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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #242096
Title: Spraying Leaves of Pear Nursery Trees with Urea and Copper Ethylenediaminetetraacetic Acid Alters Tree Nitrogen Concentration without Influencing Tree Susceptibility to Phytophthora syringae

Author
item LAYWISADKUL, S - Oregon State University
item FUCHIGAMI, L - Oregon State University
item Scagel, Carolyn
item Linderman, Robert

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2009
Publication Date: 4/1/2010
Citation: Laywisadkul, S., Fuchigami, L., Scagel, C.F., Linderman, R.G. 2010. Spraying leaves of pear nursery trees with urea and copper ethylenediaminetetraacetic acid alters tree nitrogen concentration without influencing tree susceptibility to Phytophthora syringae. HortTechnology. 20(2):331-342.

Interpretive Summary: Recent field observations by growers suggest increased tree N status resulting from foliar sprays with urea in the autumn increased susceptibility of pear OHF97 rootstock to infection by Phytophthora syringae. We investigated the effects of nitrogen (N) availability and spraying trees with urea, copper chelate (CuEDTA), and phosphonate-containing fungicides on tree N status and susceptibility to infection by the pathogen. Spraying trees in the autumn with urea, defoliants, or fungicides such as PhytoFOS or Alliette can influence tree N status and their effects on N status appear to be unrelated to susceptibility to P. syringae. Therefore, spraying pear trees with a combination of urea and Cu-EDTA after terminal buds have set in early autumn prior to harvest and storage can be of benefit to the nurserymen because the pathogen is less active in warm dry environments and the trees may be better able to heal wounds caused by defoliation or the chemical treatments. During production in the PNW, spraying trees with urea and Cu-EDTA in October may be better than in November because of the lower pathogen activity and favorable environmental conditions for wound healing. Unfortunately, trees sprayed in October had lower N reserves compared to trees sprayed in November or naturally defoliated trees; therefore, spraying trees in October may not have as much of a positive influence on tree growth in the following year. Additionally, spraying trees with a combination of urea and CuEDTA with either Aliette or PhytoFOS in early autumn (October) can be of benefit for both early harvesting and preventing the contamination and/or infection of P. syringae in the field or storage.

Technical Abstract: We investigated the effects of nitrogen (N) availability and spraying trees with urea, copper chelate (CuEDTA), and phosphonate-containing fungicides on tree N status and susceptibility to infection by Phytophthora syringae. Increasing soil N availability increased susceptibility and increased N and amino acid concentrations in stems; thus, the effects of N supply on susceptibility may be related to tree N status. In contrast, spraying trees with urea in the autumn increased N and amino acid concentrations of N but had little influence on tree susceptibility. These results suggest the relationship between tree susceptibility to P. syringae and tree N status may be specific to the form of N, delivery method, or timing of N applications. Trees inoculated before being sprayed were less susceptible than trees inoculated after they were sprayed; however, differences in susceptibility before and after spraying were related to tree N status. Similarly, timing of urea sprays were found to differentially influence tree N status without influencing susceptibility to the pathogen. Trees were more susceptible when inoculated in November than when inoculated in October, suggesting environmental factors and tree dormancy status may be responsible for changes in susceptibility to the pathogen during the autumn. Fungicide effects on susceptibility were similar regardless of whether trees were sprayed or not with urea or CuEDTA, suggesting that these fungicides can be used in combination with sprays as a strategy for reducing disease caused by P. syringae without impacting growers’ objectives of increasing N status with urea or enhancing early defoliation with CuEDTA. The N status of pear trees may influence susceptibility to P. syringae; however, our results indicate other environmental conditions and physiology of trees when exposed to the pathogen changes the relationship between N status and tree susceptibility. This suggests observed correlations between tree N status and susceptibility to P. syringae in the autumn are perhaps more coincidental than causal.