INTEGRATED CONTROL OF PESTS IN ORCHARDS BY

It. J. D~ FLmTF.R

In pest control one can distinguish between biological measures and cultural practices at one side and chemical and physical procedures on the other side. Biological and cultural methods are part of the so called ecological control which aims at increasing the overall resistance of the environm e a t against the increase of pest populations. Chemical and physical control both arc part of the technical control which in general aims at rapidly and effectively putting an end to a pest. According to FRANZ " integrated control (1) is defined as the integration of cultural, chemical and/or physical control methods with the effect of enemies of pests " This conveys the meaning that the most suitable elements of biological, chemical, physical and cultural control methods are being combined in such a w a y that the effect of the natural enemies is increased or integrated with - - b u t in a n y case not seriously affected b y - - the last mentioned three methods of control. " Harmonious " control (2), however, is the integration of ecological and technical control; " integrated control " is one of its most important objectives. The striking results obtained after World War II in the control of pests b y the application of synthetic organic insecticides made them generally accepted in m a n y fields. However, the general toxicity of the control agents entailed m a n y risks. The wide range of activity of m a n y of these insecticides strongly intervened with the biocoenosis of treated plots because beside the noxious organisms also their natural enemies, their food competitors and m a n y indifferent co-bionts were killed. The result was that the small population (t) I n t e g r a t e d c o n t r o l ~ i n t e g r i e r t e or n i i t z l i n g s s c h o n c n d e B e k ~ i m p f u n g = l u t t e intSgr6e = l o t t a i n t e g r a t a . (2} H a r m o n i o u s c o n t r o l = h a r m o n i s c h e S c h ~ i d l i n g s b e k t i m p f u n g = l u t t e h a r m o nique. ENTOMOPHAGA TOME VIii No 3p :3o TEIMESTRE 1962

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of the harmful organisms left behind after the t r e a t m e n t , generally rapidly increased again. Organisms which previously had been known only as potential pests in m a n y cases suddenly developed into real pests after the application of chemical control agents. Finally the population of harmful organisms showed more genetic plasticity t h a n was assumed at first. In m a n y cases the frequent applications of insecticides or aearicides led to the selection of races of the noxious organism which are resistant to the control agents. However, apart from those disadvantages chemical control definitely has its merits. The demerits mentioned above, however, indicate t h a t chemical control is not the most ideal method of control; it cannot give a perm a n e n t solution of the control problem. Now, what other possibilities are there? Here we t h i n k of harmonious control, a control method based on the integration of ecological and technical control, with integrated control viz. the integration of biological control with chemical and physical control and control by culture measures as the most important objective. Integration of biological and chemical control places the use of specific and therefore selective agents in the foreground. The agents with a wide range of activity - - and among them especially those with a long residue action - - in this control method will be applicable only in very special cases. Experience gained with our experiments ~ set up in moderl), wellkept, but biocoenotically " spray-killed " orchards from which we had to start - - shows us t h a t this will a t first mean an increase of the number of treatments. However, there is every reason to assume t h a t this number can be reduced to a level below t h a t of an orchard with a " normal " spray programme, as soon as the natural resistance complex will have recovered in such a way t h a t it can again assume a regulating function. However, there are circumstances - - for instance in case of a simultaneous occurrence of a number of harmful organisms which belong to very different systematic groups - - which from an economic and technical viewpoint will necessitate the provisional use of a polyvalent control agent. In such cases one should choose an agent which exerts the smallest detrimental effect on the most important beneficial organisms. The use of non-specific agents can be tolerated also within the framework of integrated control if by local application the harmful organism is much more susceptible t h a n its n a t u r a l enemies, and potential pests are not stimulated. Good examples of this are known in fruit growing (grease-bands), in silviculture and in viticulture.

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Also, when treatments can be timed in such a way that no or only little injury is done to the most important beneficial organisms, it is permitted to use polyvalent control agents within the scope of integrated control. The combined use of poisons and attractants which have a specific appeal to certain harmful organisms, is of course also tolerated.

