Honor Rose

Question: I have a White Honor Rose that has black spots on leaves, bibs, and entire plant looks horrible.  I sprayed with copper based fungicide and also sulfur based fungicide but plant looks even worse. Also sprayed for insects. Can you advise what may help this plant?  Than you

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 May 09, 2023, 1:33 PM EDT
response: Rose varieties have varying tolerances to fungal infections but environmental conditions can also impact how readily they contract diseases. Reduced air circulation from crowding by nearby plants or walls (or fences, and perhaps the Irises here) can increase their vulnerability to infection, especially in rainy weather or any other time when foliage stays wet (dew, irrigation, etc.). Rose supplier websites state that 'Honor' is disease-resistant but don't specify which diseases it has above-average resistance to. (Roses can be afflicted by several in our region and none are immune to all of them.) The photo is too small for us to enlarge to see enough detail, but black spot is a very common rose disease that might have begun to show symptoms by now. Powdery mildew is also starting to appear this time of year; you can explore our rose diagnostic page to see which symptoms match what you're seeing. Fungal spores often rely on wet leaf surfaces to more easily infect plant tissues, but powdery mildew is more unique among fungi in that high humidity but dry weather is conducive to its ability to infect plants, and our rainfall has been below-average this spring.  The leaf holes and clear-ish spots are caused by a very common insect pest called roseslug sawfly. (Despite having "slug" in its name, it's an insect larva, not a slug.) There are several kinds of roseslug sawfly here in Maryland, so the number of generations per year this insect can cycle through varies. Their feeding damage will look alike so they can be hard to tell apart. Either way, the simplest approach is to pick them off if you can find them on the leaf undersides, but since they blend-in well, you might need to resort to using an insecticide if the damage is too intolerable. If you wish to avoid pesticides, you can try dislodging them with a strong spray of water from a garden hose, aimed at the leaf undersides. If trying a pesticide, lower-toxicity options like horticultural oil, insecticidal soap, or spinosad are the active ingredients to look for (choose one, don't overlap them). Always follow product label instructions carefully, and at least one re-application will likely be needed. Leaves cannot heal damage from pests or diseases, but the main indication a treatment is working will be that young rose foliage will not develop the same kind of chewing damage.  The chewing injury to the leaves by itself does not usually cause the plants much harm if they are otherwise healthy. One major rose breeder website mentions that 'Honor' performs best on the Pacific coast, which suggests that it can struggle in our mid-Atlantic summer heat and humidity, so the plant's vigor might not be at ideal levels if that is the case.  Fungicide cannot cure existing disease, so if applied after symptoms appear, it will have little impact. They are intended to be preventative, so applications made now might help to protect new growth that is uninfected but won't reverse any current infections. Re-application of fungicides well into summer is typically needed for roses and might not be worth the expense, nor do treatments always work well, especially if weather (rain, wind) interrupts their schedule of re-application. Fungicides also might harm other organisms, including pollinators, so use them with caution if you decide to try them. Copper and sulfur are both common broad-spectrum ingredients (meaning they control a variety of pathogens), but take note of any cautions on the product label as these might interfere with certain insecticide ingredients if they overlap in timing, or might cause plant toxicity if over-applied over the course of a season (with copper, mainly).  Miri

responder: The Question Asker Replied May 10, 2023, 8:22 PM EDT
response: Thanks so much for your help.  I relocated the rose to an open area and took more pictures.   I will check for insects often. I have attached some better pictures.   Any guidance is appreciated.  Thanks againSent from my iPhone On May 9, 2023, at 1:33 PM, Ask Extension <<personal data hidden>> wrote:﻿

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 May 11, 2023, 12:55 PM EDT
response: Thank you for the additional pictures. The leaf spots appear to be Black Spot, a very common fungal disease of roses. As indicated on the linked page, aside from preventative steps which you have already taken by giving the plant better airflow, use of a fungicide is the only way to actively discourage new infections. It cannot cure existing infections so those symptoms will not disappear, but regular use (as per label instructions) of the product well into the growing season is the only way to suppress its spread. Make sure the product chosen does list black spot as one of the diseases it controls, and follow its directions so you don't under- or over-apply the chemical. Fungicides aren't foolproof and sometimes high disease pressure and uncooperative weather (especially when it delays re-treatment due to rain) can allow some disease to still persist, though at least it should keep the worst of it at bay. Stubs of dead canes (stems) that remain from last year, often dark brown/black in color as opposed to a green or light brown-gray, and which aren't producing new foliage, should be trimmed off so they don't harbor other infections that can spread to healthy growth.  Miri