Organic Garden Disease Control

squash leaf with fungal disease

Just as the weather starts to warm up for the summer, fungi, blights and other plant diseases can take hold in your garden and quickly wipe out your crops. This is especially true in parts of the country that are humid, since moist air contributes to the spread of many garden ailments.

Your first and best line of defense against all garden diseases is proper cultivation habits.

Prevent Disease with Smart Gardening Practices

  • Choose pest and disease-resistant plant and seed varieties, especially if you live in an area where particular diseases are common.
  • Give plants well-drained soil so they are less likely to fall victim to fungus and rot diseases.
  • Put plants in their proper place and microclimate within your garden. Place sun-loving plants in the sun and shade-loving plants in the shade. Grow cool-loving crops in spring and fall, and heat-loving crops during the summer.
  • Know the lifecycle of the pests in your region, which can enable you to plant crops during months when they are inactive. For example, late plantings of cucumber are less bothered by spotted cucumber beetle (which carries powdery mildew disease) than earlier ones.
  • Give plants the space they need to stretch and grow to maturity. Good air circulation around plants can help prevent disease.
  • Instead of planting in thin rows, try wide-row beds or square-foot gardening. Thin rows look like runways to insect pests. Clustered plants are healthier and less attractive to pests.
  • Sterilize your pruning and cutting tools with alcohol or boiling water after each plant, just as you would do with surgical tools after each patient.
  • Water the soil, not the plant. Avoid working near plants that have wet leaves because diseases are often spread through water droplets. Better yet, use a drip irrigation system to deliver just enough water right into the root zone.
  • Mulch the soil well to protect plants from drought and to keep disease spores and soil from splashing up on to your plants.
  • At the end of the season, clean up and compost any garden refuse that might harbor pests or disease over the winter. If you cannot make a hot compost pile that will be capable of killing pests and diseases, then place any diseased or infested plants in the garbage away from the garden.
  • Use a foliar feed made from kelp, compost tea or sea minerals once a month to boost your plants’ immune systems against disease. (Yes, the probiotics present in ferments work on plants too!)
  • To protect plants from flying insects (which can carry disease), cover your garden beds with lightweight fabric covers made either from repurposed sheer curtains or agricultural fabric bought from a garden supply store. This is very powerful pest control, but you will need to check your plants often because a few critters will make it under the fabric. If your crop is bee-dependent, take the covers off during flowering.
  • Make or buy yellow sticky traps to catch aphids, white flies, fungus gnats and other disease-carrying garden pests.

How to Properly Spray Plants

organic garden disease control
Powdery Mildew on Pumpkin Leaves

If cultivation habits and fabric covers can’t handle your disease problem, you can call on both store-bought and homemade organic remedies to help you out.

Most pest control sprays—even natural, organic ones—can also harm bees, butterflies and other beneficial insects, so be very careful when applying any pest control remedy to your plants.

Here are five key rules to remember when spraying plants with anything:

  1. If you are going to apply a treatment to the leaves of a sick plant, apply it to just one leaf to test for sensitivity. Wait 24 hours, and if the leaf does not appear harmed by the spray, apply it to all parts of the plant, especially the underside of the leaves where pests like to hide.
  2. It is best to spray first thing in the morning before the sun gets strong and the humidity rises. Never spray plants if its hotter than 90 degrees F. If you have many bees in your garden, spray away from them, or wait until evening.
  3. Don’t apply sprays in windy or rainy weather, for obvious reasons. You will have to reapply any treatments after a rain.
  4. Be sure to wear protective clothing, goggles and dust mask when spraying any kind of pest control. Even garlic spray can be harmful if it blows back into your face.
  5. Most natural or homemade pest control sprays only last about a week, so make them in small batches.

Best Store-Bought Organic Disease Controls

There are many very effective disease controls available on the market for organic gardeners. These four are tried and true for me.

