Texas A&M garden experts answer questions about fungus and scale


Q: When do I directly sow seeds for Verbena canadensis, Verbena bonariensis, Large Purple Ruellia and Kosmos?

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

Sun-loving purple bonariensis, or purpletop verbena, grow 4-5 foot long stalks that sway in the wind beneath clusters of lavender flowers. Direct sowing in late autumn. It self-seeds easily. Deadhead for new blooms. This South American native can be grown as an annual but is a tender perennial in zones 7-10. Temperatures of 60 degrees at night and 86 degrees during the day are recommended to break the hibernation.

Mexican Petunia or Ruellia brittoniana / R. simplex, is an adapted perennial growing 2 feet by 3 feet. Plant seeds in spring. Native to Central and South America, she is a solid performer but tends to spread aggressively in our climate through rhizomes and seeds. It’s considered highly invasive in Florida, and again not viewed too favorably by all, although considered a common landscape addition. Planting in pots buried in the ground, like mint, is a trick to keeping it in check.
The ‘Purple Showers’ cultivar grows to 4 feet tall and has sterile seeds. Although slightly less aggressive, it can still spread through rhizomes.

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The Lady Bird Johnson Wildflower Center lists four native alternatives, with Ruellia humilis (Fringeleaf Wild Petunia) considered the most accessible. Direct sowing in late autumn to overwinter for spring germination.

Cosmos are colourful, sun-loving annuals that thrive in our summer heat. They grow airy and move with the wind, but they also make great cut flowers. They can be sown directly into the ground in spring and midsummer for late summer and fall blooms. A general germination rate of 80% is possible when the soil temperature is 70 to 80 degrees. Seedlings are not hardy but could survive in mild seasons. If experiments are your thing, throw them away and see what happens.

Brandy Keller


Protect plants from scales and fungi

Q: Bald patches grow irregularly in our front yard. Other areas yellow and may join them. Is it brown spot or root rot? I’m not sure how to treat and would appreciate any suggestion.

A: At this time of year you see the root rot. After a wet August, we’re seeing more all-rounders in the area. Root rot is a fungal disease that causes faint brown, dead patches in lawns. The disease affects both St. Augustine and Bermudagrass. A fungicide application containing the active ingredients azoxystrobin, myclobutanil, propiconazole, or thiophanate-methyl can help stop the spread. Please read and follow all label directions. As a side note, brown patches, now known as large patches, thrive in cooler temperatures when the soil is wet. The disease occurs when temperatures are below 70oF.

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Q: I have two Bashams Party Pink crape myrtle trees that have crape myrtle bark scales. I’m almost certain it’s CMBS. I find the caterpillars under leaves and on 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 scales, it bleeds pink. I’ve done a mild soap wash and brushed off a lot of the heavy clusters but can’t get 100% off. How should I treat this?

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

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

A: Tradescantia pallida is commonly referred to as Purple Heart or Moses in the Basket. It’s a tender perennial that has a sprawling habit and won’t cling to your walls or damage the stucco. The plant does well in both sun and shade. It produces tiny three-petalled pink flowers in summer. Landscape height is 12 to 18 inches.

Paul Winsky



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