White powdery dust in soil

I have a hedge of Berberis thunbergii atropurpurea nana which I planted 5 years ago, One end of the row is healthy and thriving. The other end is weak and struggling . One plant has died back a lot. I found when I investigated the soil that there was a white powdery dust below the surface. I suspect this fungus (?) is the cause. Can any one identify the problem from this description and suggest a treatment?

 

Hmmm. Hopefully someone who is a bit more knowledgeable than me will be along shortly. What I do know is that finding fungus in the soil doesn't necessarily mean that it is the cause of your plants' demise. It's often just nature's way of breaking down dead material - so maybe your berberis plants were ailing already. Honey fungus, the gardeners' bugbear, produces dark 'bootlace' type structures under the surface of the soil. It is feared because it can kill off many plants, particularly woody shrubs. Fortunately, however, this doesn't sound like your problem.

Is there anything about the position of your unhealthy plants which could be causing them to fail?

 

I have a few patches in my garden that when I turn the soil I find white fungi threads going through it.

I've never noticed any problems with plants in such areas, but put a supporting stick or cane in the ground in such areas and the bottom rots off in one season.