There are a few common pests and diseases that can attack zinnia plants and damage the flowers and leaves. Identifying the culprit can help you take the right action to get your zinnias thriving again. Some of the most likely suspects that may be eating your zinnias include spider mites, aphids, Japanese beetles, slugs and snails, powdery mildew, Alternaria leaf spot, and Botrytis blight. Keep reading to learn how to identify, prevent, and treat these zinnia problems.
What are signs of pest damage on zinnias?
Here are some common signs that your zinnias are under attack by pests:
- Holes chewed in leaves and flowers
- Leaves appearing yellow, wilted, or distorted
- Presence of small insects on leaves and stems
- Sticky residue or black moldy areas on leaves and flowers
- Plants are stunted or declining
If you see any of these symptoms, take a closer look at your plants to try and identify the culprit. Act quickly to prevent further spreading.
What are symptoms of zinnia diseases?
Zinnias can also be affected by fungal and bacterial diseases, which cause the following symptoms:
- Powdery white or gray coating on leaves
- Brown spots or lesions on leaves and flowers
- Leaves turning yellow or brown and dropping
- Stems rotting at the base
- Flowers rotting or turning brown
If you notice any unusual spots, wilting, mold, or rot on your zinnias, disease may be to blame. Proper identification and treatment can often reverse the damage.
Common Zinnia Pests
Here are some of the bugs and critters that are most likely to attack your zinnia plants. Being able to identify the pest will help you control it.
Spider Mites
Spider mites are tiny pests that suck sap from plant leaves, causing stippling, discoloration, and wilting. Telltale signs of spider mites include:
- Stippling – White or yellow speckling on leaves
- Webbing – Fine cobwebs on undersides of leaves
- Leaf drop – Browning and leaf drop as infestation grows
- Mites – Tiny red or yellow spider mites visible on undersides of leaves
Mist zinnia leaves with water to help remove mites. Insecticidal soap, neem oil, or horticultural oil can also help control infestations. Remove badly infested leaves and destroy them.
Aphids
Several species of small, soft-bodied aphids or plant lice may feed on zinnias. Signs of aphids include:
- Colonies – Clusters of small, soft yellow or green insects on leaves and stems
- Sticky residue – Honeydew left on plants as aphids feed
- Curled leaves – Leaves becoming distorted and curling
- Sooty mold – Sticky honeydew leads to black sooty mold fungus
Blast aphids off plants with a strong spray of water. Ladybugs, lacewings, and other beneficial insects help control aphid populations naturally. Insecticidal soap, neem oil, or horticultural oils can also be applied.
Japanese Beetles
These metallic green and bronze beetles devour leaves and flowers on many plants, including zinnias. Look for:
- Skeletonized leaves – Lacy leaves left after beetles chew away soft tissue
- Damaged flowers – Petals chewed away
- Beetles – Metallic green beetles with copper wing covers are over 1⁄2 inch long
Hand pick beetles and drop them in soapy water. Pheromone traps can also capture beetles. Neem oil, insecticidal soap, or pyrethrin insecticides can control heavy infestations. Protect zinnias with floating row covers until the beetle season ends.
Slugs and Snails
These soft-bodied mollusks come out at night to chew holes in zinnia leaves, flowers, and stems. Look for:
- Holes – Large, irregular holes in leaves and petals
- Slime trails – Shiny trails of dried slime on plants and ground
- Hiding spots – Slugs and snails tucked under pots, boards, and mulch
Remove slug and snail hiding spots from around plants. Hand pick these pests and drop them in soapy water. Set out beer traps at night to attract and drown them. Spread diatomaceous earth around plants to deter them. Iron phosphate baits can also be used.
Common Zinnia Diseases
Fungal, bacterial, and viral plant diseases can also leave your zinnias with spotted, moldy, or rotten leaves and flowers. Here are some prime suspects to watch for:
Powdery Mildew
This fungal disease coats zinnia leaves and stems with white powdery growth. Symptoms include:
- White powdery coating on leaves, stems, and buds
- Distorted, twisted leaves
- Stunted plants
- Buds fail to open
Improve air circulation and avoid wetting foliage. Remove and destroy affected leaves and stems. Use neem oil or fungicides containing myclobutanil, propiconazole, or chlorothalonil.
Alternaria Leaf Spot
This fungus causes brown leaf spots ringed in yellow. Look for:
- Brown circular leaf spots with yellow rings
- Spots enlarge and merge
- Leaves yellow and drop
- Stems can also develop lesions
Avoid overhead watering and crowding plants. Remove and destroy affected leaves. Use fungicides labeled for leaf spot on zinnias. Improve drainage in gardens prone to this disease.
Botrytis Blight
The fungus Botrytis cinerea causes flowers and stems to rot. Signs include:
- Flowers, leaves, and stems rotting
- Gray fungal growth on affected tissue
- Soft watery rot
- Plants collapse
Avoid wetting foliage and provide good air circulation. Remove and discard infected plant parts. Use fungicides containing chlorothalonil or neem oil preventively. Avoid overhead irrigation and crowding plants.
