Waarnemingen betreffende Ditylenchus radicicola (Greeff, 1872) Filipjev, 1936

Summary On account of recent records ofDitylenchus radicicola (Greeff, 1872)Filipjev, 1936 in Dutch meadows, a study was made of its biology. Literature data were summarized.The eelworm attacks the roots of Gramineae and causes spiralshaped galls, which may contain up to 60 adults and some thousands of eggs and larvae each. Young larvae may actively hatch in water from whole, undecayed galls at temperatures around 17°C (Graph. 1). Root exudate of host plants did not stimulate the hatching process. The first larval stage is infective and may penetrate young root tips and also young galls (Fig. 1); it can withstand 2 month desiccation and also desinfection in a solution of an organic mercury compound. The host plant influences the number and size of the root galls (Graph. 2). Fig. 2 shows the anatomy of a young gall.The parasite is only found in grasses in this country and damage has not yet been found. Rye, wheat, barley and oats proved to be susceptible in inoculation trials; 17 plant species have been mentioned as natural hosts in different countries now and 3 are only found susceptible in inoculation trials.     

On biotypes of the cereal-root eelworm (Heterodera Avenae) and resistance in oats and barley

In the Netherlands four biotypes of cereal-root eelworm have been recognized by usingAndersen's series of test varieties. Three forms ofAvena sterilis and 14 varieties of oats were found to be resistant to the four biotypes. In barley two varieties showed resistance to four biotypes and many varieties were found to be resistant to one, two or three biotypes.     

Onderzoekingen over schimmels,die parasiteren op de cyste-inhoud van het aardappelcystenaaltje (Heterodera rostochiensis Wollenw.)

Ohne Zusammenfassung

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With a summary: Investigations on fungi, predacious on the cyst contents of the potato root eelworm (Heterodera rostochiensisWollenw.)

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Gedetacheerd door de Werkgroep Onderzoek Bestrijding Aardappelcystenaaltje T.N.O.; thans: Laboratorium voor Toegepaste Entomologie, Amsterdam.     

Het parasitaire karakter van Septotinia populiperda Waterman & Cash

Summary Mature apothecia ofSeptotinia populiperda Waterman andCash are formed in spring and early summer on leaves shed the previous autumn. The ascospores ofS. populiperda produce an infection in the form of leafblotches only when an injury of the leaf is present.P. candicans Ait. is more susceptible to the parasite thanP. marilandica Bosc. andP. brabantica Houtz. Leafblotches are produced in equal numbers when the ascospores are sprayed with an atomizer upon the upper or the lower leafsurface. The germination of the ascospores is inhibited in vitro at a concentration of 7 to 8 mg copper per liter, when copper is used as Bordeaux mixture, or as coppersulfate (CuSO₄5H₂O).     

Observation en Hollande de la forme parfaite du champignonGloeosporium perennans Zeller et Childs

Summary In October 1956 apothecia, belonging toPezicula malicorticis (Jackson)Nannfeldt (=Neofabraea malicorticis (Cordley) Jackson), the perfect stage of the parasite known in plant pathology literature asGloeosporium perennans, have been found on naturally infected appletrees in Druten and near Deest (Land van Maas en Waal) and on appletrees at Wageningen, which had been inoculated with mycelium ofG. perennans in October 1955. The apothecia occurred as well on the surface of the bark as in old conidial fructifications; they were sessile, clearly convex, bright-yellow under moist conditions and brownish when old or dry. The diameter of the apothecia was 0,4–1,6 mm. As many as 100 apothecia were found on a square cm. It is put forward that the formation of the apothecia has been favoured by the very wet weather of the preceding summer.

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Ingénieur agronome aux Stations fédérales d'essais agricoles, Lausanne (Suisse).     

