November Pest of the Month: Bacterial brown spot

Wednesday, 4 November 2020

Small (3-8mm diameter) tan spots with reddish-brown margins develop on leaves. The spots are usually circular but may be angular when bordered by leaf veins. Spots are often surrounded by a light green to yellow halo, the center of the spots often dry and fall out, leaving a shot-hole appearance, leafs often tear from spot to spot.

On stems, brown, sunken spots or lesions with reddish edges may form. On pods, circular dark-green spots with a water-soaked appearance occur, later becoming enlarged and sunken. If the pods are infected early, they may become twisted or bent where lesions develop.

Transmission: The disease is mainly introduced via infested cuttings, contaminated seed or when seed pods come into contact with bacteria in plant debris during harvest and handling. Bacteria over winter in cankers on twigs and limbs. Twig infection often occurs through leaf scars in autumn. It can enter leaves through rust pustules and hail or wind-damaged areas, survive on undecomposed crop residues and possibly other host plants. Once the disease is established, wind, rain, overhead sprinkler irrigation and the movement of workers and machines through the wet crop assist disease spread.

Favoured by: The disease is favoured by cool, wet, windy weather in autumn and early winter before and during leaf fall. Damage to trees and limbs during this period increases risk of infection. Periods of intense rainfall are particularly conducive to disease development.

Host range: The disease affects Common bean, French bean, kidney bean, Lima bean, Navy bean as well as Pea, Sweet pea, Gourd, Almond, Leaucospermum, Magnolia, Protea and all Stone fruit.

For further information, please refer to the Pest ID Tool at: https://pestid.com.au/disease/bacterial-brown-spot