Preventing Zinnia Problems
Here are some key tips to keep your zinnias healthy and pest and disease free:
- Select resistant zinnia varieties, such as Zinnia ‘Zahara’, ‘Profusion’, and ‘State Fair’
- Give plants plenty of space for air circulation
- Avoid overhead watering
- Water at soil level and do not let foliage stay wet
- Apply mulch to prevent weeds, retain moisture, and keep foliage clean
- Scout plants frequently for signs of problems
- Remove and destroy infected/infested leaves and flowers
- Keep garden beds free of debris and fallen leaves
- Rotate zinnia plantings to different beds each year
Taking steps to promote vigor, improve growing conditions, and prevent pests and diseases can go a long way in keeping your zinnias beautiful. Be vigilant in watching for problems and take quick action at the first sign of damage.
Use Integrated Pest Management
Integrated pest management (IPM) combines various organic, natural, and chemical controls as needed to manage pests and diseases. Some IPM strategies for zinnias include:
- Attract beneficial insects like ladybugs and lacewings
- Apply Bacillus thuringiensis (Bt) for caterpillars
- Use floating row covers as a barrier
- Spray neem, insecticidal soap, or horticultural oils
- Apply organic or synthetic fungicides
- Set out slug and snail traps
- Hand pick larger pests
Start with less toxic options first and move to stronger products only if needed. Combine controls for maximum effectiveness and minimal environmental impact.
Identifying Zinnia Problems
Use this handy table to diagnose what pest or disease may be damaging your zinnia plants:
Symptoms | Likely Cause |
---|---|
Stippling or yellow spots on leaves | Spider mites |
Curled, distorted leaves | Aphids |
Skeletonized leaves, damaged flowers | Japanese beetles |
Large holes in leaves and flowers | Slugs, snails |
White powdery coating on leaves | Powdery mildew |
Brown spots with yellow rings on leaves | Alternaria leaf spot |
Rotting flowers and stems | Botrytis blight |
Use this as a guide when scouting for problems. An accurate diagnosis will allow you to take appropriate action to rescue your zinnias. Don’t let pests and diseases destroy your zinnia display!
Organic and Natural Pest and Disease Control
If your zinnias come under attack, there are many organic and natural options to get the problems under control:
Insecticidal Soap
Insecticidal soaps made from potassium salts of fatty acids can control aphids, spider mites, Japanese beetles, and other soft-bodied insects. Spray directly on pests and repeat applications may be needed. Reduce watering and apply soap spray in the early morning or evening.
Neem Oil
Extracted from the neem tree, this natural oil disrupts the life cycle and feeding habits of many pests. It also has antifungal properties to control diseases like powdery mildew. Neem oil is less harmful to beneficial insects than other insecticides. Follow label directions closely.
Horticultural Oils
Lightweight summer oils smother and kill insects and mite pests. They also deter fungal disease spores from germinating. Avoid applying in very hot weather which can burn foliage. Test on a few leaves first.
Bt (Bacillus thuringiensis)
This natural bacterium paralyzes the digestive system of caterpillars when they ingest it on leaves. It is very effective and safe for the environment. Reapply Bt after rain. It only impacts caterpillars, not beneficial insects.
Organic Fungicides
Look for fungicides containing sulfur, neem oil, or essential oils like thyme, clove, and rosemary to manage fungal diseases. Test first as sulfur may burn leaves in hot weather. Follow label instructions carefully.
Prioritizing non-toxic solutions first and using more aggressive chemical pesticides as a last resort can help minimize risks to pollinators, pets, wildlife and the environment. Combine methods for best results in an IPM approach.
Chemical Pest and Disease Control
For severe zinnia pest and disease outbreaks, synthetic chemical pesticides may be warranted when natural methods fail. Some options include:
Insecticidal Soap
Insecticidal soap concentrates containing potassium salts of fatty acids can control mites, aphids, beetles and other pests. Spray bugs directly and repeat applications may be needed. Reduce watering and apply in early morning or evening.
Pyrethrin Insecticides
Derived from chrysanthemums, pyrethrin insecticides work quickly to kill bugs on contact. However, pests can also develop resistance, so alternate with different mode-of-action insecticides. Do not apply in very hot weather.
Imidacloprid
Systemic neonicotinoid insecticide applied to soil or as a drench is absorbed by plant roots and makes foliage toxic to sucking insects like aphids and leafhoppers. Use once early in season for longer control. High toxicity to bees – use cautiously.
Synthetic Fungicides
Commercial fungicides containing myclobutanil, propiconazole, chlorothalonil, mancozeb or copper salts may be needed for diseases in wet seasons. Alternate fungicides for resistance management and follow label precautions.
Insect Growth Regulators
IGRs like azadirachtin disrupt the molting and maturity process of young insects. They leave beneficial mature insects unharmed. Effective against caterpillars, beetles, leafminers and other leaf chewing pests.
Always follow label instructions carefully for any chemical pesticide. Resistance can develop with overuse. Rotate between pesticide classes and avoid applying frequently for best results. Consider the safety, efficacy, and environmental impact when selecting treatments.
Conclusion
Zinnias are easy to grow, but they can still fall victim to pesky insects and plant diseases. Identifying the culprit pest or disease affliction is the first step toward treatment. Exclude pests with row covers and physical barriers when possible. Remove infected plants promptly to prevent spread. Apply organic treatments like neem oil, insecticidal soap, and Bt first before resorting to stronger synthetic pesticides only if necessary. With vigilance and prompt action, you can keep your zinnias happy, healthy, and covered in beautiful flowers all season long.