Physical mode of action of fungicides and fungicide alternatives used

against strawberry powdery mildew

Belachew Asalf, David M. Gadoury, Arne Stensvand

Control of powdery mildew

• Cultural practices • Host resistance• Biological agents • Non-chemical alternatives • Fungicides

Biochemical mode of action of two major fungicide groups against powdery mildew

• Sterolinhibitors (e.g. penconazol) inhibit specific enzymes important for the sterol production in fungi

• Strobilurines (e.g. kresoxim-methyl) inhibit mitochondrial respiration and energy production

Physical (and biochemical) modes of actionProtectant: Stops germination, germ tube growth, and penetration Curative: Stops or inhibits mycelial growth and colonizationEradicant: Stops or inhibits established infections

Developmental stages of P. aphanis (Photo: B. Asalf)

Here we have studied how the fungal growth is affected by the different fungicides and alternatives before and after infection and after the disease has become visible

Treatments (recommended rates applied)

Product Active compound

Water

Candit kresoxim-methyl

Topas 100 EC penconazole

Thiovit sulfur

Rapsolje (Askim) rape seed oil

JMS Stylet oil mineral oil

Silwet Gold polyether modified trisiloxan(an adjuvant)

Treatments

Detached leaflets of June bearing ‘Korona’ in Petri dishes on water agar

• Preventive - sprayed just before inoculation

• Curative - sprayed 48 h after inoculation

• Eradicative – sprayed after sporulation started, one week after inoculation

• Conidial viablity was tested using fluorescein diacetate (FDA) 48 hours after eradicative treatments.

Effect on conidial germination

Candit

Control

Protectant application

Curative application

Water control

Rape seed oil

Stylet oil

Topas

Curative effect

Eradicative application

Stylet oil

Control

Sulfur

Eradicative effect

Candit: effect on conidial viablity after eradicative treatment

Stained with FDA

Silwet Gold: effect on conidial viablity after eradicative treatment

Stained with FDA

Water treated control

Stained with FDA

Both the vegetable and mineral oils may give severe phytotoxic effect in field/high tunnels

Preventive Curative EradicativeCandit +++ ++ ++Topas +++ ++ -Sulfur +++ + +Rape seed oil - - -Stylet oil ++ - -Silwet Gold - ++ -

Conclusion from these trials

+++ high efficacy++ moderate efficacy+ some effect- No effect