Rick:

I can tell you in my very limited experience that to a degree both are right. I believe that how you water depends to a point upon where you live and your climate. In Northern CA my climate is dry. Still I water by hand and in the morning to try and prevent the fostering of any diseases that might thrive in moist conditions.

That said I'm pretty shy about using any kind of chemicals. So when I discover aphids which occurs throughout the growing season I do knock them off with the sprayer. I do this in the morning though to give the plant a chance to dry off during the day.

The rose smarties here can give you advice from a much more sage perspective. Hope my experiences are helpful to you.

Kate

I've read that watering from above can encourage black spot. Powdery mildew, on the other hand, may appear when there is a lack of rain fall. I believe spraying the foliage with water can prevent powdery mildew from taking hold to a certain degree but will not help at all with black spot.

In my experience and in my climate, watering from above does indeed help keep my roses free of blackspot. In the fall when my kids' activities all increase with going back to school, my spraying schedule becomes almost nonexistent due to lack of time. My HTs get badly defoliated except the ones in the front yard. These I water with the nozzle when I'm watering my containers. That is the ONLY difference between the front ones and the back yard ones. The ones in front continue to hold their leaves and thrive, while the back yard ones begin to look pathetic. I do water early enough in the day to make sure the leaves are dry before nightfall.

Also, all of my roses are watered all summer long with overhead sprinklers. I do not have the time, energy, or monetary resources to install drip irrigation to all my beds. My roses don't seem to mind that their water comes from an oscillating sprinkler, and in fact, they seem to like a shower to wash off the leaves in the heat.

The spores of the black spot fungus are spread by water splashes, hence the concern about overhead watering. However, the spores also need 6-7 hours or more of continuous moisture to infect the leaves, and the ideal temperature is 75-85 degrees Fahrenheit. So, the relationship between overhead watering and the occurence of blackspot, may depend on, amongst a number of other factors, your climate. If you garden in warm, humid regions, overhead watering may be more of a problem than if you garden in an area with low humidity and cool nights. I heed the advice to not water overhead in the evenings, especially since black spot is a major problem in our part of the world.

An advice, however, is not a decree - you don't have to follow it if it does not work for you, or if you have a better alternative. No two gardens have exactly the same conditions. If whatever you do works for you, don't change it. If things are not working out, try new strategies. It's by trial and error that helps me figure what works best for our garden. There are gardening experts who we look up to and who dishes out useful advice. Ultimately, the gardener himself is an expert on his own garden.

rick have you ever noticed how blackspot never seems to affect new leaves? or how bs seems to show up when roses are starting to put out new growth? soil splatter? take a handful of dirt and throw it all over your roses and see how long it takes for all the leaves to get bs.couple of days?no difference? I've watered in the morning,afternoon, evening. If it's dry enough to need watering the water shouldn't sit on the leaves all night. Now the dew is a different story. water overhead,sideways,or up from under.

I wonder if it is a common misconception that the source of the spores is the soil. In fact, the spores do not survive for long in the soil. It does, however, persist in leave detritus left on or in the soil. The intial infections start off with the lowest leaves from spores that survived the winter in the infected leave debris left in the soil, or windborne. Once some of the leaves get infected, the new lesions start to appear on higher leaves, through water splashes. I can see this sequence occurring every year on some of our climbers and tall shrubs.

Interesting, isn't it, how so many of us fell for the sound bite "No overhead watering." I couldn't even tell you how many articles I've read with that advice. The best advice is right here in this thread, from each poster, i.e. consider your climate, your conditions, diseases that are prevalent in your neck of the woods, time of watering and temperatures involved, and cleanup. I hope this helps you make the right decisions for your garden, Rick. It's a great question that bears repeating so that we all question and amplify received wisdom. I love this forum for precisely this kind of interaction.

Sue

There is an old joke that I heard once from iris people. It concerned overhead watering, and the punch line was 'God, you're doing it wrong.'

I've never been able to think the same way on the subject since.

I try never to offer advice unless it's from my own experience. That said, I water over head most of the time...it rains from over head so why shouldn't I? Generally though I water using a sprinkler in late afternoon during the summer. However during this drought,I have been watering by hand with the hose to make sure all the water goes to the rose roots. I think one reason I have less blackspot the last few years is because I have concentrated on having roses than have a higher disease resistance.

