Drift rose problem

Question: Coral drift roses that I planted last season, were growing well but last few weeks developed these white spots and wilting.

responder: Best Regards,  Replied May 12, 2023, 11:30 AM EDT
response: Greetings, Shankar, and thank you for your question to Ask Extension/Ask a Master Gardener. You included some excellent photos with your question! Thank you! I believe the spots, holes and wilting that you are seeing on your roses are caused by insects, either roseslug sawfly or aphids. When I zoomed in on the bud on the third photo, I could see what appear to be nymphs or larvae. If you look closely at your plant, you might see the adults crawling or flying nearby. Check the back of the leaves, too. The good news is that this looks like a recent infestation and you have an excellent chance to control it. I will be providing you with some research-based resources that will help you diagnose your rose problem. They will also provide treatment and preventative measure options. Also included is an excellent general guide to rose problems from Oregon State. The section, near the end, about preventative measures for controlling pests and disease on roses is “must-have” information for any rose gardener. I highly recommend reading it. These articles tell more about roseslug sawfly. The photos, some that resemble your rose issues, should help you with diagnosis. There are recommendations for treatment. https://bygl.osu.edu/node/720 https://bygl.osu.edu/node/315 https://extension.unh.edu/blog/2019/06/whats-eating-leaves-my-roses These articles are about aphids on roses. Both aphids and roseslug sawflies appear this time of year.  https://content.ces.ncsu.edu/rose-aphid https://hgic.clemson.edu/factsheet/rose-insects-related-pests/ https://ipm.ucanr.edu/PMG/PESTNOTES/pn7466.html Finally, here is the link to the Oregon State publication with excellent information for every rose gardener. I highly recommend reading it to the end and tagging it as a favorite! You will likely want to refer to it again. https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1520.pdf More good news: roseslug sawfly and aphids will usually respond to the same treatment. If after reading these articles you are still uncertain how to proceed with treatment, feel free to respond to this email with any additional questions. It will come directly to me, and I will be happy to respond. Best of luck with your beautiful coral drift roses!

responder: The Question Asker Replied May 12, 2023, 12:19 PM EDT
response: Dear Debra, Thank you for the detailed email. I was thinking that this was powdery mildew but now based on your discussion it seems that this is likely rose slugs / aphids. We also had issues with Japanese battles last year. Would you suggest a single treatment/prevention for all these? I was thinking of spraying neem oil but I don’t see it highlighted in your resources. Since I am not familiar with any of the insecticides , are you able to suggest something specific for me, preferably organic. Thank you, Shankar On Fri, May 12, 2023 at 11:30 AM Ask Extension <<personal data hidden>> wrote:

responder: Best Regards,  Replied May 12, 2023, 11:11 PM EDT
response: Hello, again, Shankar. Thank you for writing back! Interestingly, powdery mildew was my first thought, too, but the symptoms did not exactly match. When I saw the nymph/larvae on the buds I was relatively sure you have an insect issue. It is a little early in the season for powdery mildew, but it is still a possibility. Please keep in mind that multiple issues can occur simultaneously on a plant, so it is possible to see, for instance, roseslug sawflies and powdery mildew at the same time on a plant.  There are many options (chemical, mechanical and organic) that you could use. Since you asked for an organic option, I will start there. Neem oil is an excellent idea, and I believe it is very briefly mentioned in at least one of the articles from OSU. (But it is would be easy to miss it!) It’s worth noting that Neem oil is effective in controlling aphids, roseslug sawfly AND powdery mildew. What a great solution! The difficult thing is that it needs to be applied frequently, on a fairly specific schedule and at the correct time of the day. Also, it has only a mild residual effect. You can purchase pre-mixed neem oil spray at most garden centers, or you can mix your own using a concentrate; personally, I keep neem oil concentrate in my bin of garden staples. Mix 1 ounce (2 Tablespoons) in a gallon of water. Neem oil will separate from the water, so you need to add an emulsifier. You can use a dish soap, like blue Dawn or another soap. Personally, I prefer Castille soap, but the choice is yours. Add 1-2 teaspoons of soap to your water+neem and shake.  Apply with a garden sprayer (or any type sprayer) in the early morning, late evening or on a cloudy day. If applied in direct sunlight, neem can cause sun damage (sun scald) to the leaves, kind of like a sunburn. Be sure to apply to the undersides of leaves and to the stems, where aphids and sawflies like to hang out. Residual neem will help deter new arrivals, but “resident” insects including new hatchlings must be sprayed directly with neem to be destroyed. It is recommended that neem be applied once or twice a week until the infestation is under control. Subsequently, apply every 7-14 days. It is possible to over-use neem, which could result in “smothering” of the leaves. You can also use your neem solution as a drench around the base of your plant to deter pests and pathogens in the soil. (I’m guessing you can see why I mix my own neem solution!) Just a note … there are other effective horticultural soaps and oils; neem is likely the most used and best known.  For gardeners who don’t have the time or inclination to use horticultural soaps or oils, chemical products are available. Many are broad spectrum and some are insecticides, fungicides and miticides in combination. Many gardeners avoid these products as they can be harmful to pollinators, to helpful insects and to “good” soil fungus. The choice, however, lies with the gardener. No judgements here! I admit I have used them judiciously from time to time. Following, I am including links to some research-based sites. Whenever I answer a question for Extension, I check my understanding against such sites. They have lots of information that you might find interesting and useful. https://hgic.clemson.edu/factsheet/less-toxic-insecticides/ https://gardeningsolutions.ifas.ufl.edu/care/pests-and-diseases/pests/management/natural-pest-control-with-oils.html https://extension.unr.edu/publication.aspx?PubID=3029 Finally, you mentioned issues with Japanese Beetles last year. Those little buggers (pun intended) usually arrive on the scene in mid-June and wreak havoc into August. Here is a link to a question I previously addressed regarding Japanese Beetles. You might find the information about how JBs are attracted to “damaged” leaves attacked by other JBs to be particularly interesting. If the link doesn’t work for you, and if you are interested in a VERY lengthy response about Japanese Beetles, lmk and I will copy and paste the information in a response to you. https://ask2.extension.org/scp/tickets.php?id=803203 If you have any additional questions, I would be more than happy to hear from you. I would also be interested to hear about how your coral drift rose issue resolves. Wishing you happy gardening and bushels of beautiful roses!