Other things that cause spotting...

This is more of a awareness raising post than anything else. Everyone knows what black spot it and it is one of the 'big three' fungus problems in rose. When I say 'big three' I mean the most common, but not necessarily the most debilitating. The other two making uo the remainder of the big three are powdery mildew and rust, in case you were wondering.

Now... all that spots our roses is not, however, just black spot. There are a host of other nasties that cause foliar marks and some of them are by far more serious than black spot. The one that is ripping through my garden at the moment is called DOWNY MILDEW. This is an insidious fungal disease that is basically going to defoliate every rose in my garden within the next few days. It appears as irregular shaped black scorch marks on the leaves and it spreads super fast. It spreads throughout the plant both externally and internally and can kill a plant in no time at all. This is especially true of very young plants. You can strip infected leaves off, however, this is a catch 22 situation as the plant needs leaves to maintain its strength to fight off teh disease and recover. Downy mildew is most prevalent in cool damp weather, like I am experiencing now. It just isn't warming up down here and it has rained almost daily for weeks. We get one warm day and then it will be freezing again for days at a time interspersed by days of belting rain and freezing nights. It actually fell below ten degrees again the other night... in summer... This is downy mildew's favourite weather but if you don't know what it is you are looking at and think that it is black spot and you spray it with black spot treatments it will have absolutely no effect. Your plants will still defoliate and there is a good chance they may in fact die. My rose garden is about an acre in size and I would say 95% of them, from every class of rose, is badly affected. To make matters worse there are very few roses of any kind that are naturally resistant to downy mildew and once it appears it is very hard to get rid of. Some say you can never get rid of it.. all you can do is minimise the effects. I am going to have to cut everything back real hard and spray the whole garden with a systemic fungicide like Fongarid or AgriPhos which has been shown to have curative properties against downy mildew. If I don't I will lose large numbers of roses. Fongarid is used to drench the soil and is taken up by the rose to kill the fungus within the plant and kill it in the soil. It is not effective against black spot or powdery mildew. If I left it the roses might recover on their own though they would still be internally affected. Spraying does not guarantee a complete recovery or cure but is your only choice. Hot dry weather is the only thing to combat it. Once it gets warm the downy mildew is killed off and is no longer a problem.

The key point here is that if you don't know what it looks like and you think that it is black spot and you treat it as such it will have no effect.

This will help you identify it: http://www.extensionplantclinics.msstate.edu/diag.keys/orn/rose/dwn.mld/rose.dwn.mld.index.html

Anthracnose is another fungal disease that affects roses. It looks like this:

http://www.sactorose.org/ipm/83anthracnose.htm

A black spot spray cycle will help control anthracnose. I don't spray my garden for black spot and anthracnose has never been a huge prblem.

Cercospora is another non-black spot fungal disease that causes black spots on rose leaves. You can read more about it here: http://gardeningsolutions.ifas.ufl.edu/mastergardener/newsletter/2010/more/rose_spot.shtml

Cercospora can be controlled with a normal black spot program and avoided using similar black spot avoidance strategies.

It's really downy mildew that's the huge problem that requires a different approach. Just planting resistant varieties doesn't work as there aren't many that are.

Simon, not sure of spelling, will check this morning at work, but, a spray we use on downy mildew is, "phosphonic acid". It is allowed on Aus grapes, but, not the great USA bound grapes.

Simon, I am so, so sorry. You must be devastated. The best of luck with the fungicides.

Phosphoric acid is the main ingredient of Agri-fos so if you could pass on the name of the product, David, I would appreciate it

Simon

Serious news indeed. I hope your plants pull through.

Not so devastated yet... I think I've got it beat on my little Baby Love seedling... and I think most roses will recover in the main garden eventually... maybe... it's terrible to watch the advance though.. it literally appears overnight and spreads like stink on a skunk and takes you completely by surprise.

I posted this list on RHA of roses that seem particularly susceptible and resistant down here:

* All the rugosa roses (Alba, Pink Grootendorst, Scabrosa, Ann Endt) seem clean. All my rugosa seedlings from Frau Dagmar are doing well. My rugosa x moderns are doing ok but are copping it from powdery mildew.

* Some of the wichurana roses... esp. 'Temple Bells' are clean. Nothing seems to phase this rose. Its progeny seem to be doing well too. Flower Carpets Scarlet, Pink, Yellow, and Apple Blossom are largely unaffected and my single pink seedling is clean. Flower carpets white, amber, and red are badly affected. Snow Carpet is only partly affected. Dorothy Perkins is a mess. Summer Evenings is better than average at about 80% free so far. Immensee is clean. Albertine is a mess as is Heidesommer... the wichurana hybrids are pretty hit-and-miss.

* The Multiflora roses are affected but not very badly. The closer to multiflora they are the better they are. My little Baby Faraux/Sweet Chariot x multflora seedling is largely unaffected. Trier is unaffected.

