--- title: Downy Mildew canonical: https://gardensuperstore.com.au/problem-solver/downy-mildew/ dateModified: 2026-08-07 09:49:54 summary: "Downy mildew is a fungus-like disease causing yellow leaf patches and greyish fuzzy growth underneath, thriving in cool, damp, humid conditions." type: article keywords: [Downy Mildew, Peronosporaceae] --- # Downy Mildew > Downy mildew is a fungus-like disease causing yellow leaf patches and greyish fuzzy growth underneath, thriving in cool, damp, humid conditions. *Peronosporaceae* Downy mildew isn't a single organism but a group of related water moulds (technically oomycetes, not true fungi) in the family Peronosporaceae. Different species attack different plants — for example *Peronospora destructor* on onions and garlic, *Bremia lactucae* on lettuce, and *Peronospora parasitica* on brassicas — but they all behave in a similar way and cause similar symptoms. On the upper leaf surface you'll see irregular, angular yellow to pale green blotches, often bound by the leaf veins so they look blocky rather than round. Turn the leaf over and, in humid conditions, you'll find the diagnostic sign: a fine, greyish-purple to white fuzzy or downy growth on the underside, directly beneath the yellow patches. This fuzz is made up of the pathogen's spore-bearing structures, and it's most visible early in the morning while dew is still present. Downy mildew is common across southern and temperate Australia wherever nights are cool and moist and days are mild — typically autumn, winter and spring in home gardens, though it can appear anytime conditions favour it. It affects a wide range of vegetables, ornamentals and grapevines, spreading via airborne and splash-dispersed spores that need free water on the leaf surface to germinate and infect. Management relies on improving airflow and reducing leaf wetness: space plants well, water at the base rather than overhead, and water early in the day so foliage dries quickly. Remove and destroy infected leaves and plant debris promptly, rotate susceptible crops, and choose resistant varieties where available. Avoid overcrowding and excess nitrogen, which encourages dense, humid canopies that favour the disease. ## How to identify - **Upper leaf surface:** angular or blocky yellow to pale green patches, often restricted by leaf veins. - **Underside of leaf:** greyish-purple, silvery or white downy fuzz directly under the yellow patches — most visible in early morning or after humid, still weather. - **Progression:** affected patches turn brown and papery as tissue dies; heavily infected leaves may collapse or drop early. - **Field check:** pick a symptomatic leaf and examine the underside with a hand lens in good light, or leave it in a sealed plastic bag overnight to raise humidity — the downy sporulation will often develop within hours if downy mildew is present. - **Lookalike – powdery mildew:** powdery mildew forms a white, powdery coating on the upper leaf surface (and often the underside too) and isn't confined by leaf veins, whereas downy mildew's fuzzy growth appears only on the underside opposite yellow, vein-bound patches. - **Lookalike – nutrient deficiency or sunscald:** these cause yellowing or bleaching without any fuzzy growth on the underside; checking for the downy sporulation is the key way to confirm downy mildew. ## Registered products we stock - [David Grays Copper Oxychloride | Fungicide](https://gardensuperstore.com.au/david-grays-copper-oxychloride-fungicide/) — David Grays - [Agri-Fos 600 | Systemic Fungicide](https://gardensuperstore.com.au/agri-fos-600-systemic-fungicide/) — AgriChem - [Tombstone Duo | Fungicide](https://gardensuperstore.com.au/tombstone-duo-fungicide/) — ProForce - [Mancozeb 750 DF | Fungicide](https://gardensuperstore.com.au/mancozeb-750-df-fungicide/) — David Grays - [Root Rot | Systemic Fungicide](https://gardensuperstore.com.au/root-rot-systemic-fungicide/) — Searles - [Chlortan 720 | Fungicide](https://gardensuperstore.com.au/chlortan-720-fungicide/) — PCT SureFire - [Copper Oxychloride | Fungicide](https://gardensuperstore.com.au/copper-oxychloride-fungicide/) — Amgrow Specialty Agriculture - [EcoCarb PLUS | Fungicide](https://gardensuperstore.com.au/ecocarb-plus-fungicide/) — Organic Crop Protectants - [Phosfusion 600 | Fungicide](https://gardensuperstore.com.au/phosfusion-600-fungicide/) - [Mancozeb DG | Fungicide](https://gardensuperstore.com.au/mancozeb-dg-fungicide/) — Amgrow Specialty Agriculture - [Stellar | Fungicide](https://gardensuperstore.com.au/stellar-fungicide/) — PCT SureFire - [Azoxystrobin 250SC | Fungicide](https://gardensuperstore.com.au/azoxystrobin-250sc-fungicide/) — EnviroMax - [Cheers 720 | Weathershield | Fungicide](https://gardensuperstore.com.au/cheers-720-weathershield-fungicide/) — Colin Campbell Chemicals - [Dedicate | Turf & Ornamental Fungicide](https://gardensuperstore.com.au/dedicate-turf-ornamental-fungicide/) — Envu - [Penncozeb 750DF | Fungicide](https://gardensuperstore.com.au/penncozeb-750df-fungicide/) — UPL ## Image credits - [Photo: Unknown author via Wikimedia Commons (CC BY-SA 3.0)](https://commons.wikimedia.org/wiki/File:Komkommer_valse_meeldauw_(Pseudoperonospora_cubensis_on_Cucumis_sativus).jpg) - [Photo: Rude via Wikimedia Commons (CC BY-SA 3.0)](https://commons.wikimedia.org/wiki/File:Mildew-back.JPG) - [Photo: Lucyin via Wikimedia Commons (CC BY-SA 4.0)](https://commons.wikimedia.org/wiki/File:Mildiou_vegne_foye_flanixhaedje_spiteures_ciproconazole.jpg) - [Photo: Lucyin via Wikimedia Commons (CC BY-SA 4.0)](https://commons.wikimedia.org/wiki/File:Mildiou_vegne_foye_dizo.jpg)