In recent years, favourable climatic conditions and growing immunity to bactericides have set the stage for an increase in bacterial blight in many Northwest cherry orchards. Last year's bacterial blight was described as the worst in 37 years by plant pathologist Gary Grove of Washington State University. Grove and colleague Youfu Zhao conducted a study of fungal pathogens in cherry orchards, identifying several pathogens, but highlighting bacterial cancer as the main threat.
Zhao analysed samples from 57 orchards, identifying the pathogen Pseudomonas syringae and checking for resistance to copper and kasugamycin. The results show widespread resistance to copper, and some strains show resistance to both treatments. Zhao emphasises the importance of cultural practices to minimise damage, as the inappropriate use of products could aggravate the situation.
To avoid infection, it is recommended to prune only in dry weather conditions, especially in summer, and to adopt strategies such as painting the trunks white to prevent winter injury. Winter pruning can be safe if conditions are dry, but for new plantings, headcuts during sensitive weather conditions can encourage infection.
Zhao recommends collecting samples for analysis if resistance is suspected in orchards. Copper resistance is widespread, and irrigating resistant strains can make the situation worse. Zhao has also identified a new risk, P. syringae pv. morsprunorum, but there is currently no indication that it is more dangerous.
Zhao has also identified two subspecies of P. syringae, further complicating the situation. For growers, the key is to understand that the bacterium overwinters in cankers and buds, spreading through wounds during wet conditions in spring and autumn. Bactericide resistance is a serious problem, and Zhao recommends practices such as pruning during dry times, especially in summer, and switching from sprinkler to drip irrigation to keep the environment as dry as possible.
Irrigation to induce bud break in spring is risky, and Zhao suggests planning carefully for weather conditions. Early leaf fall with chemical treatments can reduce the risk of infection in the autumn. Finally, Bishop, together with Zhao and Sallato, emphasises the importance of cultural practices in managing the disease, considering it manageable with careful orchard management.
Read the full article: Good Fruit Grower
Image: Good Fruit Grower
03 May 2024
In 2023, the CTIFL launched a trial to evaluate protection strategies. Six strategies were compared, two of which can be used in organic farming. These strategies are based on products available with perennial marketing authorization or 120-day marketing authorization in 2023.
18 Dec 2023
The most important factor in spindle formation is to maintain the dominance of the central leader. The central crowns can be cut back in the future, after the formation of fruit-bearing branches below the crown ends.
18 Sep 2026
Canada and the US settle the dispute over Staccato® cherries. Monson Fruit Company will pay past and future royalties, stop propagating new Staccato® trees through 2029 and refrain from exporting fruit outside the US through 2032, ending a six-year long legal battle.
18 Sep 2026
Centro Fruticultura Sur will host a seminar in Chillán, Chile, on protected fruit cultivation, featuring two new publications on covered cherry production and European hazelnut physiology and management, with tools to address climate variability in modern orchards.
