Garden Detective

Garden Detective: Fighting mosquitoes, one pot at a time

BTI is marketed in a variety of formulations for the home gardener. The most common brand name is Mosquito Dunk, a doughnut-shaped float that lasts for about 30 days in water.
BTI is marketed in a variety of formulations for the home gardener. The most common brand name is Mosquito Dunk, a doughnut-shaped float that lasts for about 30 days in water. summitchemical.com

Q: Is there an anti-mosquito chemical that I can use in the saucers beneath my potted outdoor plants? I know that mosquitoes can propagate in standing water that collects in the saucers. The saucers, however, save water and can keep the soil moist for longer periods. Is there a product on the market that I can add to saucer water that would not harm the plants?

Alan Sims, Sacramento

A: UC master gardener Vickie-Marie Ward notes that there are a number of anti-mosquito products available for purchase at nurseries and home centers. But only one can be recommended that would not be problematic for the plants in the pots, she says.

BTI – Bacillus thuringiensis sub species israelensis – is a biopesticide. In order for it to be effective, mosquito larvae must eat the compounds, which act as a stomach poison to these insects. It is not effective against mosquito pupae because they don’t feed.

BTI is marketed in a variety of formulations for the home gardener. The most common brand name is Mosquito Dunk, a doughnut shaped float that lasts for about 30 days in water and is widely available in stores in our area. They’re small enough that one should fit in your pot’s saucer.

Make sure that the potting soil is not staying too moist. Oversaturated soil can lead to root rot and anaerobic soil, which is deadly to the microorganisms that are integral to healthy soil and plants.

Q: I’ve lost about half the leaves on one camellia bush. The leaves get spotted, finally die and fall off. I have five other camellias, but they don’t seem to be bothered by this. I’m also dealing with iron deficiency, but wonder how often should I apply chelated iron? I have a Merit soil drench every year on the camellias.

Mary Ann Rea, Lincoln

A: Unfortunately, the leaves were so dried when we received them that the spots were not visible, said UC master gardener Eleanor Dong. Under the microscope, we could not see any signs of organisms that might have contributed to this problem.

If this issue is still occurring, bring some new leaves with the spots in a sealed plastic zip-locked bag for diagnosis to the UC Cooperative Extension Office, 4145 Branch Center Road, Sacramento. The office is open to the public from 9 a.m. to noon and 1 to 4 p.m. Mondays through Thursdays. Call ahead to make an appointment at 916-875-6913.

To assist in diagnosis, the following information will be helpful: Is the bush dropping leaves from old or new growth? What color are the spots? When you irrigate, is the root system receiving adequate water? Those factors may provide clues to the spots.

Dong noted that you are applying a Merit drench annually, but you don’t state the reason you’re doing this. Merit is a brand name insecticide containing the active ingredient imidacloprid. Drenching the soil with Merit allows the plant’s roots to take up this insecticide and distribute it throughout the plant. The master gardeners always recommend identifying a pest before applying any insecticide.

As for the iron treatment, chelated iron – which is used to treat camellias displaying yellowed leaves – generally takes about two weeks to show effects; i.e., healthy, bright green growth. If you don’t see any improvement after three to four weeks, give your bushes another dose. Make sure to deep water your camellias before feeding.

After that second dose, hold off on the iron. Your bushes will tell you if they need more. Iron can be leached out of the soil by heavy rain, so you may not need to apply more until after storms return (hopefully) this winter.

Garden questions?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:

  • Sacramento: 916-875-6913; 9 a.m.-noon and 1-4 p.m. Monday-Thursday
  • Amador: 209-223-6838; 10 a.m.-noon Monday-Thursday; website: ceamador.ucdavis.edu
  • Butte: 530-538-7201; 8 a.m.-noon and 1-5 p.m. weekdays
  • Colusa: 530-458-0570; 9 a.m.-noon and 1-4 p.m. Tuesdays; website: cecolusa.ucanr.edu
  • El Dorado: 530-621-5512; 9 a.m.-noon Tuesday-Friday
  • Placer: 530-889-7388; 9 a.m.-noon Tuesday-Thursday, or leave a message and calls will be returned; website: pcmg.ucanr.org/got_questions
  • Nevada: 530-273-0919; 9 a.m.-noon Tuesday-Thursday, or leave a message
  • Shasta, Tehama, Trinity: 530-225-4605
  • Solano: 707-784-1322; leave a message and calls will be returned
  • Sutter, Yuba: 530-822-7515; 9 a.m.-noon Monday-Tuesday and 1-4 p.m. Thursdays
  • Yolo: 530-666-8737; 9-11 a.m. Tuesdays and Fridays, or leave a message and calls will be returned
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