I have to admit, as a brand new market gardener, the thought of disease striking our plants is a very real fear that I have.

Think of all your hard work and effort put into growing your plants being wiped out in one fell swoop. Definitely not what you want to happen in your market garden.

The good thing is, there are measures that growers can take that can significantly reduce the likelihood of disease rearing its ugly head in your garden.

Pam Dawling, author of Sustainable Market Farming uses three main methods for sustainable disease management in her market garden which we will be exploring in this article.

How Diseases Spread

There are three factors that affect whether or not a disease will take hold.

They are:

• A susceptible host
• The presence of a pathogen
• Suitable environmental conditions

To help hedge your bet against disease, crops can be rotated, disease-resistant varieties of seed can be planted, and planting and harvesting dates can be planned to reduce vulnerability to diseases.

Additionally, soil fertility and crop nutrients can be optimized to provide the best environment for the crop and for beneficial organisms.

Plant pathogens can be soil-borne, foliar-borne, or seed-borne, or a combo of seed-borne with one of the others.

Soil-borne pathogens can live in the soil for decades, so long crop rotations are needed to eliminate them.

Foliar pathogens die in the soil in the absence of host plant debris. Practicing good sanitation (prompt incorporation of plants after the end of the harvest, effective hot composting), good crop rotations, and avoidance of cull piles can help reduce foliar pathogens.

Lettuce mosaic virus is an example of a disease in which the seed is the main source of pathogen. If seed infection is controlled, the disease is prevented.

Other seed-borne pathogens may start life as a foliar or soil-borne pathogen. Infected seeds will produce infected plants even in clean soil.

Pathogens can infect the seed via several routes:

1. The parent plant can become infected by drawing soil pathogens through its roots up the seed.
2. Pathogenic spores can float in the air.
3. Aphids, leafhoppers, thrips, and whiteflies that feed on the plants can vector viruses that become seed-borne 10% of the time.
4. Insects that pollinate the plant can bring infected pollen from diseases plants.

Methods of Sustainable Disease Management

These are three methods of disease management that Pam Dawling uses in her market garden.

Biointensive Integrated Pest Management (IPM)

The basis of IPM in bio-intensive systems involves a pro-plant, rather than anti-problem, approach to creating healthy plants and soil.

Vigorous plants are better able to withstand damage. 

The aim is to prevent disease organisms from finding the crops, keep damage to a minimum, pay attention to what is happening, and control diseases by the least ecologically damaging method.

This approach is site-specific and must be adapted to each crop and situation.

The sequence of steps is basically: prevent problems, monitor for problems, and if needed, treat problems.

1. Cultural Controls

Focus on proactive (preventative) strategies, starting at the planning stages, to minimize opportunities for diseases to become a problem.

Restore and maintain vibrant health in your crops. Increase biodiversity to provide greater ability.

Preventative actions to take:

• Apply good compost and maintain healthy, biologically active soils
• Use rotations to minimize disease and improve the environment for natural enemies of diseases
• Practice good sanitation of tools, plants, and shoes
• Optimize nutrients, moisture, and planting for crop vigor
• Enhance natural disease control strategies, such as providing good airflow
• Use mulches to reduce splashback from soil to plants
• Use drip irrigation to reduce moisture on foliage
• Plant locally adapted, resistant varieties
• Use farmscaping to encourage beneficial insects
• Time plantings to avoid peak periods of certain diseases
• Practice good soil management (eg. timing of tillage) to preserve maximum diversity of microorganisms

2. Monitor Crops For Problems

It’s a good practice to make a regular tour of your crops at least once a week to monitor growth and health.

J.M. Fortier and his wife take daily walks of their market garden every morning. 

If you notice a problem, you can take a mental picture, or real picture with your phone and consult a variety of resources to identify the problem.

Resources include:

• Cooperative Extension Service, part of the USDA
• Various websites (Google it!)
• Books

Here is a helpful phrase to help with preliminary identification:

“Fungi are fuzzy, viruses are mottled, bacteria are slimy.”

It’s important to keep good record keeping so that you may be able to prevent the disease from appearing in subsequent years by fine-tuning your bio-intensive IPM.

3. When Control Measures Are Needed

When this is the only way to deal with an outbreak, use the least toxic materials and the least ecologically disruptive methods. 

Physical Controls

Including:

• removing diseased plant parts
• protecting vulnerable plants with row covers
• mulching to isolate plant foliage from the soil
• tool and shoe sanitation
• soap washes for foliage
• hot water or bleach seed treatments
• soil solarization to kill disease spores

These are all methods that reduce problems without adding any new substances into the mix.

Biological Controls

Beneficial animals and insects are more common in insect pest reduction than in disease control, but the use of milk as a fungicide qualifies as a biological control.

Plants in danger of developing powdery mildew can be sprayed weekly with a mix of one part milk with four parts water.

When exposed to sunlight, this is effective against the development of fungal diseases.

Microbial Controls

Homemade microbial remedies employ liquids (simple watery extracts and fermented teas) made from compost.

For example, one part of mature compost mixed with six parts of water. Let it soak one week, then drain and dilute to the colour of weak black tea.

Fermented compost tea can deal with many maladies.

Check out ATTRA or Soil Foodweb site for how to make fermented compost teas.

Botanical Controls

Using plant-based products to reduce disease.

Neem oil as well as being a pesticide forms a barrier on foliage that prevents some fungal diseases from establishing. It degrades in UV light in 4 to 8 days must be reapplied if the disease organisms are still around.

Like all broad-spectrum insecticides, neem oil can kill beneficial organisms as well as pests. So caution is needed if it is used.

