Wet conditions and soil-borne diseases of herbaceous perennial plants

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

The recent and continuing stretch of cold and wet weather has resulted in water-saturated soils, and it may remain cool and wet for several weeks. These conditions are particularly suitable for the development of root-rotting pathogens for example, Phytophthora spp., Rhizoctonia, Pythium, Fusarium, Thielaviopsis and other soil-inhabiting fungi and bacteria.

Spores of these fungi and water-molds can remain dormant in the soil for many years, and it is likely that with current soil conditions, retarded development and growth of roots, many plants are vulnerable. Infected plants may exhibit symptoms that start with wilt and apparent nutrient deficiencies, and ultimately become necrotic and die. The roots lose integrity and adhesion to the soil. To check for root rot, gently, but firmly, pull the plant upwards. If the plant comes away from the soil with minimal resistance and the roots are darkened, root rot may be the problem. Samples should be sent immediately to MSU Diagnostic Services for confirmation and diagnosis of the problem in order to implement appropriate control recommendations.

Once the soil has dried out sufficiently (about 15% volumetric soil moisture), appropriate fungicides for soil-borne and root diseases may be applied. Use only fungicides recommended for the diagnosed pathogen and use label recommended rates and application methods (Table 1). Other fungicides may not be able to be tranlocated to the root zone through the phloem and others may not be able to penetrate leaf tissue without adjuvants, which can be phytotoxic. Therefore, if a fungicide has been recommended for soil application only, try to avoid foliar contact. This, of course, is not always possible especially if soil fungicides are applied curatively after transplanting. Read the fungicide label carefully before applying for root protection.

Two publications that may be useful references include:

Plant disease management for the perennial herbaceous industry.In Management Practices for Michigan Wholesale Nurseries. Kirk, W.W. 2004. 209 pp. Editor Tom Fernandez. Chapter 7, 141-159. Available from Instructional Media center, MSU, PO Box 710, MI 48826-0710 (517 353 9229);

The 2006 Pest Management Guide for Commercial Production and Maintenance of Herbaceous Perennials (Cornell publication) is now available through the MSU Extension Bulletin Office, 117 Central Services, Michigan State University, East Lansing, MI 48824-1001. Phone: 517-353-6740, Fax: 517-353-7168 Office Hours: M-F 8:00 AM - 5:00 PM.

The bulletin is also available to order at the following addresses:


Table 1. Fungicides for root diseases. Class, common name, trade names and pathogen targets for herbaceous perennial plants.

Class of fungicide

Common name

Trade names

Pathogen targets


Trichoderma sp Gliocladium virens Cinnanaldehyde

Rootshield SoilGard Cinnamite

Phytophthora spp. Pythium spp.


Propamocarb HCl


Phytophthora spp.

Coppers, Fixed

Copper sulfate

Phyton 27 Basicop Camelot Junction

Topical bacteria Phytophthora spp.

Coppers, unfixed

Copper Hydroxide


As fixed coppers

Organic phosphate



Pythium Rhizoctonia



Subdue Max

Pythium Phytophthora spp.




Pythium Rhizoctonia




Powdery mildew


Etridiazole +TPM

Truban Terrazole Banrot

Pythium Phytophthora + Rhizoctonia Fusarium Thielaviopsis

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