r m a l development of the plants m o r e than any of the other c o m ­ pounds tested. The stunting s y m p t o m s r e m a i n e d for two to three w e e k s following treatments, but the plants eventually outgrew the effects (Table II). Effect of C h e m i c a l s on Flowering and Plant G r o w t h For certain chemicals to be useful in inhibiting straw­ b e r r y runners it is essential to k n o w what effects they m a y have o n flowers and general g r owth of the plant. F o r this reason, a series of tests of s o m e of the materials w e r e m a d e to determine of 10 ml. per o 01 a aJ ft rcJ Vi Eh rate at the of formation and plant growth. The materials were applied plant at the time of runner initiation and formation. 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Vi 0) H-> > to d Vi Cd CD ^ o tj P h ‘ cd W H-H cd O ^ £ -I H (\3 Vi o • oo OO I r—t 't h N • • f t f t • r -' vO m m o^ CD Ph *"H d ft Cd ft i—H < Ph +»* M d « d Ph to s GO S ^ X (M O O ^ > —i •—i c\j <1 u H I W Ph o• o• o• o• o• o» o m o m o m rH I— I f\J (VI 33 W h e t h e r applied directly to the soil surface or to the plant, all the chemicals had an inhibiting effect on flowering (Table III and Figs. 7 and 8). T h e effect increased with in­ creasing concentration, so that at the higher concentrations used, nearly all flowers w e r e inhibited. A t the lower levels of concen­ tration, flowering appeared n o r m a l w h e r e E H - 1 , D C U w e r e used. and P E - T C A T h e lower rates of the chemicals used in these tests a pproac h actual herbicidal concentrations used in the field. 2 Th e data indicate that s o m e of these materials (2,4-D, I P C and M H ) could be u s e d to advantage to reduce the n u m b e r of flowers f o r m e d in the first-year strawberry bed, provided the right con­ centration of the chemical is used and it is applied at the proper time. R u n n e r s w e r e not adversely affected in these tests b e ­ cause they w e r e pro d u c e d about two m o n t h s following treatments. T h e reduction of runners indicated is probably due to loss of vigor of the plant at the higher concentration (Table III). 2 T e n milligrams per square foot is equal to 1 p o u n d per acre. Example: If a plant container with 0.25 sq. ft. sur­ face area receives 10 milligrams, the rate per acre is equal to 4 pounds. 34 d i 1' X •p ■ +■ p 4f-i <0 -P td ,r:> i; 5-' INV H d 0 3 d SH3M 0U QN V S 3A V 31 dO H 30n D N o. P ' r t d, t-i >5 in ■i t-i V* ! 4 (ir> r- O n, 4 4 C;E-. P 4--" V.'l .f ?' ,IL I \ ■so > G> Pi - .0 .w s ■* & i-'i <— 4 * « •H -r -il . U E Q P f~i % !d r d ■: "J '•J t.\j .‘i -u e j Mj 1 ’v f d: _LNV3 d U 3d S H 3MOHd O N V S3AV33 dO d 3 0 W n N tp •r s- t-.' ■■ rh - =fi ?-*j r-- V . 4 4 II X. - V_ f. ’. . t ..'j 4 ^’ ’ il c i- . 4—* A ■;) V-, -1 ■ I . '1 C rft/ J *P J} t il p V .1 r Sk , A v C V <5 ii i i b f5 - > 22 -1-4 f) I N V l d « 3 d S U S MCDd O N V S 3AV3 "! dO « 3 0 W n N 35 W «0 o CD c rH ft a1 fr * U o fli .d ' * *f~l & m G> +* Pi a <1* a H ft 'd o CJ ft 4> IH G> V Pi o •H t/J § O P i 5c hi) +» •r4 rH I-" (3 ■H cd a o H> rH C3 n-l o >4 rH • 4J* Pi o cl CL* C-> r1 £4 on S3 a} * t>j 36 Effect of C h e m i c a l s Applied to S t rawberry Plants in the Field T h e materials, 2,4-D at 1/2 and 2 pounds, E H - 1 3 and 4 pounds, D C U at 3, 5 and 7 pounds, P E - T C A and 3 pounds, and I P C T he strawberries on June second application coincided with the time of runner formation. Since the plants w e r e applications w e r e m a d e planting. at 1, 2 at 5, 10 and 15 pounds per acre, w e r e applied to a first-year planting of P r e m i e r 4 and July 18. at 2, 20, these 15 and 42 days, respectively, following T h e materials w e r e p er acre of the spray. set M a y applied at the rate of 40 gallons E a c h treatment w a s replicated four times and the data presented in Table IV are the averages of these replications. DCU (dichloral urea) pro d u c e d 96 per cent reduction of runners with two applications; however, the plants exhibited some retardation of growth for about six w e e k s following the last application. T h e injury occurred in the f o r m of bronzing of the older leaves which probably interfered with n o r m a l photo­ synthetic function. cation of D C U , T h e n e w leaves f o r m e d after the last appli­ however, appeared n o r m a l in color and vigor, so that at the end of the growing season the plants w e r e as IV. on made was 0 £ 01 application First field. in the i 03 GO O ;d ? 