Honeysuckle or Lonicera are prone to fungal diseases such as black spot and mildew in the driest of years but during wet springs the fungal diseases they suffer can completely defoliate the plants. As with fungal diseases the cure is quite difficult, the best treatment is with good hygiene clear up and removing the infected leaves and mulching around the base of the plant to in the autumn to stop the fungal spores splashing back onto new foliage or leaves as the plant recovers or produces new leaves in the spring.
One quite effective treatment is to apply yellow sulphur to the infected foliage, this is classed as an organic treatment