![]() ![]() This rootstock is rarely used in the UK, since fireblight is not a significant issue here. ![]() It was found that two pear varieties, Old Home and Farthingdale were largely immune to fireblight, and most pear trees grown in the USA are now grafted on a combination rootstock developed from Old Home and Farthingdale - known as OHxF. Similar approaches have been followed with pear trees. However note that "resistant" does not mean "immune". Contrary to the popular belief that supermarket apple varieties are not as disease-resistant as heirloom varieties, Red Delicious is well-known for its fireblight resistance. Resistant varieties are an eclectic mix of traditional varieties from the southern states such as Arkansas Black, and new disease-resistant varieties such as Honeycrisp. The one exception is M7, which by chance has quite good resistance - and as a result is still widely used in the USA. In contrast the Malling-series rootstocks were developed in England in the early 20th century, before fireblight existed there, so they are not resistant. The first rootstocks - G.11 and G.16 - showed good resistance and more recent releases such as G.41, G.30, G.935 and G.202 have shown further improvements. Fireblight resistance has been the central goal of the Geneva series of rootstocks developed by Cornell University. Fireblight usually only becomes fatal once the disease gets into the roots, and resistant rootstocks prevent this phase of the disease, giving the tree owner more options to cut out the infected parts of the main tree. The development of fireblight resistant rootstocks has proved to be one of the most effective ways to limit the disease. There are essentially two approaches, the development of disease resistant varieties, and the development of resistant rootstocks. Most of the work on fireblight resistance in apples and pears has taken place in the USA, where the disease is particularly aggressive in orchards in the eastern and southern states. However as noted above, although the fireblight bacteria is prevalent in large areas of northern Europe, it is not virulent in these areas and is of little consequence for gardeners and small orchards in the UK. According to Defra, the UK government department responsible for plant health, it spread through the UK in the second half of the 20th century, living on hawthorn hedges that are commonly found along roadsides and railways. Ireland, Isle of Man, Channel Islands, and Corsica) are still free of the disease.įireblight is also endemic in most of the UK. It is notable that some old local apple varieties in these areas appear to have been selected by the settlers for their fireblight resistance.īecause of poor phytosanitary controls between North America and Europe, infected plant material arrived in Europe in the 1950s, and it is now endemic in most of Europe. It appears to have arisen spontaneously in the eastern USA in the 17th or 18th centuries, and progressed southwards. History of fireblightįireblight is an interesting disease because it highlights the importance of international phytosanitary controls. It also tends to occur in cycles with heavy infections every 5-10 years. Note the browned branches, and the attempts made by the owner to beat the infection by sawing off the main stem and the limb on the right.Īlthough fireblight can be a devastating problem for commercial apple and pear growers in affected areas, it is very dependent on warm weather and rain in early spring during the blossom season. The photo shows a mature apple tree killed by fireblight. The infection progresses rapidly (up to 4cm per day in good conditions) and in a severe case leaves the tree looking as if it has been set on fire. ![]() Late-blossoming apple and pear varieties (including most European cider apple varieties) are often more at risk than earlier-blooming varieties - there will be more bacteria in the air, and the weather is likely to be warmer. It is unusual to see fireblight in very young trees since they will not have developed blossom, although the infection can also get in through aphid attacks, or even through holes created by heavy rainfall or hail. Older woody shoots are less likely to be affected. Fireblight can also attack the rapidly-growing tips of new young shoots. The most common method of infection by fireblight bacteria is through the blossom, with the bacteria being transported by pollinating bees. It requires daytime temperatures at blossom time of of 21C - 26C for the bacteria to flourish, which is rarely the case in the UK. However although it is prevalent in most of the UK, it is nothing like as virulent here. Sanity check - fire blight in the UK: Fireblight is the single most important disease facing commercial growers and home orchardists in the USA, and for this reason there are numerous online articles about it. ![]()
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