03 03 01 03 -M pu, O O i —< •H i —H O at cd aj tti cd aj cd o Pi Pi nj ai nj at H d d dd dd d Pi Pi Pi Pi U Pt U £ £ Pi Pi Pi Pi o o o o o o o 43 43 O O O O U Pt 43 rO S S £ g 6 a g & at Pi h-> £ 55 Z z Z r-( aj aj rj rj d d Pi Pi O 0 Z £ W a 0 GO Pi •H N Pi O 3-i -+J o Pf 0 ■01 +•> o 43 $ W 42 <+tH nj Ji3 01 03 -H »i—I in o u u OJ a °1 *»o-4 43 r*—I 03 42 *i— i •-H 03 q r 4h £ GO O 3 44 PP O H nj Pi GO Pi nj GO Pi •7-1 03 03 (0 <13 > > aj cd cd cd a} nj aj in o u u 43 fi GO P* i 4 •r tss Pi 03 u aj 03 aj 0 Pi 42 l-1 H nj Pi GO Pi aj -rH Pi nj GO Pi H-» Pi •pH PJ 43 H0J3 nl 6 6-s XJ 43 43 d 44 4h Pi £ £ GO GO 6 O 6 g O Q O O Q 43 4> o ® O ° Z Z Z Z Z Z Z Z < n Z w t i Z t n co J-i U U Pi Pi -+-P Pi Pi h3 . 43 4 H~2 > o Pi u 3 3h S2 XJ 43 pd 43 Ph Ph o<» oo o • o • o • o ■ o » o • o « o* o# o» o• o• o « 0 '4 >0 v0 r 0 s 0 0 ^ ' 4 > < —iO^G~xOun D D W U U U Ph Q Q Q 38 vigorous as control plants. T h e untreated plants h a d f o r m e d several runners producing a matted r o w in contrast to the spacedr o w appearance of the treated r o w s (Table IV a nd Fig. 9). The lower concentrations of 3 and 5 pounds of D C U p r oduced 55 and 82 per cent inhibition of runners, respectively. toms T h e toxic s y m p ­ at these l ow rates w e r e not as p r onounced as at the high concentration. PE-TCA (phenoxyethyl trichloroacetate) reduced the n u m ­ ber of runners b y 96 per cent with two applications of 3 pounds p er acre without serious effects on the plants. toms Some toxic s y m p ­ in the f o r m of marginal necrosis w e r e observed at this concentration. The sym p t o m s were m o s t severe o n leaves which w e r e present at the time of the last application, and in m u c h lesser degree on leaves which w e r e f o r m e d following the last application. B y the end of the growing season these s y m p t o m s had disappeared. T h e lower concentrations of 1 and 2 pounds per acre of P E - T C A p r o d u c e d 59 and 77 per cent inhibition, respectively, without appreciable toxic effects on general plant gro w t h (Table IV). T h e chemical, 2,4-D, w a s also effective in inhibiting run­ ners, especially at 2 pounds per acre; however, at this high %r '' 40 concentration the plants w e r e to recover. severely injured and a f e w failed T h e plants r e m a i n e d "stunted11 for about 3 w e e k s following the last application, but appeared fully recovered at the end of the season. A t this time the roots appeared to be swol­ len to approximately twice their n o r m a l diameter. This w a s m o s t obvious near the root— tip extending toward the base for about one inch. T h e two applications of 1/2 pound of 2,4-D per acre, on the other hand, inhibited 46 per cent of the runners without any noticeable injury to plant growth (Table IV). Considerable reduction in the n u m b e r of runners w a s also obtained with two applications of IPC, especially at 15 pounds p er acre. Some noticed at this rate. tion of growth, chlorosis on newly f o r m e d leaves w a s T h e plants, although showing s o m e retarda­ soon recovered and appeared n o r m a l b y fall. 5— and 10—p o u n d rate of I P C The inhibited 33 and 46 per cent of the runners, respectively, and the plants soon recovered f r o m the two applications of this chemical (Table IV). Two applications of E H - 1 (2,4-dichlorophenoxyethyl sul­ fate), at rates of 2, 3 and 4 pounds per acre, failed significantly to inhibit the strawberry runners of the P r e m i e r variety in the field. T h e plants treated with E H - 1 w e r e as vigorous, or m o r e so, than the control plants. 