May 2025 - Pesticide Resistance & Residues on Garden Mums
Apr 01, 2026
Why Pesticide Residues Can Impact Biological Control on Garden Mums
Garden mums are a staple crop, but they can come with hidden challenges, especially when it comes to pest control. In the May edition of Koppert Corner, published through GrowerTalks, we focused on an issue many growers run into: pesticide resistance and chemical residues affecting biological control.
If you have ever had trouble controlling spider mites or thrips on mums, even when using strong solutions, this may be part of the reason why.
One of the key points we highlighted is that pests arriving on cuttings or liners may already be resistant to certain chemical pesticides. This makes them harder to control from the start and often leads to repeated treatments without consistent results.
At the same time, those same plants may carry pesticide residues on their leaves. These residues can remain active long after application and may harm beneficial insects introduced later. In some cases, this can limit or completely prevent biological control from working effectively.
Why This Matters for Biological Control
In this month’s Koppert Corner, we emphasized that not all crops are immediately compatible with beneficial insects.
Certain chemical residues, especially from broad-spectrum products, can persist on plant surfaces and negatively affect predatory mites and other biological solutions. This creates a situation where introducing beneficials may not produce the expected results, even if everything else is done correctly.
Understanding whether residues are present helps determine the best path forward, rather than relying on trial and error.
How to Evaluate Your Crop
We outlined a few practical ways to assess whether pesticide residues or resistance may be a factor.
One approach is to check with your supplier to understand what products may have been used prior to shipment. This can provide early insight into whether residues could be present.
Another option is laboratory testing, which can identify specific chemical residues on plant tissue and help guide your pest management strategy.
A more hands-on method is to introduce a small number of predatory mites and observe their activity over several days. If they establish and begin feeding, it is a good indication that residues are not interfering. If they fail to establish, chemical residues may still be active.
What This Means for You
For growers and retailers, the key takeaway is that successful biological control starts before you ever apply a product.
If plants arrive with resistant pests or lingering residues, your options may be limited. Identifying these issues early allows you to adjust your approach, whether that means delaying beneficial releases, choosing alternative solutions, or planning differently for future crops.
This is especially important for mums, where timing and crop quality directly impact sales windows.
The Bottom Line
The insights shared in Koppert Corner highlight that pest control challenges are not always about the product you choose. They often come down to what is already present on the plant.
By understanding pesticide resistance and residue risks, you can make better decisions, avoid wasted applications, and get more consistent results from your pest management strategy.
This article is based on the Koppert Corner published in GrowerTalks and adapted for NaturalEnemies.com. To check out the original article, click here: Happy Mother's Day! Let's talk mums ...
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