D I A G N O S T 



UPDATE 



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apple rust produced spectacular 

 galls on junipers and ample leaf 

 and fruit infections on the decidu- 

 ous hosts. Ash leaf rust brought a 

 flood of samples to the PDL and 

 calls to the county Extension of- 

 fices. Ash leaf rust is a sporadic 

 disease causing striking orange 

 spots and distorted growth on 

 white and green ash. Mountain 

 ash, which belongs to a different 

 family, is not affected. The alter- 

 nate host for ash leaf rust is cord 

 grass, which inhabits salt marshes. 

 Thus, we rarely see this rust fur- 

 ther than 10-20 miles from the 

 seacoast. 



Anthracnose on sycamore was 

 prevalent in several areas, causing 

 leaf drop by late June. Many 

 American elms were showing sig- 

 nificant symptoms of Dutch elm 

 disease (DED) by mid-June. DED 



is accelerated by drought stress. 

 (The same pattern developed in 

 the 1993 and 1996 growing sea- 

 sons). Many Prunus species, par- 

 ticularly sand cherries, exhibited 

 dieback this spring due to brown 

 rot shoot blight (Monilinia shoot 

 blight). A few other diseases have 

 also been common on woody 

 plants this season: bacterial blight 

 on lilac; peach leaf curl; oak leaf 

 blister; and leaf and flower gall on 

 azalea. 



Many of the 'usual' diseases on 

 annuals and perennials have been 

 kept 'at bay' thanks to the dry 

 weather. Botrytis blight and pow- 

 dery mildew are the two excep- 

 tions. Both diseases are favored by 

 high humidity. Good air circula- 

 tion and sanitation are essential to 

 managing these two diseases. 

 When these diseases begin to cause 



problems early in the season, fun- 

 gicides are usually required to keep 

 losses to a minimum. 



As a final note. The Plant Diag- 

 nostic Lab will be closed August 

 4-13. I will be attending the an- 

 nual plant pathology meetings in 

 Montreal, Canada. 



If you wish to submit plant material 

 to the UNH-PDL for diagnosis, send 

 samples (with a check for $12.00) to: 

 The UNH Plant Diagnostic Lab, 

 00 Dr. Cheryl Smith, Plant Biol- 

 ogy Departttient, 241 Spaulding 

 Hall-UNH. Durham, NH 03824. 

 Samples should be accompanied by 

 an identification form (available 

 from your county Cooperative 

 Extension office). Cheryl Smith is 

 the UNH Cooperative Extension 

 Specialist in Plant Health, and can 

 be reached at 603-862-3841. 



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The Plantsman 



