THE PRE‘ JENTE». N C} {TUE T F0 QMATEDN ON SEL EC‘K :JWQ ffiLANTS Theisis {err fhe Degree 55 M: S. MICHEGAN S'fi‘fl LENA" ERSETY Gian Efiairce Lumés W43 6: {'I‘HES‘S LIB R A R Y Michib State UniVCL.,ity Au.“_‘_' ___£_ .__'__ ____ ABSTRACT THE PREVENTION OF FRUIT FORMATION ON SLECTED WOODY PLANTS By Glen Peirce Lumis The prevention of fruit formation is in some cases desirable for reasons of: aesthetics, plant vigor and development, lawn maintenance, and attractiveness to birds or insects. 0f the many trees used in fruit prevention work the following were used in this study: Thuja occidentalis, ggtalpa Speciosa, Ailanthus altissima, Malus zumi calocarpa, Malus pumila 'Jonathan,I and Prunus cerasus. The principal objective was to prevent fruit formation and development by preventing fertilization or causing abscission of the flower or develOping fruit. Materials selected were of three types: l) liquid plastic (Plyac and Hilt-Pruf), 2) caustic (paraquat), and 3) hormone (Naphthylacetamide and 2-(3-chlor0phenoxy)-pr0pionic acid). They were applied as sprays at full bloom. Preliminary concentration range trials were conducted in late winter using forced branches of apple, cherry and arborvitae after which field applications were made. One of the three Plyac formulations (5N2) severely desiccated llflflé strobili and thus completely prevented cone formation. The other two Plyac materials were less spectacular but did prevent cone forma- tion or greatly reduced cone size. The Plyac materials were found Glen Peirce Lumis - 2. to be of little merit on any of the other Species treated, however, the Catalpa treatments showed promise. The caustic material was ineffective on all Species causing varying degrees of foliage in- jury with little or no effect on fruit set in most cases. The hormone materials were successful on figlgg and Cataipa, but had no effect on the foliage or fruit set of the Thuia or Prunus. THE PREVENTION OF FRUIT FORMATION ON SELECTED WOODY PLANTS By Glen Peirce Lumis A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture I966 ACKNOWLEDGEMENTS The author wishes to extend sincere thanks to Dr. Harold Davidson for his valued guidance and advice throughout the Master's program, and to Dr. Martin J. Bukovac for his assistance in planning the field experiments. The author is most grateful to Hidden Lake Gardens for the financial support of this study. TABLE OF CONTENTS ACKNOWLEDGEMENTS . . . . . . . . . . . . . . TABLE OF CONTENTS . . . . . . . . . . . . . . LIST OF TABLES . . . . . . . . . . . . . . . . LIST OF FIGURES. O O O O O O O O O O O O O O 0 PURPOSE... . . . . . . . . . . . . . . . . . . INTRODUCTION 0 O O O O 0 0 O O O O O O O O O 0 LITERATURE REVIEW . . . . . . . . . . . . . . An Ancient Practice . . . . . . . . . . Need for Fruit Prevention . . . . . . . Early Fruit Prevention Work . . . . . . Discovery of Fruit Prevention Materials Variable Factors . . . . . . . . . . . . Later Fruit Prevention Work . . . . . . EXPERIMENTAL PROCEDURE . . . . . . . . . . . . Greenhouse Studies . . . . . . . . . . . Field Studies. . . . . . . . . . . . . . Morphological Studies. . . . . . . . . . RESULTS. . . . . . . . . . . . . . . . . . . . . Greenhouse Studies . . . . . . . . . . . Field Studies. . . . . . . . . . . . . . Morphological Studies . . . . . . . . . DISCUSSION . . . . . . . . . . . . . . . . . . SUMMRY. O I O O O O O O O O O O O O I O O O 0 LITERATURE CITED . . . . . . . . . . . . . . Page ii .1? WWLOVU'IUI U1 2l 2l 22 26 27 27 28 l*3 A8 LIST OF TABLES Table Page l Trees which produce objectionable fruit and the criteria for the objection. . . . . . . . . . 8 2 Review of fruit prevention studies on woody plants . I; 3 Materials used for fruit prevention. . . . . . . . . l9 A Number of fruit formed on liquid plastic treated Thuii OCCEdenta] is. I O O O I O C O I O O O O O O 30 5 Cone diameters in millimeters of liquid plastic treated Thuja occidentalis. . . . . . . . . . . . 3l 6 Number of fruit formed on treated Jonathan Apple . . 34 iv LIST OF FIGURES Figure Page I Cone diameters of Thuia occidentalis treatments. . 32 2 Thuja occidentalis treatments. . . . . . . . . . . AD 3 Thuia occidentalis treatments. . . . . . . . . . . #2 PURPOSE The purpose of this study was to endeavor to prevent fruiting of selected landscape plants. To defruit or not to defruit is a question solely dependent upon ones aesthetic evaluations of the plant in the particular situation in which it is used. What may be unsightly and a nuisance to one is of value and beauty to another. It was with this in mind that a program of study was formulated. Thuja occidentalis was chosen for extensive investigation. The justification for preventing fruiting of this plant is principally aesthetic. Completely covered with cones it may detract from the har- mony of the landscape. Prior to this time no reported work had been undertaken in reSpect to preventing fruiting of Ihglg. In order to understand the mechanism by which fruiting was prevented, provided such could be accomplished, it was necessary to become familiar with the morphology of the Iflgig reproductive parts. 