You have rust fungus on those plants. It is probably the same one that affects Holly Hocks or Snapdragon and it is very hard to treat. That reddish brown are the spores. Immediately remove all the other plants that are near them or they will be infected too. Isolate the plants that are infected. Use one of the organic cures and treat all the unaffected plants in case they are becoming infected. Then use one of the stronger treatments on the infected plants. When you water don't wet the leaves. Water splashing on leaves is the conductor for the spores.

The blurb below is from the University of Kentucky that I put in my file for pests and diseases. The link is for organic controls.

 Rust (fungus)
Symptoms: Reddish brown, powdery pustules on leaves,
stems, and seed pods. If infections are numerous, leaves turn
brown and die.
Control: Space well for good ventilation and low humidity.
Keep leaves dry. Ferbam, maneb, mancozeb,
propiconazole, and ziram fungicides control rust.

Here is a link that might be useful: Organic control for rust fungus

I can't find any literature that indicates that New Guinea Impatiens even gets a rust disease. Please share your information, oilpainter. Hollyhock rust and Snapdragon rust are quite different from each other...and don't infect plants outside their own little families. I can't find anything on a rust organism that will infect impatiens. Eeeek!

I have never seen rust on them either, Rhizo and they have been part of my spring line for a quarter century. Brown dust? Well, you might check to see if you have spider mites. I have seen heavy spider mite infestation make benches of crops look like somebody sprinkled them with cinammon. And it also makes the blooms ugly early.

calliope---I think I have spider mites as well as aphids. Today when I went out for the first time I saw some aphids on the leaves, and now there are webs all over the leaves. They took a turn for the worst last night and look bad today. I took off as many of the discolored buds, flowers and leaves that I could and sprayed them with an organic spray for fungus, mites, aphids. The spray says repeat in another 7 days. Are they gonners? :(

What can I do to prevent this from happening next year? Do you think they just came with the plants, or was it the soil I used? I re-used soil from my tulip bulbs in the fall (they are in the same planters) and added some new soil and fertilizer. The weird thing is that they have now spread to a hanging basket (different nursery, new guineas were thriving, not my soil---all I did was buy the basket, hang and water.) They are 3-4 ft. away from the other planters.... did the mites just crawl right over and attack that plant as well? Just trying to understand it all so I can avoid this next Summer.

Yes, it is absolutely without a doubt spider mites. I can see them now, and that is what explains the black ants that have been crawling on the plants for weeks now. They are attracted to the sweet substance excreted by the mites. It drives me CRAZY that I have called 3 nurseries in the area about the symptoms these New Guineas have been having for weeks now, and not ONE mentioned that it might be a 'pest'--- it was always, too much sun, too much watering, yadda yadda. I am new to gardening, and have learned so much this past year. Unfortunately, the learning is often costly. Now I know next year to put down insect control granuals when I plant. I'm now worried about the boxwoods that are nearby. They have webs forming on them. I'm planning on getting some of the Bonide systemic insect control granuals all over the bed. Hopefully that will help them from hurting anything else.

Whoa.....;-)

Spider mites are often a function of weather. They can come with the plants, they can travel in and even the best of us get them, and they can occur naturally outside, so your infected plants may not be spreading them at all.

The ants are not attracted to anything the spider mites are doing. They do have a symbiotic relationship with aphids, however. When you see ants heavy on plants, aphids are the first thing you look for.

Bonide is a brand name as far as I can tell for a whole line of pesticides. So, I have no clue which product you intend on using. I will tell you that spider mites are arachnids, and are not controlled well with products effective against true six-legged insects.

I have found products effective against mites can really be hard on your beneficials. It can throw off the whole balance of nature thing.

You have picked up some first hand experience by looking up mites and aphids (I assume you researched them when I suggested mites) and next year you will be better armed to deal with infestations. What works the VERY BEST, is to look at your plants routinely. Really LOOK at them. Under the leaves, their general thriftiness. And at the first sign of a problem, isolate that plant and deal with it as an individual before all hades breaks loose with your plantings.

Look at them well when you buy them. If they look suspicious then don't.

Misting with plain old water will often keep two spotted spider mites under control if they haven't already gotten completely out of hand. Just make sure they go into the night with dry foliage.

I am not an 'organic' grower, but just nip things in the bud early(like why are the aphid laden obedient plants not cleaned up? They should be removed from the vicinity of other plantings until they are.)

I'm sorry you got such bum advice from your nurseries. Many people you talk to could be register clerks, or summer help who really should have referred you to a grower. Your N.G. will not like being treated with an arsenal of chemicals. They go phytotoxic easily. You may want to take the highly infested ones and do a good spray with summer weight oil. Then.....cut them back severely. They will look nasty for awhile, but will return to a clean environment. And consider syringing nearby plants with a spray of water routinely. Good luck.

Calliope's comments are right on! Bull's eye.

Will do! Thank you for all of the advice