Regardless of what happened, the fact remains that pruning out fire blight was not successful in eradicating the bacteria from most treated trees. Last but not least, it is possible that the bacteria invaded the host tissues directly through the new wounds created during pruning the ugly stub in the first place! It is also possible that despite the fact that the pruning tools were disinfected with bleach between cuts, not all of the bacteria were killed and colonized the cut stubs. The fact that the bacteria spread beyond the 12” pruning cut is not too surprising and may explain why pruning did not successfully eradicate the pathogen from treated trees. This could be due to several reasons, including that the fire blight bacteria infected tissues beyond the sites of visible symptoms, and even beyond the cuts into “healthy” appearing tissue 12” away. Pruning failed to eliminate fireblight, which continues to spread. These researcher found that when pruning was carried out as recommended to growers (that is, using disinfected tools and making the cuts in a healthy area approximately 12” below the site of infection), pruning did not result in successful eradication of the pathogen.įigure 3. So, the question still remains: To cut, or not to cut? And if so, when to cut? ![]() Furthermore, it was found that sometimes it was preferable not to cut at all, because pruning affected tree health negatively. Because of these factors, there are situations in which pruning can be expected to improve tree health, but there are also cases in which pruning would make no difference, as the disease would not endanger the host plants if left untouched. So, what is the how and the when that affects fire blight? They found that how the plant is growing (i.e., health and vigor) and when the growth is occurring are factors that affect success in fire blight pruning management. 87:1083-1088.), and the results of these tests show that other factors profoundly affect the time of pruning, and affect the success of pruning and its contribution to tree health. “New considerations for pruning in management of fire blight in pears.” Plant Dis. One group in Israel tested this on pears (Shtienberg, D. Previously, management recommendations were to prune out infections as soon as they were observed. The question remains as to whether you should prune immediately after blossom infection, or wait until the trees are dormant. Many popular varieties (Gala, Silken, Ambrosia, Fuji, Braeburn) are very susceptible to fire blight. Regular scouting is essential for effective fire blight management. These cankers are always associated with shoots that were killed last year. Preventing the development these cankers is important, as these are the main areas where the bacteria overwinter. The cankers appear sunken and dark and, when the outer bark is cut away the underlying tissue may appear water soaked. ![]() After last night’s event, it is important to continue to scout! This shoot blight probably developed from the long wet spring/summer that prevented growth from hardening off, or even the hail and severe wind damage from some of the incredible storms that have blown through our region ( trauma blight). This means that any observed infection came from damage from the previous year. Early spring weather conditions were not conducive to blight infection due to the cool, dry weather. With the current extreme weather events, a review of fire blight seems timely.Īt this point in the season, we have passed through the blossom blight period, but I haven’t heard of any reports of fire blight. Epidemics of the disease develop quickly, particularly in a climate of warm, wet weather, with hail events-like last night’s 0.75” to 1.5” hail! The type of management program developed by each orchard will vary considerably based upon a variety of orchard factors, including apple variety, rootstock, age of planting, and weather conditions. Fire blight, caused by the bacterium Erwinia amylovora, is a devastating disease of apples and pears.
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