Utah Pests News Spring 2007

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Plant Pathology News

  Fire blight strike on apple

Fire Blight Update

Fire blight is the most devastating disease of apple and pear production worldwide and this is true of homeowners and commercial growers of those fruits in Utah.  The disease is caused by the bacterial pathogen called Erwinia amylovora (EA).  Pruning is a very effective means to reduce carryover of the disease as cankers serve as a reservoir of the pathogen, although it is labor intensive and expensive on a commercial basis.

Historically, two agricultural antibiotics have been used commercially as controls but in recent times EA has developed resistance to streptomycin, the most effective of the two. An extensive survey conducted in Summer 2006 in Utah County, followed by laboratory tests, found that as much as 26% of the EA isolates in that county were resistant to streptomycin.  Those isolates were found to be resistant at 2 to 4 times the concentration of streptomycin that was recommended for control of the disease.  However, there is a glimmer of good news.

Recently, the EPA established an import tolerance for residue of kasugamycin (made and marketed by Arysta Life Science), an agricultural antibiotic for control of EA used in other countries on foods being sent to market in the U.S.  What does this mean regarding the possible registration of this compound in the U.S.?  If history serves as an example, when the EPA makes a move like this, it signals the agency is considering the registration for use of the chemical(s) for which they approve import tolerances.

Dr. Howard Deer, USU Pesticide Specialist, provided us with news that the EPA had approved an import tolerance for kasugamycin residue on foods imported in the U.S., so we conducted research during the 2006 season to evaluate the efficacy of kasugamycin to control fire blight in field and laboratory experiments.  Preliminary findings suggest that kasugamycin is effective for the control of streptomycin-resistant isolates of Erwinia amylovora and for the control of fire blight shoot strikes comparable to levels of control provided by streptomycin.  Further testing is underway for the 2007 growing season with on-farm trials and further USU based research.

Potato Cyst Nematode Update

  Potato cyst nematode on host
Potato Cyst Nematodes (Globodera pallida, [ignore the statement that it does not occur in the U.S. now]), an international quarantine pathogen, was identified in five potato fields in Idaho in summer 2006.  APHIS/PPQ has established quarantine sites of the fields testing positive and an extensive screening program has been established in Idaho.  Nationwide Cooperative Agricultural Pests Surveys (CAPS) are being conducted to screen for the nematode.  Updates will be passed along if additional news develops.


 -Kent Evans, Extension Plant Pathologist (No longer at USU)