Powdery Mildew on Roses

Powdery mildew is one of the most common fungal conditions affecting Australian flora, with roses being particularly susceptible. Mildew on roses is diagnosed by visually examining the plant – if you see a soft whitish coating on the leaves and flower buds of your roses, it’s likely that your rose has picked up powdery mildew disease.

Powdery mildew, also known as Sphaerotheca pannosa var. Rosae, spreads quickly and will impact the overall health and appearance of your roses. The fungal infection can spread between plants through splashes of water and/or wind, making it an important disease to nip in the bud.

Causes of Powdery Mildew

As one of the most frequently occurring rose diseases, powdery mildew thrives in the humid Australian climate and damp conditions. In particular, climates that are warm and dry during the day and then cool at night are the perfect storm for a mildew outbreak.

The moisture in the air is perfect for helping the fungus spores travel between plants, spreading the disease across plants all throughout your garden.

Treatment

Treating fungus on roses is a delicate but necessary process that Australian gardeners must undertake to ensure that their roses thrive.

The first step to treat mildew on roses is to trim and discard any leaves that look and feel like powdery mildew. Depending on the size of your rose bushes and the extent of the spread, this may be a lengthy process. It is important to ensure that there are no remaining dead leaves, stems or decaying matter on your bush or around the base, as powdery mildew will easily spread back onto your rose bush if the fungus is still around.

When pruning your rose bushes, take the opportunity to remove additional stems and leaves if your rose bush has grown too full. This will allow fresh air to pass through your rose bush, alleviating some of the trapped moist air that powdery mildew thrives in.

If your roses only have a light case of powdery mildew and you have effectively pruned your plant, you can spray off the fungi with water on a warm, dry day. However, if the fungus is not cleaned completely it is likely to return.

For harsher powdery mildew infections, it is best to use an organic rose care spray weekly to kill the fungi and prevent further disease.

When using organic products, it is recommended that gardeners thoroughly spray underneath and on the top of the leaves until they drip with liquid. It is also recommended that you spray the ground around the infected plant. The organic spray will help clean your plant and remove any fungal problems, returning your roses to health and helping them flourish.

How to Prevent Powdery Mildew

Preventing powdery mildew problems in Australia begins when you first choose the rose variety that you want in your garden. It is best to choose new varieties of roses that are also classed as strong growers, or the rose variety that is recommended in your geographical area.

Once you have chosen your rose variety, it needs to be planted in an area of your garden with sufficient air circulation and sunshine to ensure that the moisture doesn’t get trapped.

Regular pruning will also help the airflow through your rose bush. Ensure that watering is done at ground level, and avoid using sprinklers or watering the leaves directly.

Other plant diseases

There are a number of common fungal plant diseases that affect roses, with powdery mildew just one of them. To properly care for your plant, it is important to look out for a variety of fungus on roses, including:

Black Spots

Black spots, which are caused by the fungus Diplocarpon rosae, are an extremely common disease that rlmany roses are exposed to in Australia. Once infected by the fungus, black spots form on the stems and leaves of rose bushes and severely impact the overall health of the plant.

Rust

Similar to powdery mildew and black spots, rust is another fungal condition impacting roses. Caused by Phragmidium fungus, rust can eventually kill rose bushes if left untreated.

The fungus appears on the stems and leaves of roses as growing orange/rust-coloured spots, which can then cause the roses to blacken and the roses to defoliate.    

Protect your roses

Protect your roses from mildew and ensure that your garden looks its best, year-round. At Garden Express, we have a large selection of roses to choose from, so that you can select a variety that suits your geographical climate and garden.