Het toetsen van stammen vanNectria cinnabarina (Tode) fr. op levende takken in vitro

Summary Some types of elm hybrids resistent to the Dutch elm disease turned out to be susceptible toNectria cinnabarina (Tode) Fr. This fungus may behave as a parasite, killing branches. Virulent and non-virulent strains are known. A method is described for cultivatingNectria-strains in vitro on living desinfected branches ofAcer and ofUlmus. Three weeks after inoculation with a virulent strain the branches were killed. They were covered all over by a thick layer of mycelium. The mycelium of non-virulent strains could not kill the branches. It developed only sparsely. By this method it will be possible to select the most virulent strains out of a collection of isolates in order to use them for testing elm hybrids on their resistence toNectria cinnabarina.     

Ontsmetting van bloembollen tegen Heterodera rostochiensis

Samenvatting Hoewel op metH. rostochiensis besmette grond in Nederland geen bloembollen verbouwd worden, is een ontsmettingsmethode ontwikkeld waarbij aanhangende cysten van dit aaltje worden gedood zonder de bollen te schaden.Enkele organische kwikverbindingen, die geregeld worden gebruikt als bloembolontsmetters ter bestrijding van schimmelziekten, bleken ook goed werkzaam tegenH. rostochiensis.Bij Aaventa bleek dompeling in 1/4% gedurende 6 uur, 1/2% gedurende 3 uur en 1% gedurende 1 uur juist afdoende (tabellen 1 en 2). Deze voorH. rostochiensis dodelijke concentraties bleken zonder bezwaar verdragen te worden door alle onderzochte soorten bloembollen, namelijk 2 variëteiten narcis, 4 variëteiten hyacinth, 1 variëteit iris, 1 variëteit crocus, 3 variëteiten tulp en 2 variëteiten gladiool. De enige uitzondering was de tulpenvariëteit Red Emperor (tabel 3f), die echter ook in andere opzichten sterk afwijkt van het normale tulpensortiment.Bij vergelijking van Aaventa met de gebruikelijke bloembolontsmetters bleek Aabulba eveneens goed bruikbaar en zelfs beter dan Aaventa (tabellen 6a-d). Op grond van vroegere ervaringen wordt aangenomen, dat ook Aabulba niet phytocide is bij de voorH. rostochiensis dodelijke doses.Summary Though bulbs are not grown in soil infested withH. rostochiensis in the Netherlands, a method has been developed which gives complete destruction of adhering cysts of this eelworm, without damaging the bulbs.Some organic mercury compounds, which are regularly used as dips in controlling fungus diseases of bulbs, proved to be effective againstH. rostochiensis also.With Aaventa a complete kill ofH. rostochiensis was obtained using 1/4% for 6 hours, 1/2% for 3 hours and 1% for 1 hour (tables 1 and 2).These lethal doses did not affect the germinative and productive power of the tested bulbs, viz., 2 varieties of daffodil, 4 of hyacinth, 1 of iris, 1 of crocus, 3 of tulip and 2 of gladiolus. The only exception was the tulip variety Red Emperor (table 3f), which is an exceptionally susceptible variety in several respects.A comparison of Aaventa with the more common commercial bulb dips proved that Aabulba was also useful and even better than Aaventa (tables 6a-d). From former experience we conclude, that Aabulba is also, not phytocidal to bulbs in doses completely lethal toH. rostochiensis.     

Resistance as a Means of Control of the Potato Root Eelworm

A survey of the resistance of wild potatoes to the potato root eelworm and the use made of this property in potato-breeding is presented. Several biotypes of this parasite have been found to exist. The use of resistant varieties in the control of the potato root eelworm, in connection with other methods of control (crop rotation and soil disinfestation), is discussed.     

Can native grass species outcompete invasive goldenrods? Results of a replacement series experiment

Invasion by alien species is a serious threat to the biodiversity and function of semi‐natural grasslands and may impede restoration efforts in degraded meadows due to high competitiveness. Goldenrods (Solidago and Euthamia species) are considered among the most injurious invaders of grasslands in Central Europe. We tested the hypothesis that native grass species are able to outcompete the invasive goldenrods. A replacement series experiment was established to determine levels of interference between native grass taxa and goldenrods. In the experiment, four alien goldenrod species (Solidago altissima, Solidago canadensis, Solidago gigantea and Euthamia graminifolia) and one native species (Solidago virgaurea) were studied. The native grasses were represented by Lolium perenne (forage and turf varieties) and Festuca pratensis (forage variety). Total biomass was higher in the mixture of species compared with that in monoculture. The higher total biomass was due to higher productivity of the goldenrod species, whereas that of the grasses was reduced. These results demonstrated the high competitiveness of alien goldenrods compared with native grass species.     

