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
14 Nov 2024
Sage essential oil is known to repel a variety of agricultural pests but the effect on D. suzukii remains uncertain. In this chinese study researchers implemented behavioural essays to investigate the repellent properties of sage oil on larvae and adults of D. suzukii.
11 Aug 2023
The Giovanni Quercia company is a family-run business located in Bisceglie (Bari). The business manages a total of 120 hectares, of which 15 are entirely dedicated to cherry production. For Cherry Times, company owner Giovanni Quercia spoke.
10 Sep 2026
In stone fruit, auxins, gibberellins, cytokinins and ABA regulate fruit set, cell division and early fruit growth. The Prunus review explains how hormonal balance influences yield, fruit size, early fruit drop and harvest quality, highlighting its value for orchards.
10 Sep 2026
Drought and high temperatures cut the cherry harvest in the Czech Republic: at Mendel University in Brno, production fell by 16% and some fruit was up to half its usual size, making irrigation increasingly crucial for maintaining stable cherry production in coming year.