Garlic can be used against fungal diseases. Blend two whole bulbs of garlic in one quart (litre) of water with a few drops of liquid soap. Strain and refrigerate.

For prevention, dilute 1:10 with water before spraying. For control, use full strength.

Kelp sprays are also used to generally boost the resistance of plants to pest, disease, and weather related problems.

Inorganic Controls

These include bicarbonates, oils and soaps, and copper and sulfur products.

Several of these need to be used with caution if the plants and the planet are to survive the treatment. Further details below.

Reduction of Diseases by Maintaining Healthy Soils

Management of soil-borne diseases focuses on making the soil environment less welcoming to pathogens.

Soil-borne diseases are the result of a lack of biodiversity of soil microorganisms. Restoring beneficial organisms can make the soil disease suppressive.

Compost is a food source for beneficial microorganisms and encourages a more diverse soil population.

Mature compost can reduce resistance in plants by acting as a source of weak pathogens.

The plants develop a response to the pathogens and are ‘vaccinated’ against stronger pathogens.

Compost can be made more disease suppressant in three ways:

1. Ensuring the compost is properly measured before applying it.
2. Incorporating the compost in the soil several months before planting.
3. Inoculating the compost with specific biocontrol agents, such as Trichoderma species of Flavobacterium balustinium.

Beneficial organisms introduced via the compost have a better chance of thriving and being effective in the soil than they do if they are introduced directly to the soil, where there may not be suitable food or a congenial environment.

Plant roots may be protected from disease organisms by symbiotic associations with mycorrhizal fungi, which physically cover roots with a fungal net, produce antibiotics, and other compounds toxic to pathogens, and increase the supply of nutrients to the plant.

Mycorrhizal fungi may already be present in biologically active soils and are also available commercially.

They may be used as a seed dressing, or added to growing plants, to improve yields and frow healthier plants.

Symbiotic bacteria can also release nutrients to plant roots.

Crop rotation can reduce the chance of some diseases but will not prevent diseases that blow in on the wind, are brought in by flying insects, or arrive with infected seeds or dirty tools.

Crop rotations are most effective for soil-borne diseases that survive five or fewer years without host plants. Examples are root rots of beans and peas, blackleg and black rot of brassicas, parsnip root canker, and sweet potato scurf.

Damping-off in seedlings can be reduced by inoculating the growing mix with 1-4% fish emulsion, 28 days before sowing seeds. The fish emulsion produces a biological environment that suppresses disease.

Hot Water and Bleach Seed Treatments

Hot water or bleach seed treatments are most easily done immediately before sowing the seed, as this removes any need to dry the seed.

Hot water treatment destroys seed-borne fungi and bacteria.

Method:

1. Put the seed into a small cloth bag or tea strainer
2. Warm it
3. Soak seed at 122-125 degrees Fahrenheit (50-52 degrees Celsius) for twenty to twenty-five minutes
4. Use a thermometer and nearby supplies of hot and cold water to regulate the temperature
5. At the end of the time plunge the hot seeds into cold water
6. Drain and dry on a paper towel

Fresh seed withstands heat treatment better than 1-2-year old seed.

Bleach treatment kills pathogens on the seed surface only.

Method:

1. For one pound of seed, make one gallon (4L) of a solution of commercial bleach in water with 24oz/gallon
2. Put the seed in a cloth bag
3. Submerse it in solution
4. Agitate continuously for 40 mins.
5. Rinse under running water for 5 mins.
6. Dry

This process can stimulate germination so use the seed within three weeks of treatment, or risk reduced germination later.

For more detailed information on seed treatments, check out the Cornell Extension website.

Soil Solarization

This is a very effective way to control soil-borne diseases and pests.

It involves taking a patch of land out of production in the height of summer and using solar heating through clear polyethylene to cook the top layers of the soil.

Method:

1. Water thoroughly, or run drip tape over the surface to keep the soil continuously damp.
2. Cover the soil tightly with clear plastic.
3. Bury the edges so that hot air does not escape.
4. Keep plastic on for a minimum of 6 weeks, 8 or more is preferable

Biorational Disease Controls

Several leaf spot diseases and powdery mildew, caused by several species of fungus, can be controlled using inexpensive materials you likely already have or that are cheap and easy to buy.

To prevent the fungi from building up resistance to any one remedy, spray only once a week and rotate remedies.

An example of a simple remedy is:

One teaspoon baking soda in one quart (litre) of water, with a few drops of liquid soap as a spreader-sticker.

Other materials you can use include:

• Hydrogen peroxide
• Sulfur
• Copper fungicides

You can use microbial controls to help control disease as well, including:

Ampelomyces quisqualis: a parasitic fungus effective in preventing (not curing) powdery mildew.

Bacillus pumilus: tackles powdery mildew and downy mildew.

Coniothyrium minitans: fungus tackles the lettuce drop fungi.

These are just a few microbial controls you can use to help control disease spread in your market garden.

Bottom Line

As with most tasks on your market garden, planning, organizing, and record-keeping are keys to success. Effective disease management is not different.

Prevention is the name of the game here. When you are planning out your beds for the season, include disease prevention measures as well, such as rich compost, effective crop rotation, and seed sterilization.

Our plan as new market gardeners is to take our time, educate ourselves, and plan as best as we can. We know that incidents will pop up that we did not plan for, we just have to accept that and adapt. 

Good record keeping is also going to be very important so we can improve our methods for future seasons.

How do you keep diseases at bay in your market garden? Please let us know in the comments below.

Stay Local,

Kathy & Jon

your friendly neighbourhood growers