The fresh new leaves on the surviving 2008 seedlings that were recently planted in pots outside the greenhouse started to fall on Monday last week. I finally got to spray on Wednesday (many more leaves on the ground). The rain washed off most of the spray material shortly after it was applied. Today was a beautiful sunny day. Hopefully the weather will make it go away…
Next year I think that I will spray prophylacticly.
Jim Sproul
One of the up sides of living in a very warm climate is not having to deal with DM. I’ve seen it. It’s scary stuff.
Jim,
You’re not the only one. Suddenly last week my entire greenhouse and everything in it except the R. arkansana seedlings showed downy mildew. First time I’ve ever had it. Been a weird year…
There’s not a year that goes by that I don’t see some of it. Its just part of the deal, it seems. 
You’re scaring me. Downy mildew hit my greenhouse some years ago and killed many of my seedlings. I hope it’s not heading this way.
Are any of you using a combination of Stature and Decree?
You have my sympathies. I agree that the late rains with moderate temperatures are the perfect storm for DM in California this year. After all the rain, last night we had a dense cold fog. Ugh! I’ve noticed the vineyards spraying, and it isn’t their go-to fungicide, sulfur. I stopped all pruning a couple of weeks ago for just this reason. Leaf symptoms seem to resolve themselves, but once DM is in or on the canes, it really knocks a rose down. I’ve seen it enter at the cane bud eyes, at damage points, and at pruning cuts. Trying to prune it out is problematic, to say the least. I’ve had some limited luck burying or mounding soil on affected canes.
The last time this happened in the early 2000’s (2003?), I sprayed different fungicides for almost 3 months, until I couldn’t stand it any more - Phyton 27, Aliette, Decree, fixed copper, Compass, Daconil, mancozeb (Fore) - you name it, I tried it. Nothing showed visible effectiveness on DM, and some caused a good deal of leaf damage to boot. The only cure was the hot days of mid-summer, after the soil surface dried.
Part of the problem with the newer 2008 seedlings just planted out in pots, is that they are very closely spaced and I pushed their growth along with a fairly heavy dose of soluble fertilizer. Both situations seem to promote the spread of DM.
Older roses, planted out in the yard with more space between them are showing very little signs of it.
Because we don’t get it every year, I haven’t been able to breed for it. One year that we were hit particularly hard with it, I had one seedling that appeared to be immune. Unfortunately, it got powdery mildew, so I eliminated it.
I used Fore and Aliette, but will try to get my hands on Stature if it persists.
Jim Sproul
Can you guys get Fongarid (furalaxyl) over there? It’s a systemic fungicide that is effective on downy mildew (see link and search for ‘fongarid’ on pages 9 and 10)… From what I have read so far it doesn’t seem effective on powdery mildew or black spot so probably wouldn’t affect normal selection for these diseases. I use it on my cuttings (my cuttings get smashed by DM) and seedlings to prevent damping off though switching to perlite for both cuttings and seedlings has reduced this a lot.
Link: www.publish.csiro.au/?act=view_file&file_id=APP978-1.pdf
Managing a greenhouse can be very fun- however the three things I hate the most are listed in order of most disliked:
1- Watering
2- Pests (fungi, algae, bugs, people)
3- Weeds
I totally understand how frustrating it is to get a pest(in your case Downy Mildew).
I have discovered that sometimes it is almost IMPOSSIBLE to prevent some things from happening- and you simply have to cope and minimalize damage.
Here is an article that discusses some of your options:
http://plant-disease.ippc.orst.edu/disease.cfm?RecordID=985
My best wishes on the control.
Ryan
Ryan, under greenhouse pests, don’t forget cats who like to nest amongst the seedlings!
I had a feral cat a few years ago that loved to “nest” amongst the asparagus ferns---- there was hair EVERYWHERE!
Oh-- and the funniest-- we had planted some ornamental millet next to some draceana(green spikes)-- well some mice decided to harvest the millet seed and make a home inside the pots of draceana. Let me tell you-- watering was sure scary-- you never knew when a mouse would come flying up out of a pot! I sure wish I had that feral cat back leaving hair all over! – Snakes showed up instead! YOU JUST CAN’T WIN CAN YA?!
