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Control of Blossom, Shoot and Rootstock Fire Blight In Young, Dwarf Apple Trees Through Nutrition, Pruning and Growth Regulators 2001

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Project Leader(s): Terence Robinson, Dept. of Hort. Sci., NYSAES, Cornell University, Geneva

Herb Aldwinckle, Dept. of Plant Path., NYSAES, Cornell University, Geneva

Type of grant: Cultural methods

Project location(s): Throughout the Northeast

Abstract: Control of fire blight control on dwarf apple trees of highly-susceptible cultivars is an increasing problem in NY. Fertilizer practices can have a small but significant effect on tree growth and on shoot blight severity. In general, we found that the lower the nitrogen fertilization rate the lower the severity of fire blight infection; however, the unfertilized treatment had the poorest tree growth. High K levels alone had a similar level of fire blight infection as did the unfertilized control but much better tree growth and production. Tree growth was poor if nitrogen alone was added but if both nitrogen and potassium were added then growth was much better. The best combination of growth and the least severity of fire blight was with the high K treatment. It appears that the soils used in this experiment have adequate levels of nitrogen to produce good tree growth if supplemented with K.

The new environmentally-friendly shoot growth retardant, Apogee, has a suppressive effect on fire blight development in shoots. Our results show that it does not control blossom blight, but does significantly reduce the amount and severity of shoot blight. Although shoot blight was reduced on Apogee treated trees, rootstock fire blight and tree death were not reduced.

From a practical point of view apple growers should manage new orchards with a relatively low level of N and a relatively high level of K. This could be combined with late season applications of Apogee to reduce the risk of fire blight infection. Although Apogee will reduce shoot blight progress it does not reduce rootstock death. Growers should utilize the new fire blight resistant rootstocks from Geneva (G.16 or G.30) to prevent tree death. An integrated approach with fire blight resistant rootstocks, low nitrogen fertilization, high K fertilization and late season use of Apogee should give good tree growth and minimize fire blight risk.