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Prevent and Control Rust Fungus in the Flower Garden

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Prevent and Control Rust Fungus in the Flower Garden

Healthy Hollyhocks Deter Rust Fungus

Photo © Valerie Zinger

Rust Fungus Identification:

There are many species of the rust fungus disease, affecting host-specific plants and flowers, but gardeners can recognize this problem by observing the speckled masses that form on the surfaces of leaves. Like the namesake, many of these pustules are rust-colored, but gardeners should also suspect rust if they see dry spots that are:

  • Brown
  • Orange
  • Purple
  • Red
  • Yellow

Rust spots are usually tiny, scattered across plant leaves like so many freckles. Affected plants can have dozens of rust spots on each leaf, and it’s possible for a single leaf to have more than a hundred rust spots.

Flowers Affected by Rust Fungus:

Rust disease is legendary in hollyhock flowers, but they aren’t the only potential victims of this fungus. Pay close attention to signs of rust fungus in these flowers during the summer months:
  • Aster
  • Carnation
  • Geranium
  • Iris
  • Lily
  • Pansy
  • Primrose
  • Snapdragon
  • Sunflower
  • Sweet pea

Damage Caused by Plant Rust Fungus:

Flowers with a heavy rust infestation may experience curling or withering of leaves, and the plant can lose its leaves entirely. With this much damage to leaves, gardeners can expect to see stunted growth in their garden plants.

Organic Sprays for Rust Control:

A weekly dusting of sulfur can prevent and treat garden rust disease. Neem oil, a botanical fungicide and pesticide, also controls rust. Some organic gardeners swear by baking soda for garden fungus control. The efficacy of baking soda spray may be enhanced by mixing it with light horticultural oil.

Cultural Control of Rust Fungus:

Rust fungi, like many plant fungal diseases, flourish in wet conditions. The most important step you can take to reduce rust in your flower garden is to stop overhead watering. Instead, use a drip irrigation system to deliver water at ground level. If this isn’t possible, water your flower garden early in the morning, so the sun’s rays will quickly dry your flowers’ foliage.

Practicing good garden hygiene can decrease rust attacks. If you see signs of rust, remove and destroy the affected foliage to prevent the spores from spreading. Do not compost diseased foliage.

Conventional Control of Rust Fungus:

You can choose from several commercial fungicides to control rust fungus. Apply the sprays when you see the first signs of disease, and continue applications according to package directions through July. Look for these fungicides and brand names:
  • Chlorothalonil- Daconil 2787
  • Mancozeb- Fore, Dithane, or Penncozeb
  • Myclobutanil- Systhane
  • Trifloxystrobin- Compass

Rust-Resistant Flowers to Grow:

Hybridizers are continuously developing new flower varieties resistant to rust fungus. If you’ve experienced rust for multiple growing seasons, it might be time to remove susceptible plants and replace them with these proven varieties:

  • Aster- ‘Crimson Beauty,’ ‘Honeysong Pink,’ or ‘Purple Dome’
  • Hollyhock- ‘Happy Lights’
  • Rugosa rose
  • Snapdragon- ‘White Monarch,’ ‘Orange Glow,’ the Rocket series

Even when choosing rust resistant varieties, you’ll get best results by not overcrowding your plants. Proper spacing promotes air circulation, carrying disease spores away from the garden.

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