Question: My name is Lee Dudley CEA Ag & NR in Limestone County. A home owner brought an immature Asian pear to my office to identify the fungus on the fruit; I could use your expertise. I have taken digital pictures and attached them. Not seen in the pictures is an orange dust developed by the fungus which is covering the tree, but it seems the spores are limited only to the fruit.

Answer: This is most probably Japanese pear rust ( I say probably
because there are a couple of other rusts that occur with much less frequency). The symptoms are the result of infection by the rust fungus Gymnosporangium asiaticum. What you are seeing are aecia (rust fruiting structures where aeciospores are produced)---the aecia are somewhat tubulat and elongated and white in color...but are filled with orange-brown spores (aeciospores) that are released when the aecia rupture...which is clearly happening in the images that you included.
This rust has 2 hosts--the pear and Juniper spp--its alterbate host --probably J. procumbens oor J. chinensis. Spores from the pear infect the juniper which produces 2 additional and different spore stages, one spore stage of which then re-infects the pear, probably in mid spring in your area. Infection in the pear can occur to both the fruit and to the
leaves. Even though symptoms can be significant, control is rarely
warranted.
Spraying the pear with triadimefon (Strike or Bayleton--or Eagle/Spectrcide Immunox)in early spring may help...but some years the disease is prevelant and other years, non-existant.

Larry W. Barnes
Professor and Extension Plant Pathologist
Texas Plant Disease Diagnostic Laboratory
Texas A&M University
College Station, TX 77845
PH 979-845-8032
FAX 979-845-6499
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ANSWER FROM JIM KAMAS IN FREDERICKSBURG:

Either as you suggest or perhaps quince rust, which we saw in the Lightsey orchard about nine years ago. Absolutely devastates varieties such as 'Kieffer'. Other hybrids like 'Orient" and 'Ayres' were untouched. The SI fungicides did take care of the problem. Bayleton is no longer on the market I believe, but Nova is and is labeled for pears. I suggest a 4 oz per acre rate as perscribed for powdery mildew. Elice had great success. This kind of spring is ideal for all of the rusts.