Q: I have noticed on a couple of plants in my yard (a rosemary bush and a flowering plant with carnation-like flowers) a white substance (looks like a dollop of spit) at the top of some of the branches. Is this an insect depositing something?

A: This gooey little surprise, common in Bay Area gardens at this time of year, is caused by immature spittlebugs, otherwise known as froghoppers. These insects, which are similar to leafhoppers, surround themselves with “spittle” to discourage predators. They are sucking sap from your plants, which is not a serious problem unless it disfigures the plant. Some, like rosemary, show little evidence of damage, but the blobs themselves are still unsightly. The best solution for small-scale infestations is to spray them off of your plants with water every few days. This not only gets rid of the blobs but usually kills the insects inside them as well.

Spittlebugs will disappear by mid July, when all of the year’s froghopper eggs have hatched, since they have only one life cycle a year. Once they mature, the adults do little damage to plants.

If you have room for California coffeeberry (Rhamnus californica) or California buckwheat (Eriogonum fasciculatum) in your garden, these could help prevent spittlebugs. Their flowers attract tachinid flies, which eat spittlebugs, and they bloom at about the same time that the spittlebugs are causing problems.

Q: I have a comment and question. In a recent column on whiteflies, you wrote, “This happens because whiteflies often develop resistance to pesticides …” This is a perfect example of when “evolve” should be used, not “develop.” The whiteflies that you described have evolved, not developed, resistance to pesticides. That is, there was a population of whiteflies that was exposed to the pesticide, and most were killed by it, but some (by chance) had mutations that turned out to be protective against that pesticide. They survived. Those whiteflies were resistant, and when they reproduced, their progeny inherited that resistance.

“Develop” refers to what happens to one organism during its life, not the change in the chromosomes of a population over generations. So development would refer to my hair turning gray as I get older, or the puberty phase of young adults. Evolution would refer to the differences between blood groups in humans, and every example of genetic differences between populations, species, etc. in plants, animals, fungi, etc.

I am a graduate student in paleontology and evolutionary biology in UC Berkeley’s integrative biology department. When learning introductory biology or evolution, students are often (very!) confused about terminology like “develop” and “evolve” and don’t understand the difference. I (and the biologists and paleontologists in the department) think that this is an important distinction that would educate the public. I would love to see it in your articles!

On to my question: I am planning to make recycled paper with embedded flower seeds as wedding invitations, so the card itself could be planted. Could you recommend seeds that are small and would work for this purpose and that ideally aren’t invasive plants in North America?

A: On the first point, I do teach pesticide resistance as an evolutionary process in my classes, but the column is more how-to than theory, and has to be short. I used the word “develop,” which, in everyday conversation, is an acceptable term for change in general, but I like the idea of using the technically correct word even when the longer explanation can’t be included. Will do.

Regarding your question, this is such a large continent, with so many habitats, that you are wise to think about invasiveness. Many flower mixes contain one or more species someone would rather not grow because it invades wildlands. My other concern with this sort of seed-embedded paper is that the small size doesn’t give you much room for larger plants. I’d suggest small plants, nice to grow under roses or in a wide container. Consider the following, which are not, to my knowledge, seriously invasive anywhere in North America: deep blue edging lobelia, Lobelia erinus ‘Crystal Palace’; signet marigold (Tagetes tenuifolia ‘Golden Gem’), pink annual clary sage, (Salvia horminum ‘Marble Arch Rose,’ available from Select Seeds, at www.selectseeds.com), and an annual viola, such as Johnny jump-up (Viola tricolor).

Another option, if you have culinarily inclined guests, would be to use a mesclun mix: red, green and speckled leafy lettuces, mizuna, red orach, arugula, etc. This you could embed rather thickly, since they are intended to come up thickly and be cut an inch from the ground several times to make salad.

Q: I’ve effectively kept raccoons out of our backyard fish pond. A motion detector activates a low-watt bulb and an old electric leaf blower placed near their entrance point to the yard. To the tip of the leaf blower pipe I’ve added about 6 feet of soft plastic tubing (the kind sold in hardware stores, flat, on a roll, used to attach to downspouts to take water away from the house).

When the blower kicks on, the plastic tubing waves and flaps and jerks. The noise and motion seem to do the trick. I’ve set the motion detector to last about 4 seconds, and in the 10 years or so I’ve used it, no complaints from neighbors.

A: I’ll bet it’s satisfying to watch the action, too. This solution sounds good for those with the know-how to set it up, a particular garden entry point for the animals, and either distance or patience from neighbors.

Pam Peirce is the author of “Golden Gate Gardening” and “Wildly Successful Plants: Northern California.” She teaches gardening at City College of San Francisco. Read her blog at goldengategarden.typepad.com or e-mail questions and comments to her at home@sfchronicle.com. We cannot guarantee a response to all questions submitted.

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