Rose Disorders and Disorderly Roses

April is surely the month of roses in the Sacramento Valley. The first flush of blooms is about to burst. The foliage is nice and shiny, the buds are fat and plentiful. These are the largest blossoms of the season, and spring temperatures bring out the best color. But'

When Things Go Wrong.

* The shoot suddenly wilts, curling like a shepherd's hook and withering. This is caused by the Raspberry horntail borer, the larva of a wood wasp. You can find the red spot on the stem where the egg was deposited. The larva burrows down the cambium, and after couple of complete circles around the stem the upward flow of water is blocked. Find the red spot, go down a few more inches, and cut it out. The adult is a long, slender wasp, but is rarely seen.

* The flower bud develops to the point of just showing color, and then the blossom doesn't open properly. Petals are brown on the edges and crinkly.  Early in the season this is caused by erratic weather. Rose blooms develop best with even temperatures and humidity. Just cut it out. The next blooms will open fine.

* The leaves are covered with a white powdery growth, are crinkled and deformed. The blooms open fine. This is powdery mildew, one of the most common rose diseases here. Some varieties are very susceptible, some moderately, and some are immune. There are fungicides you can use, including some organic and less-toxic alternatives: neem oil and jojoba oil sprays can help prevent mildew. These won't make the powdery leaves better, but the next growth will come out unaffected so long as you keep spraying. Spray it away. Even better, replace susceptible varieties.

* There are yellow and black spots on the leaves, and leaves are dropping off. This is downy mildew, which is mostly a problem just after wet weather. There don't seem to be varietal differences in susceptibility. Instead, downy mildew attacks roses which are overgrown, have dense foliage, or which we pruned less severely. Miniatures and climbers seem to get it more severely. In a bad year, it can cause much of the foliage to drop. Harder pruning in winter reduces the problem: cut it out. Removing affected leaves does help to reduce the spread of the fungus: pinch it off.

* There are bugs all over the stems and flower buds! Aphids. Squish 'em, or spray them off: blast them off with a hose, spray with light oil (neem works well) or another low-toxicity material. You can release ladybugs, or just watch as other beneficial insects move in to devour them.

When Things Go Right.

Your nice blossoming rose bush is a joy to behold, with its upright stems and blooms held neatly above the foliage. But the orderly rose is a 20^th century phenomenon. Most roses were big spreading garden plants, with short stems, big flowers packed with petals, lots of fragrance, but sprawling 6' or more across, or scrambling up into trees. These can be fun if you have the space, but compact growth habit was one of the goals of rose breeders.

Commercial rose growers graft roses onto reliable rootstocks, leading to a more uniform product in your garden center. Grafted roses bloom earlier and tend to branch less when young. Note: if the rootstock sprouts it will usually over-grow the desired variety, but it is pretty obviously different and can be pruned out. If you have a scrambling rose with a semi-double red flower, it is probably rootstock. Cut it out. I have sometimes gotten so fed up with a persistent rootstock sprouting again and again that I dig out the whole plant and replace it. We call this pruning with a shovel.

As old-time rose growers know, many roses do root readily from cuttings, so it can be easy to make new plants. In fact, some growers have returned to production of 'own-root roses' for certain varieties they are selling to use as hedges. Heirloom roses are on their own roots ('heirloom roses' are usually defined as varieties introduced prior to 1867, when the first Hybrid Tea variety was released). Caution! Heirloom roses on their own roots may spread vigorously to form thickets! This can be great for informal gardens, but may not work if you are thinking of planting them in the traditional grid pattern of modern rose beds. I am still rooting out a Gallic rose and an Autumn damask rose that we planted nearly 20 years ago. I think of them as lovely weeds.

Want to cover an ugly out-building or fence, or screen a two-story neighbor's house? Try the species roses. This term is used for roses which are either wild types, or are hybrids or selections from a single species. The Lady Banks rose (Rosa banksia) just finished blooming locally. There is a white form ('Alba Plena') and a yellow form ('Lutea') in the trade, and I have the rarer single-flowered form happily swallowing up a fig tree in my back yard. How vigorous can the Lady Banks be? The World's Largest Rose is a 100+-year-old Rosa banksia covering 8000 sq. ft. (1/5^th of an acre) in Tombstone, Arizona.

In an informal landscape or rural setting these rambunctious growers can be very useful, providing screening, habitat for birds, and seasonal charm. I have a Rosa soulieana climbing up into, through, and over nearby trees. It roots when allowed to touch the ground, so I make an effort (more or less successfully) to keep it from doing that. A slip of Rosa odorata (below) given to me by a customer many years ago (thanks, Carl!) has spread freely, rooted, and clambered more than 20' up into a pear tree. The spring bloom is brief but spectacular, and the dense canopy provides cover for a covey of quail. A maple tree nearby provides support for 'Alchymist', a spring-blooming climber which looks old-fashioned but was actually introduced in 1956 (as I keep telling my kids, 50 is NOT old).

The key to managing these vigorous types is annual pruning. You needn't be afraid to cut these vigorous roses severely if necessary! Just wait until right after the bloom, and then cut them back to the structure they're climbing on, or even to the ground. Grub out branches which have begun to root, unless you want a thicket. The birds may appreciate that, but after many hours of chopping out R. soulieana my son would probably urge otherwise.

We live in a very favorable climate for roses. The low humidity here much of the year keeps disease problems at bay. Insect problems tend to be very seasonal and manageable. Their reputation for fussiness comes from the problems growers encounter in muggier and buggier climates. Between the modern types, and the heirloom and species types, there is a rose for nearly any garden situation and style.

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