Controlling Strawberry Powdery
Mildew with Frequent Overhead
Sprinkling with Water
Belachew Asalf,
Andrew Dobson,
David Gadoury,
Arne Stensvand
Trends in strawberry production
• Plastic tunnels are popular
• Reduce gray mould, anthracnose,
root rot
(Xaio 2001)
• But powdery mildew is major problem
2
Strawberry powdery mildew
• Podosphaera
aphanis
• Obligate
• Heterothalic
• Short
generation
time
• High conidia
production
Symptoms and signs
Attack all parts of the plant except the root
4
Infection on the fruit
•
•
•
•
•
Up to 50% yield reduction
Fruit cracking and deformation
Decrease fruit set
Inadequate ripening
Reduce shelf-life
Effect of water on powdery mildew
• Under open field production P.aphanis is not
very important disease compared to tunnel
• The incidence of powdery mildew decreases as
rain fall increases (Yarwood, 1957)
• Growers use overhead sprinkler to control
powdery mildew in the nursaries
• Many laboratory experiments emphasize the
detrimental effect of water on some powdery
mildew species
• There was no quantitative information under
field or tunnel condition
Hypothesis
• On the base of the literature and growers
experience, we hypothesized that P. aphanis
might be directly suppressed by a water film
or the action of water applied through
overhead sprinklers
Experimental design and plots
• High plastic
tunnel (9m X
29m)
• It had 6 rows
• Experiment
middle four rows
• Six
treatments
• Three
• RCBD
reps
Treatments
1. Control
2. Water twice per week
3. overhead sprinkling for 1 minute with water
four times per day (from 11:00 am - 3:30 pm)
4. Sulfur half the recommended rate twice per
week
5. Sulfur the recommended rate once per week
6. Signum (pyraclostrobin + boscalid) or Topas
100 EC (penconazol) at recommended rates
alternately once per week
Incidence of Powdery mildew
Disease severity
60
Disease severity (%)
50
Unsparayed control
Water twice per week
Water sprinkler 4 times per day
Sulfur half dose twice
Sulfur full dose once
Signum and Topas alternate
40
30
20
10
0
10
17
24
Days after inoculation
30
Powdery mildew Incidence on fruit
at harvest
70
a
Incidence on fruit (%)
60
50
b
40
30
20
c
c
10
c
c
0
Control
Water twice
per week
Water
sprinkler
Sulfur half Sulfur full Signum and
dose twice dose once
Topas
alternate
Botrytis incidence on fruit
(%)
Gray mould (Botrytis
cinerea)
9
a
8
7
6
5
4
ab
3
2
ab
ab
1
b
b
0
Control
Water
Water
Sulfur half Sulfur full Signum
twice per sprinkler 4 dose twice dose once and Topas
week
times per
alternate
day
• Botrytis incidence
was very low
How water affect powdery mildew?
• Mechanical washing of conidia
• Hydrophobic effect of the leaf and conidia
(Lotus effect)
• Reduce conidia dispersal
• Conidial germination inhibition
http://www.ehow.com/info_12099041_drip-vs-overheadwatering-vegetables.html
Mechanical washing - water
pressure
The Lotus Effect
• Lotus Effect is a striking feature of many
plant leaves that water tends to bead into
drops, and roll to the ground, collecting
and washing particles and debris from the
leaf surface. This self-cleaning mechanism
is, termed the ‘lotus effect’.
• It may also play an important role in
washing away pathogen spores and conidia
Lotus leaf
Lotus effect
Lotus effect
Conidia dispersal
Landing
Transportation
Take off
Effect of water on conidial
germination
Source:
Peries, 1962
Summary
• Frequent overhead sprinkler application of
water reduced powdery mildew incidence and
severity on both fruits and leaves.
The mechanism could be
• the lotus effect
• washing of conidia
• Reduced airborne conidial dispersal
• inhibit conidial germination
• It could be used to control powdery mildew in
the nurseries and high tunnel.
• The timing is important to reduce the problem
from gray mould.
Acknowledgement