Thursday, August 14, 2008

Greenhouse - Black Root Rot in Pansies

It is fall pansy production time and black root rot can be a problem disease in production areas, especially where produced on the ground. The following is information on this disease and its control.

Black root rot, caused by the soilborne fungus, Thielaviopsis basicola, can be very serious on pansy. This fungus attacks the fine feeder roots. Infected roots are black due to the presence of the fungus. Thielaviopsis basicola also causes a root rot on Helleri holly and vinca. This fungus is common in soils across Delaware and it is active over a very wide temperature range. The fungus infects the feeder roots and gradually kills the entire root system. Black root rot has been a serious problem in pansy production in the Southeast for the past five to seven years. It appears to be related to production in August and September when it is too hot for pansy plants and they are "stressed."Control measures for black root rot during production include:

>Grow pansies off the ground
>Avoid excessive heat stress, especially on young seedlings.
>Avoid other stresses, such as high substrate pH that can lead to micronutrient deficiencies (mainly boron and iron), excessive soil moisture, or excessive salts.

Preventative drenches with labeled fungicides such as 1-[1-[[4-chloro-2-(trifluoromethyl) phyenyl]imino]-2-ropoxyethyl]-1H-Imidazole (Terraguard 50 WP) and thiophanate methyl products such as Cleary's 3336 may help.

Information extracted from "Commercial Pansy Production" by Douglas A. Bailey, Professor, Department of Horticultural Science, North Carolina State University

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