Dragon fruit, Lao Minimize
   

February 2013. Two pieces of dragon fruit stem were brought in by a local farmer from a village near Vientiane Capital, Lao PDR. The plants are about 5-6 years old and the farmer noticed the damage 3 days ago. Many plants are affected. We have looked for insect pests but found nothing on the material submitted. 

A member wrote that this may be caused Guerreronis mites which affect coconut fruits also. Spray with sulphur products or abamectin mixed with agriculture oil every month if pest persist as it will affect fruits too.

There is a review of dragon fruit diseases in the Australasian Plant Pathology December 2012 (see below). Also, over the years a couple of members have sent images somewhat like the one above showing damaged stems of dragon fruit. See Summaries at: 
http://www.pestnet.org/SummariesofMessages/NonPests/Physiologicalresponses/Dragonfruit,pathogenorsunburn,Malaysia.aspx or search under dragon fruit, dragonfruit and Hylocereus.

Later, it was reported from Lao that sunburn was the most likely cause of the symptom.

Original:
http://tech.groups.yahoo.com/group/pestnet/message/9534
Reply:
http://tech.groups.yahoo.com/group/pestnet/message/9535
http://tech.groups.yahoo.com/group/pestnet/message/9536
http://tech.groups.yahoo.com/group/pestnet/message/9537
http://tech.groups.yahoo.com/group/pestnet/message/9538
http://tech.groups.yahoo.com/group/pestnet/message/9539
http://tech.groups.yahoo.com/group/pestnet/message/9543

  
 A brief overview on pitahaya (Hylocereus spp.) diseases Minimize
 TitleOwnerCategoryModified DateSize 
A brief overview on pitahaya (Hylocereus spp.) diseasesGrahame Jackson 6/13/2013347.48 KBDownload