Mycorrhizae-Based Fertilizer – Made from kelp and other plants, this probiotic-rich formula energizes soil biota and boosts your plants’ immune systems against pest and disease attacks.

Fabric Insect Barriers – Summer-weight agricultural fabric is super-light, and can be cut and pinned down to protect your wide row beds from flying insects, which are often vectors for plant diseases.   They don’t make the garden look very nice, but nothing else keeps the bugs off—and therefore the diseases at bay—like agricultural fabric barriers. Be sure to lift them when your crops have flowers that need pollination!

Garden Sentinel Biofungicide – This is a preventative, broad-spectrum treatment for both fungal and bacterial diseases in vegetables, ornamentals, fruit trees, shrubs, flowers, bedding plants, potted ornamental plants and lawns. Instead of harsh chemicals like sulfur, this product uses naturally-occurring probiotic bacteria called Bacillus amyloliquefaciens,

Yellow Sticky Traps – These protect your plants from small flying insects that feed on their roots and leaves, like fungus gnats, whiteflies, leafminers, aphids, thrips, and other small flying insects that cause damage to your plants and can spread disease. And they come in cute, butterfly shapes!

DIY Garden Disease Control

If your disease problems are minimal, or if you prefer to make your own disease prevention formulas, here are two of my favorite recipes for homemade, organic garden disease control:

squash leaf with fungal disease
4.75 from 4 votes

Extra Strong Disease Prevention Spray

This disease fighting spray for your organic garden also treats soft-bodied, sucking insects like aphids.
Makes1 gallon
Prep Time 15 minutes
Steeping Time 2 days
Total Time 2 days 15 minutes
This recipe may contain affiliate links. As an Amazon Associate I earn from qualifying purchases.



  • In a small glass jar, cover the minced garlic with the oil and let sit for 24-48 hours.
  • Strain the oil and save aside 2 Tablespoons for the rest of the recipe.
  • Save the rest of the garlic oil in the jar for future use. It lasts indefinitely in the fridge. (Clearly mark the jar and lid with “Do Not Eat” if you put it in the fridge!)
  • In a bowl, mix the baking soda, insecticidal soap, and 2 Tbsp. garlic oil with 1 cup of water.
  • Add the vinegar. Don’t mix the vinegar until last or the mixture may bubble over.
  • Stir molasses into a gallon of warm water until thoroughly mixed. Add kelp or fish emulsion.
  • Pour the molasses and water mixture into a one-gallon garden sprayer, and then add the baking soda mixture.
  • Shake or stir to combine ingredients.
  • Spray plants as needed, in the early morning or late evening, covering the tops and undersides of leaves.

You Might Also Need:

Horsetail Fights Fungus

Horsetail – Equisetum arvensis

Horsetail plants (Equisetum arvensis) are some of the oldest plants in the world, and can be found throughout North America, where they are often considered an invasive weed.

They look like tiny Christmas trees, and are sometimes called “shavegrass” or “meadow pines,” although they are not related to pine trees at all. Horsetail plants are toxic to livestock.

Wild horsetail is high in silica and sulfur—natural insect and disease fighters that can help you beat fungi, mildews and rusts on your garden plants.

squash leaf with fungal disease
5 from 1 vote

Foolproof Fungus Fighter

This remedy based on horsetail plants is great for treating fungal and mildew diseases in your organic garden.
Makes5 gallons
Prep Time 15 minutes
Steeping Time 1 day
Cook Time 1 hour
Total Time 1 day 1 hour 15 minutes
This recipe may contain affiliate links. As an Amazon Associate I earn from qualifying purchases.



  • Bring horsetail leaves to a boil in the gallon of water, then let simmer for one hour.
  • Let steep and cool overnight.
  • Strain out the horsetail leaves and add 1 teaspoon castile soap to the “tea.”
  • Dilute mixture to 20% or one part mix to 4 parts water in your garden sprayer.
  • Spray weekly as a preventive or curative treatment for fungus and mildew diseases on your plants and trees.