Forecasting the Incidence of Aphids Using Weather Data1

Aphids have been trapped continuously at several heights at Aberystwyth (United Kingdom) since 1969. Relationships have been found between prior meteorological parameters (normally recorded at Agricultural Meteorological Stations) and numbers of aphids flying during both summer and autumn peaks, and with the first occurrence in the trap each year. Numbers of cereal aphids caught in the autumn are associated with previous winter and spring temperatures and particularly with summer rainfall. Cereal aphid numbers are also associated with the yields of their summer grass hosts which in turn are related to summer rainfall, thus providing a causal relationship. The value and accuracy of using meteorological parameters to forecast the incidence of aphids of agricultural importance is discussed.     

Forecasting Aphids in Field Crops (Swiss Model)1

A new prognostic system for aphids in field crops, based on long-term ecological investigations, was developed in Switzerland during the years 1971 - 1976 and tested successfully in practice in 1975 and 1976. Within the region, population densities of aphids and mortality caused by predators, parasitoids and fungus diseases were measured weekly at different places. Sampling was started in early spring (parthenogenetic overwintering of the aphids was never observed) in permanent and temporary grassland and continued in annual field crops after aphid migration. Typically, in years during which aphids caused damage (1973, 1975, 1976), there was a late progression of aphid population densities in permanent grassland in spring. But, during years without damage (1971, 1972, 1974), an early and intensive aphid development was observed in permanent pastures in spring. Thus, the intensity of the spring development of aphids in permanent grassland is of general importance for the development of the pests later on in annual field crops. This conclusion was considered in the forecasting system for which guidelines have been developed, enabling the Regional Plant Protection Services to establish exact prognoses. Farmers can then start making observations in their fields, in order to find the right moment for insecticide applications. Un nouveau systemè de prévision pour les pucerons des grandes cultures a été developpe en Suisse au cours des annees 1971–1976; il repose sur des recherches écologiques de longue durée et sa mise en place en 1975 et 1976 s'est révelée très utile. Les densités de populations de pucerons dans la région ainsi que la mortalité occasionée par les prédateurs, les parasitoides et les maladies ont été déterminées chaque semaine à des sites differents. L'échantillonnage commence au printemps (L'hivernation des populations parthénogenétiques n'a jamais été observée) dans les prairies permanentes et temporaires et se prolonge dans les cultures annuelles apres la migration des pucerons. Les annees au cours desquelles les pucerons ont provoqué des déghts importants (1973, 1975, 1976) sont caractérisées par un developpement tardif des populations de pucerons dans les prairies permanentes au printemps. A L'inverse, les annees caractérisées par I'absence de dommages (1971, 1972, 1974) ont vu un developpement printanier intensif des pucerons dans ces mêmes sites. Ainsi, L'intensité de ce développement exerce une incidence sur l'évolution ultérieure du ravageur dans les cultures annuelles. Cette conclusion a été incorporée dans les directives pour la prévision dont I'établissement a permis aux services regionaux de la protection des végétaux detablir un pronostic precis. Les agriculteurs peuvent ensuite observer leurs champs afin de determiner la date optimale pour le traitement chimique.     

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.     

An Integrated Approach in the Control of Potato Root Eelworm

During the last decade, new control possibilities for the potato root eelworm have come to the fore, namely resistant potato varieties and soil disinfection. These have led to an integrated approach to the control of the potato root eelworm in the Netherlands. For this purpose, a number of potato rotations, aiming at the prevention or elimination of non-detectable populations of the potato root eelworm, are prescribed for non-infested fields. These regulations allow the farmer to grow potatoes more frequently on non-infested soils if he uses control measures (i.e. resistant potato varieties, soil disinfection). More stringent restrictions are in force for infested fields on which the growing of susceptible crops and propagation material is, of course, prohibited.     