12313 flower (strobilus) buds were examined microsc0pically prior to their opening. Microsc0pic observations were also made after treatment application in order to determine the mechanism by which the materials did or did not prevent fruiting. Similar studies should be sought or conducted for any plant in respect to fruit prevention work. In order to adequately study fruit prevention certain other work would be beneficial. Some of which is: l) studying the physiology of flower and fruit development and the abscission phenomenon, 2) screening various plant growth regulators over a concentration range in order to determine the most active materials and their most effective con- centrations, 3) studying combinations of plant growth regulators and certain adjuvants in an effort to inhibit fruiting, and 4) testing various types of physical barriers such as liquid plastics as contra- ceptives for pollination. The work here was generally along three lines; I) using materials which may act as physical barriers to pollination, 2) using certain plant growth regulators over a concentration range and 3) studying flower and fruit morphology. The following plants were selected for study: Ailanthus altissima (Mill.) Swingle. (Tree of Heaven) Catalpa speciosa Warder. (Western Catalpa) Malus pumila Mill. 'Jonathan' (Jonathan Apple) Malus zumi calocarpa (Rehd.) Rehd. (Redbud Crabapple) Prunus cerasus L. (Sour Cherry) Thuja occidentalis L. (American Arborvitae) Selected materials for fruit prevention were of three general types: l) caustic, 2) hormone and 3) liquid plastic. A caustic ma- terial was used in an effort to selectively 'burn' the sensitive flower parts and thus prevent fertilization or halt deveIOpment after fertili- zation. Hormone materials were employed as agents which would cause flower or deveIOping fruit abscission. The liquid plastics were used as a means of physically preventing pollination and fertilization. The studies were conducted at the Michigan State University campus, horticulture farm and grounds nursery and at Hidden Lake Gardens in Tipton, Michigan. INTRODUCTION Since the beginning of time the production of fruit* by plants has been essential for the existence of man and beast. Man was a wanderer in primitive times, quite dependent on plants for food. Almost every sort of fruit was used in some way. Then, as now, fruit was an integral part of the diet. The production of fruit and seed is the means by which higher life exists. The adaptation of fruit production by plants has not been in vain for it has enabled both the plant and animal kingdoms to advance to the degree at which they now stand. With the advent of communal living came the art of landscaping and the use of plants for aesthetic appreciation. In many instances the productiOn of fruit is indeed a desirable aspect although some- times the fruit are unwanted. It is the purpose here to deal with the latter aspect -- that of unwanted fruit. *Fruit - a structure consisting of one or more matured ovaries, to- gether with any accessory structures adhering to them (29, p 526). LITERATURE REVIEW That vegetative and reproductive growth are antagonistic and that fruiting is an exhaustive process has been recognized ever since man began to observe plants. The0phrastus (60) in the Third Century B.C. observed that some men pluck flowers of the cucumber, which are borne at the ends of the shoots, for these hin- der the cucumber's growth. He thought fruiting to be an exhaustive process. Pliny the Elder (50) in the First Century A.D. observed that trees were unproductive as long as they remained growing, pre- sumably in a vigorous state. Flowering and fruiting do indeed occur at the expense of vegetative growth and vice versa. The need or desire to remove flowers and fruit from plants is by no means a new idea. For as The0phrastus observed, such may be necessary for desirable plant growth. It is a commonly observed fact that plants which have been recently tranSplanted, injured or are in poor health tend to produce fruit in great abundance. Such fruit production is not advantageous for establishment, recovery or sur- vival of the plant. The devel0ping fruit draw heavily upon the car- bohydrate supply which in most cases could better be used for vege- tative growth and devel0pment. If such a plant was defruited, it could develop more favorably (IA, 28, A6, #7). Certain fruit trees, eSpecially Apple, tend to flower and set fruit* at a very early age. This is often due to the use of a dwarfing root-stock. Some varieties naturally set fruit early. The production of fruit at such an early age is generally not de- sirable, for the weight of the fruit tends to ruin the structure which should be attained for a well formed tree. Excessive fruit growth also inhibits shoot growth. If the flowers or fruit were removed the young tree could more readily develop