Tuesday, July 14, 2009

Got Thielaviopsis?

Your only shot at controlling Thielaviopsis, better known as black root rot, is with a fungicide. Cornell University's Margery Daughtrey spoke to a ballroom full of growers Monday about the signs, symptoms and plants black root rot targets.

"This season, it seemed like there were a lot of Thielaviopsis-infected bugs," Daughtrey says. "Many blamed [poor quality plants] on the rain, but plants didn't grow because of this fungus. You may have some white roots, but not enough white roots to sustain healthy plants."

Perhaps the most obvious sign of black root rot is black or brown roots. Black root rot may not be obvious to the naked eye, but unhealthy plugs may be infected at their center where growers can't diagnosis the fungus. Another more obvious symptom is yellowing foliage, which can also indicate an unsteady pH.

"But yellowing might also be a root rot problem that's prevening roots from taking in nutrients properly," Daughtrey says.

If growers want to be certain, they can diagnose plants with a microscope. They should also be aware black root rot pathogens spread through the five following carriers.

1. Soil
2. Water
3. On infected plugs
4. Shore flies
5. Fungus gnats

"We send it across country in tractor trailers in plugs," Daughtrey says. "It can also move in water. Thielaviopsis produces a second spore type produced in long strands in high humidity. If you happen to grow something on flood [floors], there may be some Thielaviopsis.

The good news, Daughtrey says, is black root rot won't affect all crops. The bad news is it's a nightmare for commonly grown crops like calibrachoas, petunias, violas, pansies and vinca. And now, a wide range of herbaceous perennial plants are becoming susceptible to the fungus, too.

Daughtrey says black root rot will become an increasing problem with time, but there are controls to combat it. The best control, she says, is thiophanate methyl, and two recommended products are Cleary 3336 and OHP 6672. At Cornell's trials, Daughtrey says triflumizole has been effective on black root rot.

However you decide to combat it, good luck!

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