The famous Don Juan of the Rosa gang.

Rosa 'Don Juan' (bane of my existence)

The climbing Rosa 'Don Juan' was introduced in 1958. A time in which pesticides, herbicides, fungicides and heavy fertilizers were used. With this in mind, it is my perspective that many roses bred and produced from this period and on wards are depleted of the needs they required in their prime as less chemicals are used today. 

Water When Dry

Don Juan specifically suffers with regular, predictable, and heavy coatings of powdery mildew (Sphaerotheca fuliginea). Even more so if the spring weather fluctuates from hot to cold on a weekly basis. Every season that this rose is grown in a greenhouse setting, from bare root to 5 gallon, 3 ft height shrubs (February - September), they always suffer with this disease. No matter the spacing, air flow, watering, fertilizing, or soap spraying, this rose always suffers; thus being the bane of my existence. The matte, crimson new growth is especially susceptible to diseases and pests in comparison the the glossy, wax coated firm and upright foliage on newer breads and sports of common roses. 

Green leaf Nursery 

Powdery mildew on roses can be treated in many ways. Always check the soil in which the bare-root plant was potted in and the mulch it was topped with. A supplier had multiple root tips extruding from the surface and had topped up the square pots with too much mulch, resulting in the plant being potted up "too deep." This adds 2-4 inches of potential anaerobic soil as there are no roots to absorb the moisture held against the crown. Not to mention the excess water against the stem and its potential to rot the bark. Pot up said plants into larger pots, remove top soil and majority of soil around woody roots while keeping in mind the safety of micro root development. This applies within a garden bed as well; skip the transplanting and remove the mulch, replaced with vegetable compost as a mulch and be aware of how deep the roots are, as this creates a 'crown' at the stem which I'll talk about later. 

Rose gardening made easy

1. Prune away the worst of the mildew
2. Use a nutrient rich potting soil (trust the more expensive brands!)
3. Use bone meal in the soil
4. Top with epsom salts, a slow release granular rose food, and a good dose of fish compost as a mulch
5. Don't top dress too much. Plant the rose high and top dress to appropriate height without burying the stem and crown
6. Water in and let the water run through the bottom of the pot
7. Water in with liquid transplanter (5-15-5) and bio-fish liquid concentrate 
8. Mist or spray with a Natria and soap concentrate 
1. The soap will act as a surfactant to the Natria, which is oil based, and will better coat the leaves
9. Liquid fertilize a few days later with an all purpose water soluble fertilizer such as a 20-20-20, and give it a deep soak as it will need it to produce lush new foliage to cover up the old moldy growth.  

@http://www.rose-gardening-made-easy.com/powdery-mildew-on-roses.html

@https://www.greenleafnursery.com/index.cfm/fuseaction/plants.plantDetail/plant_ID/3843/

@http://waterwhendry.blogspot.ca/2009/04/desert-rose-ramblings.html