As concerns modification of the control methods it should be pointed out that in integrated control, in principle, chemicals are applied only when it is necessary. The chemical control then works as a temporary checking factor which forces the population of the harmful organism back again within the control of the natural resistance complex. Good results with this procedure have already been obtained in European silviculture, in fruit growing in Switzerland, Germany and in Nova Scotia and also in alfalfa- and in citrus culture in California. In the integrated control, the application of pathogenic microorganisms, in particular bacteria and viruses, may take an important place. According to their effect they may be utilized either in connection with chemical control (among others B. thuringiensis with its toxic crystal) or within the framework of biological control (espccially viruses). Integrated control aims at increasing the resistance of the environment of the harmful organism through sparing the natural enemies, through brecding and releasing natural enemies which are resistant against given control agents, through improving the possibilities of development of the natural enemies in or in the vicinity of the habitat concerned for example by establishing refugia, by increasing the number of flora elements which are necessary or attractive for them, by periodical treatment of alternate strips of the crop a.s.o.

Problems involved in integrated control. After the aspects of integrated control we now will deal briefly with the problems involved in applying this method in practice. First we should point to the difficulties arising in ~owing crops as monocultures. These monocultures generally have a one-sided fauna with few species which are often specific for the crop concerned and for its cultural practices. Such a poor fauna endangers the stability of the biocoenosis and ~ e a t l y aggravates the possibility of harmful components developing to a pest. 111 addition the changeable climate of our temperate regions promotes the occurrence of fluctuations in the population density of harmful organisms. Furthermore experience has shown that the cultural practices (pruning, dressing, etc.) necessary for an effective culture, entail

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the appearance of pests which are specifically adapted to the cultural method. The " equilibrium ", if actually present, therefore is an extremely unstable one which requires our constant alertness. In integrated as well as in harmonious control chemical agents are used only when it is necessary, that is to say, when the crop is threatened b y economic injury. This means t h a t it should be known where the critical population level lies since overstepping this level m a y lead to fatal consequences. Although the results of the first profound investigations on this problem have already been published, our knowledge a b o u t the position of this level is v e r y insufficient in m a n y eases. Y e t we should t r y to learn more a b o u t it as soon as possible, because this critical level can also give us information concerning the size of the rest population of the harmful organisms to be tolerated after applying control measures, in order to give the natural enemies an o p p o r t u n i t y to maintain themselves. Since integrated control is based on good cooperation between chemical control and a successive effect of a natural resistance complex, which will have to keep in check the rest population as much as possible, the presence of a regulating complex of factors is a prime demand. U n f o r t u n a t e l y our knowledge a b o u t useful organisms occurring in our crops and their w a y of living still has m a n y gaps. This is even more pronounced in as far as our knowledge a b o u t their significance as regulators of the population density of the noxious organisms is concerned. Often their importance in this field is inferred from the fact t h a t after chemical control with an all-round agent certain harmful organisms occur more frequently than before the application. It is t h a n frequently assumed that b y the control of the harmful organisms also the natural resistance eomplex has been eliminated. This conclusion, however, can be misleading since other causes, for instance a modification of the physiological condition of the host plant under the influence of the treatment, m a y lead to this increase. The research concerning population dynamics which is so urgently needed to increase our knowledge in relation to the regulating function of natural enemies, is difficult and time-consuming. It is conducted only incidentally and an extension of this t y p e of work is highly desirable. One of the most important problems is the integration of biological and chemical control. Not only insecticides and aearicides are a threat to the beneficial elements in the bioeoenosis, b u t also fungitides which often have to be applied much more frequently than insecticides. I only will mention here the m a n y preventive spray t r e a t m e n t s necessary for an effective control of scab and mildew in our apple orchards. In laboratory and in field experiments m a n y valuable data have

