Friday, June 22, 2018
Home and Garden

Ask Dr. Hort: She's vexed by bugs, rust fungi and a poinciana relocation

Vexed by bugs, rust fungi and a poinciana move

Q: What will really rid my big gardenia shrub of mealy bugs, and where do I get it?

Are typical pink geraniums (not red) particularly frail? I can't seem to keep them growing.

Any idea how to get rid of the yellow invasion of the undersides of my frangipani/plumeria trees' leaves? Seems to get more devastating every year. All my neighbors also now have had a similar problem; we went years without it.

My Roebellini palms lean gracefully over our lawn. Where do I target palm fertilizer — out at the drip line in a circle, concentrate more where the fronds lean over the lawn, or elsewhere? I must not be placing the fertilizer correctly.

How do the roots of a 4-year-old poinciana tree spread — straight down or only outspread? I must move a growing pair to a new location where there's room for the spreading head and want to make sure I can transplant. Is April the best time to transplant them?

Sandy Oestreich

A: Are you sure you have mealybugs and not whitefly on your gardenia? Either way, neem oil-based products are great for controlling sucking insects including mealybugs, both killing adults and acting as a growth regulator for the young; birth control for mealybugs. Neem oil-based products are very safe for both you and the environment. Apply as label directed.

It is not really the color of geraniums, Pelargonium hortorum, it is whether they are seed grown or zonals (vegetatively propagated from cuttings). Seed-grown plants have only single flowers, are smaller (under a foot tall) and are treated as annuals, and the flowers have a tendency to shatter. Zonals have a purplish band in the leaf, produce double flowers, grow to 18 inches and grow as a perennial. So it comes down to seed versus zonal, with zonals being more hardy.

As for yellow leaf undersides on frangipani, Plumeria spp., the bright orange pustules on the undersides of the leaves are the spores of a rust fungus. You can spray repeatedly with systemic fungicides such as Spectracide Immunox or Fertilome F-stop, or watch them defoliate. Since it is a fungus, keep foliage dry by growing in full sun and redirect sprinklers away from plants. Also discard infected and fallen leaves on a continuous basis. It is a very difficult disease to control.

When placing fertilizer for specimen palms, spread evenly from the trunk out just past the drip line, because palms sit on their root system. Roots for woody plants (oaks, elms) extend three to four times the diameter of the tree outward, so fertilizer placement is from 1/3 inside the canopy to 2/3 outside. No fertilizer should be placed by the trunk.

Transplanting a 4-year-old royal poinciana, Delonix regia, is no easy task and the success rate is about nil. The tap root will be down a foot or so, but the lateral roots will spread beyond the canopy, so you'll remove 90 percent of the root system. One cubic foot of soil weighs 100 pounds, so have plenty of hefty helpers. Thoroughly wet the root zone the day before to help hold sand together. Dig the receiving hole first. With a sharpened garden spade, dig straight down 24 inches from the trunk to cut the roots loose. With a sharpened garden shovel, dig at a 45-degree angle into the spade slice. Shave the bottom of the root ball to eliminate excess weight. Run the shovel under the root ball to break loose the tap root. Lift the tree out of the hole onto a blanket, canvas or tarp to make the move easier. Slide the tree into the receiving hole, making sure that the first surface root is level with top of hole. Fill the hole with water and backfill soil. No amendments are needed. Create a 6-inch soil saucer around the edge of the root ball and add slow-release fertilizer to the surface. Water every day for the first month, then every other day for the next three months, then once a week until established. Place three tie wraps around the trunk to secure it to the ground with a stake in pyramid fashion, and leave that on for the first year. March through April would be a good time to attempt your project.