Southern Blight Control for Organic Tomato Growers

Organic tomato growers’ worst nightmare is southern blight brought about by Sclerotium rolfsii. It does well in warm, humid soils, which spread quickly and wreak havoc if not checked early. For organic growers such as myself, the use of chemical fungicides is a no go area, so I began a search for suitable, sustainable, biological alternatives. Southern blight on tomatoes can always be a nightmare, no doubt about that. For that it is necessary to understand southern blight control.

After trials of several cultural and biological approaches for southern blight treatment, I resorted to the wisdom of fellow growers on gardening communities, where many of those had written about disease management. It was while engaging with this community that I came across HarzShield, a Trichoderma based bio-fungicide produced by Novobac, the best organic fungicide for tomatoes, that ended up being excellent at controlling southern blight. In this blog, I’ll share the methods I used in order to control southern blight on my organic farm using HarzShield as a major part of my strategy.

Understanding Southern Blight On Tomatoes and Its Impact

Southern blight disease is a soil borne fungal disease introduced by Sclerotium rolfsii. It is notorious for its high spreading rate especially under high temperatures and under moist conditions. When it appears, at first this disease causes tomato plants to wilt suddenly, usually in mid to late season. Near the bottom of the plant a white fungal growth occurs that is typically of the appearance of a fluffy mold.

One of the most frightening aspects of southern blight is the formation of sclerotia, small mustard seed like bodies that can survive in the soil for years. These sclerotia represent a reservoir for the pathogen which makes it difficult to manage when the disease has become established in a field. Southern blight is a disease that if left unchecked can rapidly creep across to thus infect surrounding plants with extensive destruction and even an entire crop loss. There are however certain plants which are highly sensitive to this disease, tomatoes being at the top on this list with younger plants and those with dense canopies most at risk.

Recognizing Early Signs in the Field

The detection of early indications of southern blight is very important for effective control. The first signs you’ll notice would be yellowing and drooping of the lower leaves. Such symptoms usually mimic nutrient deficiencies or water stress, so you should look for other symptoms.

Shortly after the leaves start yellowing, you will start seeing white mycelium of a webbing shape growing at the base of the stem especially round the soil line. This fungal development is a major alert to infection. As this disease advances, the mycelium develops sclerotia which are themselves small and hard and are round and generally tan or brown. The presence of sclera tells that the disease has been established in the soil.

After infection of the plant, wilting will develop quickly – and the plant may reduce entirely within days. This speedy development emphasizes the need for early control to curb the spreading of southern blight about your crops. Getting to know the early signs and doing southern blight tomato control is a necessity for having good yield.

Insights from the Organic Farming Community for Southern blight control

The organic farming community has a great deal of information concerning disease management and much of it has been invaluable in dealing with southern blight. For example, nice drainage and raised beds will fight the illness by moving water away from the plants’ bases and making them less soggy.

Certain producers suggest using pine bark mulch rather than straw to lower the surrounding soil’s humidity. Though mulching can be helpful in conservation of moisture, it is quite very important to use mulching with a lot of care since too much retention of moisture can cause the development of disease.

Another widely suggested was to use crop rotation. Plantation of tomatoes alongside non-host species such as corn or grasses has the effect of interrupting the disease cycle. The practice avoids soil build up in sclerotia and thus makes it difficult for southern blight to develop in subsequent growing seasons. Also, the application of compost teas that contain beneficial microorganisms is a wonderful method to increase the soil health and enhance general microbial ratios which can naturally inhibit the pathogens such as Sclerotium rolfsii.

At last, Trichoderma harzianum, a beneficial fungus, has attracted attention due to its attention in fighting soil-borne pathogens for southern blight organic treatment. A number of organic farmers campaign for its use because it out-competates dangerous fungus in the soil, hence protecting the tomato roots from any disease.

Traditional Methods and Their Limitations for Southern Blight Treatment

Although a number of conventional organic approaches can control southern blight, all of them have their drawbacks. Soil solarization for instance can effectively eliminate the pathogen load in the soil but is weather dependent and requires warm weather with a few weeks of sunlight to succeed. This makes it suitable in areas with long hot summers only.

