There is an abundance of pests and diseases that target your garden, veggies, and beautiful flower crops. It’s even worse when the pests spread the disease, such as the case of aster yellows.
We are not talking about the color of flowers here, unfortunately. Aster yellows is a disease that can infect numerous types of plants and is spread by insects. And it won’t just infect your aster collection.
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What is Aster Yellows?
Aster yellows is a chronic and highly destructive plant disease that affects aster flowers as well as around 350 flowering plant species across about 40 families of annual and perennial plants. Even some native species aren’t immune to this plant plague.
This disease is caused by a phytoplasma called Candidatus Phytoplasma asteris. This phytoplasma is primarily transmitted by the insect the leafhopper (family Cicadellidae). By the way, a phytoplasma is similar to a bacteria.
These pests transmit the phytoplasma as they move from one plant to another, biting and feeding as they go. All it takes is for them to feed on an aster yellows-infested plant and then feed on an uninfested plant. Now the disease has spread.
Affected Plants
Herbaceous plants, which are plants that lack a woody trunk or stems, are typically the ones infected by this disease. There are a few woody plants that can be infected, but it’s uncommon. This is just a small list of those plants vulnerable to aster yellows.
- Asters
- Marigolds
- Coneflower (Echinacea)
- Delphiniums
- Hydrangeas
- Phlox
- Zinnia
- Snapdragons
- Petunia
- Daisies
- Sunflowers
- Veronica
- Chrysanthemums
- Coreopsis
- Anemones
It doesn’t stop there. Crops such as carrots, lettuce, potatoes, celery, onions, wheat, tomatoes, garlic, and other vegetables can also harbor this disease. Weeds like plantain and dandelion can also host aster yellows.
It’s not transferred to the seeds of the plants, so saving seeds from infected plants won’t continue the disease cycle.
Signs of Aster Yellows
Aster yellows phytoplasma disrupts the normal growth of the plants it infects, leading to poor nutritional uptake and development in both the root system and above-ground parts.
Generally speaking, the newly infected plant will show symptoms anywhere from ten to 40 days after contact.
Symptoms can be a little difficult to pin down. The plant becomes stressed and stunted, but there are also other things to look out for:
- Pale foliage and stems
- Yellowing of new leaves
- Abnormally bushy growth
- Rotting flower buds
- Deformed flowers
- Curled, twisted leaves
- Stunted growth
- Bunched growth
- Virescence (uncharacteristic greening) of petals
- Phyllody, which are leaf-like structures that develop in flowering parts
- Unusual hair-like development on root vegetables
- A bitter taste of edible flowers, fruit and/or vegetables
Lookalike Problems
Although eriophyid mites like coneflower rosette mites aren’t known to spread aster yellows phytoplasma, it’s important to know that they can create the same symptoms and mimic similar issues in the same types of plants.
These microscopic pests cause galls to form on the end of the stems, inhibiting the growth of any blooms. Hygienic removal of the plant in its entirety is the best practice, particularly if a large number of plants are infected.
If in doubt, throw it out, whether you know the source of the symptoms or not.
In much the same way as leafhoppers, planthoppers, of the vast family of Fulgoroidea, are vectors of phytoplasma.
They nibble away at plants, contracting and dispersing the pathogen by secreting saliva into the leaf, stems, and petals. The phytoplasma then circulates in that plant through the veins.
The planthopper’s life cycle consists of an egg, several stages of nymph, and then an adult. Only when fully mature can it reproduce and fly. Before the flight stage, it can skip between plants nearby and still spread disease.
While they spread phytoplasma, they don’t spread the specific pathogen that causes aster yellows.
How Aster Yellows Spreads
There are several ways this devastating disease can infiltrate plants in your garden. Here, we take a look at all possible things that can spread aster yellows.
Leafhoppers
The aster leafhopper (Macrosteles quadrilineatus) is a gardener and flower farmer’s worst nightmare.
It can easily travel between plants because it can fly when it’s a mature adult and is a highly efficient reproducer. It can generate six or more generations in one growing season.
The aster leafhopper is not alone in its disease-spreading habits. The two-spotted leafhopper (Sophonia rufofascia syn. S. orientalis) is also a high flyer in aster yellows carnage. Several other leafhopper and sharpshooter species can spread the pathogen.
The glassy-winged sharpshooter (Homalodisca vitripennis) and the blue-green sharpshooter (Graphocephala atropunctata) are two such troublemakers.