a desirable struc- ture (ll). The fruit of numerous landscape trees is often undesirable for one reason or another. The Ginkgo has fruit which produce such an odor that one would think nothing of crossing the street to avoid it (IA, 61, 6A). Fortunately, most nurseries now sell only the male trees, the species being dioecious, which produce no fruit. A number of street trees such as Elm, Maple and Ash fruit so prolifically that drains are clogged and sewers become blocked. Quite a few trees drop their fruit on lawns and other areas making mowing and maintenance operations difficult. Cleaning up after these trees is expensive and exhaustive (IA). Homeowners often have old specimen fruit trees which are valued for shade but whose fruit is of no value, drOpping over lawn and walk areas, attracting bees and flies and causing a *When successful fertilization occurs there is a burst of growth of the ovary and the fruit begins its deveIOpment. Simultaneously, there occurs a wilting and even abscission of petals. Such changes mark the transition of the flower into a fruit (37, p 259). general nuisance. If fruit set could be prevented these trees would be fine landscape Specimens. It is also the case that fruit trees would be planted for their profusion of bloom if there were means to prevent fruiting. Trees such as Mulberry produce fruit which stain autos and driveways. The fruit also attract birds which are nuisances in other ways (IA). Certain landscape plants are very unattractive when covered with fruit. The Arborvitae (Ihgjg) is a good example. Some individual Specimens of the genus become so covered with small cones that some people imagine the plant has suc- cumbed to some sort of strange infestation. If fruit devel0pment could be prevented the plant would be held in greater esteem as a landscape Specimen. In public, even private places, children will sometimes use fruit as projectiles, climb trees for access to the fruit and in the process break branches. In connection with defruiting, pe0ple often ask “why?” Haskell (28) put it well when he said ”While most of us think very highly of trees, like to have them around, and readily forgive them their little failings and drawbacks, sometimes it seems that when the fruit is formed certain of our leafy friends strain this forgiveness until it wears thin.” A partial list of landscape trees which produce ”objectionable” fruit is given in Table I. In early times defruiting, generally thinning, if practiced at all was done by hand, primarily in the orchards where it was practical. Table l. Trees which produce objectionable fruit and the criteria for the objection. Species Criteria for Objection Arborvitae Ash Black Locust Catalpa Cherry Crabapple Elm Ginkgo Honey Locust Horsechestnut Kentucky Coffee Maple Mulberry Pear Persimon POplar Sweetgum Tree of Heaven aesthetic, drain CIOgging drain clogging lawn maintenance lawn maintenance, aesthetic lawn maintenance, birds lawn maintenance, insects drain clogging odor, lawn maintenance lawn maintenance lawn maintenance lawn maintenance drain clogging staining, lawn maintenance, birds lawn maintenance, insects lawn maintenance drain clogging, lawn maintenance lawn maintenance aesthetic, drain clogging This method has its advantages for one can be very selective, leaving only a certain number of fruit per limb or leaf area. Fruit size is directly related to leaf area (2A, Al, A2). Aldrich (2) observed that a larger leaf area per fruit increased growth rate of the fruit. Thinning increases the size of the remaining fruit and reduces biennial bearing (1, 26, 3A, 59). The need for thinning arose from the problem of biennial bearing. It soon became apparent that hand defruiting was costly and slow so workers began the search for compounds which would ac- complish this task. Some of the first chemical defruiting or thinning work was begun in the I930's using inorganic compounds. During the middle l930's to early l9AO's many growers wanted to completely eliminate a fruit crOp. Because of the depression and war they could not afford to Spray and continue normal orchard operations. The growers wa1ted some material to inhibit fruit set or defruit without permanently injuring the trees. If fruit were left to mature without cultural practices or picking, insects and diseases would have an ideal refuge and build up drastically. Early workers who concerned themselves with finding defruiting compounds and techniques were: Auchter and Roberts (A) I933, Cole (l6) l9A2, and Schneider and Enzie (S6) l9A3. They used such things as copper sulfate, lime sulfur, sodium nitrate, zinc sulfate, Bordeaux, tar oils and cresylic acid. The oils seemed to be most effective. The lO results showed none to be completely satisfactory and in almost all cases were variable, leading them and others to search for new and better compounds. One material, Elgetol (Sodium dinitro- ortho-cresylate) which was reported by MacDaniels, et al. (38) in I939, was used to a great extent. Later