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been obtained concerning the susceptibility of predators and parasites for the control agents which are now in general use. Apart from affecting the harmful organisms m a n y of them also appeared to have a fatal influence on the beneficial fauna-elements. We arc already more or less informed a b o u t control agents which directly or indirectly have a stimulating effect on the abundance of certain harmful organisms, and our knowledge concerning the effect of cultural practices such as dressing and pruning on the development of harmful organisms has been considerably increased in recent time. However, our knowledge about the causal relationship which exists between treatment and effect is still very small and should therefore be extended in order to gain a clearer idea a b o u t the phenomena observed. There is an urgent need of thorough experimental investigations into the influence of the " physiological condition " of the host plant on the development of phytophages feeding on it and also into the basic processes in the plant which m a y influence this physiological condition toward a favourable or unfavourable direction. Finally, there is the problem of resistance against chemical control agents. It is of the utmost importance that the mechanism of this resistance be studied profoundly. D u t c h research workers have made important discoveries in the field of resistance to organo phosphorouscompounds. Let us hope t h a t their work ultimately will be able to show farmers the way to control populations resistant to organo phosphorouscompounds. An other way to overcome the difficulties of the resistance problem m a y be the use of hormones, which are effective in extremely small concentrations, which can penetrate through the skin of m a n y insect species and when present in excess m a y disturb their biological functions. Theoretically they offer possibilities of controlling harmful insects. However, much fundamental research will have to be done before we will be able to apply these substances efficiently in practice. It is encouraging therefore t h a t attention is now being focussed on t h e m and that t h e y are being studied in m a n y countries. In the Netherlands a Research Team for Harmonious Control of Pests " has been established to coordinate the research in this field conducted at the various institutes in the Netherlands. It operates under the auspices of the National Council of Agricultural Research and comprises approximately 80 researchworkers working" at 15 institutes. One section of this working p a r t y deals with integrated control. PICKETT and collaborators in N o v a Scotia developed an effective control of insect pests in orchards b y applying very small quantities of fairly selective insecticides. Using as low concentrations as possible "

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t h e y applied these insecticides only when it was necessary to prevent the occurrence of harmful insects as a pest with the result t h a t only a small percentage of the n a t u r a l enemies were k i l l e d . Prcx~.TT discovered his method more or less b y intuition in the course of his experiments. Actually it is still impossible to explain precisely why he was so successful. Conditions in Holland are different from those in Nova Seotia, so t h a t the Pickett-method cannot be adopted here unaltered. The realization of integrated control in orchards in Holland has been sought in two ways : 1. B y investigating the fundamentals of the method. 2. By reduced and modified spray programmes and ascertaining the influence these have on the fluctuations of the population density of the harmful arthropods and their enemies. BRaV~.NBOER could limit the glasshouse red spider mite (1) pest in the " Westland " by a single application of a selective acaricide. Under these conditions the pests could be kept in check further by the natural enemies. So here was a remarkable success, although under conditions widely different from those in the field. F a r less favourable however are the results obtained so far in applying " modified spray progranunes " in orchards. In the experimental complexes which are being treated according to a modified spray programme the principle followed is t h a t only selective chemicals are used, which spare as m a n y as possible of the natural enemies of the harmful organisms and in addition are of little or no danger to the consumer. Only when these fail are other less selective agents used in order to prevent too great economic losses. The field experiments in orchards are carried out by DE FLUITER, EVENHUIS, DE JONG and VAN DE VRIE of the I . P . 0 . (2) and ANKERSMIT, VELTHUIS and ZWART of the Laboratory of E n t o m o l o g y of the Agricultural University while BESEM~R (P.D.) (3) gives advice concerning the " normal " and the " modified " spray programmes. In the field experiments of the I.P.O. in the Betuwe and in Zeeland, the development of populations of harmful and beneficial organisms in parts of t h e orchard which were treated according to the " modified control method ", are compared with the development of populations of these organisms in normally treated parts or in parts t h a t were not treated with chemicals. DE JONG "studies in particular the leaf rollers and their enemies, VAN DE VRIE the fruit tree red spider mite (4) and its predators and EVENHUIS the aphids and their predators and parasites. (1) Tetranychus urticae r o c m (2) I.P.O. : I n s t i t u u t voor P l a n t e n z i e k t e n k u n d i g O n d e r z o e k at W a g e n i n g e n . (3) P.D. : P l a n t e n z i e k t e n k u n d i g e Dienst at ~Vageningen. (:~) Metatetranychus ulmi (c. L. KOCh).