41 Besides inhibiting strawberry runner plants to varying degrees, the chemicals us e d in these field tests also controlled the w e e d s to varying degrees, as previously reported (4). Since the land w a s moved required for other purposes, the plants w e r e to another location, w h e r e they flowered and fruited in a n o r m a l manner, indicating that the chemicals had no delayed effects on the plants. A second-year b e d of several varieties w a s sprayed after harvest, but the data of those tests are not available. H o wever, early observations in the fall of 1951 indicated that the results are c o m p a r a b l e to those in the first-year planting. A chart w a s p r e p a r e d f r o m the field data pertaining to the growth cycle of the strawberry plant (Fig. 1). The chart also indicates the approximate time to apply the chemical for maximum runner inhibition. T h e time to spray strawberry plants to reduce the n u m b e r of runners will vary with the time of planting, the variety, and the location. DISCUSSION E x p e r i m e n t s in the greenhouse and in the field clearly indicate that certain chemicals can be used to reduce the n u m b e r of runner plants p r o d u c e d in s o m e varieties of strawberries. Many strawberry varieties produce a superfluous n u m b e r of run­ ners to the extent that the plants tend to be o v e r c r o w d e d in the matted r o w which is formed. Varieties w hich have a tendency to produce fewer runners perhaps need not be thinned by hand or chemical m e a n s . Some of the chemicals prevented runners f r o m develop­ ing rather early in the b u d stage. Apparently these buds are v e r y tender and susceptible to these chemicals. TCA were m o s t effective in this respect. DCU and P E - 2,4-D, if applied prior to initiation, evidently prevented the runner buds f r o m forming, since they w e r e not noticeable to the naked eye. It is important to note that as the runners w e r e inhib­ ited, the n u m b e r of succeeding crown-shoots w a s increased. Apparently, with the elimination of s o m e of the runners f r o m the m o t h e r plant, a condition w a s provided w hich favored c r o w n shoot development. It is safe to a s s u m e that the runner plant 43 depends up o n the m o t h e r plant for certain nutrients, at least until the runner plant is established on its o w n roots. Since the m o t h e r plant has fewer runner plants to feed, it is capable of producing m o r e c r o w n — shoots. A further explanation of an increase in c r o w n — shoots with the elimination of runners is that the grow t h cycle of the plant is such that, rather than producing additional runners, crown-shoots are produced. Evidently the plant produces a certain n u m b e r of runners followed by the p ro­ duction of crown-shoots. m o r e productive the m o r e Obviously, the m o t h e r plant b e c o m e s crown-shoots it produces, because each crown-shoot initiates flowers after it is formed, thus in­ creasing the fruiting potential of the m o t h e r plant. The produc­ tivity of the m o t h e r plant which has been deprived of n o r m a l runner development is an important factor, aside f r o m the other advantages derived f r o m the use of chemicals in strawberry planting s . With the use of various chemicals for the control of w e e d s in strawberry plantings, it appears feasible that with proper t i m ­ ing these materials can serve a twofold purpose: nate the w e e d s (a) to elimi­ and (b) to inhibit strawberry runners. S o m e of the chemicals u s e d in these tests are effective herbicides and 44 others have s h o w n p r o m i s e of being effective in killing germinat­ ing seeds of both grasses and broad-leaved w e e d s — an e x a m p l e of the former, and D C U , 2,4-D being and e x a m p l e of the latter. M a n y w e e d seeds germinate at the s a m e time that runner— shoots are initiating, so that b y properly timing the sprays the w e e d s could be controlled and the n u m b e r of runner plants reduced. T h e w o r k so far completed indicates that strawberry runners are greatly reduced with two applications of the c h e m ­ ical (such as D C U or P E - T C A ) in the field, w h e r e a s a similar application is not as effective under greenhouse conditions. T he m o s t likely reason for this is that strawberry plants (especially s o m e varieties) do not respond satisfactorily to greenhouse