Lackluster Leaves a Sign of Trouble?

The ancestors of our Hybrid Tea Roses are still haunting us. After all, Hybrid Teas were first developed by breeding together an Old Chinese Tea Rose with an Old European rose. So it stands to reason that the genes of our Alec’s Red, Julia’s Rose, Kardinal, Blue Girl, Granada, and Ambience Roses still carry some of the genes of their ancestors.

Old Roses had one characteristic that for the most part had been bred out of the Hybrid Teas. The healthiest, most splendid Hybrid Teas have always had shiny leaves. The plants are bursting with fragrant oils, even before the blooms are produced. These oils come out on the leaf surfaces and produce a healthy shine.

Old Rose leaves, on the other hand, were—for the most part—matte. Pedro explained this to me over a latte as I shared my concern that some of our Kardinal Roses seem to have lost the shine on their leaves. “Lackluster, is how I’d describe it,” said Pedro.

So do dull leaves on Roses mean an unhealthy Rose? “Not necessarily,” said Pedro, “it could simply mean that the old, dull leaf gene came to the foreground in this generation, only to recede for the next ten generations to come.”

I hoped that this was the case, but I did notice that some of the dull leaved ones had a leaf here and there which I would strongly suspect of having Black Spot.

Pedro filled me in. Caused by the fungus Diplocarpon rosae, Black Spot is a very common and persistent rose disease. I’ve seen it in friends’ gardens and was told it was hard to get rid of.

Circular black spots with fringed margins appear on the leaves of the infected plants. Soon, yellow outlines appear around the spots and eventually the entire leaf yellows and drops off.

Left untreated, the plant becomes defoliated and the result is reduced bud set, poor flower quality, and susceptibility to environmental stresses. When grown outdoors, winter injury is highly likely. Indoors, the plant becomes overly sensitive to drafts and any drop in temperature.

Since it is a highly infectious disease, always wear gloves when handling infected plants and leaves. Remove each leaf as soon as any signs of Black Spot appear. Collect leaves in a plastic bag and dispose of them without allowing the infection to touch other plants, tools, walls, floors, etc.

According to Pedto, Spanish growers burn infected leaves and plants immediately. In his family greenhouses, Black Spot was always taken seriously and he recalls the contents of an entire greenhouse being destroyed in order to eradicate this disease.

Cancers can also develop on rose stems, which are concentrations of the fungus. Usually most severe in wet weather outdoors, high humidity conditions in the greenhouse can also be fertile ground for this insidious affliction of roses.

We couldn’t take the chance of having all of our Kardinal plants become infected, so we removed the plants in question and sprayed the surrounding ones with Scorpion Juice thoroughly. Pedro increased the amount of Barricade that he mixed in to our weekly nutrient solution.

You don’t want to spray with Scorpion Juice every week, so alternate with a mild solution of baking soda and horticultural oil, week by week. The oil serves a double purpose. Not only does it protect the unaffected parts of the rose plant from further infection, but it also makes the dull leaves shinier.

Our Kardinal roses are halfway through their vegetative cycle, so we’re feeding them generously with Iguana Juice Grow, as well as Organic B, and Humic and Fulvic Acid. Good nourishment is also a way of dealing with any kind of an infection, whether bacterial, fungal, or viral.

The three Advanced Nutrient root colonizers, Piranha, Tarantula, and Voodoo Juice, also play a major role in the eradication of disease. By inundating your roots with beneficial fungi, bacteria, and microbes, respectively, these three products help the plant fight off pathogens and pests throughout the growing season.

Sensi Zym is another product that Pedro loves. It supplies over eighty different types of living enzymes that nourish themselves with plant debris in our root medium, i.e. cocopeat. They devour this debris and turn it into digestible nutrients which are in turn absorbed by the roots.

Powdery Mildew, caused by the fungus Sphaerothece pannose var. rosae, is a very common affliction of roses throughout the world, and is especially troublesome for roses grown in glasshouses, such as ours. A white, powdery growth suddenly appears on leaves, shoots, and buds.

New shoots can become distorted and twisted by this fungal infection. Buds infected by Powdery Mildew often fail to open. This fungus doesn’t need wet conditions to develop, as long as the air is humid and warm. Pedro checks the humidity levels in all our greenhouses constantly, in order to ward off an attack by this fungus.

Unlike many other fungal infections, the Powdery Mildew fungus does not require moisture on the leaf tissues for an infection to take place. Small, black, pepper-like structures called cleistothecia are produced by this fungus, and these hide in plant debris. The fungus can survive in these structures, even without a suitable plant host.

Common sense sanitary procedures are vitally important in dealing with any fungal infections. Remove all infected plant material and place in airtight, plastic bags. Diseased stems should be pruned back to healthy wood in the spring, prior to budbreak.

Sufficient space between plants is essential to reduce the risk of this fungal disease. Adequate air circulation is also necessary. Stagnant, hot, humid air is a fertile breeding ground not just for this fungus, but for many other fungal enemies of healthy roses.

There are thousands and thousands of different fungi that infect plants. Aside from the two already mentioned, Roses are particularly prone to Downy Mildew, caused by the fungus-like organism, Peronospora sparsa, and usually propagated in cool, wet conditions.

Botrytis Blight, caused by the fungus Botrytis cinerea, is also a common disease of Roses. Cool, cloudy, humid weather can give rise to this infection. Grayiish-brown fuzzy growth appears on infected plants. Pruning cuts or any wounds on the plant are open invitations for this fungus.

In addition to believing in plant science, Pedro also has a superstitious side. He conducts a little ceremony after planting a new crop in each of our greenhouses. It involves a candle, a crucifix, and supplications to Mother Nature to make our Roses safe from any and all infections.

We dealt with the Black Spot problem (knock on wood) and hope to avoid any other fungus, bacteria, or virus before it is time to harvest our hopefully healthy and vigorous blooms.