LW-I-4: Infestation with harmful organisms – case study

The picture shows a close-up of a rape flower with numerous black beetles feeding on the flowers.Click to enlarge
Rape beetles can cause considerable damage to rape flowers if they occur en masse.
Source: Photograph: © agrarmotive / stock.adobe.com

2019 Monitoring Report on the German Strategy for Adaptation to Climate Change

Table of Contents

 

LW-I-4: Infestation with harmful organisms – case study

In the case of brown rust, powdery mildew and rape beetle it is understood that climate change entailing warmer winters and dry, warmer springs, will further the spread of infestations. However, it is important to note that the development of pests 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 infestations. It will not be possible to update the time series before 2023.

The line graph shows the infestation as a percentage of infested plants of winter wheat, namely brown rust infestation and powdery mildew infestation, both for Saxony-Anhalt.
LW-I-4: Infestation with harmful organisms – case study

The line graph shows the infestation as a percentage of infested plants of winter wheat, namely brown rust infestation and powdery mildew infestation, both for Saxony-Anhalt. The data series from 1976 to 2013 show some data gaps. Brown rust infestation is significantly increasing, powdery mildew infestation is significantly decreasing. In addition, the infestation of winter oilseed rape with the canola gloss beetle is shown as the maximum infestation in numbers per plant for Mecklenburg-Western Pomerania from 1990 to 2013. The time series shows a significantly increasing trend.

Source: Julius-Kühn-Institut (analyses of infestation-data of the federal states)
 

Increased pressure from harmful organisms – a distinct possibility

Climate change does not just change the conditions for agricultural crops but also for pests and plant diseases. Warmer weather and the extension of the vegetation period improve the opportunities for some pests to increase their range and to produce several generations per annum. However, other pests which depend on extended moist periods, might decline. In the next few years, it is therefore to be expected that climate change 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 mildew – will probably diminish in many areas. On the other hand, the importance of 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 pests 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 any conclusions as to the increase or decrease of infestations with pests. It is not possible yet to make any detailed prognoses. It is undeniable, however, that numerous pests can respond very sensitively and spontaneously to changed weather conditions; this requires farmers to respond flexibly and with utmost speed in order to get problems with pest infestations under control.

So far there has not been any comprehensive research regarding any particularly close relationships between pests and their development under changing weather or climate conditions. To obtain clarity in this regard will depend entirely on systematic evaluations of infestation data for a wide range of different pests. According to the current state of scientific knowledge in respect of brown rust (Puccinia triticina) and powdery mildew (Erysiphe graminis) affecting wheat, barley and triticale – a hybridised form of wheat crossed with rye – and in respect of the rape beetle (Meligethes aeneus) – it is understood that climate change entailing warmer winters and dry, warmer springs will benefit the development of mass reproduction.

However, long-term data series are not yet available nationwide. Only some Federal Länder have processed data, and these were used in preparing the 2015 Monitoring Report. Updating the time series will not be possible before preparing the 2023 Monitoring Report.

Cases of brown rust occurring in Saxony-Anhalt and rape beetle in Mecklenburg-Vorpommern show signs of an increasing tendency. 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, an examination of the time series as a whole reveals a significant decline. The data also show that the strength of infestations with a specific pest can vary considerably. There is no singular definitive weather pattern which furthers pest infestations.

For the time being, it is not possible to make any representative statements on the development of pest issues on the basis of data on brown rust, mildew or rape beetle provided by Saxony-Anhalt and Mecklenburg-Vorpommern. Obviously, there will be major differences in the infection risk and infestation between different pests and from region to region and year to year. In plant breeding there is an increasing focus on developing varieties with strong resistance to pests because, at least in some crop varieties, the strength or frequency of infestation is closely associated with the variety cultivated. It is worth mentioning that also the ways in which plant protection measures are carried out vary considerably. The Julius Kühn Institute which has responsibility for plant protection nationwide is in the process of conducting analyses on the climate and weather dependence of pest infestations. On the basis of the outcomes of this research it is expected that it will be possible to make comprehensive and representative statements on the development of pest infestations.

 

Interfaces

LW-R-5: Use of pesticides

 

Objectives

Reducing the introduction of new pests, efficient control of new harmful organisms, setting priorities for pest control on the basis of risk potential (including fast risk assessment and associated decision-making), efficient monitoring systems for certain harmful organisms (National Action Plan on the sustainable application of pesticides, 2013, ch. 5.2.4)