Tammy

Karl has extensive experience basically proving that overhead watering reduces blackspot, presumably by washing off spores. Watering should be done in the morning so that it dries promptly, in which case blackspot cannot spread. If you are using a surface-protectant fungicide such as sulfur or mancozeb, then there might be some concern about washing off the fungicide, but one early overhead watering per week followed by fungicide would obviate that concern. It is most important not to get any water on the foliage in the evening, when it may stay wet overnight. BS only genrminates during long continuous wetting at moderate temperatures.

In the case of powdery mildew, spores cannot germinate on wet leaves; overhead watering washes off spores; and a hard spray of water can partially break up the exposed fungal body. Watering the soil surface in the evening could increase PM by raising humidity in the garden overnight, so non-overhead watering should be done early enough to let the mulch dry in the sunlight.. Overhead watering in the wee hours, when natural humidity is highest and most germination occurs, can prevent PM germination. PM only germinates on dry leaves with very high humidity. Very high relative humidity only occurs during the coolest hours.

My roses are watered daily using overhead sprinklers. My system comes on at 4:00 A.M and is done by 11:00 so any moisture on the leaves dries before dark. Over the years I've not seen any more fungus diseases with overhead watering than with drip or soaker hoses. I've tried them all. Temperature and humidity plus Mother Natures natural moisture (rain) play a much bigger role in the onset and spread of fungus diseases than any watering method you might try.
That said, Constant late day or evening watering will encourage blackspot.
The secret is early morning watering so the moisture dries fast and does not sit on the leaves all night.
Plants like a good bath once in a while.

I use a good fungicide program, so it doesn't matter how I water. It is easier for me to water overhead. I can't afford a drip system right now. I do hand water some, but now with our water ban I can't watewr at all!!!

It does rain somewhere,sometimes-making the whole subject a moot point.

I think since nature waters from overhead it certainly can't be all bad. In fact, I agree that plants like a bath now and then. Rain both waters the plants and cleans them off. I mostly irrigate with drip irrigation because it is efficient, and conserves water. Hand watering with a hose does the same thing.

I think either method is fine. The exception would be that I wouldn't generally water at night if the leaves are going to sit wet and soggy all night, although when I have broken that "rule", I haven't seen any more disease on my plants.

Sandy

I received wisdom from James Mills of K&M nursery that overhead watering is good. And Pete's right..sometimes it rains.
Linda

I'm with Karl, morning watering is best. If it rained all night, I get out there with the hose and wash off the leaves and let the sun dry the plants. If it rained all week, I get out the sprayer. Its been a good no fungus year for me because it never rained! If your mulch is thin or you don't have any, a good fresh layer of mulch helps keep down the blackspot and rust.

Washing the plants down before 11 has made all the difference for me and saved $$$ on chemicals.

I might add that drip irrigation or soaker hoses are a must if you live in an area with water shortages or restrictions.
I'm fortunate that I live in an area with a high water table. We all have wells and good drinking water can be found at 20 feet. Most people in my area have sand point wells. Even during times of low rainfall our water table stays high. I guess it's due to our sandy soil and proximity to Lake Michigan.
We have little runoff and everything that soaks in helps the water table.
I had a four inch well drilled with a submersible pump for volume to supply my sprinkling system. With no city water or sewage bill, daily watering is not expensive for me.
I feel for those who have to conserve..

HAHAHAHA. I remember asking the same question myself. I was so careful not to get the leaves wet on my roses. Water in the morning..But I kept reading about blasting aphids with a hose. LOL

My overheads go on from 3:30 to 4:30 a.m. and the roses are dry several hours later in summer. I also noticed more spider mites from roses on drip watering than overhead. The worst thing about overhead here is the water spots, as our water is full of minerals.
BS is not a problem here but PM really is. I get more PM on the drip roses.
Kathy

Well, over-spraying the foliage cannot be all bad, because God does it often when it rains. I have never questioned His wisdom on this, and doubt I ever shall. If you have sprayed, and your spray formula has dried on the foliage, any amount of water or rain will NOT wash it off. It will be there until you spray again. My roses here at the house get watered overhead, and I see no more blackspot because of it. I really think it is up to you how you handle the situation.