work again showed that when used at about 2,000 ppm Elgetol destroyed the receptive nature of the stigma and inhibited pollen germination, thus proving to be a good thinner or defruiter (6, 30, 31, A8, 57, 59, 63). During the early 1930's the question arose as to what effect materials which were being used for control of fire blight and scab had on fruit set. MacDaniels, et al. (39, A0) carried out some of the first work. It was found that Sulfur used in scab control sometimes reduced fruit set by preventing pollen germination. Some of their other work showed no reduction in set. In I937 Gardner, et al. (2i) found that a hormone type material, Naphthylacetic acid (NAA) reduced abscission of parthenocarpicaily induced holly fruit. The observation led workers to the realization that fruit which tended to drop just prior to harvest might be held on the tree until picking. Gardner and co-worker (22) in I939 Showed a reduction in pre-harvest fruit drop with NAA and Naphthyla- cetamide (NAD) applied at about 2.5 ppm. The following year Burkholder and McCown (l2) pointed out that if NAA and NAD were applied at or shortly after bloom there was a reduction in number of clusters setting fruit. They observed some leaf injury when using the acid form of NAA but very little injury when the amide form was used. At 50 ppm.NAA there was a 77 percent reduction in fruit Set but serious injury occurred on young leaves, which scorched and drOpped. With NAD at 50 ppm a reduction in set of 3A percent and no leaf in- jury were observed. Thus, when NAA and NAD were used at the same concentrations, NAA was the more effective as a defruiting agent but caused leaf injury. Starting in about the mid l950's hormone type Sprays and Elgetol began to be applied on a commercial basis in orchards. In northwestern United States the caustic sprays became and still are widely used while the hormone type were and are commonly used in eastern United States (62). Various carbamate formulations have been used in thin- ning work but with no great success (32). In the late l950's the insecticide Sevin (l-naphthyl N-methylcarbamate) came into use in orchards. It was soon observed that this material caused thinning (7, 10). Workers have tried various materials in an effort to find better deflowering, thinning and defruiting compounds. White and Kennard (67) in l950 reported the use of maleic hydrazide on Apples. Appli- cations at concentrations of 1,000 - 3,000 ppm.to buds in the pink stage were used in an effort to delay flowering. They found little vegetative or floral retardation but abscission of the fruit occurred at an early stage of development. Maleic hydrazide was applied to plants such as tobacco, corn and cocklebur in order to observe effects on flowering. Treated tobacco plants produced no new flowers and all those initiated at the time of treatment were dead (A9). Flowering of certain azaleas was inhibited by maleic hydrazide (l3). Gibberellic acid has been used by a number of workers (9, 23, A3, A5, 5A). Bradley and Crane (9) showed that gibberellic acid inhibited the development of lateral meristems in several Prunus Species, thus, reducing bud development. Working with Apple, Marcelle and Siroval (A3) concluded that flowering was decreased corresponding to an increase in shoot growth. A latex type material when combined with certain insecticides was also found to have a thinning effect (20). A material called DCIB (Sodium dichlor- oisobutyrate) has been found to reduce subsequent fruit set in to- mato (35). When thinning or defruiting work is undertaken a great number of factors are encountered which can and will vary the results. For this reason results from year to year, tree to tree and region to region differ. ”There will probably never be an ideal thinner that will give satisfactory results in all varieties, in all years under all condi- tions. The factors involved in fruit set are too many and too com- plex to hope for such (62).” Continued research is the only means toward this goal. A very excellent discussion of the many factors affecting thinning l3 can be found in Fruit Thinning With Chemicals (5). The bulletin also reviews the history of thinning and discusses thinning of stone fruits in detail. The factors affecting fruit thinning include: a) concentration, b) timing, c) weather, d) additives, e) Species or variety, f) tree vigor, 9) number of applications, and h) amount of bloom. a) The concentration range is a factor of prime importance. NAD, for example, is used at l0 to 20 ppm.for thinning and A0 to 60 ppm. for defruiting while higher concentrations cause leaf'burn“. Since many factors affect the performance of a chemical, it is particularly difficult to recommend an inflexible rate of application. b) Time of application appears to be less critical than some of the other factors. Davidson, et al. (18) showed that most successful thinning could be accomplished with NAA from full bloom to about two weeks after. If applied much beyond