I had a beautiful lilac colored thornless rose. It has developed thorns and now has red roses. Is it possible that it crossed with a red knockout rose bush that is nearby?

No, but it is possible your rose is grafted. If some of the shoots are coming up from the soil instead of the stem above the graft, the roots are taking over. The traditional root stock is a red rose that is extremely vigorous, and very thorny. If you don't cut the suckers out, your thornless rose will be lost.

... if it wasn't lost already during winter...

Good point. Its why I only plant self-rooted roses.

There are some roses that simply don't perform well, unless budded ... but if they CAN make it on their own roots, I personally prefer it.

hopkimy --
Your rose, yes, may have been budded to 'Dr. Huey' rootstock, and as Daisy suggests, that rootstock may be taking over.
Huey isn't the ONLY rose used as Rootstock, but it is the most-common, in the U.S.
Learn more about 'Dr. Huey' at:
https://www.helpmefind.com/gar...

If you think that at least part of your lavender rose is still living, and you want to save it, you will have to remove all of the canes of 'Dr. Huey' down below ground -- right where they emerge from the roots. If not, it will just keep growin' and growin' -- and in your conditions, it's going to blackspot like crazy.

If you think the lavender rose is gone, I recommend that you dig the Good Doctor up and get rid of him, before he reaches the size of a house.

That's what I dont get about my Dr. Its loaded with thorns. I guess maybe the seed I happen to select at seedling isnt all Dr. Huey. The flower was pollinated by a different rose. So maybe it's like half n half. That's why it has thorns and possibly now on its 4th year alive 3rd year in the ground this year it threw flowers more than the one time in the beginning of spring. The only differences I see is thorns, very very strong fragrance, and now has flowered twice. I guess not flowered bc it's only 3 flowers this time. And the flowers are darker than I've seen online.

jerijen said:There are some roses that simply don't perform well, unless budded ... but if they CAN make it on their own roots, I personally prefer it.

hopkimy --
Your rose, yes, may have been budded to 'Dr. Huey' rootstock, and as Daisy suggests, that rootstock may be taking over.
Huey isn't the ONLY rose used as Rootstock, but it is the most-common, in the U.S.
Learn more about 'Dr. Huey' at:
https://www.helpmefind.com/gar...

If you think that at least part of your lavender rose is still living, and you want to save it, you will have to remove all of the canes of 'Dr. Huey' down below ground -- right where they emerge from the roots. If not, it will just keep growin' and growin' -- and in your conditions, it's going to blackspot like crazy.

If you think the lavender rose is gone, I recommend that you dig the Good Doctor up and get rid of him, before he reaches the size of a house.

Oh, I've seen Huey with prickles. 'Dr. Huey' has been bred for decades ONLY as rootstock. It's been selected for vigor, rather than any other characteristics. It's probable that a series of slight mutations has crept in.

Likewise, look at 'Gloire des Rosomanes' ("Ragged Robin") -- which likewise was used as rootstock for a long time. You really see a wide variation in characteristics, from one rootstock reversion to another.

Alternatively, I suppose you could have a different red rose used as rootstock. I bought a rose years ago that turned out to have been budded onto David Austin's 'Claire Rose.'

I thought I read that it had few to none. As in the way of thorns. And the one I have is loaded to the brim.

But by the look of the flower. I'd say its Dr. Huey. Wouldnt you? I had several seeds sprout. But this was the best one of the bunch. And it has shown to be super vigorous. And very heavily scented.

jerijen said:Oh, I've seen Huey with prickles. 'Dr. Huey' has been bred for decades ONLY as rootstock. It's been selected for vigor, rather than any other characteristics. It's probable that a series of slight mutations has crept in.

Likewise, look at 'Gloire des Rosomanes' ("Ragged Robin") -- which likewise was used as rootstock for a long time. You really see a wide variation in characteristics, from one rootstock reversion to another.

Alternatively, I suppose you could have a different red rose used as rootstock. I bought a rose years ago that turned out to have been budded onto David Austin's 'Claire Rose.'

I've never heard of Dr. Huey being "heavily scented." To me it has a very light, and most of the time no fragrance.

I have not smelled it. The flowers are nice and turn shades of red. They start like Weluvroses's picture. Sometimes they turn dark purplish, almost blue, as they age.

Hope it is not getting a case of RRD.

If it's not a clone, it would have the genes from both parents. Even if selfed it has many genes in its backround that can generate diversity.