LW-I-4: Infestation with pest organism – case study | Umweltbundesamt

LW-I-4: Infestation with pest organism – case study

As far as brown rust, powdery mildew and rape beetle are concerned, it is understood that climate change will alter the course of infestations. The two first-named species may become increasingly relevant. That notwithstanding, it is important to note that the development of pest organisms takes place in very specific ways. On the basis of currently available data it is not possible to make any generalised statements on the impact of climate change on the infestation scenario.

Increased pressure from harmful organisms is possible

Climate change does not just alter the conditions for agricultural crops but also for pest organisms and plant diseases. Warmer weather patterns and the extension of the vegetation period improve the opportunities for some pest organisms to increase their range and to produce several generations per annum. However, other pest organisms which depend, for example, on extended moist periods might decline. Given the progress of climate change, it is to be expected that in the next few years, this development will bring about shifts in the species range of organisms harmful to plants. Damage caused by fungal diseases – apart from diseases triggered by thermophilic fungi such as Pucciniales (types of rust) – will probably diminish in many areas. On the other hand, thermophilic grass weeds and other weeds, animal pests and non-parasitic diseases might increase. Furthermore, insects basically always benefit from warmer temperatures. It is to be expected that new risks will arise from pest organisms which have so far not occurred in our latitudes. Once introduced, these alien species will be able to establish themselves and spread owing to the changed climatic conditions in our regions. However, observations so far do not permit to draw any conclusions as to the increase or decrease of infestations with pest organisms. It is not possible yet, or at least very difficult, to make any detailed prognoses at this stage. It is undeniable, however, that numerous pest organisms can respond very sensitively and spontaneously to changed weather patterns; this requires the agricultural sector to respond flexibly and with utmost speed in order to get problems with pest infestations under control.

It is essential to conduct a systematic assessment of infestation data for a broad spectrum of different pest organisms in order to make overarching statements on the influence of climatic changes on pest organisms possible. In respect of brown rust (Puccinia triticina) affecting wheat, barley and triticale, a hybridised form of wheat crossed with rye, and in respect of the rape beetle (Meligethes aeneus), the current state of scientific consensus is that climate change entailing warmer winters and drier, warmer springs will benefit the development or even mass reproduction of such pest organisms. As far as powdery mildew (Erysiphe gramins) infestations on wheat are concerned, the relationships are not quite clear yet. So farthere are no analyses available in Germany nationwide of any long-term data series in respect of the relationships. However, it was possible to process data from two Länder (Saxony-Anhalt and Mecklenburg-Western Pomerania) which provide a first glimpse into temporal development trends for the three pest organisms mentioned above. Unfortunately, it has not been possible to date to derive any distinct information of the influences of climate change.

In respect of brown rust observed in Saxony-Anhalt and rape beetle in Mecklenburg-Western Pomerania, it has been possible to discern a significantly rising trend towards higher infestation since the 1970s. As far as powdery mildew is concerned, for which there are also data available from Saxony-Anhalt, there have been, since the 1970s, recurring years of high infestations. However, it must be said that judging by the time series illustrated, the infestation seems to be in decline. The data also show that the degree of infestation with a specific pest organism can vary considerably. There is no singular definitive weather pattern discernible which furthers pest infestations.

However, the situation in the particularly hot and dry year of 2018 demonstrates that specific weather scenarios can entail a massive spread of pest organisms. For example, 2018 was a pronounced brown-rust year. Most fungal-type pathogens do not play an important role under such difficult circumstances, but brown rust does not need any rain – dew is sufficient for causing infection. This fungus which in the past was mostly found in warm agricultural areas, has now become relevant throughout Germany and is increasingly becoming the predominant disease afflicting winter wheat. The earlier in the year high temperatures are reached, the earlier the point when brown rust can become infectious and the more favourable the conditions for the continued development of this infection. The rape beetle likewise benefits from high temperatures. It overwinters in beetle form in loose soil layers at woodland edges or in hedges, thus enabling it to start its ‘season’ as soon as warm spring temperatures set in. The beetle lays its eggs in the buds of rapeseed blossoms. Basically, the use of early-flowering varieties (cf. Indicator LW-I-1) can reduce the infestation in the sensitive budding stage, but in very warm spring temperatures even this preventative measure may lose its effectiveness. When interpreting the trend towards increased rape beetle infestation, it has to be borne in mind that by now the species has developed increased resistance towards the usual insecticides. The decline in infestations with powdery mildew can be attributed (among other factors) to lower demands on temperatures compared to brown rust. It is conceivable that in the course of climate change, its optimum temperature range of roughly 17 to 18 °C might be exceeded more frequently. This might have adverse effects on its development and the infestation conditions.

Representative statements regarding infestation issues are not yet possible on the basis of the data presented here. There are major differences in the infection risk and the infestation between different pest organisms, from region to region and from year to year. In recent years, it has been possible to increase the resistance level to fungal diseases in particular. The frequency and intensity of infection, at least for some crop species, have therefore become very dependent on the varieties grown. It is worth mentioning that also the ways in which plant protection measures are carried out vary considerably from one crop species to another.

The Julius Kühn Institute (JKI) carries out analyses on the climate and weather-related dependence of infestations with pest organisms, which means that in future it may become possible to make more comprehensive and representative statements on the development of infestations with pest organisms. A further development of the indicator – where possible towards a nationwide illustration – is planned for the next DAS Monitoring Report in 2027. It is expected that extensive synergies will evolve – both at contents and organisational level – with the aid of findings from surveys for the indicators contained in the 2013 National Action Plan for the sustainable application of pesticides (cf. Indicator LW-R-5) and activities carried out within the framework of the national monitoring of biological diversity in agrarian landscapes (MonViA).