one month after full bloom, thinning could not be accomplished. The dinitro compounds have little latitude due to their mechanism of action. It has been found that thinning is best done at or shortly after petal fall, while defruiting is best accomplished at full bloom (IA, I9, 27, 28, AA, 58, 62). c) One of the most variable factors is the weather. In the case of hormone and caustic type materials unfavorable conditions such as cool temperatures, low light intensity and rain at time of application result in heavy thinning (5). It was shown by Westwood (66) lA that when under very high humidity, leaf cuticle was altered in reSpect to the spreading and absorption of Elgetol. d) It has been observed that certain materials used as surfactants will in themselves act as mild fruit thinners and when used with thin- ning materials such as NAA will increase the thinning effect of that chemical (25, 65). Horsfall and Moore (33) tried various inorganic salts as adjuvants with NAA. Of all the ones used only ammonium possessed thinning activity. e) Certain varieties of Apple are thinned more easily than others. Those considered hard to thin are Golden Delicious, Yellow Transparent, Rome Beauty and Baldwin. Red Delicious, McIntosh, Jonathan and Northern Spy are easy to thin, while Grimes Golden is considered intermediate. It has been observed that varieties which set heavier fruit loads, being partially self-fruitful, are harder to thin (5). f) Tree vigor is another factor affecting thinning. Heavy thinning usually occurs on trees that are low in vigor because of low fertility, winter injury, low food reserve, light pruning, low light intensity or other factors. Such trees tend to have few fruit and the fruit are easily thinned. 9) Other factors which influence the effect of thinning Sprays are the number of applications, bee activity and amount of bloom. As early as l9lA it was observed that dust from cement mills 15 inhibited pollen germination of certain fruit trees. The dust con- tained alkali and calcium salts which went into solution on the stigmatic surface (3). Attempts to prevent fruit set are directed at the gynoecium rather than the androecium. The gynoecium appears to be more sensitive to injury and exposed in Such a condition for a greater period of time. If only the local pollen source is con- trolled, pollination may still occur from a source far remote from the controlled area. The stigma and petals are the most sensitive parts of a flower. Caustic materials must be used within a critical concentration range so that the stigma or other flower parts are l'burned" while the leaves are not adversely affected. A material which only destroys the receptivity of the stigma would have to be applied before pollination. If the material progressed to injure the ovary, it could be applied well after pollination. NAA and re- lated compounds have been found most effective for deciduous trees. These materials can generally be applied over a wide time period, generally within a seven to ten day period after full bloom. For defruiting purposes, the materials are best applied at full bloom. The material to be found in the literature concerning thinning is almost infinite but references to actual defruiting are few. Most of the latter work has been conducted by city maintenance workers and landscape horticulturists concerned with Specific problems. The first defruiting work was done by hand. Murneek and Hibbard (A8) had good results by using Elm switches to thin or defruit Peach trees. Needless to say, hand defruiting was slow, tedious and not very efficient. Some of the early work was sup- ported in connection with the National Shade Tree Conference in an attempt to find methods and materials for economically preventing fruit formation on numerous landscape trees. Miller and Erskine (AA) in l9A9 conducted tests on over a dozen tree Species. They showed that materials such as NAA, NAD, dinitros and maleic hy- drazide could be used for defruiting purposes on some trees. Very good elimination of fruit was observed on Ash, Catalpa, Crabapple, Elm, Horsechestnut, Norway Maple, Tree of Heaven and Poplar. Haskell (28) in I953 reported good success in preventing fruit set on Catalpa, American and English Elm, and Horsechestnut. NAA and Elgetol (a dinitro) were found to be the most effective. The caustic dinitro type materials were only practical when flowering preceeds leaf emergence as in Populu . Table 2 summarizes the work which has been reported in connection with fruit prevention work. In past years the defruiting of Ginkgo has received some atten- tion because of the obnoxious odor of the ripened fruit. Turner (6l) in I953 had little success with chemicals because of leaf burn so he experimented with other methods. Sending men into the trees armed with Spiked poles was not too successful. It took four to six l7 :: co_umc___oa vouco>mca 0N: nu_3 meow .co_uco>mca _m_ucmm soc—n __:m 0N". 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