December 2013 Newsletter (vol.24)   >>   Introduction to Organic Fertilizers



Providing a healthy growing environment is often the best defense against plant disease and fungus. Despite the best plans, fungal issues find their way into gardens and greenhouses of all shapes and sizes. Plant symptoms such as wilting, leaf curl and decaying tissue along with red, white or black powdery spots, are all indications that your plants have a fungus problem. These problems can show up on the leaves or seeds but also make a home in soils and can be hard to detect without visual symptoms. Proper identification is pertinent, not only for treatment of the issue but also for future prevention. Regular scouting and early detection are key to good management of fungal diseases.


Once you have determined that you have a fungus and you have correctly identified it, organic fungicides are an excellent treatment. Some organic products originate from natural predators while others are minerals which are readily available. While these products are labeled as organic, they are still toxic and precautions should be taken upon applications. As with any pesticide, the label is the law and following all the instructions will provide safe, legal and effective treatments. Organic products can prove to be safe and effective weapons against an array of fungal issues.


Several organic fungicides stem from naturally occurring microbes that act in several ways to disrupt and prevent fungal infections. Bacillus subtilis is a microbe contained in products like Cease. This species generally out-competes fungi for root space and food and can also be a systemic preventative. B. subtilis products will fight a wide variety of fungi such as Botrytis, powdery mildew, pythium and fusarium.


Actinovate is another product that uses a microbe as a weapon against fungus. This product contains Streptomyces lydicus, a colonizing species that forms a synergetic relationship with the plant surrounding its foliage and roots. This species can fend off powdery mildew, downy mildew, sclerotinia, verticillium and fusarium and also offer benefits such as enhanced roots and increased nutrient availability.


Rootshield WP and Rootshield G contain a third microbe that is effective in the battle against fungi. This microbe, Trichoderma harzianum, has a similar mode of action as the above species in Actinovate but also offer an enzyme that attacks fungal pathogens. Although this product works only as a preventative in the root zone it will reduce the need for other fungicides during the growing season.


One of the most effective fungicides from the miner world is copper. Copper products come in various forms and have a wide array of control factors. When considering using an organic fungicide, copper sprays are the best option. When these sprays contact water they release ions that disrupt the proteins in the cells of fungi. Most new copper sprays are Bordeaux mixes containing hydrated lime. This added ingredient makes the sprays more effective and less phototoxic. Best results occur when applied before the onset of fungi and when reapplied throughout the growing season.


Sulfur is the oldest recorded pesticide and has been as a fungicide since the early 1800s. Sulfur Plant Fungicide - RTU is a product that employs this element to inhibit spore germination and growth in a variety of fungi including powdery mildew and rusts. Do to the mode of action of sulfur products it must be applied prior to the onset of a fungus to be effective. Sulfur products are often associated with fertilizer products and soil applications. They can come in powders or liquids, however liquid lime sulfur will carry a strong rotten-egg smell.


Bicarbonates, both potassium and sodium, have often been promoted as being very effective against powdery mildews. Sodium bicarbonate (baking soda) has been listed as a home remedy for mildew but is not allowed as an organic treatment unless it is used in a regulated form. Bicarbonates work much like other minerals to disrupt cellular functions, eventually causing cell walls to collapse. Bicarbonates demonstrate various levels of phytotoxicity to various crops and users must fully investigate the situations before applying these minerals. Milstop is a great product that uses potassium bicarbonate to inhibit growth of diseases such as powdery mildew, anthracnose, blights, Botrytis and downy mildew.


As previously mentioned, good growing practices and clean growing areas are the best defenses against fungal diseases. Products such as Oxidate RTS and Zerotol RTS are organic oxidizers that can be used as quick curative spray against almost all plant diseases. These products can also be used to clean tools and other surfaces and keep them clear of pathogens.


Fungi, and the damages they cause to plants, are simply a part of nature and the growing process. Using natural and organic treatments to prevent and cure fungal diseases are most often the best and safest choice for any growing environment. Keep in mind that cultural practices play a significant role in the prevention of fungal infections and proper identification is the first step to effective treatment. Employing organic methods when growing your produce and flowers will provide better and safer products and a healthier environment for everyone.




Beckerman, Janna. Disease management strategies for horticultural crops: Using organic fungicides. Purdue University Cooperative Extension Service BP-69-W

Caldwell, Brian; et al. 2013 Resource guide for Organic Insect and Disease Management, 2nd Ed.  Cornell University