Invasive Species Exploit Climate Change
Invasive pests such as the rootworm, capsule worm, Japanese beetle, armyworm, and rice bug are exploiting climate change to thrive. These heat-loving insects pose an increasing threat to corn crops as temperatures rise.
Green Rice Bug: A Growing Threat
The Green Rice Bug (Nezara viridula), while not traditionally a maize pest, has begun to appear in corn and soybean fields. It is now widespread along the Rhine Valley and has recently established populations in northern Germany. The long-term persistence of these populations is uncertain but increasingly likely due to the ongoing climate crisis. Natural enemies like parasitic wasps are critical in controlling their numbers.
Rootworm Expands Its Range
The corn rootworm (Diabrotica virgifera) continues to spread northwards and into higher altitudes, especially in areas with consecutive corn crops. The larvae feed on roots, causing lodging and significant yield losses. In affected areas, up to one-third of the yield can be lost. The biological treatment Dianem, which uses nematodes to combat larvae, is an effective control method when applied directly to the seed furrow with specialized injection equipment.
Cotton Bollworm Approaches from the South
The cotton bollworm (Helicoverpa armigera), a noctuid moth larva, is not yet established in Germany but may soon survive north of the Alps. In Hungary, it has become a major corn pest. This invasive species damages crops by mining larvae and secondary fungal and bacterial infections. Selective biological controls, including Bacillus thuringiensis-based treatments and parasitic wasps, are effective against this pest.
Armyworm: A Major Pest in Africa
The armyworm (Spodoptera frugiperda) is a significant invasive corn pest in Africa. Though it occasionally appears in the Mediterranean, it is unlikely to establish itself in Germany due to its inability to develop at temperatures below 10°C. This pest prefers grasses like corn, millet, and rice, causing substantial yield losses in warmer climates. Natural migration and trade contribute to its spread.
Japanese Beetle: A Transported Threat
The Japanese beetle (Popillia japonica) poses a potential threat to maize and over 300 other plant species. Originating from Asia, it spreads through transportation and plant trade. In 2023, the first population north of the Alps was found in Zurich, with additional sightings in Freiburg. Its larvae damage roots, while adults feed on leaves. Control methods include parasitic nematodes and various insecticides, including neem-based products.
As these invasive species adapt to changing climates, monitoring and biological control methods become essential to protect corn crops in Germany. Farmers and researchers must stay vigilant to manage these pests effectively.