help pleaase

Standen1

Help please - I have a raised flower bed - boredered by old sleepers. Last year when hoeing I found a 'substance?' it appeared initially like a bright white root system within the soil, then it looked like a white slime 'mass' on both the wood but also around the base of a couple of plants. I panicked but read that it might be 'slime mould that is not harmful to palnts'. I calmed down and removed as much as I could. Over winter it seemed to disappear.

With the lovely weather this weekend, I have spent hours in the garden but wen I checked this particular flowerbed I found that a curry plant and a lavender have died - rotted away at the base. the curry plant was also covered in the white slime again and the  'root system' was back where the roots of the curry plant should have been. the lavender had no 'slime' on it. It may be purely coincidence, the plants may have died as a result of other causes but I am very confused and concerned. Could this have been due to this 'slime', should I risk planting other palnts there or should I use fungicide which may affect other plants in the area???  Other plants such as viburnum, geranium, fuschia, lavender and phorniums have not been affected  so far but could they be??? Will be grateful for any help - this is the front flower bed in the garden and am concerned that this might spread.....