It only takes two weeks for the pathogen to travel from the insect’s digestive system to its saliva glands. If it contracts the disease early in the season, it can multiply in your plants and garden tenfold in just one season. That is not a great thought.
Once leafhoppers are infected with the phytoplasma that causes aster yellows, they remain contaminated throughout their life span.
The lifecycle of a leafhopper goes from egg to nymph and then adult. They can live for a few months as an adult, giving them plenty of time to wreak havoc.
Evidence shows that the phytoplasma isn’t transmitted to the young via the mother, but rather the adult feeds on an infected plant and becomes the host carrier. Thank goodness for small favors.
Grafting
If you graft plants to create new ones or to improve rootstock, be aware of the health of both plants being joined. If the rootstock or scion is infected with any pathogen, it will circulate to all parts of the plant.
Remember, plants can be asymptomatic for up to 40 days after contracting the disease, so it’s a good idea to quarantine plant parts before using them in your grafting efforts.
New Plants
Introducing new plants into your home and garden always has an element of risk. You never know what pests or disease the new plant might be carrying.
Insect eggs of the leafhopper, planthopper, and other vector insects can be present on leaves and well hidden at the time of purchase.
Treatment and Prevention
Unfortunately, once aster yellows take hold, there isn’t much that can be done apart from removing the entire plant. Not that the plant will die necessarily, but it won’t thrive, and you risk the disease being spread elsewhere by letting it stay in place.
With aster yellows, the best weapon is prevention.
If your plants are infected, lifting out any infected plants and soil will reduce the risk of spreading to other plants, but it is the insects responsible that need to be targeted to stop the disease in its tracks.
Make it a weekly routine to check your garden for pests and diseases. Catch things early, and it will take less time and resources to correct or treat infestations.
Using neem oil and other specific insecticidal sprays to limit pests can help, but here are some other steps you can add to your garden maintenance rituals:
Crop Rotation
If there’s a history or even a hint of aster yellows in your backyard, consider rotating your crops to prevent reinfection.
Avoid planting susceptible plants, as we’ve listed above, in the same location for multiple growing seasons. If susceptible plants are in the same area year after year, more and more pests will come to visit.
Plant & Soil Health
As a rule, healthy, strong plants aren’t overly attractive to pests, or at least are better able to withstand their attacks. Stressed plants become a beacon for pests and the transference of disease.
Maintaining optimal growing conditions for your plants can help them withstand aster yellows and other diseases.
Provide adequate water, balanced fertilization, and proper sunlight exposure to promote overall plant health.
Manage the soil, ensuring the soil in the garden is well-drained and has a good organic matter content. This will help promote root development and overall plant vigor, which can increase their resistance to diseases like aster yellows.
Encourage Predatory Insects
To create a natural balance that enhances the equilibrium of your growing space, encourage or consider introducing natural pest predators. All kinds of predatory insects will keep leafhoppers and other pests under control.
Here is just a small list of the kind of insects and other predators you want around:
- Ladybugs
- Lacewings
- Praying Mantis
- Dragonflies
- Parasitic Wasps
- Hoverflies
- Spiders
- Assassin Bugs
- Lizards
- Frogs
- Birds
You can encourage predators by creating a healthy garden environment with many different plant species, available water, hiding places, and other things that insects and birds need to be happy.
You can add strategic plants to help draw in beneficial critters. Alyssum will attract those beneficial insects that target leafhoppers and other carriers of disease. Trees of all species are important to support bird life.
Quarantining
Consider quarantining any new plants you bring into your garden. Whether you buy them or are gifted them, you should keep new plants away from the the garden or other plants for at least a few weeks to watch for symptoms.
Obtaining plants from a reputable source in the first place can reduce risk, as can examining any plants or seedlings for symptoms or insect issues before purchasing them from the store and taking them home.
Keeping plants you plan to graft in controlled conditions until you are sure they are fine is a necessary prevention method.
Minimize Weed Hosts
As many weed species can also harbor aster yellows, it’s essential to keep your garden weed-free.
Any empty areas without any plants are a welcome area for weeds to take hold. Apply a thick layer of mulch to prevent weeds from popping up. Otherwise, dig up or poison any weeds that start growing.
You can also plant a thick groundcover that can suppress weeds.
Resistant Species
Consider planting aster yellows-resistant types of foliage and flowers.
In general, annuals tend to be more resistant than perennials.
