Prevention and Control Go Hand in Hand.  This is critical.  Taking a few preventative steps at key times of the year will go a long way toward preventing this fungus from attacking your roses, and ultimately controlling (and possibly even eliminating) its presence and its effects.  Over the years, my roses (only some of them) have been discernably afflicted with Botrytis blight on only two occasions.  And both of these times coincided with my own failure to take proper preventative steps.  The following items constitute a simple plan³⁻⁶ for ensuring that little brown rose buds and flowers seldom, if ever show up in your own rose gardens.

1. Good housekeeping.  Cleanliness and sanitation are absolutely vital.  Remove any and all infected parts from each plant when you find them, and dispose of them in a covered container.  This fungus overwinters on dead plant material in the form of sclerotia (hardened masses of fungal “roots” [mycelia]⁹),³’⁸ and in the spring, spreads via water-borne or wind-borne spores.³’⁸  Web blight (fungal mycelial strands) from old infected plant material can infect healthy plants.³’⁹  So, again, get rid of infected plant parts as soon as they appear.  And again, when you do, dispose of them in a covered receptacle where there will be no chance of the fungal spores spreading and reinfecting your roses.  You’d be amazed at how easily this stuff spreads.

   (Note: I’ve mentioned this time and again here in The Renaissance Garden Guy, and I’ll say it again – Sterilize your pruners after you’ve done any cutting on a particular plant, and before you start cutting on another one.  If you don’t, you’ll spread this fungus (and any other pathogens waiting in the wings) from one plant to the next, just as sure as I’m sitting here.  This is HUGE.  Isopropyl alcohol and a paper towel will do the job just fine.

2. Avoid over-fertilizing.  I’ve learned the hard way that too much nitrogen can make existing rose stems weak, and new rose stem growth exceptionally tender.¹⁰  In both cases, these stem structures are easy marks for Botrytis cinerea.  Remember, this fungus attacks tender, soft, weak, damaged, or dying plant tissues.  Don’t over-fertilize!
3. Give your roses plenty of elbow room.  Providing your rose plants sufficient air circulation, and keeping them from coming into physical contact with one another is critically important in your efforts to keep the brown rose buds and flowers of Botrytis blight at bay.³⁻⁶ This fungus thrives in cool, wet/moist/humid conditions.  By allowing sunlight and warm, dry air to circulate throughout your roses’ aerial structures, the ability of the fungus to survive and spread is mitigated or eliminated.  And preventing plants from growing on top of one another reduces the possibility of contamination through contact.  Some of my own practices – one of which I recommend here in another article – ostensibly fly in the face of this important directive.  I like to bed my plants in fairly dense fashion, which means particular plants may crowd each other, thereby compromising air circulation and violating the above No Contact Rule.  My work-around in this case is careful (and admittedly artful) pruning and deadheading that promotes the densely-planted look I like for my beds, while maintaining healthy spacing for proper sunlight penetration and air circulation.  Regular RGG readers and subscribers will know of my other, seemingly counterintuitive practice advocated in “Should You Underplant Your Featured Perennials?” (published here in 2022).  Underplanting with groundcover plants is an awesome technique that creates massive ecosystem benefits and, in my opinion, improves planting bed aesthetics.  But, in the case of rose underplanting, the groundcover involved could possibly swarm close enough (and high enough) to rose plants to prevent good air circulation and sunlight penetration, and actually foster the growth and spread of Botrytis cinerea.  In my case, the stonecrop sedum varieties which grow as groundcover in my rose garden planting feature will indeed crawl right up to the main canes of each rose bush and actually mingle with each bush’s foliage.  It’s a perfect condition for Botrytis blight to do its thing, and it could be a problem.  But it’s not.  Why?  Because, as a personal change of pace, I employ common sense: I keep the sedum adequately reined in (through pruning or pulling) so it doesn’t crowd the roses at their bases and give the Botrytis fungus a leg up.  It’s a win-win: the underplanting still looks cool, and the brown rose buds and flowers of Botrytis blight are headed off at the pass.
4. When you water, aim for the ground.  Seriously.  I never water my roses with a sprinkler.  I use a nozzle and hose, and I direct the water toward the base of the plant.  This minimizes the humidity and moisture levels at my roses’ aerial structure level, and helps contribute to the high and dry (again, I’m serious) environment that Botrytis blight doesn’t like.  Obviously, in spite of the fact that I always aim low (God, that does sound bad), my roses’ foliage does get a little wet while I’m watering, and I definitely can’t stop the rain.  But minimizing wet foliar conditions – particularly when the weather is cool – goes a long way toward preventing and controlling Botrytis blight, and keeping brown rose buds and flowers off your bushes and vines.
5. Prune and deadhead as you normally would, and let the rising temperatures, dryness, and sunlight of summer help you out.  The good news about Botrytis blight (and its awful brown rosebuds and flowers), at least as far as roses are concerned, is that it can’t function or spread in warmer and dryer conditions.  The first time my roses were infected with Botrytis blight, I engaged in normal pruning and deadheading activities (after initially removing some compromised stems, buds, and blooms), and I let the summer heat and dryer weather take care of the rest.  I also applied an organic, copper-based fungicidal product (sadly, not until after the infection had taken hold and had already begun to abate), but, as you’ll read shortly, its application was almost certainly not a factor in the resolution of the issue.
6. Use a fungicide, or fungicides.*  I use three kinds, all of which are definitely effective as hell.  There are a number of effective fungicides available that will kill or control Botrytis cinerea, and many of them are not approved for organic gardening.  But the three that I use definitely are approved for organic gardening (two of them are OMRI listed),¹¹ and they’re the only ones I’ll discuss and recommend in this article.  The first two are organic copper fungicides which are incredibly effective at preventing Botrytis blight infection.  Both products have, as their active ingredient, copper octanoate (Copper Soap),¹² which works by disabling/denaturing fungal proteins and enzymes of fungal spores and prevents them from infecting the plant.¹³  They must first be applied BEFORE the plant is infected and symptoms of the fungus appear.¹³  I’ve found that the best time to start applying this stuff is in mid to late March (here in my hardiness zone of 5B/6A) right after I hard prune my bushes for the coming growing season(s).  Remember, rose plants are extremely susceptible to Botrytis blight when they’ve got open wounds (like the kind made from hard pruning), so this is the perfect time to start prepping them with copper fungicide.  After the initial application, you can continue application per each manufacturer’s respective directions, or you can let the summer heat and dryness take over.  I’ll usually do several applications over the course of April, May, and early June, and then stop applying it and let summer do its thing.  The two times (including this year) that my roses were infected with Botrytis blight, I did not prep them with an application of either of these copper fungicide products, nor, in fact, did I take any preventative measures at all (I know, I know… ).  The third fungicidal product relies on a voracious fungus-devouring bacteria as its active ingredient, is definitely organic, and is one that I’ve been using for the last several weeks with great success.  If I’m understanding my own research and observations correctly, this biological product is incredibly effective when applied not only initially as a preventative, but also at any point during an active Botrytis infection.  The assertive bacterial agent (Bacillus amyloliquefaciens strain F727) evidently goes to work coating the rose’s foliage, suppressing the fungus’ mycelial growth, and literally eating the fungus right off the blooms and foliage – just like corn off the cob, so to speak.¹⁴  It is proving to be an extremely effective product.  

*Federal law mandates that all fungicide products must be used in accordance with each respective manufacturer’s product label.  When using any fungicide, read all manufacturer’s information and follow all manufacturer’s directions as provided in the product label.  Failure to do so is a violation of federal law.