FUNGUS AMONG US … Fungicides

by JoAnn Mukherjee
September 2007
DVIS Newsletter

 

Editor’s Note:  The first portion of this article, FUNGUS AMONG US … or Leaf Spot which treated non-chemical methods to prevent leaf spot, appeared in the Augus 2007 Newsletter.  The first paragraph is repeated here.

Leaf spot is a very common disease that affects irises in our area.  It can affect bulbous and rhizomatous types of irises, but it is most often a problem on bearded irises.  Leaf spot is caused by the fungus Mycosphaerella macrospora, which was formerly known as Didymellina macrospora.  In this instance it is important to also know the old name of the disease because some of the available fungicides still have Didymellina leaf spot listed on the label as the disease to be treated rather than the revised name.

A number of fungicides are available to regular homeowners.  The important thing to know about fungicides is that it is a preventative program; therefore, you need to start the spraying regimen before you notice you have a problem with leaf spot in your garden.  However, if you had leaf spot infections in previous years, chances are you will have it again the next year, especially if you did no implement all the cultural and sanitation practices listed previously.

The spraying program typically starts when the leaves are 4 to 6 inches high, and then the fungicide spraying is repeated every 7 to 10 days.  In unusually rainy periods, you may need to spray more frequently, sometimes every 5 days.  Unless the label states that the product has a sticker built in, a commercial spreader-sticker or ¼ tsp. of liquid dish detergent should be added to each gallon of the mixture so it effectively adheres to the leaves.

All of the products available for homeowner use are considered to be safe when used in accordance with the label directions.  Copper, however, is toxic to fish in low doses.   So if you are near a pond or stream, or water from your property flows into one, you may not want to use a copper-based fungicide.

Some of the chemicals available to homeowners to combat leaf spot are listed in the table below.  This list is not intended to promote any specific product.  And there may be additional alternatives that are available to homeowners that are not listed here.

Hopefully you now have the ammunition you need to a spotless garden.

 

CHEMICAL NAME	TRADE NAME
Chlorothalonil	Bonide Fung-onil Multi Purpose Fungicide
Chlorothalonil	Garden Tech Daconil Fungicide
Chlorothalonil	Monterey Fruit Tree, Begetable, and     Ornamental Fungicide
Chlorothalonil	Ortho Garden Disease Control
Copper Salts	Bonide Liquid Copper Fungicide
Copper Salts	Prescription Treatment Camelot
Copper Sulfate	Bonide Copper Dust or Spray (Bordo)
Mancozeb	Bonide Mancozeb Flowable with Zinc
Myclobutanil	Specticide Immunoc Multi Purpose     Fungicide Spry Concentrate
Potassium Bicarbonate	BioWorks Milstop
Potassium Bicarbonate	Bionide Remedy
Potassium Bicarbonate	Monterey Bi-carb Old Fashion Fungicide
Tebuconazole	Bayer Advanced Disease Control for Roses,      Flowers, and Shrubs
Thiophanate-Methyl	Cleary 3336G
Thiophanate-Methyl	Green Light Systemic Fungicide