Garden Mum Refresher 2025: Insect Pest and Disease Management

In case you missed it, earlier this week we talked about nutrient management and growth regulation/tracking for garden mums.

This post will focus on which pests most often affect garden mums in Ontario, and preventative actions you may want to take. Keep reading to learn more.

A tarnished plant bug feeding on a bud of chrysanthemum, which can cause petal distortion. Photo by OMAFA.

Insect Pests on Garden Mums:

Summer production for a fall crop can be challenging, but planning your pest management program ahead of time can help ward off issues.

If you grow your garden mums inside for a significant portion of their lives, then you’re likely going to want to treat them much like a standard pot mum, when it comes to pest management. This includes predatory mite sachets and applications of products like BotaniGard, to prevent damage from thrips (both western flower thrips and onion thrips in Ontario). It may also include the use of preventative chemical applications for aphids, or the use of biocontrol and companion strategies, such as banker plants for aphid parasitoids.

Note that you should NOT dip your incoming garden mum cuttings in oil, as this causes significant phytotoxicity, but dips in insecticidal soap and BotaniGard can help reduce incoming thrips. (See more about dipping in this post).

Left: One predatory mite sachet per pot, used for thrips control when garden mums are produced in greenhouses; Right: Garden mum flowers showing the aborted petals that are characteristic of tarnished plant bug feeding.

The good news is that garden mums grown outdoors simply don’t get the same pest pressure as pot mums in Ontario. Why? A lot of this has to do with natural enemy populations from surrounding agricultural lands that seem to keep a lot of pests in check. To conserve these free biocontrol agents, avoid spraying if you can.  If you DO spray, do yourself a favour and chose something that’s compatible with beneficials so you don’t end up with a bigger problem on your hands from secondary pests.

While generally not a problem on garden mums, recall that all plants produced outside from June 15 to September 30 need to be treated for Japanese beetle if you plan to export or ship to a JB-free zone. See this post for details.

If you do feel like you need more help with your planning your IPM program for garden mums, check out Table 2, below, to see what pests often happen when, and some solutions.

Table 2: Suggested pest management program for most problematic pests, grouped by week after transplant.

Week after transplant Suggested Program Target Pest/Disease Tips
Propagation Nova (mycobutanil)       Chrysanthemum white rust     Propagation growers often use Nova as a precautionary application.
Transplant Dips in BotaniGard WP Thrips – (Western Flower Thrips and Onion Thrips) Garden mum cuttings do not tolerate oil dips.
Weeks 1-9 Predatory mite sachets (Amblyseius cucumeris)


Beauveria-containing biopesticides (BotaniGard, BioCeres)


Mass trapping cards  
Thrips                     For indoor-grown garden mums:
Sachets at 1 per pot are best for long term thrips protection.

More information about mass trapping with cards here
Weeks 10-16 Drench of 1 of these:

Atlus (flupyradifurone)


Beleaf (flonicamid)  


Intercept (imidacloprid)
 
Aphids


Tarnished Plant Bug (also known as Lygus bug)


Leafhoppers (more of a nuisance pest to customers, but can lead to credits)
For outdoor grown garden mums:
Pests are typically seen in late August /September – walk the crop regularly and make an application only when insects are detected.  

Beleaf – soft on beneficials, can be applied via drench through irrigation lines and it’s cheap! However, all 3 chemicals will reduce the pests listed.

Note that for field-produced garden mums, it’s much easier and more cost-effective to put insecticides through the drip lines than to try and spray the field, which will limit your product selection. Make sure to check Ontario’s Crop Protection Hub for pesticide information for greenhouse crops. Here, you can select your pest as well as your application method (e.g. drench) to make finding an appropriate product easier. Make sure to confirm the product you choose is also appropriate for outdoor ornamentals by checking the label. (Updates coming to the Hub soon that will address this).

Disease Issues:

Chrysanthemum white rust (Puccinia horiana), while a quarantinable disease, has only been detected in Ontario once in the last decade. This is thanks to regulations requiring plant material be sourced from white rust-free facilities.

However, since other, more common diseases like powdery mildew can look like white rust, it’s always best to schedule your inspections with CFIA a few weeks out from shipping, if possible. This way, if any suspect plant material needs testing, you have time to be cleared well before your planned ship date. 

Geranium rust, which can look similar to Chrysanthemum white rust. Photo by OMAFA.

However, some growers apply a preventative fungicide for rust, just as an extra insurance policy, and to provide assurances to customers.

Nova (FRAC group 3) and Heritage (FRAC 11) are the only fungicides currently registered for rust in Canada, and are effective against multiple Puccinia (rust) species. If you also are concerned about diseases such as botrytis or powdery mildew, which can pop up suddenly in humid summers, then any fungicide in FRAC groups 7&11 will give you protection against those diseases as well as rust, so that might be a good option.

FusariumPythium and Rhizoctonia are more common root diseases in mums, but generally aren’t big issues in Ontario production.  If problems develop, a good guide to disease symptoms and cultural management in garden mums can be found here.



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