Cut off the cane as close to the bud union as you can. It looks like that should be enough as there isn't too much black on the bud union itself. You might need to cut off the other cane next to it that is brown and possibly the one thicker one behind it that seems to have some canker although that could just be a shadow. Be ruthless - anything black = canker and you need to get rid of it. I don't think I'd try to cut into the bud union itself. Hopefully it will be healthy enough to fight off the infection. What fungicide do you have? If it is a systemic it might help, but even the Bayer Advanced stuff that I use doesn't do much to canker. Oh, and be sure to clean your pruners between each cut with a disinfectant. I use rubbing alcohol but you can use a bleach solution if you prefer that.

Well, though not all that old - I have them going on 30 years since purchase and my grandparents also grew roses- moving bushes from home to home over approx 50 of their 65 yrs being married. I don’t believe there is an age limit. The big issue is grafted roses require a little more attention to details when planting. Own root once they are old enough to plant - not necessarily when you get them, can just be planted with no thought. But all grafted roses, you have to make sure the bud union is well buried or you will get suckers. I have never had an issue because - well, I make sure the bud union is buried 3-4” and to protect from cold also - absolute minimum of 2-3” in my zone 7 east coast garden. In my early years of growing roses, our winters were colder and we got more snow and I hilled teas, shrubs, etc and wrapped in burlap/stuffed with pine-tags . Climbers were laid over and covered in soil or well hilled, wrapped and stuffed. And of course after spring frosts, everything has to be unhilled and set right again. However, our winters have warmed so much it isn’t as necessary if you select the right rose for the right location in the garden and hardiness zone. Dr Huey is a very common used rootstock - bred in 1914 and and is extremely vigorous though not particularly fungal resistant but that isn’t of concern when using the rootstock. It is a hybrid of the Wichurana lines named after the German botanist Max Ernst Wichura and produced sometime in the mid 1800s. It is a beautiful rose on its own and they are seen across the country in old graveyards, estates and plantations blooming without any assistance with lots of showy dark red blooms. It’s main down fall is its propensity to black spot but yet it seems to overcome that and come back each year. The strong marketing push to own root is one of a labor shortage, lack of skilled budders, and greed. If you can selling a tiny cutting that at the very most is 32 weeks old (from a grower who gives a 5 year warranty) and the rest are at best 16-20 weeks (with little to no warranty) compared to full 2 year olds that have had a full year in the field and then another year+ in the field with its graft —- and sell for the same price - which do you think corporations will demand are grown to help their bottom lines? Do not be afraid of well grown, healthy, well budded/grafted roses. Grafting has been the primary method of rose production which began in the late 1800s with a beautiful but week growing hybrid tea called LaFrance. Grafting it allowed for a much stronger growing plant and it has survived to this day and you can still purchase it. Many of the beautiful old roses full of fragrance just weren’t all that strong on their own roots. And today they are own rooting roses with little to no warranty that may not last you a year or two. No one has ever tested many of these roses - because everything was grafted and the couple of under-stocks were strong so no issue would be expected. Unless you want a particular rose that you can only find as own root, and if you are a beginner gardener and have just started with roses — look for grafted roses from an old established company like Jackson Perkins or go with David Austin who offers both in various types but they offer 5 year warranties.