Vroege vergeling bij erwten een aaltjesziekte

Summary The symptoms of early yellowing in peas, a disease occurring on sandy soils, could not be reproduced by inoculation withFusarium oxysporum formapisi race 3. Early yellowing in peas is most probably caused byHoplolaimus uniformis. Large numbers of this eelworm were found in the soil around the roots of diseased plants from several fields.     

Een oriënterend onderzoek naar het voorkomen van en de schade veroorzaakt door het havercystenaaltje (Heterodera avenae = H. major) in 1955

Samenvatting Op vele bedrijven, waar een sterke rotatie van granen in het bouwplan is opgenomen, kan het havercystenaaltjes veelvuldig moeheidsverschijnselen in haver veroorzaken. Ook op bedrijven, waar dit gewas geen afwijkingen in de groei vertoont, komt het aaltje, zij het in geringe concentraties, algemeen voor. Tussen de besmettingsgraad van de grond en de schade aan het gewas bestaat een zeker verband. Dit verbank kan sterk beïnvloed worden door verschillende bijkomende factoren, waaronder de watervoorziening van der planten een belangrijke rol speelt.Het is nog niet duidelijk in hoeverre de techniek van het grondmonsteronderzoek gewijzigd dient te worden om te voorkomen, dat de levende inhoud van de cysten terugloopt.Summary The cereal root eelworm has become a serious pest in oats in some parts of the Netherlands, especially on light, sandy soils.In March and April 1955 1400 soil samples were collected from farms where the occurrence of the nematode was to be expected.In two different areas the degree of infestation was 78 and 96% of the total of fields under investigation. These figures indicate that the concerning farms were generally infested, but they do not represent the mean situation of the area.During the growing season each oat crop was examined for symptoms of the disease. The data collected were compared afterwards with the degree of infestation. There proved to be a positive correlation between the degree of infestation of the soil and the damage to the crop (tables 1 en 2). Several circumstances influence this correlation, among which the water supply of the plants seems to be a very important one.Cyst populations were identified by morphological characters to separate them from the clover root eelworm,Heterodera trifolii (Goffart, 1936), which was also present in 6,5% of the samples in one, and in 32% of the samples in the other area.The larvae in the cysts ofH. avenae evidently do not stand dry preservation, which is in accordance with recent experience in England (2).Dry preservation inplastic cavity slides for 1–3 weeks resulted in a decrease of viable cysts and larvae of 52%. A more suitable technique for collecting and handlingH. avenae in studied for further work.Het onderzoek werd verricht in samenwerking met de Rijkslandbouwconsulenten te Zutfen en Horst (L.) en het kantoor van de Plantenziektekundige Dienst te Doetinchem.     

Over de cicadellidenfauna van de kers

Summary In connection with the investigation of a possible vector of the Eckelrader virus disease of sweet cherry in the Netherlands, an examination was made of the leaf hopper fauna of cherry. Five species were found breeding regularly on this hostplant viz.Typhlocyba quercus (F.),Erythroneura alneti (Dhlb.),Erythroneura flammigera (Geoffr.),Empoasca flavescens (F.), andEupteroidea stellulata (Burm.). Some details about their biology are given. Other leafhopper species found on cherry, but which are probably only there by accident, are mentioned.      

