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Ask Dr. Hort: Let nature do its thing with plumerias

Let nature do its thing

Q: I have a plumeria in the front yard in East Lake Woodlands that is beautiful with flowers in the summer, shown above left. However, the leaves soon get yellow blotches on them, turn brown, above right, and fall off. This year I sprayed the leaves with Schultz Fungicide 3, which states that it is three products in one: fungicide, insecticide and miticide. This application had little or no effect. Can you please tell me what to put on the leaves next year to keep them healthy? Jake

A: The yellow blotches that you refer to are the spores of the rust fungus that attack plumerias. Since plumerias are deciduous (lose their leaves) and rust doesn't harm the flowers, it is easier and healthier on the environment to let nature take its course. Throughout the growing season, remove infected leaves and any that fall, and discard in the garbage while redirecting any sprinklers to keep water, which hastens spore germination, away from the foliage. However, if you feel compelled to keep the rust at bay, you can apply fungicides containing myclobutanil such as Spectracide Immunox on a weekly spray schedule as soon as the very first appearance of the disease. These products are systemic, becoming part of the plant sap and work much better than topical products such as copper or mancozeb.

Spray in spring, summer

Q: I am trying to rid my flower beds of torpedo grass and have purchased some Fusilade. I know it recommends three applications spaced three weeks apart. What are the best months to spray in Pinellas? Is it too late to spray now? Should I wait until spring? Some of the weed is about 18 inches high. Jeanne Pitman

A: Follow your label directions first and foremost. Since Fusilade (fluazifop) is a growth-regulating compound — by its mode of action in killing your target weed — the more leaf surface and the faster the weed is growing, the sooner you achieve control. You will get some control (die-back) with an application now, and then it will go dormant. Monitor closely this spring, and if it begins to show its little face again, apply your follow-up applications spring through summer when growth has fully resumed.

Bacterium can cure caterpillar crunch

Q: What is eating my mandevilla leaves this time of year? Mary Telford, Clearwater

A: Without a picture, the diagnosis may not be totally accurate, but I'll try. Beetles, grasshoppers and caterpillars chew foliage, and I am going to lean toward caterpillars.

Mandevilla splendens is a cousin to oleander, Nerium oleander, in the family Apocynaceae. There is a caterpillar that seriously attacks oleander, is orange with black tufts of hair and has a voracious appetite. Being in the same family, it also is a host, as is desert rose, Adenium obesum.

Look for small round black droppings — frass (caterpillar poop) — on the foliage as well as the caterpillars. Hand-pick any large critters and spray your plant with Bt, a bacterium, Bacillus thuringiensis, sold as Thuricide or Dipel. The small caterpillars will ingest the bacterium, get sick and die. The products are nontoxic to beneficials or humans. Follow label directions for application information.

Need help? Dr. Hort (Greg Charles) answers questions about garden problems. Email drhort@tampabay.rr.com or mail HomeLink, Features Department, Tampa Bay Times, P.O. Box 1121, St. Petersburg, FL 33731. Describe problem in full, include name, city of residence and contact information. If possible, include a quality photo. Fuzzy ones won't do. Photos can't be returned.

Ask Dr. Hort: Let nature do its thing with plumerias 01/21/12 [Last modified: Saturday, January 21, 2012 3:31am]

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