Marin Master Gardeners
University of California
Marin Master Gardeners

Marin IJ Articles

Backyard Sleuthing

June 04, 2011
Nanette Londeree

I LOVE ROSES. Joyfully strolling through the spring rose garden, I peruse abundant jewel-like new growth cloaking the rapidly growing plants and revel in their extraordinary transformation from spindly sticks a few short months ago, to bountiful mounds of perfumed blossoms.

But there, out of the corner of my eye, I see, oh no — orange spots dotting the foliage! And, over there, droopy buds peppered with tiny holes and little lacquer-red crawly things. Yikes! What's going on with my plants? I can't say how many times I've asked myself that question.

Sometimes the answer is simple, like when the wilted, rapidly shriveling plant is lying flat on its side, roots completely gone — clearly a pesky, chewing gopher at work. Or the tree rose with not a leaf in sight, just an enormous envelope of webbing encasing a wriggling mass of tent caterpillars.

More often, figuring out what's ailing your rose is not that straightforward. Like the vet determining what's wrong with your vomiting, sneezing cat, it takes some detective work to diagnose the cause of plant problems, and in order to find an effective remedy, it's vital to correctly identify the cause.

Figuring out what's troubling your roses, your indoor plants or anything else you've got growing, takes a Sherlock Holmes approach — collecting and evaluating information, and narrowing the range of possible villains. To help with your sleuthing, look for signs and symptoms.

A sign is direct evidence of the cause of the problem, either the presence of the actual pest or some part of it, while a symptom is the change in appearance of the plant part — like spots on leaves or deformed flower buds. Observing a mass of foamy froth on a new rose bud would be a sign of spittlebugs; dry, grey, crispy-looking leaves in the summer would be a symptom of spider mites.

While pests and diseases are often the first thing a gardener looks for, the culprit may not be caused by any living thing, but, instead, be the result of nonliving factors — mechanical or physical (being torn, cut, crushed, chewed, sliced or punctured from wind, animals and lawn mowers), environmental (temperature extremes, light, water) or chemical (nutritional deficiencies, toxicities, exposure to herbicides).

Some things to consider when figuring out what's bugging your roses:

• Know what a healthy plant looks like. This may seem like a no-brainer, but not all roses look alike. Having a clear idea of the size, color and form of a healthy plant and its blooms is a good tool for comparison.

• Take a real good look at the plant; the cause of the problem may not be in the part of the rose that displays the symptoms. Check every visible portion of the plant; look for physical evidence of an injury, a pest or disease.

• Know your enemies. Having an idea of the most common pests and diseases can give you a leg up on early detection. Find out who they are, what they look like, when they show up in the garden, and what damage they do.

• Think about the history of the plant and its surroundings — how long has the plant been in its current location? Has anything changed for the rose itself or near it? What's the weather been like — frosty cold, devilishly hot, super windy and dry? Sometimes problems arise from activity in areas near or adjacent to the plant, like soil compaction after the addition of a new fence or patio.

• Consider that it may be multiple problems; a plant stressed by drought or temperature extremes may be more susceptible to attacks from pests and diseases. Or, you might observe one problem that is really a symptom for another, like ants on roses — they're just an indicator of some sucking type of pest.

• Look for patterns; do other roses have the same problem? What about different types of plants? Are all the plants with the problem in the same general area or different locations? Do you see damage to the same parts of the plants (e.g., growing tips, edges of leaves) on different plants?

• Eliminate what it's not. Narrow down your list of possible suspects by ruling out those problems you know for certain are not the cause of the problem.

• Double-check the obvious. It never hurts to look again for apparent problems; are raccoons chewing holes in your drip irrigation line? Did the next-door neighbor use an herbicide that may have drifted into your garden?

• Make a preliminary diagnosis. Once you've collected all your information, decide what you think the cause of the problem is.

• Keep an open mind and be patient; don't jump to conclusions about what the problem is. On more than one occasion I've reacted before confirming what's wrong with my plant, like dumping lots of water on a wilted potted plant only to see it look worse. When I finally got close enough to  determine what the problem really was, I found the drain hole in the pot had roots plugging it; the plant wilted because it was drowning!

Back to those orange spots I observed on rose leaves, my sleuthing confirms it's the oft-present fungal disease of the spring and fall garden, rust. And the lacquer-red crawly things are rose curculios, the varmints drilling little holes in my new blooms. While I'd certainly prefer them not to be at home in my garden, knowing what they are is my first step in determining an effective remedy.

Top of page

Webmaster Email: banielsen@ucanr.edu