A Synoptic Approach to Regional Forecasting in Plant Protection (The Hungarian Forecasting System)1

Forecasting is of primary importance for the effectiveness and profitability of plant protection on a regional and on a farm level. Farmers should be guided by regional forecasts outlining major trends of pest infestations and epidemics. However, additional farm observations are also needed to adapt general trends to local farm conditions. The Hungarian National Plant Protection Organization embraces the Agrochemistry Centre and 20 regional Stations. Plant protection forecasting activities are organized and supervised by the Forecasting Department of the Centre and every Station has a Forecasting Group. Data acquisition is the first step in the forecasting procedure. It is organized on an ecological rather than on an administrative basis. A national system of ecological forecasting regions has been set up and the results of observations are processed on a regional basis. There are permanent and temporary sampling localities and additional phenological stations within the regions. At the permanent sampling sites and at the phenological stations, observations are carried out according to a national sampling plan consisting of detailed routine instructions for quantitative and qualitative surveys. Three types of biological information are included: appearance of pests/diseases and their seasonal development, density distributions of pests/diseases over forecasting regions in selected periods of the year, and crop plant phenology. Information is coded at the Stations and forwarded to the Centre by telex every day during the growing season. At the Centre, the data are plotted immediately into maps combining the ecological forecasting regions and a national grid system of the country. Final data processing is done on a daily basis by using a synoptic mapping technique and forecasts are regularly released by means of several media to the large farms, home gardeners and private growers. The media include forecast circulars, at irregular time intervals, released by the Centre and the Stations, as well as weekly journals of agriculture or horticulture and national and local daily newspapers. The Hungarian Radio and Television also broadcast plant protection forecasts weekly and fortnightly, respectively. La prévision est trés importante puisqu'elle détermine L'efficacité et la rentabilité d'une mesure de protection. Les exploitants devraient pouvoir bénéficier d'un service de previsions régionales faisant état des grandes lignes de I'évolution des infestations et des épidemies. Ces données doivént cependant être doublees d'observations faites au niveau de I'exploitation, afin dajuster I'information generale aux conditions locales. En Hongrie, I'organisation nationale phytosanitaire comprend le Centre de la protection des végétaux et d'agrochimie, ainsi que 20 stations régionales. La prévision est assuree par le département du Centre qui est rélie aux groupes de specialistes pour la prévision, installés dans chacune des stations. L'acquisition des donneés, qui constitue la premiere étape de la prevision, repose sur un concept écologique. Le pays est ainsi subdivisé en régions écologiques et les observations sont traitees au niveau régional. Dans chaque region, il y a des stations d'echantillonnage permanentes ou temporaires, ainsi qu'un certain nombre de stations phenologiques. Les observations aux stations permanentes et phenologiques se font conformément à un plan national, qui precise la fqon de proceder aux inspections quantitatives et qualitatives de routine. Les données nécessaires comprennent: 1) I'apparition des déprédateurs et leur evolution au cours de la saison; 2) la distribution et la densité des depredateurs dans les regions a certaines epoques precisees; 3) la phénologie des plantes. Elles sont enregistrees aux stations et sont quotidiennement transmises par telex au Centre pendant la periode de vegétation. Au Centre, les données sont rapportées sur des cartes representant les régions écologiques et qui sont superposees sur une carte du pays. Le traitement final des données est assuré tous les jours par le recours à une technique synoptique de cartographie. Les prévisions sont communiquees selon les nécessites aux grandes exploitations et aux exploitants privés par bulletins expédies par le Centre et les stations, ou par la voie de revues hebdomadaires dagriculture ou dhorticulture et de journaux nationaux ou locaux. La radio et la television transmettent des prévisions phytosanitaires à intervalles d'une ou deux semaines.     

Fungi and the Decrease of Cereal Cyst-nematode Populations in Cereal Monoculture1

Populations of the cereal cyst-nematode decrease when cereals are grown frequently or continuously because the females that develop on the roots between May and July fail to produce eggs, or produce a smaller number than expected. Consequently, cysts in the soil after harvest are fewer and contain fewer eggs. The role of fungal parasites and competitors in limiting populations of cyst-nematodes is reviewed. Parasites of eggs and females of Heterodera avenae Woll. were widespread in British cereal fields, an Entomophthora-like fungus and Verticillium chlamydosporium Barron & Onions being the most common species found. Although fungal parasites may be the cause of the failure of the nematode to increase, it has not yet been established unequivocally.     