Grondonderzoek op phytophthora sabdariffae

Summary For the successful cultivation ofHibiscus sabdariffa for fiberproduction in Java a preceding determination is necessary whether either soil or organic manure are contaminated byPhytophthora sabdariffa or not. To this end a method has been elaborated analogous to the method to determined soil contamination byPhytophthora nicotianae.According toGarrett's scheme ofWaksman's classification of soil fungi into soil inhabitants and soil invaders,Phytophthora sabdariffa has to be classified as soil invader.To test the presence of this fungus in soil or in organic manure leaves ofRicinus communis prove to be useful as a detector, since leaves ofHibiscus sabdariffa are too small and too quickly given tot decay. A method is to spread a paste of the soil or of the organic manure on the leaves and to keep these leaves contaminated during 24 hours (spreading method). Afterwards the paste is washed away and the leaves are kept in humid conditions during another 24 hours or 2×24 hours.The number of spots caused by Phytophthora is a measure of soil- or manureinfection (Table I). A more sensitive method is obtained by making a suspension of the soil or of the manure and by streaming this suspension (submersion method) during two hours over Ricinus leaves (Thung, 3). Afterwards the leaves are kept in humid air to give the fungus occasion to form spots (Table 2). Since Ricinus leaves are also susceptible to tobacco- and Ricinus-Phytophthora, these fungi will also be detected by these leaves. Owing to the fact that these fungi are also a parasite ofHibiscus sabdariffa, these method prove to be useful to detect suspected soil or manure regarding the cultivation of this fiberplant.     

Schurft op Pyrancantha

Summary Spilocaea pyracanthae (Otth) v. Arx comb. nov. (Syn.:Fusicladium pyracanthae (Otth) Viennot-Bourg.), the scab fungus ofPyracantha coccinea, overwinters in its conidial stage on the living leaves and on twigs. No perithecial stage could be found the last three years on overwintered fallen leaves.     

Geelnervigheid,een virusziekte van luzerne

Samenvatting Door middel van de erwtebladluis (Acyrthosiphon pisum Harris) werd het topvergelingsvirus van de erwt op luzerne (Medicago sativa L.) overgebracht. De besmette planten vertoonden na verloop van tijd het verschijnsel van geelnervigheid, te weten een regelmatige, lichtgroene tot gele nerftekening op de bladeren. Dit verschijnsel blijkt veelvuldig in luzernepercelen in het zuidwesten van het land (het gebied waar topvergeling in erwt algemeen voorkomt) op te treden. Het gelukte uit vier van vijf van verschillende plaatsen van West-Brabant en Zuid-Beveland afkomstige monsters geelnervige luzerne het topvergelingsvirus te isoleren.Uit waarnemingen bij planten, groeiende in het veld en in de kas, is gebleken, dat de omstandigheden een grote invloed hebben op het te voorschijn komen van het ziektebeeld. In het voor- en najaar treedt de geelnervigheid doorgaans zeer duidelijk op; in de zomermaanden verdwijnt dit verschijnsel veelal tijdelijk bij de besmette planten en onderscheiden deze zich niet van virusvrije luzerne.In een veldproef bleek het topvergelingsvirus, gezien het voorkomen van geelnervigheid in de loop van het seizoen, vrij snel in luzerne verspreid te worden.Summary Tip yellows (leaf roll) virus of pea was transmitted to lucerne (Medicago sativa L.) by means of the pea aphid (Acrythosiphon pisum Harris). After some months the infected lucerne plants showed a regular lightgreen to yellow discoloration of the veins and the adjacent tissue (fig. 1). No differences in growth and in shape of the leaves between infected and healthy plants were found to exist.This disease—for which we have chosen the name of vein yellowing of lucerne—is very prevalent in lucerne fields in the southwestern part of The Netherlands where tip yellows is often found in peas. We succeeded in isolating tip yellows virus from four out of five samples of lucerne showing vein yellowing collected in western Brabant and Zuid-Beveland.In carrying out transmission tests, it was found that the pea aphid often hardly sucks on lucerne in the greenhouse. Although it generally is present in large numbers in lucerne fields, it refuses to feed on lucerne after having been reared on peas for a prolonged period. This behaviour of the vector impedes the experiments. It may be due to the fact that the different generations of the insect differ in host plant requirements (Evans & Gyrisco, 1956) but also to the fact that morphologically indistinguishable forms of the insect exist, which may differ in host plant preferences (Hille Ris Lambers, 1947).Furthermore, in our experiments seldom a 100% infection of pea plants was obtained, even when using pea aphids which fed on a tip yellows diseased pea plant for a period of 48 hours or longer, and using five to ten aphids per test plant.Observations on infected plants growing in the field and in the greenhouse indicate that the environment has great influence on the appearance of the vein yellowing symptom. Generally, vein yellowing occurs very strikingly during the spring-time and the late autumn but disappears in the summer months.According to observations on the rate of occurrence of vein yellowing at different times of the year in a field experiment at Wageningen (fig. 2), it appears that tip yellows virus is capable of spreading fast in a lucerne field.The experiments and observations described in the present paper confirm the idea expressed byde Fluiter & Hubbeling (1955) that lucerne fields are important as a reservoir of the tip yellows virus of pea in The Netherlands.     