cul­ ture. That is, the artificial conditions provided are not o p t i m u m for m a x i m u m runner production. Further, it is easier to p r e ­ dict runner initiation in the field than under greenhouse condi­ tions, b y the natural g r o w t h cycle of the plant. is m o r e clear cut in the field. T he sequence R u n n e r s initiate after flowering and fruiting, w h e r e a s in the greenhouse the processes are likely to occur simultaneously, especially with s o m e varieties and with a long photoperiod that is provided too soon. F o r practical 45 purposes, it is significant to note that the chemicals tested are effective in reducing runners under field conditions. It w a s further found that two applications w e r e required for m o s t inhibitory effects of strawberry runners. Evidently an accumulative effect is p ro d u c e d with two applications as well as m o r e complete contact with the tissues that produce the run­ ners. In the first-year strawberry planting the first application of the inhibiting chemical should be m a d e immediately after the flowers have b e e n r e m o v e d . In m a n y cases this m a y be the latter part of M a y or the first part of June, depending on the season, variety, and w h e n the plants are set (Fig. 1). ond application should be m a d e T he sec­ about one m o n t h later. T h e fruiting b e d also requires two applications of the chemical for m a x i m u m be m a d e T he first application should after the fruit is picked and after the planting has been rejuvenated. states. inhibition. This is often the middle of July in the northern This application is followed by a second spray about 3 or 4 w e e k s later (Fig. 1). F o r practical use of these chemicals it s e e m s to use D C U at the rate of 5 pounds per acre, P E - T C A advisable at 3 46 pounds, or 2,4— D at 1— 1/2 pounds pe r acre, at each, application. Since complete wetting of the foliage is essential, it is advisable to use a r o u n d 50 gallons of the spray p er acre. F o r best re­ sults the plants should be observed daily so as to determine w h e n the first runners are forming. If a great n u m b e r of runners are p r o d u c e d before material is applied, no favorable results can be expected. In the greenhouse tests it w a s found that s o m e of the chemicals h ad an inhibitory effect on strawberry flowers. Some chemicals p r o d u c e d no serious injury to the plants, but others w e r e injurious to the entire plant (Fig. 7). The fact that flowers w e r e inhibited has a practical importance in that perhaps these chemicals can be used to eliminate the flowers in the first-year planting. In that case the first application for runner inhibition in the first-year planting could be m a d e before the flowers are removed. Or, perhaps three applications w ould be practical in the first-year planting the first to r e m o v e the flowers and the next two for runner reduction. All these applications w ould keep m o s t of the noxious w e e d s f r o m b e c o m i n g a problem. SU M M A RY A N D CONCLUSIONS 1. Several chemicals ( DCU, P E - T C A , 2,4-D, IPC, E H - 1 and M H ) w e r e tested on strawberry varieties (Premier, Robin­ son, N Y 23502, Sparkle, R e d Star, and Fairpeake) for the effec­ tiveness in inhibiting runner plants. S o m e plants w e r e treated at the time of runner formation, while others w e r e treated at the time of flowering to determine possible injury to flowers. E x p e r i m e n t s w e r e conducted both in the greenhouse and in the field. 2. DCU, P E —T C A and 2,4-D w e r e m o s t effective in re­ ducing runner formation, w h e r e a s I P C and M H tive, depending on the concentration used. w e r e less effec­ EH-1 did not signif­ icantly eliminate any of the runners f r o m plants either in the greenhouse or in the field. T h e percentage reduction under greenhouse conditions ranged f r o m 10 to 80 per cent, depending on variety and concentration, w h e r e a s under field conditions the reduction w a s greater. 3. F o r m a x i m u m inhibition of runners, two applications w e r e ne e d e d at the time of actual runner initiation and formation. 