I can't quite understand where this is occuring. On the leaf surface?

Are you familiar with powdery mildew? Or do you think it might be some sort of insect? I've not grown agapanthus myself, so I can't speak about its primary pest problems.

It's basically on the leaves, closer to where the stalk is. Actually more leaves are becoming limp and yellow. I thought agapanthus are hardy (it's winter here) but maybe they're being affected by the cold conditions, plus recent rain/moist conditions here (it's usually dry).

I'll try and see if this is powdery mildew. Maybe look the powder up under a microscope or something...sounds fun already :)

weeddummie, I'll get some limp yellow leaves (slimey, actually) on agapanthus after a hard freeze, possibly some yellowing of outer lower leaves after several days of winter rain. My soil is amended clay, drains reasonably well, but the plant most exposed to our marine weather suffers more than the others. It comes back with new growth in late winter.

I haven't seen the 'white' you are talking about...could it possibly be white and webby, like spider mite or mealy bug? Have you tried looking very closely in good light like with a flashlight...possibly torch to you? I do have roses in that same bed that will get mildew, and euphorbia chameleon will pick it up too...none on agapanthus as of yet.

From much further south:

on the nearby Agapanthus there are yellowing leaves and old flower stalks.

Deep in the leaf clumps there are snail casts. However, there are no white deposits at all.

We have had a couple of mild 1-2degree frosts and it's been hosing down for all of June.

The plants in question are on a clay-loam that was pasture. They're competing with a variety of tree roots and are trapped by a fence. The clumps are very congested. They get half-day sun and flower reliably. They are the evergreen kind of Agapanthus, not deciduous.

If you're in the NSW drought zone the plants may be feeling the pinch and have become host to something like mealy bugs. First shot at eradication - Lux flakes melted in water and poured on with a jug. Some cayenne pepper mixed in could be useful, too.

If the edges of your clump are still healthy you might want to take some pieces and pot them up, as insurance.

If you think they could be droughted and you're on water restriction, you could use the rinsing water from your washing machine to really soak the area. You should get about 60 litres from one wash load - enough to improve the water availability for the plants.

Hi, I have a white powder on my aggies, that is also making the leaves yellow and also distorted. my nurseryman has suggested Confidor for mealy bugs, but also said to be patient for the improvement. the best way to spray them is to shear them back so the spray gets into the base better, but at this time of year I will loose all the flowers, so I am going to just spray as often as recommended. will let you all know how it goes.