Chemical Controls for Powdery Mildew

Some of our past posts have looked at cultural and biological controls for powdery mildew. These, along with Greencure, are all typically approved for use in certified organic agriculture.

Now, it’s time to talk dirty. So, get out your PPE (personal protective equipment), take a deep breath, and prepare to kill some bacteria and fungi…

Synthetic chemical fungi killers come last in this series because, ideally, they are a last resort. While undeniably useful components in an integrated disease management plan, they should not be relied upon as a substitute for good gardening practices.

You may be familiar with foggers or “bug bombs” for pests like spider mites. They also exist for fungal diseases. Fungaflor TR‘s active ingredient is Imazalil. TR stands for total release. Once you trigger the fogger, the entire contents of the canister are emptied. One small two ounce fogger treats up to 1,500 square feet (1,000 square feet for powdery mildew). As with other bombs, thoroughly read and follow all directions on the label. The fog is flammable so make sure there aren’t any open combustion sources, like a pilot light. Once the treatment is over, ensure ventilation has completely removed the product from the space prior to reentry. We recommend airing out your grow space for a minimum of 24 hours to protect you and your pets from the harmful fumes.

Fungi bombs work very well as a preventative measure when preparing a new garden or to treat a space that previously contained pathogenic spores. Foggers provide excellent coverage over a large area and won’t leave residue behind, as burning sulfur tends to do.

Use with Caution

While Fungiflor can be used in a garden while plants are in it,  be careful. Do not trigger a bomb too close to your plants or they may be cause damage. In the Keys to Success listed by the maker of the product, it says to “clear out a three-foot area around the canister to prep for application”. Remember, one small can is intended to treat 1,000-1,500 square feet which is larger than many indoor gardens. If used in too small of a space, the increased concentration could also cause damage to your plants.

Eagle 20EW  is effective and, therefore, popular with many gardeners. The active ingredient is Myclobutanil. Eagle 20EW acts as a systemic with a residual presence in the plant. For this reason, treating a plant once or twice in its vegetative stage is often sufficient enough to successfully suppress powdery mildew. This is also the reason to avoid treating plants with it during the latter stages of growth.

Eagle 20EW can be used as a preventative treatment when introducing new plants to your garden from outside gardens. It can also be an effective knockdown treatment when other options have failed to break the pathogenic cycle. That being said, it should not be overused. Science has proved that overuse of fungicides, like Eagle 20EW, can result in some fungi becoming resistant to them. For this reason, the product label recommends alternating it with other products after two consecutive uses.

Do Your Homework & Use Caution

Carefully read the label/instructions prior to using the product. Since you shouldn’t require too many applications for the life-cycle of a plant, make them count by combining Eagle 20EW with a surfactant (like Coco Wet or Humboldt Sticky) to maximize plant coverage and keep it in place. If plant size permits, consider mixing enough solution to dunk the entire plant in order to guarantee complete coverage.

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