* Two Tea out of all the Tea I have are unaffected. They are Lorraine Lee and Nancy Hayward (a hybrid gigantea).

* Lamarque is only partly affected.

* The only HT unaffected is an Alister Clark rose called 'Lady Huntingfield'.

* The only China/polyantha unaffected is the bush form of Cecile Brunner. The climber is a mess. The fairy isn't too bad but nothing to get excited about.

* None of the gallica are affected.

* None of the moss roses are affected including my moss seedlings.

* The damasks are affected badly.

* All the modern minis are badly affected... even Popcorn and Little Wonder. Two that aren't, however, are Laura Ashley and Nozomi.

* Knockout is unaffected by anything.

* Carefree Wonder seems pretty good so far.

* Species unaffected: wichurana, bracteata (clinophylla seems affected as a seedling... not sure I like much about clinophylla yet... it's not done much to impress me here so far), gigantea, multiflora, setigera, longicuspis sinowilsonii, laevigata, rugosa(as mentioned), banksiae (all of them). My spin. seedlings are ok but not 100% free.

* Paul's Carlet Climber seems ok.

* Euphrates is free of DM, has a little PM, no BS (or any other acronym), but has serious dieback.

* Golden Chersonese is partly affected.

* Everything else pretty much is badly affected. The worst, so far, are the Delbards...

This is only scratching the surface really... but these were the ones that stood out this afternoon

Simon, try copper sulphate type products like Fungus Fighter. No doubt there are larger commercial size packs available over there.

Best of luck, you might get some Summer weather shortly which will help.

That sounds terrible Simon , and the timing sucks too . Most people like their garden looking nice over the Christmas holiday season .

Is it worth trying feeding them with some extra potash and magnesium to try and strengthen them from the inside out ?

Interesting to read through your list of roses re. what's afflicted or not.
Do you think this is due to a species/varietal thing or perhaps to these bushes growing in different parts of the garden where conditions might be slightly different ?

I wondered where it has come from . Have you ever had PM in your garden before ? Do you have grape vines or are there any vineyards in your area ?

I don't have any chemical suggestions but I do remember my mum using Fongarid with pretty spectacular results on her hippieastrums . I've still got a couple of satchels kicking around here somewhere that she gave me.

Good Luck.

cheers. Rosalie

It's not powdery mildew Rosalie... It's downy mildew. I get powdery mildew all the time and it is unsightly but usually doesn't cause much harm. Downy mildew is a far more sinister nasty and I get it every year but it is usually gone by now as it warsm up. This year it is still cold and rainy... it's ridiculous... I'm sitting here in my trackies and a polar fleece jumper cos I'm freezing my butt off. Everyone in town is getting it too... it's just a bad year for everything fungal this year and I have to spray or lose things that are usually resistant to most fungal diseases.

I would say the disease resistance I am seeing in the list above is due to genetic differences between varieties as they are interspersed with the badly affected ones in the same areas. It is very windy here most the time as we are smack bang in the path of the Roaring 40s and so fungal spores get circulated pretty evenly throughout the whole garden.. .not many microclimates here due to excessive 'mixing'

Anyway... it's great seedling testing conditions

Oh Simon that is bad news for you. I do hope that your roses will recover, you must be so unhappy with them. It sounds devastating.

Sorry, I meant DM . that was a typo due to too many kids making too much noise too early for me after a late night.

David, here are the photos I promised... just random samples nearly every rose is showing something within this range.

Early


Intermediate


Advanced


About to drop


Time frame from first photo to last is only about 3 days.

What made you twig to it being DM rather than BS Simon ?
It was only a little while ago that you said to me that your Black Spot had Black Spot on it , when all along it could have been something else altogether . Or both together I guess.
Is there some way to test to find out exactly what one's roses are suffering from ?

cheers. Rosalie

My black spot does have black spot... but black spot is distinctive. It is visible from the underside and causes yellowing. It is much slower. This appeared only in the last week or so and is ripping through everything. It is not visible from the underside until late stage infection and doesn't cause yellowing like black spot does. It just appears as black scorch marks on the leaf. You don't need to test it because the symptoms are quite distinctive and cercospora and anthractnose respond to black spot treatment. The conditions at the moment coincide with the outbreak.. cool, wet, and humid weather and then BANG along it comes and hits you in one big hit.

The purpose of putting this up is for people who are not aware of ailments other than black spot and who treat them all accordingly and when they have no luck using black spot treatment they get disenchanted with roses altogether and write all black spot treatments off as ineffective.

So normally this is something that you might expect to see late autumn , early spring ?

It's quite hot and very dry here this year so I'm putting the BS down to having to water at night.

I guess not being someone who bothers to spray for BS often , accounts for not being able to tell the difference .
However I have made note of the difference in the symptoms in my notebook so I can keep an eye out during the cooler months.

cheers. Rosalie