Hi, this is Steve and thanks for contacting Ask an Expert. I’m sorry you are having so many problems and issues. That is frustrating. When we hear of a rapid decline in plants, we usually think of either a root problem or a water issue. In addition to those, we will discuss other possible problems.

Your roses are certainly experiencing a problem. I know you report that the water is the same as every year. But, I must say that this certainly looks like the roses have dried out. Are you sure the irrigation is working properly? I would think there would be some green plants/weeds growing in the picture if there was adequate water. I have also given an insecticide to use on the roses and other plants (following label directions) toward the bottom. Powdery Mildew is also a possibility which would have looked like a powder on the leaves and can cause leaves to fall.   

https://extension.colostate.edu/docs/pubs/garden/02902.pdf

 You can also look through this information to see if there are any diseases your recognize.  http://planttalk.colostate.edu/topics/insects-diseases/1433-rose-diseases/

Are you also confident that no type of herbicide has been used near the roses?

For the lilac, sometimes portions of plants die back for what appears to be no reason. There are also some possible culprits. One is the lilac ash borer which could have damaged one limb as shown. Here is information about that insect and control – though likely too late for this year. https://extension.colostate.edu/docs/pubs/insect/05614.pdf

Another possibility is oyster scale which attaches to the branches. Here is information on their control. http://extension.colostate.edu/topic-areas/insects/oystershell-scale-5-513/

I would remove the dead limb and throw it away.

My best thought on the petunias is a sucking insect which attaches to the plant with straw like mouthparts and draws out the fluid. They are very tiny mites and difficult to see. You can place white paper underneath part of the plant and tap the plant. Look at the white paper to see if you observe tiny moving insects. The bug dust you used likely would not have worked. In this case, horticultural oil can be used. Be sure to read and follow all label directions. Any parts of the petunias which are obviously dead should be removed and discarded. I would also use this same spray (following label directions) on the roses and lilacs as a precaution. https://extension.colostate.edu/docs/pubs/insect/05569.pdf

http://extension.colostate.edu/topic-areas/insects/insect-control-horticultural-oils-5-569/

I realize there is a lot to read and consider, but hopefully you can find a remedy to these issues. Best of luck.

Thank you for your response! I could only post 3 photos so I did not post sections of the roses where the leaves look fine. So it is not under watering. The link seemed to be referring to hybrid roses that are susceptible to the diseases mentioned. These are wild roses from the CSU tree program. I have included a couple more photos of the roses showing where some are healthy looking among the damaged ones - showing it is not lack of water.  I read all your links and we can try some oil product. There does not seem to be any powdery looking substance on anything. The petunias do not drop any bugs when a white paper is placed under them and I shake the branch. The ones left look great now, but when they begin to die, they are gone in a day or two. There is no removing part of it - it all goes quickly. The branches of the lilac do not appear to have the issues mentioned in your link. there was no herbicide sprayed anywhere. We live in the country and are not close to neighbors and we did not use any ourselves. We do appreciate your time and thoughts! Thank you, Ann & Wayne Huppert

Thank you for getting back to me with more pictures and taking time to go through all the information. I did understand the roses were wild, but many types have the same issue. There is a disease called rose rosette virus and you can google for pictures of that, however, on your pictures, I don't see any of the symptoms. At this point, I think I have exhausted all avenues and I appreciate your working with me to try to diagnose the problem. I would suggest you take samples and pay a visit to a Master Gardener in person. Different ones work each M/W/F from 9 till noon at the Weld County Extension Office (if you live in Weld Co - if not, I can direct you to other counties). The office is in Greeley is at 525 N 15th Ave, in Island Grove Park. For the roses, take several canes which are dead, dying and healthy along with the pictures you have sent. You can also bring the petunias (the entire plant in the pot if that is how they are grown, or dig a dead one out (roots, etc) and bring them. I'm not overly concerned about the lilac as such since it just appeared to effect one branch. However, you can certainly bring in the dead part along with a healthy stem. If the Master Gardener on duty cannot answer directly, I believe they can send the samples off for diagnosis. I hope we can solve these issues and you can get back to more carefree gardening! Steve