PestFacts WA

Chocolate spot in faba beans

• Wittenoom Hills
• Neridup

Chocolate spot on faba bean leaves. Photo courtesy of Quenten Knight (Agronomy Focus).

Quenten Knight (Agronomy Focus) has found widespread chocolate spot infection in a PBA Samira faba bean crop near Wittenoom Hills. The crop had already received two applications of Mancozeb fungicides and was going to be sprayed again with MIRAVIS® Star.

Chocolate spot infection in faba beans. Photo courtesy of Quenten Knight (Agronomy Focus).

Quenten has also reported widespread chocolate spot infection in another faba bean crop (variety unknown) at nearby Neridup. The crop had been sprayed four weeks ago with Aviator® Xpro® and will be sprayed again with Veritas as soon as possible.

Chocolate spot lesions on faba bean flowers. Photo courtesy of Pam Burgess (DPIRD).

Chocolate spot in faba bean usually appears as red-brown spots on leaves, stems and flowers but is usually not conspicuous until after the crops starts flowering.  The spots on leaves and stems enlarge and develop a grey, dead centre with a red-brown rim or margin. 

Senior research scientist Mark Seymour (DPIRD) notes that conditions in early August were conducive to chocolate spot development in the Esperance region.  From August 7, the Esperance region experienced seven days with relative humidity continuously at 100% compared to the same period in 2021 when disease pressure was much lower and only a few hours of high humidity was measured. Consequently, more disease is being seen in beans, lentil, canola and cereals than most years.

Under this pressure all varieties of faba bean are showing some chocolate spot, albeit the best rated variety PBA Amberley (MSMR) is less affected than other varieties. For more variety information refer to DPIRD’s 2022 WA Crop Sowing Guide – Pulse Guide.

Foliar sprays provide disease control even in susceptible varieties but must be applied before rain or wet periods to be effective. For more fungicide information refer to DPIRD’s 2022 Registered fungicides for pulse crops in WA guide.

For more information refer to Agriculture Victoria’s Chocolate spot of faba bean page.

For more information contact plant pathologists Jean Galloway, Northam on +61 (0)8 9690 2172 or Mark Seymour, Esperance on +61 (0)8 9083 1143.

Article authors: Cindy Webster (DPIRD Narrogin), Jean Galloway (DPIRD Northam) and Mark Seymour (DPIRD Esperance).