Prevalence and distribution of Potato mop‐top virus in Scotland

This study was undertaken to determine the current occurrence in Scottish seed potato crops of Potato mop‐top virus (PMTV), which is transmitted by Spongospora subterranea and causes spraing (brown arcs and lines) in the flesh of potato tubers, rendering them unsaleable. In 2004, a stratified survey of four commonly grown cultivars was conducted, while in 2007 and 2008, only samples from powdery scab‐affected crops were collected. The incidence of crops in which infection by PMTV was present was 37·5% in the stratified survey in 2004, but was greater in surveys in which tubers with powdery scab were tested (47·2% in 2007 and 44·6% in 2008). Similarly, the frequency of crops with incidences of more than 10% tuber infection was lower (9·4%) in 2004 than in 2007 (25·4%) and in 2008 (26·2%). Significant differences in crop infection were found amongst the four major seed‐producing regions and the counties within these regions. The incidence of crop and tuber infection was least for class Pre‐basic seed potatoes and greatest for class Super Elite 3 and Elite seed potatoes. The results indicate that the prevalence of PMTV has not increased since surveys in the early 1970s.     

Experience in Denmark with Cereal Cultivars Resistant to Cereal Cyst Nematode (Heterodera avenae Woll.)1)

On the basis of investigations on the cereal cyst nematode's distribution, it is presumed that one third of all the cereal growing areas in Denmark is infested to a degree, and that yield losses of 5 % or more may be assumed. This means an annual loss of about 100 million D.Kr. By using resistant cultivars every second year, the population of Heterodera avenae Woll. can be kept at a harmless level. It may be assumed that intensive growing of nematode-resistant cereals includes a risk of promoting the occurrence of pathotypes other than the 2 known to exist in Denmark. So far, there is no indication for their existence.     

Phytophthora ramorum: the situation in Scotland1

In Scotland inspections for Phytophthora ramorum on plants in the horticulture nursery trade started in July 2001 and are currently carried out four times per year. In addition, approximately 130 established gardens have been inspected for the disease during the years 2003 and 2004. Phytophthora ramorum has been found on Rhododendron, Viburnum, and lilac (Syringa vulgaris); the most important host plant is Viburnum tinus. The pathogen is confined to nurseries and garden centres with the exception of one private garden. The first finding was in April 2002 with 17 more outbreaks the same year. Since then the number of outbreaks per year has declined dramatically to 6 in 2003, 5 in 2004 and 3 until November 2005. Altogether, there have been 21 different outbreaks sites since the first finding, some with repeated occurrences of the disease.     

Distribution of Cereal and Grass Cyst Nematodes in the Federal Republic of Germany1

A survey of cereal and grass cyst nematodes in the Federal Republic of Germany revealed that Heterodera avenae is the most widely distributed heteroderid species and common mainly in areas with light sandy soils and intensive cereal cultivation. The so-called ≪race 3 ≫ was recovered several times, and other populations differing morphologically from ≪ typical ≫ H. avenae were found. H. hordecalis, H. bifenestra, H. mani, H. iri and Punctodera punctata were also recovered in many parts of the country. In arable soils these species constituted only 7 % of all records of cereal and grass cyst nematodes, whereas they prevailed in grassland, forests and other habitats, where they amounted to almost 80 % of the records. 93 % of all H. avenae records came from agricultural soils, but only 21 % of the records of the five other species. H. hordecalis and H. bifenestra are obviously of no economic importance in FRG.     

Incidence and severity of dieback in birch plantings associated with Anisogramma virgultorum and Marssonina betulae in Scotland

Betula pendula and B. pubescens were surveyed at nine Scottish Woodland Grant Scheme (WGS) sites in 2004 to assess the incidence and severity of two fungal pathogens, Anisogramma virgultorum and Marssonina betulae , and their association with crown dieback. Of the surveyed trees, 47% had at least 40% crown dieback, with B. pendula more severely affected than B. pubescens at most sites. Overall, 57% of surveyed birch trees had A. virgultorum and 28% had M. betulae , with the incidence of trees infected with both species varying among sites. Incidence and severity of A. virgultorum were greater on B. pubescens than on B. pendula , whereas the reverse was true for M. betulae. The relationship between incidence of M. betulae foliar disease and sunken cankers was significant, with 83% of M. betulae -infected trees having these cankers. The presence of M. betulae foliar disease resulted in a greater percentage of crown dieback compared with non-infected trees in both birch species, whereas the presence of A. virgultorum caused greater crown dieback in B. pubescens only. Across all sites and both birch species, as severity of infection with either A. virgultorum or sunken cankers increased, so did the severity of crown dieback. This study showed that A. virgultorum and M. betulae appear to contribute significantly to birch dieback at the nine sites surveyed.