help diagnose and recommend fix for Roses

Question: My roses are turning dry and crispy- no visible bug- I have more than these 3 photos

responder: The Question Asker Replied August 28, 2024, 2:49 PM EDT
response: We have over 18 roses on our property and all have some sort of this happening to them - the leaves look like Black spot and some just turn yellow and eventually crispy like brown paper. There are no fuzzy bugs on the back side. I have been spraying with horticultural Oil thinking it was a but but im afraid its a virus.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied August 29, 2024, 10:26 AM EDT
response: These are symptoms of both stress and very common leaf spot type infections, for which horticultural oil will not provide any benefit. (Spraying oil, or any pesticide, in hot weather can also damage foliage. Only treat, when needed, while temperatures are below 85 degrees.) Roses are susceptible to an array of issues, though each variety has its own degree of natural resistance or vulnerability. You can learn about the various symptoms on our rose diagnostic web page (see link).  Nothing can cure existing disease (fungicide sprays are only preventative, and their use begins in spring, well before any symptoms appear), but fortunately, most leaf infections on roses are just an aesthetic nuisance and won't impact long-term plant health. While the virus roses are most likely to contract, Rose Rosette Disease, can be fatal to the plant, we do not see any symptoms in the photos that suggest a viral disease is present.  Have the roses been monitored for watering needs this summer? Anne Arundel County is currently out of drought status on the linked map, but for most of this growing season, there has been a drought that is stressing many plants if they weren't being watered. If the soil about six inches down next to the roots has become somewhat dry to the touch, watering will be needed to alleviate plant stress. (If damp to the touch at that depth, watering can probably wait.) As a guideline, most perennials and shrubs in hot, dry weather would benefit from one good soaking per week. (For shrubs of this size, a soaking may use about 5 gallons of water per plant.) When watering, avoid wetting the foliage, as leaf surfaces that remain wet for long periods are easier for disease spores to infect. If getting the leaves wet is not avoidable, then water early enough in the day so that the foliage can be dry by nightfall.  Some of the leaf yellowing may just be due to the minor amount of leaf infection visible, but it could also be tied to under-watering (or over-watering, if the plants are being irrigated heavily or very often) or under-fertilization. While established shrubs generally don't need regular fertilization, depending on soil factors and watering frequency, or plant vigor, roses might benefit from it once or twice during the growing season (if using a slow-release organic type of fertilizer).  A laboratory soil test can help determine which nutrients (if any) are deficient in the soil so you avoid over-applying those the plant doesn't need, though testing won't measure nitrogen [N], a nutrient which contributes to deep green leaf color, since it naturally varies too much in the soil to provide a reliable measurement. The leaves on the pictured plants do look yellower-green than is ideal for most rose varieties, so perhaps the plants would benefit from some supplementation. This late into the growing season, it won't provide much benefit since leaves will be shedding in the next two months, but for next year at least, occasional fertilization starting in spring might improve the plants' density and productivity.  Overall, the roses don't look that bad (we've seen way worse infections), and we'd expect that they will regrow and bloom normally next year. If you don't do this already, pruning any shrub varieties (as opposed to climbers, which are treated a bit differently) back in late winter will help the regrowth be vigorous and potentially bloom better than on older stems.  Miri