Pitaya stem problem
I sprayed my pitaya with a 50/50 solution of dish detergent and water to control ants. Shortly afterward all of the fruit and maybe 20% of the stems turned a yellowish color and the stems in various sections got very soft like it was decaying or rotting. I have since cut most of these parts out and the remainder seems ok but has a few orange spots along the stems. If the tissue dies back to the stem itself will it still support growth of the plants and fruiting ? I am really concerned about next year as it looks like this season is gone. On a branch there may be some sections of 15 to 20 inches where the flesh has become very gooey and will be falling off the stem. I assume photosynthsis takes place in the fleshy parts so I do have some concerns. Any help you can provide will be much appreciated.
Outside United States
Do not spray household detergent on plants. If you do spray dish detergent on plants rinse it off as soon as possible with clean water. Insect pests such as ants may be controlled by spraying with Safer Soap which is a potassium fatty acid, organic product when the ants are present. Safer Soap does not provide residual control (the pest needs to be present when sprayed to control it). Apply any pest control according to label directions. Another option would be to apply diatomaceous earth, an inert naturally abrasive substance, to the surface of the soil the pitaya is growing in. Ants and other insects walking across the surface of diatomaceous earth scratch their cuticle or outer skeleton and die from dehydration. Diatomaceous earth must be reapplied following watering which wets the product.
Other questions regarding the plant may be answered by reviewing a Wikipedia article on pataya, see https://en.wikipedia.org/wiki/Pitaya . That article mentions a bacterium, Xanthomonas campestris, which may be the cause of browning and rot. It is also possible that the damage was caused by the application of dish detergent solution. It is unlikely the plant is photosynthesizing in the areas damaged with brown rot. It is advisable to cut the dead, dying and rotting portions of the pataya well below the transition between healthy and damaged plant tissue. Bacterium spread easily: wash the knife or shears used in cutting the damaged plant parts after each cut.