GreenCure Organic Fungicide: Product Review


It’s easy to scoop powder out of the wide-mouthed tub using the provided measuring scoop.

Do you battle black spot on your roses? Powdery mildew on phlox and squash? I’m sure you’ve tried all sorts of fungicides to eliminate the problem, possibly even resorting to some of the more toxic chemicals to get the job done. Personally, I’ve occasionally used Immunox and the commercial fungicide Eagle to save my roses from complete defoliation, but I’ve never liked using chemicals. And now I don’t have to.

GreenCure Kills Fungus

Once your plants are infected with a fungus, such as black spot, downy mildew, anthracnose, rust, or powdery mildew, it’s difficult to prevent it from spreading throughout the entire plant. Given the right conditions (cool, humid weather or frequent light rain), complete coverage of the plant with ugly, fuzzy or dark spots or defoliation of the plant as the infected leaves die, is almost a given.

GreenCure has been shown to kill the mold spores that result in common garden fungus. It doesn’t just control the spread of the fungus, it actually kills it. You can find details about the research behind this on the GreenCure website.

We tried GreenCure in two common and difficult situations; roses that were heavily infested with black spot, and garden phlox covered in powdery mildew. We reasoned that if GreenCure really worked, it would stop the fungus dead in its tracks and any new growth would be fungus-free.

To test that theory, we mixed 1 tablespoon of GreenCure in ½ gallon of water and applied it using a pump sprayer. We were careful to fully cover both the top and underside of all leaves, as well as the stem and branches. This treatment was repeated after 2 weeks and again 10 days later.

Black spot on roses

We tested GreenCure on roses covered in black spot.

So, did it work??

The answer is a resounding “Yes!”

The rose leaves that had been hit hard by black spot eventually died, but all of the new growth was healthy – not a single spot. Normally, all my susceptible roses that haven’t been sprayed are totally defoliated by this time of year (I mostly grow disease-resistant varieties that don’t need spraying, but some of my old favorites, like Zephrine Drouhin, are black spot magnets). The same result was found with the phlox; there was no evidence of additional powdery mildew after spraying with GreenCure.

GreenCure fungicide stops black spot in roses

After just one application, new growth showed no signs of black spot. With continued application, the leaves stayed healthy.

All in all, GreenCure worked as well or better than the heavy-duty fungicides I’ve used in the past.

GreenCure is Organic

What sets GreenCure apart from other fungicides is that it’s organic. The key ingredient is potassium bicarbonate, a material that’s used in food and is deemed safe by the FDA. The fungicide also is registered “For Organic Production” with the USDA’s National Organic Program (NOP).

GreenCure is Safe

In fact, GreenCure is so safe that you can harvest and eat sprayed fruit and vegetables as little as one hour after spraying. Furthermore, research by Dr. Ken Horst at Cornell University shows that it does not have a negative impact on honeybees or other beneficial insects. Don’t be alarmed by the EPA warnings on the label – these are required for all fungicides and are good precautions to take whenever you’re working with chemicals of any kind, even those that are considered safe.

Easy to Apply

All you do is mix the powdered GreenCure with water.There’s no need to add anything to help the spray adhere or spread on leaf surfaces – that’s already included.

There’s a handy measuring scoop already in the tub; just measure one or more scoops into a spray bottle or tank, add water, and you’re ready to spray. One gallon of water with one scoop of GreenCure will cover about 450 square feet – that’s a lot of plants! Don’t use a hose-end sprayer as you won’t get a good mix in the right proportions.


5-shovelsWe give GreenCure a 5-shovel rating. It is highly effective, safe to use, and a welcome addition to an organic gardener’s disease-fighting toolkit.

Where to Buy It

GreenCure can be purchased in many independent hardware stores and garden centers (check the GreenCure website for a location near you), through a variety of online outlets, and an 8 oz tub of GreenCure Fungicide on Amazon. The 8 ounce tub can be used to make up to 16 gallons of fungicide; it also comes in a larger 40 ounce tub.

Did You Know?

Fungi are host-specific. This means that a specific type of fungus will only attack a specific plant. So, for example, the powdery mildew covering your garden phlox won’t attack your zinnias, squash, or apple tree.

Disclaimer: We received a free 8oz tub of GreenCure to test and review for the Gardening Products Review. There was no expectation that it would be a positive review, and we received no compensation for writing the review.

Please note that the Amazon link above is an Amazon affiliate link. Should you choose to purchase GreenCure products through this link, GPR will make a small commission (at no extra cost to you) that helps to support this website and our gardening product reviews. Thank you!