Pests of Specific Crops

Pest Description
Downy Mildew (Peronospora sparsa): Infection by
wind-blown sporangia produced by the
organism cause reddish-purple leaf spots to
appear on the upper leaf surface during cool,
wet weather. Infected leaves yellow and drop,
leading to poor plant vigour and growth.
Disease symptoms resemble those caused by
crown gall, nutritional or environmental factors
and even black spot. The fungus can be
systemic in infected plants, which may not
show symptoms in the greenhouse, so is often a
problem in propagation nurseries.
Powdery Mildew (Sphaerotheca spp.): A white,
powdery growth appears on leaves. Young
leaves curl and are more purplish than normal.
Rose Graft Canker (Coniothyrium rosarum): Cankers
develop in forcing beds at the graft union.
Canes die when the canker has encircled the
graft.
Rust (Phragmidium spp.): Rusty yellow and brown
spots appear on leaves and stems.
Stem Canker (Leptosphaeria spp.): Black spots and
stem cankers form, often at tips where canes
have been pruned back.
Viruses:
Mosaic: Chlorotic areas appear along midribs of
leaflets and leaves may be distorted. Infected
plants may do well until stressed, then can
quickly drop leaves and decline.
Streak: The streak virus causes brown rings and
brown vein-banding on fully expanded leaves
and brownish or greenish rings on canes.
Transmitted by grafting.
Insects:
Rose Midge (Dasineura rhodophaga): Larval (maggot)
feeding occurs within the emerging leaf and
flower buds, which causes the buds to wither
and turn black. Midge feeding can cause
complete failure of a bloom cycle. Peak injury
occurs from mid-June to early July, and in late
August/September.
Sawfly (Rose Slug) (Endelomyi aethiops): The larval
stage of the rose slug feeds only on roses. It
skeletonizes the upper surface of leaves. The
larva has a brown head and pale-green body
that is up to 13 mm long. It moves to the soil in
mid-summer to overwinter and pupate the
following spring. There is only one generation
per year.
Chemical Control
(rate per 100 L water; or per
unit area if indicated)
COPPER 53W: 560 g
Cultural Management
Management:
In the polyhouse, monitor plants and remove infected leaves;
control humidity; clean up crop debris at the end of the season;
alternate crops if possible.
In the nursery, avoid overhead watering in the evening.
Some of the most popular roses, including ‘Austin’,
‘Meidiland’ and mini-roses are highly susceptible. Climbing
roses are often infected but tolerant of the disease, which
produces only mild leaf spotting. However, they are a source
of infection for other roses in the nursery and landscape.
See General Disease Management: Powdery Mildew, Chapter 9.
For resistant varieties see Appendix J.
See General Disease
Management: Rust, Chapter 9.
Use disease-free wood for
grafting. Rogue out diseased
plants.
Remove all infected
overwintering leaves. For
resistant varieties see
Appendix J.
See Brand Canker (above).
Sterilize pruning tools.
Provide good growing
conditions.
Use virus-free rootstocks and scionwood for propagation.
Many roses will sustain some mosaic virus infection without
serious injury, unless grown under stressful conditions. Water
and fertilize to promote healthy, vigorous plants.
Use virus-free rootstocks and
scionwood for propagation.
ORTHENE 75% SP: Mist
blower = 1,312 g/1,000 L;
Hydraulic sprayer = 637
g/1,000 L
See General Insect and Mite Management: Sawflies, Chapter 11.
Thrips: Elongate, very small insects. Cause bronzing and drying of leaves and petals. Buds turn black and fail to open.
See General Insect and Mite Management: Thrips, Chapter 11.
38 • Pests of Specific Crops Nursery Production Guide