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A N K E R S M I T , VELTHUIS, ZWART and BESEMER apply a " modified spray programme " in an orchard near Wageningen and jointly s t u d y its influence on the various harmful and beneficial organisms. Although in all cases the harvest results obtained with the modified programmes are still less favourable than those obtained by normal spraying, VAN D~. VRXE, in controlling the fruit tree red spider mite, obtained very good results b y applying a method in which phosphoric esters were entirely lacking and only selective ovolarvicides were used. DE JONG and EVENHUIS, in order to prevent considerable economic damage b y the fruit leaf roller (1), in the late summer however had to apply a chemical which did not fit into the " modified programme ". In one of the experimental complexes where a modified scheme was used control of the rosy apple aphid (2) was unduly delayed with the result that considerable damage occurred in spite of the fact that later the pest could be controlled efficiently with a selective agent. This case demonstrated clearly how accurately the control should be timed and the consequences which m a y result by overstepping the limits of the critical population density. In the experimental complex of Thedinghsweert (the " Betuwc ") this aphid was satisfactorily held in check b y the timely application of a selective agent. Other problems in integrated control in orchards are the control of the harmful leaf rollers (1) and the control of the mildew-fungus because the agents which can be used successfully against these pests are not enough selective, and -as appeared from extensive laboratory experiments- can have a very unfavourable influence on the beneficial organisms, in particular on the p r e d a t o r y mites. The possibilities of controlling the caterpillars with the aid of pathogenic bacteria and viruses are now being studied. Observations in a part of the experimental orchard at Thedingweert in the Betuwe (prov. of Gelderland), where a biologicaldynamical method is applied and where neither insecticides nor fungicides were used, showed that it entails very serious dangers in as far as the production of a profitable yield is concerned, at least in the first year of the change over. In order to s t u d y the spray programmes aimed at the maintenance of parasites and predators it is necessary to learn the effect of insecticides and fungicides on them, so VAN DE VRIE and ANKERSMIT conducted m a n y laboratory experiments. The results of these investigations will be utilized for planning programmes in following years. The results obtained to date have clearly shown that no great success m a y be expected from modified spray programmes designed (t) Adoxophyes reticulana (liB.). (2) Dysaphis plantaginea (eAss.).

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m o r e or less i n t u i t i v e l y w i t h o u t sufficient k n o w l e d g e a b o u t t h e f a u n a of t h e o r c h a r d . The p r o g r a m m e s s h o u l d be modified on t h e basis of d a t a o b t a i n e d in f u n d a m e n t a l research a n d in t h e field. I h a v e t r i e d t o s u r v e y t h e a i m s o f i n t e g r a t e d c o n t r o l in orchards, its a s p e c t s a n d p r o b l e m s . L o c a l l y this m e t h o d has a l r e a d y been successful, elsewhere efforts are b e i n g m a d e to s t u d y h o w far this m e t h o d c a n yield a s o l u t i o n t o t h e d e a d l o c k c a u s e d b y exclusive c h e m i c a l control. Y o u will u n d e r s t a n d t h a t in o r d e r t o p r e v e n t p u r e l y i n t u i t i v e p r o c e d u r e s , or t r e a t m e n t s a c c o r d i n g to t h e trial a n d e r r o r - m e t h o d , m a n y i n v e s t i g a t i o n s in m a n y fields h a v e t o be carried o u t t o give i n t e g r a t e d c o n t r o l a w e l l f o u n d e d scientific basis on w h i c h a d v i c c s c a n be g i v e n w i t h success a n d w i t h o u t risks for t h e growers.

RI~SUMI~ La (~ lutte int6grde ~, ((c integTated control , des Am6ricains) se propose de recourir h une combinaison avantageuse des d!ff6rcntes m6thodes chimiques, biologiques et culturales de lutte contre les ennemis des cultures. Son objet est d'aceroitre le potentiel de d6fense intrins~que du milieu eultiv6 contre les attaques des ennemis des plantes, particuli~rement en modifiant les formes usuelles de la lutte chimique pour assurer une meilleure sauvegarde des organismes utiles. Ses problbmes, singuli~rement dans le cadre de la monoeulture intensive, conccrnent : (~l'int6gration ,, des m6thodes de lutte biologique dans un programme de lutte ehimique modifide, la d6termination du niveau du seuil de tol6rance (!conomique des d6g~ts commis par les d~pr6dateurs, la meilleure connaissanee du r61e des organismes utiles eomme r6gulateurs de la densit6 de population des organismes nuisibles. Pour atteindre cet objeetif et r6soudre ces problSmes, il cst indispensable de proe6der h des reeherehes de base approfondies.

(Instituut voor Plantenziektenkundig Onderzoek (I.P.O.). IVageningen, The Netherlands.)