Controlling Strawberry Powdery Mildew with Frequent Overhead Sprinkling with Water

Belachew Asalf, Andrew Dobson, David Gadoury, Arne Stensvand

Trends in strawberry production

2

• Plastic tunnels are popular

• Reduce gray mould, anthracnose, root rot

(Xaio 2001)

• But powdery mildew is major problem

Strawberry powdery mildew

• Podosphaera aphanis

• Obligate

• Heterothalic

• Short

generation

time

• High conidia

production

Symptoms and signs

4

Attack all parts of the plant except the root

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 growersexperience, we hypothesized that P. aphanismight be directly suppressed by a water filmor the action of water applied throughoverhead sprinklers

Experimental design and plots

• High plastic

tunnel (9m X

29m)

• It had 6 rows

• Experiment

middle four rows

• Six

treatments

• Three reps

• RCBD

Treatments

1. Control

2. Water twice per week

3. overhead sprinkling for 1 minute with waterfour times per day (from 11:00 am - 3:30 pm)

4. Sulfur half the recommended rate twice perweek

5. Sulfur the recommended rate once per week

6. Signum (pyraclostrobin + boscalid) or Topas100 EC (penconazol) at recommended ratesalternately once per week

Incidence of Powdery mildew

Disease severity

0

10

20

30

40

50

60

10 17 24 30

Dis

ease

sev

erity

(%)

Days after inoculation

Unsparayed control Water twice per week

Water sprinkler 4 times per day Sulfur half dose twice

Sulfur full dose once Signum and Topas alternate

Powdery mildew Incidence on fruit at harvest

0

10

20

30

40

50

60

70

Control Water twiceper week

Watersprinkler

Sulfur halfdose twice

Sulfur fulldose once

Signum andTopas

alternate

Inci

denc

e on

frui

t (%

)

b

c

c

cc

a

Gray mould (Botrytis cinerea)

• Botrytis incidence was very low

0123456789

Control Watertwice per

week

Watersprinkler 4times per

day

Sulfur halfdose twice

Sulfur fulldose once

Signumand Topasalternate

Bot

rytis

inci

denc

e on

frui

t (%

)

a

ab

ab

bb

ab

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-overhead-watering-vegetables.html

Mechanical washing - water pressure

The Lotus Effect

Lotus leaf

• Lotus Effect is a striking feature of manyplant leaves that water tends to bead intodrops, and roll to the ground, collectingand washing particles and debris from theleaf surface. This self-cleaning mechanismis, termed the ‘lotus effect’.

• It may also play an important role inwashing away pathogen spores and conidia

Lotus effect

Lotus effect

Take off

Transportation

Landing

Conidia dispersal

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