Many gardeners are experiencing problems with Black Spot on roses at the moment. This isn’t surprising as it’s spring and September was very cool and wet.
Black spot produces tell tale, irregular black spots on rose leaves. As the disease progresses leaves turn yellow and can fall off. On young roses and very susceptible varieties, black spot, can also infect canes.
I think as the days slowly get sunnier and warmer, you’ll probably see even more black spot out there. It’s sort of that “honeymoon” period for the fungus, there’s still a fair bit of moisture around, cool night temperatures and warmer days.
As we enter the more normal late spring-summer weather pattern, foliage tends to dry out quite quickly so conditions don’t suit fungal growth, so we don’t see it as much.
The best way of dealing with black spot is some preventative spraying to keep the fungus at bay or to treat existing outbreaks. I’d recommend fortnightly spraying with a suitable product to check black spot during this it’s most prevalent period.
Black spot is virtually a natural part of rose growing. It’s an environmental disease, as the spores are usually always out there, just waiting for the right weather conditions to get started.
Products suitable for black spot control are:
Yates Rose Shield – A good all in one rose doctor which treats all the major rose fungal diseases as well as insect pests.
Sharp Shooter – Another all in one product like Rose Shield.
Eco Fungicide – Organic registered. Used in conjunction with Eco Oil. Eco Fungicide has an interesting mode of action it actually changes the pH of the leaf surface controlling existing infections and inhibiting new fungal spread and infection.
Triforine – (Fungicide only) for most rose fungal infections.
Yates Liquid Copper – Anti fungal effect, works on black spot.
On the do it yourself front, there is quite a bit of evidence that milk sprays also work. A spray of 1 part milk to 10 parts water applied weekly.
Remember with rose spraying, good coverage over all surfaces (above and below foliage is essential).
Cultural things also help; avoid overhead watering where possible, space plants appropriately to get good ventilation, good feeding, plenty of sun, good hygiene (cleaning old fallen leaves particularly in winter).
Enjoy your roses,
The Dawson Gardener