Diff: Powdery Mildew

== Powdery Mildew ==

== Powdery Mildew ==

Rose powdery mildew produces white to grey powdery growth on leaves, shoots, buds, sepals, and sometimes petals. Young tissue can curl, distort, and fail to open well.

Rose powdery mildew produces white to grey powdery growth on leaves, shoots, buds, sepals, and sometimes petals. Young tissue can curl, distort, and fail to open well.

=== Conditions that favour it ===

=== Conditions that favour it ===

* Susceptible cultivars.

* Susceptible cultivars.

* Shaded or crowded growth with poor airflow.

* Shaded or crowded growth with poor airflow.

* Dry roots combined with humid air.

* Dry roots combined with humid air.

* New soft growth pushed by heavy feeding.

* New soft growth pushed by heavy feeding.

=== Cultural controls ===

=== Cultural controls ===

* Grow roses in enough light and air.

* Grow roses in enough light and air.

* Water the root zone consistently so plants are not drought-stressed.

* Water the root zone consistently so plants are not drought-stressed.

* Prune out badly affected shoots and remove diseased debris.

* Prune out badly affected shoots and remove diseased debris.

* Avoid pushing excessive soft growth with too much nitrogen.

* Avoid pushing excessive soft growth with too much nitrogen.

* RHS and UC IPM both note that direct contact with water can disrupt powdery mildew, but avoid leaving foliage wet long enough to encourage black spot or rust.

* RHS and UC IPM both note that direct contact with water can disrupt powdery mildew, but avoid leaving foliage wet long enough to encourage black spot or rust.

=== Direct treatment notes ===

=== Direct treatment notes ===

* Preventive or early treatments may include sulfur, potassium bicarbonate, horticultural oils, neem oil, or labelled biological fungicides such as Bacillus products where available.

* Preventive or early treatments may include sulfur, potassium bicarbonate, horticultural oils, neem oil, or labelled biological fungicides such as Bacillus products where available.

* Oils can burn stressed plants and should not be applied close to sulfur sprays.

* Oils can burn stressed plants and should not be applied close to sulfur sprays.

* Fungicides are not a substitute for resistant cultivars and airflow. They usually need timing before heavy infection.

* Fungicides are not a substitute for resistant cultivars and airflow. They usually need timing before heavy infection.

* Check current local labels. RHS advice currently favours non-chemical methods for home gardeners, and UK product availability must be checked through HSE-authorised products.

* Check current local labels. RHS advice currently favours non-chemical methods for home gardeners, and UK product availability must be checked through HSE-authorised products.

=== When to worry ===

=== When to worry ===

Mild powdery mildew often looks worse than it is. Escalate when buds fail repeatedly, new growth is distorted across the plant, or the same cultivar is heavily affected every year.

Mild powdery mildew often looks worse than it is. Escalate when buds fail repeatedly, new growth is distorted across the plant, or the same cultivar is heavily affected every year.

=== Sources ===

=== Sources ===

* [RHS: Rose powdery mildew](https://www.rhs.org.uk/disease/rose-powdery-mildew)

* [RHS: Rose powdery mildew](https://www.rhs.org.uk/disease/rose-powdery-mildew)

* [UC IPM: Roses diseases and abiotic disorders](https://ipm.ucanr.edu/home-and-landscape/roses-diseases-and-abiotic-disorders/)

* [UC IPM: Roses diseases and abiotic disorders](https://ipm.ucanr.edu/home-and-landscape/roses-diseases-and-abiotic-disorders/)

* [UC IPM: Powdery Mildew](https://ipm.ucanr.edu/PMG/r280101011.html)

* [UC IPM: Powdery Mildew](https://ipm.ucanr.edu/PMG/r280101011.html)

* [Clemson Extension: Rose Diseases](https://hgic.clemson.edu/factsheet/rose-diseases/)

* [Clemson Extension: Rose Diseases](https://hgic.clemson.edu/factsheet/rose-diseases/)

[[Category:Diseases]]

[[Category:Diseases]]

[[Category:Care]]

[[Category:Care]]