As they grow, sunflowers may experience issues caused by pests or diseases. Things such as location, weather, and upkeep determine which problems your plants may encounter and how well they stand up against them. Your first line of defense is to buy disease-resistant seeds.

But routine good practices are also helpful, including adequate watering, sufficient spacing, fertilizing only as needed, preventive and active spraying, and fall cleanup of all plant debris.

Sunflower diseases are caused primarily by bacteria and fungi. The diseases can spread through the soil, water, air, infected tools, animals, insects, and even gardeners themselves.

Spot diseases on your sunflower plants sooner so you can treat plants before they are destroyed by disease and can successfully manage symptoms. Here is a three-step approach to keeping vigilant about the presence of sunflower tree diseases:

1. Research the risks. Find out about sunflower diseases that are prevalent in your geographic area. When possible, buy disease-resistant seeds to avoid diseases in the first place.
2. Examine your plants daily. Check your sunflower plants every day to be sure no disease symptoms are present or emerging.
3. Spot diseases early. Catch and treat disease quickly so your plants can recover and thrive. Throw away or burn infected branches instead of composting them to prevent diseases from coming back to your garden via the compost.

Here are some of the diseases you may spot on your sunflower plants.

Alternaria leaf spot

Cause: Fungi present after warm summer rain

Symptoms:

• small black dots appear on leaves, most obvious on the underside
• light spots with dark borders on leaves
• spots enlarge as disease progresses, forming a bull’s eye pattern
• leaves turn yellow between the infected spots
• leaves wither and die
• will not kill the plant, but can significantly weaken it

How it spreads:

• rain helps spread spores in temperatures between 65 to 75 degrees F.
• splashing water
• wind
• more than 12 hours of warm rain can distribute spores so much that the plant cannot recover

Treatment:

• remove and discard infected leaves; this will reduce the number of spores and increase air circulation around plants

Prevention:

• buy disease-resistant seeds
• do not save seeds from infected plants
• avoid planting in cool, wet weather
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• rotate crops annually

Apical chlorosis

Cause: Bacterium that infects and causes symptoms only on young plants

Symptoms:

• leaves turn yellow to white, closer to the stem
• only affects young plants
• will not kill the plant or significantly affect flower growth

How it spreads:

• in cooler, rainy weather
• splashing water that transfers bacterium to leaves

Treatment:

• the plants will recover, with little likely effect on the development of the flower
• once the weather warms up, subsequent upper leaves should grow normally

Prevention:

• good plant spacing to promote air circulation

Aster yellows

Cause: Bacteria

Symptoms:

• deformed flower heads; bracts or ray petals may appear in the middle of the flower head

How it spreads:

• spread by leafhoppers, which feed on the plant juices and cause a systemic infection

Treatment:

• remove and discard infected parts
• no effective treatment

Prevention:

• reduce leaf litter and garden debris, where leafhoppers overwinter
• install sticky traps to trap leafhoppers
• break up compacted soil
• plant in well-draining areas
• put straw or aluminum foil under plants to confuse leafhoppers
• sprinkle kaolin clay on plants to discourage leafhoppers

Bacterial leaf spot

Cause: Bacteria

Symptoms:

• leaves have circular spots with irregular edges
• spots may turn yellow and water-soaked
• leaf drop

How it spreads:

• water
• wind
• garden tools
• thrives in warm, moist conditions

Treatment:

• remove and discard infected leaves
• if infection becomes serious, discard entire plant
• do not compost infected plant material

Prevention:

• mulch around plants to prevent water from splashing onto leaves
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• sterilize garden tools before each use
• spray plants weekly with neem oil or a commercial fungicide such as Bonide Revitalize
• rotate crops annually

Bacterial stalk and head rot

Cause: Bacteria

Symptoms:

• stem turns dark green to black
• blackening is worst around a petiole axil (where leaf stem meets the stalk)
• infected stems may soften and dry up
• flowers and seeds are discolored
• head of flower has coalescing lesions on the back
• lesions develop watery, soft rot that dries and darkens as the disease progresses
• rotting heads may exude a smell similar to that of rotting potatoes
• bacterial activity may cause sugars in the plant to ferment, dripping ooze onto the leaves
• foam may appear on infected stem or head tissue

How it spreads:

• water
• wounds on the plant open to infection

Treatment:

• remove and discard infected leaves
• if infection becomes serious, discard entire plant
• do not compost infected plant material

Prevention:

• remove infested crop debris
• pathogen survives in many plants, including sunflowers, potatoes, onions, and carrots
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• sterilize garden tools before each use
• rotate crops annually

Downy mildew

Cause: Fungi

Symptoms:

• pale spots or long pale patches on leaves
• fuzzy growth on underside of leaf surface
• leaves turn pale, then yellow
• leaf tips collapse

How it spreads:

• splashing water (rain, irrigation) disturbs spores
• cool temperatures favor growth
• soilborne pathogen

Treatment:

• destroy infected plants
• apply foliar fungicides

Prevention:

• purchase disease-resistant seeds
• plant in well-draining areas
• use homemade fungicides
• choose planting sites with good air movement and no shade

Fusarium wilt

Cause: Fungi present in the soil

Symptoms:

• leaves wilt and turn yellow
• wilting spreads to the whole plant
• vascular tissue turns red-brown
• plant death

How it spreads:

• fungus lives in moist soil for up to seven years

Treatment:

• remove and discard infected plant matter

Prevention:

• buy disease-resistant seeds
• avoid planting in cool, wet weather
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• rotate crops annually

Powdery mildew

Cause: Fungus overwinters on infected plant debris and emerges in warm, humid weather

Symptoms:

• white, powdery patches on tops of leaves
• usually affects the tops of lower leaves

How it spreads:

• fungus overwinters in infected plant debris
• optimal conditions are high humidity and moderate temperatures (68 to 81 degrees F)

Treatment:

• removed and destroy infected areas

Prevention:

• apply liquid copper fungicide
• if necessary, apply sulfur-based fungicide
• plant disease-resistant varieties
• remove plant debris year-round

Septoria leaf spot and blight

Cause: Fungus

Symptoms:

• irregular pale spots on the oldest leaves
• lesions enlarge, turn brown, and dry out
• leaves look tattered

How it spreads:

• splashing water (rain, irrigation) disturbs spores
• cool temperatures favor growth
• frequent rain invites infection

Treatment:

• destroy infected plants

Prevention:

• purchase disease-resistant seeds
• avoid working in the garden when plants are wet
• plant in well-draining areas
• choose planting sites with good air movement

We’re believers in not using toxic materials in the garden—they can hurt the plants, hurt the soil, damage the environment, and harm you.

Have you had problems with diseases attacking your sunflower plants? What types of problems do you regularly face with your plants? Please tell us how you treat and prevent diseases from destroying your sunflower crop.