Phomopsis
Phomopsis cane and leaf spot (Phomopsis) of grapevine is caused by the fungus Phomopsis viticola. Phomopsis infects grapevines grown in many viticulture regions of Australia but has not been reported in Western Australia.
Phomopsis develops during wet springs when spores are spread by rain splash. Infection appears as elongated cracks on shoots, leaf spots and bleached canes. Cool wet weather and prolonged leaf wetness increase the appearance and severity of Phomopsis symptoms.
Spores need moist conditions to germinate and infect the vine. Prolonged periods of cool wet weather in spring create the greatest potential for crop losses from Phomopsis. The risk of Phomopsis infection is low if there are few extended rainfall periods in spring.
Pruning systems that retain high bud numbers and infected shoots from the previous season may assist in the build-up of Phomopsis. Vineyards with topographies that restrict airflow or vines that have dense canopies will be at greater risk of infection due to prolonged periods of wetness following rain events.
Monitoring is critical to determining whether Phomopsis is present in the vineyard. The majority of infection occurs during or shortly after budburst. Early detection and knowledge of any previous infection are critical for control of the disease as first chemical sprays are required at 50% budburst to avoid infection of newly emerged shoots.
If the disease is not present in the vineyard, preventative treatment is not necessary. If the vineyard was infected in the previous season and an infection period is suspected, early-season fungicide applications are recommended. Do not wait for leaf and shoot symptoms to appear, as the infection has already occurred by this time.
Crop loss occurs as a result of girdling at the base of shoots, weakening and cracking of canes, which consequently lowers vine productivity. Yield loss can also occur due to infection of bunch stems and berry rot.