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Aster Yellows is a devastating problem when widespread. Both 2023 and 2024 were tough years in Minnesota due to a spike in Aster Yellows affecting many plants. Many MN garlic farmers had tragic losses in 2024 to this disease. Personally, I had quite a few flowers affected by Aster Yellows in 2023, but 2024 saw significant losses of many flower varieties. Almost all of my Coneflowers, Cosmos, Dara, Strawflowers, and Marigolds were lost to Aster Yellows in 2024.
Understanding Aster Yellows
Aster Yellows is caused by a phytoplasma, a form of bacteria that affects various plants. The Aster Leafhopper acts as a vector, hopping between plants and propagating the disease when they eat the plant.
Aster Leafhoppers are born in the southern US. In the spring, they ride the winds to reach us in the north. Leafhoppers are active in temperatures over 59 degrees. Aster Leafhoppers are roughly 4mm in length and can be identified by the 3 pairs of dots on their heads. They are very active and fly or crawl away quickly. Once a leafhopper eats from a plant infected with Aster Yellows, after 2+ weeks it is able to plass along the pathogen. These migrant leafhoppers go on to produce 2 to 3 more generations over the summer in our Minnesota gardens.
The pathogen may be brought along with the leafhoppers as they arrive in the spring, or picked up from infected local perennial weeds such as dandelions.
Common symptoms of Aster Yellows
<> Yellowed or sometimes red/brown leaves
<> Stunted plant growth, compact
<> Discolored and/or strange-looking flowers, often with odd light green growths
<> Abnormal, twisted, or light green growth
<> Foliage may turn red or purple especially in flowers from the carrot family, such as Dara and Ammi
Most plants infected with Aster Yellows will show several of the above symptoms. However, individual plant types may exhibit differing responses to the Aster Yellow pathogen. Crops often affected are carrots, lettuce, and garlic. Over 300 varieties of flowers are susceptible to Aster Yellows, particularly those in the aster and carrot families.
Since most plants do not show symptoms for 20-30 days after being infected, this makes control of Aster Yellows even more challenging. Recognizing the signs early is crucial. There is no cure and all infected plants must be removed and destroyed immediately.
See the gallery below for more photos of flowers with Aster Yellows for reference.
My Multi-Prong Strategy for 2025
-An Integrated Pest Management Plan
I never wanted to develop what's called an "Integrated Pest Management Plan"…but in order to keep my plants healthy, I need to be proactive and organized in my approach.
Integrated pest management (IPM) is a method of controlling pests that doesn't just rely on pesticides. IPM integrates multiple practices for effective pest management, encouraging a sustainable garden ecosystem. It's sensitive to the environment and takes a preventative approach to pests.
Key pieces of IPM plans involve identifying and understanding the pest problems, choosing and applying the appropriate strategies to control the issue, and then evaluating the results.
Key IPM Techniques
Cultural controls change practices and the environment to discourage pests.
Physical and mechanical controls aim to separate plants and pests.
Biological controls use living, natural means. Healthy plants are less likely to become diseased and attract pests.
Chemical controls utilize pesticides, ideally organic, as needed.
Notes on My IPM Plan
Reflective & Straw Mulch
Reflective fabrics and straw mulch disorient and confuses some flying insects such as Aster Leafhoppers. There have been several studies showing significant help from this straightforward, non-harmful tactic. Toward the end of the season, it appears to help less as plants have grown greatly. However, I still think this will be a key strategy to employ.
Mulches, of course, also provide additional benefits, such as moisture and weed control plus soil temperature regulation.
I plan to use a combination of DeWitt black/white reflective mulch fabric and high-quality garden straw in all my flower beds.
Soil for Healthier Plants
Healthy, happy plants come from healthy, happy soil. Happy plants are less likely to succumb to pathogens and disease—plus are of less interest to pests! So, a key strategy to fewer pests is fostering good soil.
Late last summer, I ran across some flower folks online talking about soil well beyond pH and soil type. I was intrigued and followed the bunny trail. I knew I wanted to make my soil as healthy as possible, but didn't know what to do or where to start. I had done soil tests for a couple years and got back generic recommendations on fertilizing. After implementation, my plants were okay, but not super healthy like I wished for.
Then I saw a couple small soil testing companies mentioned that are truly passionate about soil health. They test in much greater depth using the best methods available. AND the experts go through the results of even home gardeners like me, and they gave targeted recommendations based on what I grow and my situation.
