Rust diseases

There are hundreds of types of fungi that cause ‘rust’ on plants but each type has a limited number of host plants so that your whole garden is not likely to be overrun by rust.
Rust can occur in various seasons but it does need moisture to grow. It typically causes yellow or brown markings on upper surface of leaves, and small yellow or brown powdery growths on the underside of leaves. The powdery substance consists of fungal spores that can be blown about by wind, infecting other plants that are susceptible to that type of rust fungus.
Below, on the left, are pictures of rust on the underside if a frangipani leaf and typical signs of rust on grasses. Some leaf markings can be confused with fungal diseases. On the right are pictures of hail damage on a cycad and spores on the underside of a fern frond – which is how ferns reproduce.

Basically, rust diseases are a sign of malnutrition that produces an unsuitable pH on the leaf surface. Plants, like humans and animals, are more prone to diseases when they have a poor diet, and rust diseases can be avoided by keeping plants growing vigorously – but this is not always possible in extreme weather conditions. Sulphur or copper are the usual treatments for rust. Both of these are nutritional elements that can be supplied by various fertilisers, including seaweed extracts. Seaweed also contains plenty of potassium that strengthens cell walls, sulphur, and trace elements (including copper) that boost plants’ immune systems.
For mild cases of rust, remove damaged parts of the affected plant and burn these, or dispose of them in a sealed plastic bag. Don’t ever compost them, as the spores may not be killed. Then give the plant a foliar feed of seaweed extract tea and water some into the ground over the root area. Improve your fertilising program using a complete organic fertiliser.
For deciduous plants, rake up and dispose of dropped leaves to avoid reinfecting the plant. Apply the seaweed tea at bud swell.
For more severe cases, after removing damaged foliage, plants can be dusted with elemental sulphur (flowers of sulphur. However, as the spores are under leaves and the dust can be difficult to apply, affected plants can be sprayed with wettable sulphur in cool weather only, as sulphur will damage plants when temperatures are over 24 degrees Celcius. Be aware too, that sulphur will also kill pest predators. If these are present on affected plants, apply chamomile tea (one tea bag to 500 ml water) instead.

3 thoughts on “Rust diseases

  1. Hi,

    Grateful gardener from Port Macquarie here. I think you’ve just solved my cicad problem. RUST!! We have the dreaded blue moth also but I have not been convinced by local advice suggesting they’re also responsible for the dying leaves that don’t have the telltale see-through fronds. I’m not sure what type of cycad but the largest is 3 mts high and approx 10 years old. They have weeping fronds. The spots begin as the ones on picture 3 of your Rust Diseases August 9 post 2011!!
    We’ve stripped most of the leaves and have begun to give them some extra loving care as you recommend.
    Finally I feel we might be on the right track.
    many many thanks


  2. I have just found your Blog.. WOW. Wife, kids and I are new Gardeners, slowly turning all of our lawn area to growable ( foods and flowers ) land. Our second year in, we are finding all manner of headaches.. something in the millions loves our silver beet.. lots of tiny black dots.. the wet weather drowned many of our trees: ( so we are swapping out for more lake survivable ones.. ha ha.. we seem to have lots of fruit flies which sting our fruit for us.. so have lots of orange things to kill males.. ( is there a better non poisonous method?) Tomatoes get hammered by black stuff too.. trying some copper sulph. spray to see if this fixes it.. Knowledge is something we are lacking in.. but gee its good fun learning.. 🙂 We are in the wide bay region of Qld.. ( perma lake since Nov.) thanks for putting up something so informative.. your a Bottla Mate 😀 Be safe all be happy 🙂 Nick and Family
    Your plants are very stressed Nick, which is why you have so many pest and disease problems. Following basic organic cultivation methods, such as described in my book, will improve the health of your plants and make them more naturally pest and disease resistant. Your local library may have a copy of my book. – Lyn

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