009-Organic Disease Control with Jeff Gillman

| Care, Podcast

When it comes to maintaining a healthy garden, organic disease control comes down to a few main options.


Jeff Gillman, Ph.D. dishes out the details on organic disease control with Joe Lamp’l during the taping of an episode of Growing a Greener World.


In this podcast episode, we close out our 3-part series with Dr. Jeff Gilman. This time, we’re discussing the most common steps anyone can take towards organic disease control for creating and keeping a healthier garden.

Maintaining the healthiest growing environment, from what you plant where, and focusing on the soil health where your plants will live, has more to do with organic disease control and the growing success of your plants than anything else you can do.


Of all the time I spend in the garden, most of it is investing in building soil health. I add lots of compost. Healthy soil equals healthy plants which are more resistant to pest and diseases.


Besides focusing on building the health of your soil, space your plants in the ground, so they have plenty of sunlight and air circulation. That alone will also go a long way in reducing the opportunity for diseases to thrive.



Without a doubt, I know my plants are healthier because I use drip irrigation and soaker hoses to keep water in the soil and off the foliage. When connected to portable timers I can fine-tune the irrigation requirements of my plants – not too much, not too little and in just the right place.

Right out of the gate, Jeff points to proper watering as one of the best methods for organic disease control. His advice – not too much, not too little, and in just the right place. Where we water is important. Generally, it’s a bad idea to water the leaves. However, there is one exception: powdery mildew. You can control (not prevent) powdery mildew with water (or any liquid). But don’t use water to fight disease issues over all because it leads to many problems.

Another tip Jeff offers is to get rid of diseased plants. He believes the best way to reduce the risks of diseases spreading in your garden is to get rid of the entire plant.

It’s certainly a quick fix to the option I usually take of pruning all infected parts of a plant showing problems. But that requires many potential return visits and a lot more pruning work.
Either way, the key is being proactive and taking out everything you need to get the problem plants or plant parts out of the garden, so they don’t have a chance of spreading.

Use controls that are safer. Even among organics, there are controls that are safer than others.

One of Jeff’s favorite organic disease controls is sulfur. While its use in the garden is a fungicide, it’s not the most effective. But it is very safe. For that reason alone, this is his go-to choice for fungus control on plants.

Jeff also has least favorite organic controls: Bordeaux mix and copper products. Copper is a general killer that makes it hard to justify using since it is so broad spectrum. Plus, copper never breaks down in the soil. Although approved for organic production, the excess use can build up and lead to issues that impact plant growth and human health.


Powdery mildew is a disease that affects many plants. It’s also the one disease that is mitigated by wetting the foliage. Mixed with milk and treat before the problem starts provides an effective organic control.


Powdery Mildew control: 1-part milk to 2-parts water. Apply 1-time per week or 1-time every other week as a control. Black spot on roses is one of the most effective applications.

Milk sprays will slow down or prevent spreading but will not cure the disease. Very few or any organic controls will cure the disease. With milk, you need to apply it before you even have the disease for it to be effective.

Another time-tested organic disease control is crop rotation. Diseases that live and persist in the soil only survive for 2 or 3 years if no host plant has been provided. So to eliminate the risk of a recurring problem in following seasons, don’t put plants from the same family back in that same soil for three seasons or more.

For rapid control or soil diseases living near the surface, solarization can be an effective solution. Placing clear plastic for several weeks over the soil will kill microbes. Once removed, new beneficial microbes will move in to repopulate the soil.

Another contributor to disease issues in the garden is due to over or under fertilizing. Finding a healthy balance with a focus building soil health naturally is the best option.

Finally, good air circulation is key to fewer diseases. Creating the opportunity for more light and air around plants is very important to minimizing disease risks. Wherever air stagnates is a place where disease can take hold.


I attribute my organic disease control success to stay ever-vigilant and proactive (vs. reactive) in my garden. It makes a world of difference.


My Methods of Disease Control:

While the following steps are critical to a healthy organic garden, being proactive in your garden and ever-vigilant in looking for subtle changes in your plants will be the best thing you can ever do to prevent any pest or disease-related problem for getting out of control.

  1. Start off with healthy soil. The more you can do to feed the soil, the better. Microorganisms you’ll have there to help fight the bad guys.
  2. Site plants properly. Right plant right place. A happy plant is a healthy plant. Unhappy plants are more prone to pests and diseases.
  3.  Never add a plant that shows signs of disease, to begin with. Never introduce a diseased plant into your garden. When it doubt, keep it out. Wait to find clean plants even if you must go elsewhere to get them.
  4. Add mulch to the soil. It provides a protective barrier from soil borne diseases splashing up onto your foliage
  5. Set up proper watering protocols. How and when you do has everything to do with keeping weeds at bay. The goal is to minimize the amount of time the foliage stays wet. Micromanage that with drip irrigation or soaker hoses connected to a portable battery operated timer. It focuses the water exactly where you want while keeping water away from feeding the weeds.

Links & Resources:

Episode 002: Five Steps to Your Best Garden Ever

Episode 007: Organic Weed Control

Episode 008: Organic Pest Control

The Truth About Organic Gardening book by Jeff Gillman

The Truth About Garden Remedies book by Jeff Gillman

Episode 314 of Growing a Greener World – Just Because It’s Organic, featuring Jeff Gillman

Episode 419 of Growing a Greener World – Garden Myths, featuring Jeff Gillman

Milorganite: Our podcast episode sponsor and Brand Partner of joe gardener®

About Joe Lamp'l

Joe Lamp’l is the creator and “joe” behind joe gardener®. His lifetime passion and devotion to all things horticulture has led him to a long-time career as one of the country’s most recognized and trusted personalities in organic gardening and sustainability. That is most evident in his role as host and creator of Emmy Award-winning Growing a Greener World®, a national green-living lifestyle series on PBS currently broadcasting in its tenth season. When he’s not working in his large, raised bed vegetable garden, he’s likely planting or digging something up, or spending time with his family on their organic farm just north of Atlanta, GA.

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