Rose leaves turning yellow and dropping off

[mummyh]

I have a miniature red rose 'Peter Pan' in a tub in my garden. Its leaves have recently started turning yellow and dropping off, but there is no obvious sign of blackspot (which I have dealt with before on other plants). What else could be wrong - could it be malnourished, or over/under watered? Any suggestions? I have started treating the plant for blackspot just in case, but it's a very sorry looking specimen indeed. Any help appreciated. Thanks

[Clanad]

Firstly, are the afected leaves on the bottom and working their way to the top? Additionally, have you been having bright, sunny and warm days? If so, I'd look at reflected light being the culprit. Minature roses, especially are susceptible to strong sunlight being relfected off the surrounding materials... such as mulch in the tub or other sources.
I'd also take a close look at the underside of the leaves that are still on the plant. Are there any small (pinhead size) reddish, dots that suddenly start to move... if so, spray the plant lightly for spider mites...
Lastly, have you recently fertilized or changed fertilizer for the plant? The minatures don't like a lot of fertilizer... especially nitrogen rich ones (it's the first number of a series of three on any fertilizer package...

[Berkshirelad]

Perhaps Summer is over and the break in the weather is signifying the start of Autumn...