Disease on rose plant

Asked June 15, 2020, 10:53 AM EDT

Hi there! I have attached photos of my rose plant showing holes and spots on the leaves. Earlier in the season I could see worms on the leaves and also much more black spots (which I looked up and found out to be fungal infection). Following some online suggestions, I applied insecticide spray and also soap-baking soda mixture (for the fungus). That helped for a while. The plant flowered. But now it shows these holes quite a lot. I can't see worms or other insects on it. I guess the black spots are still there, but much less. Could you please let me know the diagnosis and the treatment? Thanks in advance for your help!

Prince George's County Maryland

3 Responses

The leaf holes were likely caused by the common rose pest Rose Slug. Despite the name, this is the larva of an insect, not a slug. Some can produce multiple generations per year and so may need controlling several times over the course of the summer. More information can be found here, along with control options: https://extension.umd.edu/hgic/topics/rose-slugs-shrubs. If you spray with the horticultural oil or spinosad, be sure to cover as much of the leaf surfaces (upper and lower) as possible to ensure good control. Read the product label instructions regarding when to re-apply, and try not to spray the plant with anything during temperatures over 85 degrees F to avoid tissue damage. The holes will not heal, but new leaves should remain fairly hole-free if the treatments control the rose slugs (and possible scarab beetles later in summer).

Black Spot is a common rose disease and could be what you were seeing symptoms of. Home remedies do not often work (and can be harmful to plants) and a registered fungicide would be best if you are going to spray to control it. Many different products help suppress black spot, so check the label on the bottle to verify the one you choose lists this disease. Here too, this will not cure ailing leaves but should protect new growth from infection. Repeat treatments for this will also likely be needed, but read package instructions as different products work in different ways.
https://extension.umd.edu/hgic/topics/black-spot-roses

Roses grow best in full sun (6+ hours per day), and ideally, bare soil should be covered with mulch or ground-covering plants to protect the soil surface from weed seeds, temperature extremes, and losing water through evaporation. If the plant isn't in a full sun exposure and cannot be moved to one, susceptibility to pests and disease may be more likely, and the plant will gradually lose vigor and flower more sporadically. If it is in full sun, consider pruning it back heavily this winter (around February or March) to promote better bushiness and vigorous new growth, which tends to flower much better than lanky older growth.

Miri

Many thanks Miri for your valuable reply! I will do as you suggested.