Rose Guide - Otto and Sons Nursery

Disease & Pest Control
Control Overview
The amount of spraying you do will depend on
your tolerance of diseases and pests. Prevention
is the key to a disease free plant. If you have any
questions regarding spray material, check with
your local California Certified Nursery Professional
or Cooperative Extension Service for your spray
program. Please do not hesitate to contact us for
suggestions or insights we may have to offer. We
have listed some suggestions below.
When spraying, please make sure that you spray
the roses in the cool early morning so the foliage
won’t be wet overnight. It is important that the
plant’s soil is well watered and the leaves are dry
prior to any application.
Some of the “softer” sprays that will control many
diseases are Ultra Fine, Rose Defense, and Safer
Garden Fungicide. Water can be used effectively to
control many diseases. By washing the rose plant
with water in the early morning, insects and fungal
spores will be dislodged from the plant and may
reduce their occurrence.
Dormant Spray
When your winter pruning is finished, usually in
January, a good Dormant Spray should be applied.
Volk Oil and Kop-R applied thoroughly will reduce
insect eggs and fungal spores that over-winter on
your plants.
Beneficial insects and mites can also be released
to control pests, but you must be willing to put up
with some pest damage on your roses.
Rose Diseases
Powdery Mildew
Powdery mildew is first visible as a white powderlike
substance on the leaf surfaces or flower buds.
New plant growth is the most susceptible to
infection. Infection is most likely when humidity is
high (but no moisture) and temperatures are cool.
Look for it during warm days and cool nights.
Recommended products for prevention control
are Green Light Fung-Away or Immunox applied as
per the label instructions.
Rust
Rust symptoms generally appear first as orange
powdery spots on the under surface of the leaves.
Rust can cause leaf drop and reduce growth.
Recommended products for prevention control
are Immunox, Funginex, or Green Light Fungicide
per label instructions.
Blackspot
Blackspot symptoms are well described by the
name. They appear on the upper side of the leaves
surrounded by yellow tissue. Chlorosis may extend
throughout the leaf before leaf drop occurs.
This fungus disease occurs during cool and wet
periods.
Recommended products for prevention control
are Bravado, Funginex, Immunox, and Green
light Systemic fungicide. Spray coverage on the
underside of the leaf is important for control.
Botrytis Blight
aka; Grey mold, “Balling”, brown spots on petals
and brown cane die-back. The disease occurs
during high humidity and cool rainy nights.
Recommended product is Bravado.
Downy Mildew
This can be the most devastating disease for roses.
This disease rarely causes mortality, but it can
cause severe leaf drop. This can necessitate the
restarting of the rose crop with cutting back and
re-growing.This delay will mean an additional 6
weeks from cutback for flower production.
Symptoms of downy mildew occur on leaves with
the development of purplish red to dark brown
spots. The leaves may turn yellow and drop. Leaf
symptoms may resemble black spots or burns
from pesticide toxicity. Under humid conditions
lesions appear in large numbers on the surfaces
of the leaves. Fungicide application must provide
coverage on the bottom of leaves for good control.
Spore reproduction and infection slows when the
humidity drops below 85%. In ideal conditions,
spores can multiply in as little as 3 hours. The ideal
condition exists for infection when temperatures
are 55-65 degrees with humidity over 85%.
Control is achieved by lowering the humidity,
raising the temperature and preventative
application of fungicide. Since neither the
temperature nor humidity can be controlled
in an outdoor environment, a regular fungicide
application is necessary. A regular application of
Agri-Fos per labeled instructions is recommended.
A program that alternates material such as
Subdue, Agri-Fos and Stature has been effective.