Texas A&M Gardening Experts Answer Fungus and Scale Questions

Q: When should I direct sow seeds of Verbena canadensis, Verbena bonariensis, Ruellia with purple flowers and Cosmos?

A: Verbena canadensis is a common perennial in the southern home landscape with its prolific pink/purple flowers that can bloom year-round in winter. Direct sow verbena seeds in the fall as cold exposure helps. Also known as Homestead Purple and Trailing Verbena due to its low, spreading habit, it grows 12 inches tall and 2 feet wide.

The sun-loving purple bonariensis, or purple verbena, grows 4-5 foot stems that sway in the wind beneath clusters of lavender flowers. Direct sowing in late fall. It sows easily. Deadhead for new flowers. This South American native can be grown as an annual, but is a tender perennial in zones 7-10. Nighttime temperatures of 60 degrees and 86 degrees during the day are recommended to break dormancy.

Mexican Petunia, or Ruellia brittoniana/R. simplex, is an adapted perennial that grows 2 by 3 feet. Plant the seeds in the spring. It is native to Central and South America and is very successful, but tends to spread aggressively in our climate by rhizomes and seeds. It is considered very invasive in Florida and not viewed too favorably by everyone here either, although it is considered a common addition to the landscape. Planting in pots buried in the ground, like mint, is a trick to keep under control.
The “Purple Showers” cultivar grows up to 4 feet tall and has sterile seeds. Although slightly less aggressive, it can still spread by rhizomes.

Lady Bird Johnson Wildflower Center lists four native alternatives with Ruellia humilis (wild fringe-leaved petunia) as the most accessible. Direct sow in late fall to overwinter for spring germination.

Cosmos are colorful, sun-loving annuals that do well in our summer heat. They have airy growth and move with the wind, but also make superb cut flowers. They can be sown directly into the ground in spring and mid-summer for late summer and fall blooms. A general germination rate of 80% is possible when the soil temperature is 70-80 degrees. Seedlings are not winter hardy but could survive in mild seasons. If experimentation is your thing, throw them out and see what happens.

Brandi Keller

Protects plants from scale and fungus

Q: I have irregular bare patches growing in our front yard. Other areas turn yellow and can join them. Is it brown patch or root rot? I don’t know how to treat and would appreciate any suggestions.

A: At this time of year, you see root rot. After having a wet August, we are seeing more totes in the area. Pull-out root rot is a fungal disease that causes faint brown, dead spots in the lawn. The disease affects both St. Augustine and Bermudagrass. A fungicide application with the active ingredient either: azoxystrobin, myclobutanil, propiconazole or thiophanate-methyl can help stop the spread. Please read and follow all label instructions. By the way, brown spot now called great spot thrives in cooler temperatures when the soil is moist. The disease occurs when temperatures are below 70oF.

Q: I have two Bashams Party pink crape myrtle trees that feature crape myrtle bark cochineal. I’m pretty sure it’s CMBS. I find the caterpillars under the leaves and the trunk, and the branches are heavily covered with white scales. The lower third of the heavily infested tree is black. When I crush the white balance, it bleeds pink. I’ve done a mild soap wash and brushed off a lot of heavy bunches, but can’t get 100% off. How should I deal with this?

A: Everything you described – bleeding pink caterpillars under the leaves and trunk and black bark – leads to the diagnosis CMBS. In our area, there can be up to four generations in a growing season. Your first action of brushing the bark with a mild soap is a good first step in reducing the population. You can also apply horticultural oil or horticultural soap to surviving adults. Do not apply dormant oil at this time as it may have a negative effect on the plant. You can also apply a drench with imidacloprid, which will help prevent an increase in population throughout the rest of the growing season and into dormancy. I haven’t seen crepe myrtle killed by CMBS, but it affects the aesthetics of the tree with the sooty mold produced by the cochineal. The actions you take now to control the population will result in reduced populations in 2023.

Q: Is Tradescantia pallida considered a “climber”? I want to plant it as a ground cover but my house has a stucco exterior and I don’t want to damage the surface.

A: Tradescantia pallida is commonly called Purple Heart, or also Moses in the Basket. It’s a tender perennial that has a hiking type habit and won’t attach itself to your walls or damage stucco. The plant performs well in both sun and shade conditions. It produces tiny pink three-petalled flowers in summer. Landscape height is 12 to 18 inches.

Paul Winsky