Ryan
I know this is now seriously off topic, but…
Years ago I was rearranging my living space and decided to move the big Cerwin-Vega floor speakers to a new location. Oddly, one of the two speakers was conspicuously heavier than the other one. I didn’t think too much about it at first, but then I decided to investigate further. These speakers had large “tuned bass ports” in the back, which were tubes about 2.5" in diameter, a couple inches above floor height that opened up into the interior of the speaker cabinet. I shined a flashlight into the bass port and immediately discovered why there was a weight discrepancy: mice had been stealing the cat biscuits for years and stashing then inside the speaker! I vacuumed out fifteen pounds of old cat biscuits from that speaker. Ahh, the joys of country living.
Back on topic: mice are actually a big problem for me in the greenhouses at times as well; I am forced to sow my rose seeds in flats in rather tight rows and then put the flats inside a wooden frame box with 1/4" wire mesh walls and lid to prevent mice from eating all of my seeds. Back in the early 2000’s I found out the hard way that mice can find rose seeds in a flat and dig them up with remarkable precision. Clearly they can smell the seeds and know exactly where to dig. I came out into the greenhouse one morning and found tray upon tray that the mice had systematically gone up and down the rows precisely where the seeds were and dug up and eaten 90% of them in one night. Shocked and angry, I remedied the problem immediately and have had to resort to “caging” my seed flats ever since. (No free range rose seedlings for me!)
Once they have two true leaves they get transplanted to 3" pots and the mice are generally no longer interested in them. If, however, there are a few stray seeds buried around the roots of a transplanted seedling, they will find it and dig it up, often destroying the seedling in the process. I envy folks that can just row out their seeds in big benches and bloom them out in situ.
Paul
Paul, be glad it was mice and not ferrets! It would have been your car keys, wallet and everything else! I sympathise with your mouse problem. Alas, that’s why I allow the cats in the greenhouse in the first place.
Back to the original topic though, I need some advice.
I turned the heat in the greenhouse so it stays around 80 in there (so, about 10 degrees too hot for Fa), and the mildew problem seems to be slowly abating. Curiously, my yearling roses (the ones the rabbits ate the roots off of, that I brought in) are clean (so far), it’s just the seedlings that are affected. I’ve started cutting off the worst-affected leaves, but I wonder; if the problem seems to be abating, should I leave the leaves in place? After all, these poor little guys don’t have all that many. How many leaves can one cut off a seedling without killing it?
by the way, i’ve been trying to post a message about my mysterious paper-leaf seedlings, but for some reason it won’t let me… so please excuse the dopey “The” title and the retry that came up with none at all. Mod? Admin? Help!
-Fa
“How many leaves can one cut off a seedling without killing it?”
Well, in my experience you are between a rock and a hard place. You can’t leave a Downey infected leaf on a seedling or you can be guaranteed that it will continue infecting others. But if you remove ALL the leaves, you will probably lose that seedling. There is no happy ending if Downey really gets a foothold in seedlings, honestly. If I get it happening, odds are that I will lose any seedling it infects. I suggest you apply Aliette as often as the specs allow (I think thats every three days for ten days) and remove any seedling that has infection on every leaf. Increasing the temperature will help. Documents I have read all say that Downey spores are killed when ambient temps remain at 90F or higher for 24 hours straight, so you may want to consider that if all else fails. This may have adverse effects on germination, so consider your options carefully.
I have also found that Downey is thwarted when ambient temps stay below a certain range as well. The disease only starts to show up in my greenhouses when day temps rise above 60F or so. (approximately; I have never actually documented the relationship between first evidence of infection as it relates to daytime temps) So if you can keep the air temp below 50F (give or take) at all times, you may prevent the spread of the infection. Couple this with Aliette applications and you may solve the problem entirely.
Best of luck, Fa. This is surely the worst greenhouse problem for rose growers.
Paul
I was reading the old RHA newsletters and in the Winter 1995- 1996 an article explains that hot water sprayed at about 135 degrees will kill the Downey mildew for about a week and then have to do it again.
Patrick
Well, this past week has been very good for stopping the d#m@! DM in its tracks. Though it hasn’t been hot, it has been sunny and dry with the dew drying fairly early in the day.
It is interesting to see the various stages of DM. Plants that just started getting it before the weather change lost few leaves, but bear the marks of the scourge.
While plants hit first were completely devastated and had severe foliage drop.
This is one disease that I really hate…
Jim Sproul
It gives me the willies when I see it as bad as that. You have my sympathies, Jim.
Hi Jim,
thanks for the pictures.
I think one or two of my seedlings have DM and a lot of other seedlings have PM.
Now I can select the disease seedlings.
I hope you have DM-free seedlings yet.
Andrea