You Are Here: Management Updates 2008 Archive June 10, 2008

Date: June 10, 2008
Category: Diseases
Subject: Maximizing Turfgrass Disease Control

Maximizing turfgrass disease control by understanding spray volume and the topical mode of action of fungicides
Contact fungicides such as mancozeb (Dithane™, Fore™) and chlorothalonil (Concorde™, Daconil™, Echo™) along with systemic fungicides play a crucial role in management of turfgrass diseases. Preventative application is the best way of using contact fungicides. Once visible symptoms are apparent, contact fungicides will prevent further infection only on plant parts covered by the contact fungicide. Unlike systemic fungicides, contact fungicides stay on the plant surface and do not penetrate into the plant. Therefore, they are active only when fungal spores or mycelia come in contact with the fungicide on the plant surface. Contact fungicides usually remain on the plant surface for 7 to 14 days, which will be significantly influenced by rate of plant growth, rainfall, irrigation, height of cut, mowing frequency and spay volume. Preventative application of contact fungicides should use a lower spray volume (1-2 gallons/1000 sq ft), which will provide better control by reducing fungicide dilution.

Managing lower stem, crown and root infecting diseases, such as anthracnose basal rot is particularly difficult; because the fungicide applied must be able reach all susceptible plant parts. Therefore, a higher spray volume (3-4 gallons/1000 sq ft) for systemic fungicides will allow for better control by allowing the fungicide to be placed deeper in the root-zone and thatch, where the pathogen will attack. Also, all systemic fungicides except for fosetyl-Al, only move upward, which means that the point of initial absorption is critical to provide adequate control. However, a lower spray volume is recommended for fosetyl-Al (Chipco Signature™) since it is the only true systemic fungicide with up and down movement from the point of absorption. On the other hand, when managing foliar diseases, such as dollar spot, utilizing a lower spray volume (1-2 gallons/1000 sq ft) for both contact and systemic fungicides will provide the best control. A lower spray volume will maximize the fungicide on the target area without diluting the fungicide.

In particular, contact fungicides are a significant part of fungicide resistance management due to their multi-site mode of action in fungi. This greatly reduces the risk of resistance development by reducing some systemic fungicide applications. Systemic fungicides can give longer disease control, but are more susceptible to fungicide resistance. This is due to their inhibition of only one biosynthesis pathway (single-site mode of action). By avoiding repeat applications of the same single-site mode of action systemic fungicides, fungicide resistance can be managed more effectively. As a result, single-site systemic fungicides can be used for a longer period of time. Also, different fungicide trade names do not correlate to different modes of action, so check the label for active ingredient (a.i.) and refer to the FRAC codes to make sure you are rotating your chemicals properly. For information on current fungicides, the diseases they control, and FRAC codes refer to our current Turf Fungicide Chart .

If you are suspicious about lack or failure of chemical control, please send your samples to the UMass Extension Plant Diagnostic Lab. Complete instructions for submitting samples to the lab are available at: http://www.umass.edu/agland/diagnostics

Submitted by: Dr. Geunhwa Jung

DISCLAIMER - As always, it is the responsibility of the applicator to verify the registration status of any pesticide BEFORE applying it. Different states have different regulations as well. The author and the University of Massachusetts are not liable for any consequences of any pesticide "recommendations". Mention of any trade name is not to be considered endorsement of a product.

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