|I have 2 groundcover rose bushes in front of my house and though the new growth looks healthy enough, the older leaves look as though they have been burned by a chemical spray. I haven't sprayed them with anything and I can't see any insects and can't figure out what is causing it. Could it be a nutritional deficiency or is it some kind of disease? The leaves aren't curling up and falling off they are just turning brown and yellow.
I'd appreciate any advise you can give, as this has never happened to me before.
|Roses are susceptible to a number of foliar diseases including rust, which might account for the discoloration. Check the undersides of the affected leaves for rust pustules. If none are found, you may be dealing with downy mildew (the yellowing will stay between the veins of the leaves), verticillium, leaf burning due to overfertilization, or even overwatering. We've had a cool and rainy summer this year, which may have stressed the plants or at least contributed to their ill-health. If possible, take a sample to your local Extension office or Master Gardener clinic for a positive ID of the problem. You can contact King County Cooperative Extension at (206) 296-3900. Hope this helps solve the mystery!|