Crop rotation is another useful device, but it becomes problematic if lands are scarce, or if the turning points are few in number. In such, the disease pressure can accumulate very fast on the soil, thus making rotation less effective. This is when farmers like me search for biological control of southern blight.

Compost amendments can enhance overall healthiness of the soil, but they do not always have that ability to restrain diseases such as the southern blight. More so, manual removal of infected plants could do little to help, but not to stop the spread of the pathogen through the soil, which is the real problem.

Introducing HarzShield: A Biological Solution, Organic Fungicide for Tomatoes

I started trying out HarzShield- a Trichoderma bio-fungicide developed by Novobac as a solution to add to my organic farming efforts. Trichoderma harzianum, a beneficial soil fungus largely known for its activity against many soil-borne pathogens including Sclerotium rolfsii, is the active ingredient in this organic fungicide for tomato blight.

HarzShield, organic fungicide for tomato blight,  performs by out-competing the dangerous pathogens in the root zone for space and nutrients. It also makes enzymes that digest the walls of the pathogens killing it. In addition, the fungus triggers plant defense and enhances the rhizosphere microbiome, allowing plants to resist future attacks.

One of the major benefits of HarzShield is its full compatibility with organic farming requirements, so the product can be used safely and sustainably by growers, who are searching for the natural ways to control diseases and helps for biological control of southern blight. It is not harmful for soil, beneficial insects and crops in the proximity and once it is applied consistently, protection lasts a long time. This product not only brings an immediate relief but acts prophylactic thus decreasing the chances of future infections.

Application and Observations

I started applying HarzShield as a soil drench at transplanting and reapplied after two weeks for better effect. I also experimented with the use of it together with compost teas in order to speed up colonization of beneficial fungi in the soil.

The results were promising. I noticed better development of the roots; plants had increased their vigour and healthiness. Consequently, the pressure of the disease from southern blight reduced considerably from approximately 30% infection in previous years to less than 5% in the year I applied HarzShield. My yields also improved because the plants kept having better growth throughout the growing season especially during the mid season when apparently the disease is highest.

Preventive Measures for Sustainable Cultivation

In order to maintain a sustainable control over southern blight on tomatoes and other soil borne diseases, I practice a couple of preventive measures. Crop rotation is a part of my disease management plan; I rotate tomatoes with resistant ones such as corn or sorghum, every 3-4 years to eliminate soil pathogens build-up.

I also am very careful about deep watering as always having a wet base of the stems can create perfect grounds for fungus and southern blight treatment. I instead use drip irrigation and exercise proper spacing between the plants preventing accumulation of much humidity around the soil surface through enhanced good air moving around the plants.

I use organic mulches in moderation for southern blight control, taking care not to lock in the excess moisture that will encourage the growth of the fungus. I use HarzShield as a previously bio-fungicide at the onset of every season to control early infections.

Soil health and disease symptom monitoring during the growing cycle is necessary regularly. I keep a close eye on my plants and do something about whatever stress or disease I see as soon as I notice it, so I can nip anything serious in the bud.

This has enabled me not only to cope with southern blight but also create a general health and productivity of the organic tomato crops. Combining biological solutions, such as HarzShield which is organic fungicide for tomatoes, with techniques of traditional organic farming, I have been able to develop a more robust and sustainable farming system that succeeds year-to-year.

Reference: 

• Liu, Bo, Deborah Glenn, and Katrina Buckley. "Trichoderma communities in soils from organic, sustainable, and conventional farms, and their relation with Southern blight of tomato." Soil Biology and Biochemistry 40.5 (2008): 1124-1136.
• Upadhyay, J. P., and A. N. Mukhopadhyay. "Biological control of Sclerotium rolfsii by Trichoderma harzianum in sugarbeet." International Journal of Pest Management 32.3 (1986): 215-220.