Sunflowers are a common garden plant. They grow from spring until autumn. They have long stems with many flowers on them. Their seeds contain oil which they produce when pollinated by insects such as bees or butterflies. Sunflowers are not native to North America, but were introduced here through European settlers who brought their crops with them from Europe. Today sunflowers are grown all over the world including Australia, New Zealand and South Africa where they are called “sunies”.
The leaves of sunflowers are usually smooth and dark green. They may be up to 3 inches (7 cm) long and 1/2 inch (1 cm) wide.
The flower stalks are brownish yellow, sometimes with purple spots, and have five petals that open outwards like a fan. The outer two petals are white while the inner one is pink. There is no seed inside the flower so it does not need protection against pests or disease problems.
When sunflowers are young, they are covered with tiny hairs that wiggle around. These hairs make the leaves slippery and cause them to curl up at the tips.
When these little hairs dry out, they become brittle and fall off easily. If the sunflower plants start growing too tall, the delicate little hairs will break off and fall down onto other parts of the plant causing damage.
Sunflower Leaves Wrinkled
Sunflower leaves develop wrinkles on the surface.
Sunflower leaves develop white, brown or black spots.
Weak growth with wrinkled sunflower leaves
Sunflower plants slowly weaken and die.
Sunflower plants may suffer from a fungal disease called anthracnose. This fungus starts out as small, dark spots on the lower leaf surfaces.
It moves in and starts to destroy the tissue. Spots may appear water-soaked at first and then turn brown as they age. They gradually grow until they merge and cover large portions of the leaf. Sunflower plants with a heavy infection may suddenly wilt and die. You can use fungicides to treat anthracnose on sunflower plants, but this fungal disease is hard to get rid of once it becomes established.
It is important to practice crop rotation and plant disease resistant varieties when growing sunflowers. Always remove and destroy infected plants.
Try not to use overhead irrigation if possible; wet leaves are more susceptible to fungal infection. If you see the disease, treat immediately or you will lose your sunflower crop.
Pests: Sunflower Maggots
Sunflowers become riddled with small holes after an infestation of sunflower maggots.
The sunflower maggot, also known as the pyralid moth, lays its eggs on the flowers, leaves or stems of sunflowers. The tiny greenish-white eggs hatch into worm-like larvae that burrow into the flower head and start feeding on the seeds, preventing them from growing.
They make small holes in the florets and leave a white, mealy substance everywhere they go. They also leave a green, slimy trail everywhere they go. They are very hard to spot unless you look closely. The whole time the larvae are inside the sunflower head they are protected by a tough skin so most garden insecticides will not kill them. Your only option is to pick off and destroy infested sunflower heads and replant healthy seeds or plants.
Pests: Sunflower Moth
The sunflower moth, sometimes called the sunflower head moth, lays its eggs on sunflower leaves. When the eggs hatch, the larvae immediately start eating the leaves.
If you look at the sunflower head, you might notice some of the smaller leaves have holes chewed in them. The mature caterpillar is a shiny, blackish-blue color and has distinct white stripes running lengthwise down its body. The mature caterpillar is about 1 inch long.
How to Control Sunflower Moths: Crop Rotation
Sunflower moth eggs hatch into larvae and start eating sunflower leaves.
Always remove and destroy infested sunflower heads.
Crop rotation is essential because the sunflower moth can survive in the soil for two years without a host plant.
How to Control Sunflower Moths: Insecticides
Insecticides such as carbaryl (Sevin) will kill the caterpillars infesting sunflower plants.
Spray insecticides exactly as recommended. Over-spraying can destroy honey bees and other beneficial insects necessary for sunflower pollination.
Harvesting Your Sunflowers
Harvest sunflower seeds when flower heads are completely brown and the seeds rattle when you shake the flower head.
Cut the flower head from the stem and place it some place to dry. Breaking or punching the seed head open lets the seeds fall out more easily.
Bag up the sunflower seeds for storage.
Common Sunflower Diseases
There are several diseases that attack sunflower plants, including:
Bacterial blight: leaves have yellowish spots that grow and spread. Bacterial ooze can drip from the leaf lesions.
Sources & references used in this article:
Sunflower necrosis disease-an emerging viral problem. by RK Jain, AI Bhat, A Varma – Sunflower necrosis disease-an …, 2003 – cabdirect.org
Observations on the current status of Orobanche and Striga problems worldwide by C Parker – Pest Management Science: formerly Pesticide …, 2009 – Wiley Online Library
Reactive extraction of itaconic acid using tri‐n‐butyl phosphate and aliquat 336 in sunflower oil as a non‐toxic diluent by KL Wasewar, D Shende… – Journal of Chemical …, 2011 – Wiley Online Library
Insect problems of sunflowers by AP Arthur – Journal of the American Oil Chemists’ Society, 1983 – Wiley Online Library