MANAGING PESTS IN A CHANGING CLIMATE
Of the many challenges we face in our industry, among the most difficult are those beyond our control. And when it comes to managing pests and diseases, while there’s a lot that we can do to prevent the spread of disease and mitigate the threat of insect damage to plants, the factors influencing the degree of insect and disease pressure are largely unpredictable, complex, and constantly evolving. At Mariani Plants, this has been a painfully clear lesson this year as we’ve struggled to control an exceptionally resilient population of aphids in the nursery that has made its way to every Spiraea, Crabapple, and purple-leaved Heuchera on the property. This has left us seeking to understand what led to the unprecedented number of aphids, why they’ve been so successful, and what we can do to better manage them going forward.
One factor that’s likely contributed to a larger, more robust population of aphids in the nursery this year is insecticide resistance. Several studies have documented the development of insecticide resistance in soybean aphids since what is believed to be the first known case in 2015. While it’s unlikely that soybean aphids would feed on other types of plants (according to researchers), we know that several species of aphids are now exhibiting signs of resistance to a wide range of insecticides, including Organophosphates, Pyrethroids, Carbamates, and Neonicotinoids. Resistance can spread extremely quickly within a population of insects, so it’s all the more important that we take measures like rotating between chemicals with different modes of action and implementing sustainable integrated pest management practices into our spray programs. While we often talk about economic thresholds in the context of pest management, in our industry we’re held to aesthetic thresholds that are driven by consumer base that is generally intolerant of imperfection.
Climate change is also affecting insect populations in ways that we’re only beginning to understand, especially since the responses of insect pests to warming temperatures vary widely and can’t be easily generalized. For example, aphids have many natural enemies, including parasitic wasps and other insect species. If warming temperatures cause natural enemies to develop faster than their prey, then the populations of those insect species will decline due to lack of food in spring. When you also consider that reproduction rates are higher at warmer temperatures, that higher temperatures speed up many insects’ metabolisms, causing them to eat more, and that warmer winters lead to increased survival rates, it’s easy to see how even small changes in temperature patterns can have complex and wide-ranging effects on insect pest populations.
The increase in invasive weed species in the Midwest is another important factor that’s likely contributing to rising insect pest populations. A 2020 census of trees by The Morton Arboretum revealed that more than 45% of woody plants in the Chicago region were invasive species, with the most common offenders being European buckthorn, Amur honeysuckle, and black locust, among others. Studies have shown that invasive weed species not only serve as hosts to many of our most common insect pests, but they often harbor viruses that insects such as aphids spread to neighboring crops. A great example of this are soybean aphids, which rely on buckthorn to lay their eggs and overwinter.
We’ve always been diligent about using strategies designed to minimize the risk of insecticide resistance and manage pests in a responsible way, but we’re also impacted by the pest management tactics of our neighbors, and it’s becoming clear that conventional methods of pest control are becoming less and less effective as we’re faced with a multitude of environmental pressures beyond our control. We’ll need to be prepared for more summers like this one as they become the norm and not the exception, and our industry will need to invest more in biological control options and other traditionally non-conventional methods that are practical for large scale use in outdoor nurseries.