Over het verband tussen de aantasting door de koolzaadgalmug,Dasyneura brassicae Winn. (Diptera,Itonididae) en de Koolzaadsnuitkever,Ceuthorrhynchus assimilis Payk. (Coleoptera,Curculionidae)

Samenvatting De tegenstrijdige meningen, die bestaan over de vraag of de koolzaadga Imug (Dasyneura brassicae Winn.) voor zijn ei-afzetting is aangewezen op beschadigde hauwen, gaven aanleiding dit punt nader te onderzoeken. Uit infectieproeven, waarbij de galmug òf planten met uitsluitend gave òf planten met beschadigde hauwen kreeg aangeboden om zijn eieren te leggen, bleek, dat deze eieren uitsluitend in de van te voren beschadigde hauwen werden gevonden. Ook waarnemingen over het gedrag van de mug in het veld ondersteunden de opvatting, dat de eieren uitsluitend door reeds bestaande boorgaten in de hauw worden afgezet. De koolzaadsnuitkever (Ceuthorrhynchus assimilis Payk.) zal ongetwijfeld de belangrijkste veroorzaker van deze beschadigingen zijn. De bestrijding van de kever zal in de regel niet in staat zijn het aantal beschadigde hauwen zo sterk te verminderen, dat de eerste galmugvlucht geen gelegenheid tot ei-afzetting meer heeft. Door de vermindering van het aantal keverlarven als gevolg van de effectieve keverbestrijding, kan een vermindering van het a antal uitkruipgaten der larven bereikt worden, die wèl belangrijk is, daar de tweede galmugvlucht voor ei-afzetting vooral op deze gaten is aangewezen.

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On the relation between the infestation by the cabbage seed pod midge, Dasyneura brassicaeWinn. and the seed pod weevil, Ceuthorrhynchus assimilisPayk

Summary The controversy of whether or not the cabbage seed pod midge (Dasyneura brassicae Winn.) uses only damaged pods for depositing its eggs was reason for further investigation. Experiments with potplants were started. Midges were caged on colza-plants which had only undamaged pods as well as on plants which had pods artificially damaged by prickling with a needle. Eggs were only found in the damaged pods. The behaviour of the midge in the field, when it is intending to oviposite, also shows its need for damaged places as the midges were observed continuously walking on the pods, trying with their ovitubus to find a hole in the wall of the pod. The cabbage seed pod weevil (Ceuthorrhynchus assimilis Payk.) is undoubtedly the chief contributor to the number of damaged pods. Economic control of this weevil will only have a limited indirect effect on infestation by the first midge flight. However as it reduces the number of pods with weevil larvae, it reduces the number of exit holes in the pods. These exit holes are especially used by the second midge flight which therefore is controlled indirectly to some extent.

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Destijds werkzaam bij het Instituut voor Plantenziektenkundig Onderzoek (I.P.O.) te Wageningen; thans werkzaam bij het Laboratorium voor Entomologie van de Landbouwhogeschool te Wageningen.     