High nitrogen can hurt root and flowering ability in cotoneaster plant. See excerpt from below link: http://www.sciencedirect.com/science/article/pii/0304423881900649 " Although root growth was not increased by either Nitrogen or Phosphorus, high N levels inhibited root growth." More link to show that too much phosphorus can hurt root & flowering: https://laidbackgardener.wordpress.com/2016/05/18/the-myth-of-starter-fertilizers/ "further studies showed that large quantities of phosphorous were not necessary for rooting. Yes, the soil must contain a small amount of phosphorus in order to stimulate rooting… but that’s also true of any other nutrient. If the soil totally lacks nitrogen, zinc or iron, that too will hamper rooting. In fact, plants actually root poorly in soils excessively rich in phosphorous. You’re far more likely to kill plant roots with 10-52-10 fertilizer than to stimulate their growth. " http://davesgarden.com/guides/articles/view/3788/ " When plants are grown in low phosphorus environments they emit organic acids from their root tips. These acids allow mycorrhizal fungi to penetrate the roots and form the networks that assist roots in absorbing water and nutrients. If the phosphorus levels are too high the roots do not emit the acid and the mycorrhizal networks do not form. This forces the plant to put more effort into root growth to compensate for the lack of mycorrhizae." U. of Colorado Extension has excellent info. on Organic fertilizers: "recent CSU research has shown that phosphorus from bone meal at NPK 3-15-0 is only available to plants in soils that have a pH below 7.0." On rock phosphate: Recent CSU research results concluded that no rock P (regardless of mesh size) is available for plant use unless the soil pH is below 7.0. http://www.ext.colostate.edu/mg/gardennotes/234.html According to CSU, Kelp powder has NPK of 1-0-4, decent potassium, plus trace elements, only need 1/4 to 1/2 teaspoon per gallon, due to its high salt. **** From Straw: I tested bone-meal many times, with negative result in my soil pH near 8. 1) killed over a dozen geraniums by topping with bone-meal in hot summer .. that burnt their roots, but their colors were vivid at first. 2) put bone-meal in the planting hole of Sharifa Asma, the color DID NOT deepen, but really wimpy root, plus the soil got hardened. 3) Killed a $30 gallica rose gifted by a friend with bone-meal in the planting hole. 4) Made Crimson glory really wimpy by putting bone meal in the planting hole. 5) Made wimpy Yves-pink-seedling into a Black-spot fest by moving it, then put bone-meal in the planting hole. CONCLUSION: phosphorus is best in small amount as in 1/10 of potassium in rose-tissue analysis done by U. of CA at Davis. Phosphorus is best AS soluble, as in leaves, manure. Chicken manure at NPK 5-3-2 has plenty of phosphorus, plus trace elements zinc, copper, and boron.

R. Multiflora is hardy to zone 4b, and Dr.Huey-rootstock is hardy to zone 6b. Dr.Huey-roostock can live forever in my zone 5 since its roots is at the end of a long-stick (1 foot deep), so it can survive deep underground while the upper-own-root dies. The temp. at DEEP underground is 32 F, while the above temp. is -20 F in my zone 5a. The secret of Dr.Huey's living forever is its roots are at the end of a long stick to be at 32 F underground. I saw only one multiflora shoot appearing at local library, versus countless Dr.Huey-taking over. Leaves are acidic when not fully decomposed, so I consider that peat (Peat forms when dead plants are not fully decomposed). Once time I buried a bunch of leaves underground when I fixed the planting hole of Wise Portia. IT GOT WORSE !! I dug that up and the leaves turned into pitch-black & acidic peat. Wise Portia as own-root hates it (it likes alkaline with dark-green leaves). Multiflora-roostock can take acidic leaves on top better than grafted-on-Dr.Huey or own-roots. Multiflora-species thrive in high-rain & acidic soil. But Dr.Huey was bred in dry & alkaline CA. Back in 1998 I winter-protected a dozen hybrid-teas (grafted on Dr.Huey) with acidic maple leaves (not decomposed to neutral pH). They all got black canker & died through the winter. But my neighbor's dozen hybrid-teas (grafted-on-Dr.Huey) were winterized with dry & alkaline wood-chips and they survived winter great. Own-roots absolutely hate acidic leaves on top when their roots mature to be chunky & woody like Dr.Huey. When I winterized 10th-year-own-root Golden Celebration with leaves, it was only 4" tall in spring & gave me 4 lousy blooms for spring flush. So this 11th-year winter, I switched to DRY & ALKALINE wood-chips, and Golden Celebration had over 1 foot of green cane, with 20+ blooms for spring flush (in only 4 hrs. of sun). Multiflora-rootstock prefers loamy soil since it's a cluster root (spaghetti strands), versus big-fat & woody chunky Dr.Huey for dense & thick clay. Multiflora-rootstock declines in my salty & dense & alkaline clay. Dense clay need a thicker-stick like Dr.Huey to push through. Here in rock-hard & dense alkaline clay (similar to CA), Dr.Huey-rootstock is the choice but folks plant it so deep that Dr. Huey lives forever.