I could write a whole post on my positive experience with CSI. I sent several samples in for both regular soil tests and biological testing last fall. It cost a bit more, but was not overly expensive. Detailed results were emailed to me and as part of their testing, they also provide a 30 minute phone conversation with Dane Terrill, owner and soil expert, to go through the results and answer questions. In my call, I came to both understand my results and learned a mini-course worth of soil health basics. I am excited to see how my soil and plant health improve this summer by following the plan.
CSI, Crop Services International, Michigan
Home Gardening Program/Information
Row Covers for Insect Exclusion + Weather Protection
Typically, I use frost row covers over my early planted flowers, but this year I also plan to use it on the flower varieties that are most sensitive to Aster Yellows. It will go over them at planting time and stay put until mid to late June. This early-season barrier serves multiple purposes: It shields vulnerable young plants from pests, such as the leafhoppers, and protects young plants from winds/storms, adding an extra layer of protection against late frosts. The fabric I use is Agribon AG-19, the industry standard, which provides 2-4 degrees of frost protection. It also works for insect exclusion and allows 85% light transmission.
Monitoring for Early Signs of Distress
Constant vigilance is essential in preventing Aster Yellows from taking hold. Throughout the growing season, I will closely monitor my plants weekly for typical symptoms of Aster Yellows.
If any plants show symptoms, I immediately remove the plant to stop the spread of the disease. They should not be composted, but must be destroyed. Once the plant material is 100% dead, it will no longer carry the pathogen. Early intervention can reduce the impact of the disease significantly, preserving the health of unaffected plants.
Choosing (Mostly) Less Susceptible Plants
In 2025, I will not be growing most of the plant types that seem most appealing to Aster Leafhoppers. This includes plants in the carrot family (Dara, false Queen Anne's Lace, Ammi), Strawflowers, Asters, Orlaya, Coneflowers, Marigolds, Parsley, and Garlic). I had issues with Cosmos, Pincushion Flower, and Statice as well in 2024 and will be growing far fewer of these and watching them very closely.
Aggressive Weeding
Since many perennial weeds, such as dandelions, are host to Aster Yellows, it is important to keep my gardens—and entire yard—regularly weeded.
Organic Chemical Sprays: AzaGuard & Pyganic
As for chemicals, I will be using a couple of very safe organic insecticides to manage pest populations. These eco-friendly options can help control Leafhoppers without jeopardizing beneficial insects, people, animals, and the environment. I am especially attuned to my land as I garden right along the beach at our Brainerd-area lake home. Water and land quality are important.
Leafhoppers are small and fast moving; they are hard to control. But these chemical measures will still be useful in keeping the leafhopper population in check. I started researching chemical controls in 2024 so that I could be confident in choosing safe, useful products.
The primary insecticide I will use is AzaGuard. Unfortunately, it's rather expensive. It is derived from the Neem tree, but is not the same as Neem oil. Azadirachtin, the primary ingredient in AzaGuard, works as a molting/growth disruptor. As an insect growth regulator, it interrupts the life cycle between infant and adult stages and ultimately causes the insect to die before maturity. Neem oil, from what I understand, may help with leafhoppers to some degree as well, plus is helpful in fighting other pests and fungal issues. It is much easier to find and more affordable.
Pyrethrins are insecticides derived from a type of chrysanthemum. They target the insect's nervous system and are used for rapid knockdown of many pests. I use a pyrethrin-based product called Pyganic.
If you have a significant sized area you plan to spray in, I highly suggest you get a pump sprayer. It saves your hands and saves money. A little 1 gallon spayer is very reasonable and so helpful. I bought a 4 gallon backpack sprayer last summer and it's made things much easier to cover my many beds. Another good use for a sprayer is foliar sprays of gentle fertilizer or compost tea.
Another thing to keep in mind is that most organic sprays need to be applied weekly or every 2 weeks. This is also true for the organic fungicides I use. The last couple years I've had a lot of powdery mildew at our lake and so I spray (close to) weekly all season. I follow the recommendations of Erin from Floret Flowers and use Cease and Milstop on alternating weeks.
As needed I will also use Diatomaceous Earth, which is puffed onto plants as an almost physical guard against pests. This safe dust has microscoptic sharp edges that are lethal to many pests.
A Flourishing Garden in 2025
Aster Yellows is a tough challenge, but with multiple measures in place, I hope to keep most of my plants healthy and happy this upcoming warm season. May you enjoy a summer full of flower joy as well!
**Online Resources
A few sources you may find helpful regarding Aster Yellows
Arbico Organics Leafhopper Info
Photos of Flowers with Aster Yellows from 2023 & 2024
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