Het optreden van plaatselijke rassen bij Helopeltis antonii Sign. op Java

Summary Helopeltis antonii was bred at different constant temperatures at the experimental station at Semarang in 1939 and 1940. Some of the results concerning the duration of development from hatching of the egg untill the imaginal stage are recorded in the table and the graph. By comparing these data with those published byLeefmans (1916) (Helopeltis bred on tea in West Java) andZehntner (1901) (Helopeltis bred on cocoa in Central Java) we find that the time of development mentioned by these authors is shorter. In accordance with the experiments ofBonnemaison (1946) this probably can be attributed to the breeding ofHelopeltis at alternating temperatures (day and night). The duration of development at 19°C, mentioned byLeefmans (19 days), however, differs so much from the duration found in this investigation (32–34 days) that this explanation seems improbable. Other experiments at constant temperature, that will be published elsewhere, show that the population used for breeding was well adapted to the average temperature at the estate, Djati Rungo, from where this population came. This extreme adaptation suggests that this may also occur at other localities. Therefore it is probable that the populations ofH. antonii from different localities do not have the same genetical composition. The differences mentioned above can probably be attributed therefore to this fact. Data are given to strengthen this supposition. The existence of genetically different populations has already been suggested by ProfessorRoepke in 1909. He called them biological races. The occurrence of the varietybradyi ofH. antonii is probably caused by such a difference too and thus could better be considered as a subspecies.Helopeltis theobromae Mill. is without doubt only a subspecies ofH. theivora.Thus we suggest:Helopeltis antonii subspec.bradyi Wat. new comb. Helopeltis theivora subspec.theobromae Mill. new comb.

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Deventer     

Distribution of Potato Cyst Eelworm in Scotland1

Although potato cyst eelworm has been known in Scotland for more than 60 years, infestations are fewer than might have been expected. In 22 years of soil testing, based on nominal 500 g samples and sampling units of up to 6 ha, 80% of the farms examined were found free from detectable infestation and 10%, i.e. half the infested farms, had one infestation only. Most populations were light; one third of all infested samples contained a single viable cyst and 80%, ten cysts or fewer. It is suggested that long rotations have kept eelworm populations in check over much of the country, but in some areas their effectiveness has been reduced by persistent groundkeepers. Surveys indicate that Heterodera pallida Stone is uncommon and so the progressive use of resistant varieties, which are proving popular with seed growers for their commercial qualities, coupled with the long rotations generally practised, may well tip the balance even more favourably towards increased control.     

Een ziekte in erwten,veroorzaakt door het aaltje hoplolaimus uniformis thorne

Summary In some gardens on light sandy soil in Ede a poor growth and yellowing of the leaves beginning with the lowermost ones was observed in peas together with root rot and reddish discoloration of the vascular bundles. The soil was heavily infected withHoplolaimus uniformis Thorne,Pratylenchus penetrans (Cobb)Sher andAllen,P. minyus Sher andAllen and aTylenchorhynchus species.The disease symptoms described above were reproduced experimentally by growing peas in soil inoculated withHoplolaimus uniformis.The other species mentioned above did not damage peas grown in soil inoculated with numbers five times as high as in the original soil.     

Een aantasting door een mijt,vermoedelijk phyllocoptes fockeui nal., bij perziken en pruimen onder glas

Samenvatting In het Westland is in den zomer van 1946 op perziken en pruimen onder glas een aantasting door een mijt, vermoedelijkPhyllocoptes fockeui Nal., waargenomen. Deze parasiet was voorheen in die cultuur in het Westland niet bekend.Het blad van de aangetaste boomen krijgt een kleur als bij loodglans en krult dikwijls naar boven om. Mogelijk is de mijt afkomstig van de boomkweekerijen.Stuifzwavel en nicotine gaven goede resultaten bij de bestrijding.

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Avec un résumé: Un acarien, probablement Phyllocoptes fockeui Nal., attaque des pêchers et des pruniers (cultures de serres)

Resume L'été 1946 on a observé un acarien, probablementPhyllocoptes fockeui Nal., qui attaque des pêchers et des pruniers (cultures de serres) en Westland. Avant 1946, dans ces cultures de serres, ce parasite était inconnu.Le feuillage des plantes parasitées, présente une teinte plombée et plusieurs feuilles sont repliées en forme de cornet, dont l'ouverture est tournée vers le haut.Probablement l'acarien fut importé en serres pendant l'hiver de 1945–1946 avec des jeunes arbres, qui venaient des pépinières.Contre cet acarien on a obtenu des bons résultats avec du soufre et de la nicotine.