48 It w a s found that timing the application of the chemical materials was ext r e m e l y important. T h e first-year strawberry planting should be sprayed the first part of June and then again in July. The second-year, or fruiting bed, should be sprayed about the middle of July (or after rejuvenation of the planting) and then again about 3 w e e k s later (Fig. 1). 4. T h e concentrations that w e r e m o s t effective under greenhouse conditions (two applications of each) w e r e as fol­ lows: DCU, 12 m g m s . per plant; P E - T C A , and 2,4— D, 2 m g m s . per plant. U n d e r field conditions the m o s t effective concentrations per acre were: TCA, 3 pounds; and 2,4-D, 8 m g m s . per plant; DCU, 1-1/2 pounds. 5 pounds; P E - T e n milliliters per plant under greenhouse conditions, and 50 gallons per acre under field conditions, p r o v e d m o s t effective. 5. T h e r e w a s a difference in varietal response. Th e Robinso n and P r e m i e r varieties w e r e not affected as m u c h as the N Y 23502. This probably is tied up with the n u m b e r of run­ ners pr o d u c e d by the variety, since the N Y 23502 is a sparce runner producer, P r e m i e r , m e d i u m , and Robinson, very prolific. 49 6. Some injury in the f o r m of marginal necrosis w a s ob s e r v e d at the higher concentration of P E - T C A , ing with D C U . and s o m e br onz­ T h e high concentrations of 2,4-D delayed and dwarfed the plants for about 3 w e e k s following each application. Some chlorosis app e a r e d on the n e w l y f o r m e d leaves on plants treated with IPC. except s o m e 7. N o visible s y m p t o m s occurred f r o m E H - 1 , t e m p o r a r y wilting. T h e runners w e r e inhibited in the early bud-stage of development, appearing as discolored buds and death of the growing point. T h e materials w e r e effective on young runner- buds and on y oung runner-shoots less than one inch long. After the runner— shoot w a s over one inch in length, the chemicals had no effect. 8. T h e data obtained in the greenhouse and in the field s h o w that runners can be reduced if the chemical is applied w h e n the runners are being initiated or are in the b u d stage. This m e t h o d of reducing runners appears to be practical with varieties that tend to produce an excessive n u m b e r of runners whi c h causes overcrowding in the row. 50 9. Other chemicals m a y be m o r e effective in inhibit­ ing runners* since only a small n u m b e r of chemicals w e r e tested in these experiments. T h e tests described in this paper clearly demonstrate that with proper timing and correct concentration of certain chemicals, strawberry runner production can be con­ trolled. 10. T h e materials that are effective in reducing runner formation are also effective in killing germinating w e e d seeds, and therefore serve a dual purpose. LITERATURE 1. CITED Carlson, R. F. Control of w e e d s in strawberry plantings b y the use of 2,4-Dichlorophenoxyacetic acid. Proc. A m e r . Soc. Hort. Sci. 49: 221-223. 1947. 2. Carlson, R. F. W e e d control in small fruits. C h e m i c a l s 4: 37-38, 71. 1949. Agricultural 3. Carlson, R. F., and Moulton, J. E. C h i c k w e e d control in strawberries with IPC. Proc. A m e r . Soc. Hort. Sci. 54: 200-204. 1949. 4. Carlson, R. F., and Moulton, J. E. Further testing of herbicides in strawberry plantings. Michigan State Agr. Exp. Sta. Quart. Bull. 33: 262— 268. 1951. 5. Darrow, George M. D e v e l o p m e n t of runners and runner plants in the strawberry. U S D A Technical Bulle­ tin No. 122, 1929. 6. D a r r o w , G. M . Inter-relation of temperature and photo— p e r i o d i s m in the production of fruit-buds and run­ ners in the strawberry. Proc. A m e r . Soc. Hort. Sci. 34: 360-363. 1936. 7. D a r r o w , G. M., and Waldo, G. F. Responses of strawberry varieties and species to duration of the daily light period; U S D A Tech. Bui. 453. 1934. 8. Gilbert, Frank, Control of w e e d s in strawberries with 2,4-D. Proc. Northeastern States W e e d Control Conference 123-125. 1948. 9. H a m n e r , C. L., and Tukey, H. B. 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