Fireblight Updates – 2024
This year’s wet spring, coupled with the increased production of fireblight-susceptible varieties, has caused disease problems for many local apple growers.
While fireblight is an indigenous disease, it recently began to increase in its severity. As we reduced the acreage of tolerant varieties like Red Delicious and Golden Delicious, while planting new blocks with susceptible varieties like Gala and Fuji, fireblight became an important orchard risk.
The precocity of Gala and Fuji and other new varieties, budded onto precocious, size-controlling rootstocks, increased the risk of fireblight. Planting floriferous varieties such as Cripps Pink, Evercrisp and CrimsonCrisp which bloom over an extended period, further increased the risk of blossom blight.
Difficulty controlling blossom blight has led to an outbreak of shoot blight in a number of young Maryland orchards. Growers began cutting out shoot blight during the past few weeks to avoid additional strikes and reduce the chance of losing blighted trees to trunk and rootstock blight.
Chemical control measures focus on the use of bactericides, growth retardants, and activators during the bloom and post-bloom period. To have the greatest effect, growers typically time their applications to infection periods as predicted by computer programs such as MaryBlyt.
Despite these efforts, growers are still struggling to control Erwinia amylovora, the bacterium which causes fireblight. To gain better control in the future, we will need field-tolerant varieties, better control methods and improvements to fireblight-predictive models.
This article appears in Volume 15, Issue 4 of the Vegetable and Fruit News.