Rust colored powder on new guinea leaves?
I'm not getting much as far as google searches....
Can anyone help me out here? I have some new guineas in morning sun on my porch that are not doing as well as the others. Granted, the others are a different variety, and are from a different grower, but they are thriving beyond belief. The other ones are losing leaves left and right (they eventually turn brown) and the flowers do not last long at all....I'm constantly deadheading wilty flowers, where as the others I barely need to touch. I've been trying to figure out if it's a sun issue, a water issue.... but my gut says it's something else because the others (that are all in similar conditions) are doing so well.
I notice that there are black ants often crawling on them. I don't see any aphids, although I do have some potted obedient plants in the same area that are covered in aphids (but that's another issue.)
I also notice that the underside of the leaves has a sandy/powdery film on it---kind of a reddish brown rust color. Should I spray for fungus? Or for aphids?
I sprayed them with dishsoap/water---is that an effective treatment for aphids, or should I get a pesticide?
Thanks so much for your help. I invested quite a bit in these new guineas and cannot afford to replace this summer if I lose them!