Man what a problem. Mildew is attacking the outdoor zucchini now – just like last year. If I don’t get on it it will take out the plants within a few days. There are only a few small spots, but …
Yesterday I made a batch of colloidal silver. Since silver is anti-fungal I figured it couldn’t hurt to try a fogger over the small plants.
I made a canopy with plastic with the fogger underneath and a fan. It didn’t work very well because the fogger wouldn’t produce enough fog to mist all the leaves to deposit the silver. Gave up and used a hand sprayer to apply the mist to the affected leaves. Lets hope.
I’ve been using sulfur on most of the leaves. The problem is that it isn’t a very durable solution because the sulfur gives out. I found this page that provides a pretty good list of solutions – but none of them seem to last very long. I’m wondering if silver in the nutrients will permeate the plant, and provide resistance?… I lifted this list from: http://www.cannabisculture.com/v2/articles/2250.html
AQ10: AQ10 uses a totally new method of fighting powdery mildew, a biofungicide. The active ingredient, Ampelomyces quisqualis, is a fungus that parasitizes the powdery mildew organism. It offers control over a long period of time. (Not Easily Available)
Cinnamite: Cinnamite is an extract of cinnamon used as a miticide which is also effective as a fungicide. It is very easy to use, is effective and has a pleasant cinnamon odor. Studies show it is not harmful to marijuana plants.
Copper: Copper ions inactivate some fungal enzyme systems, killing the mycellium. Copper has been used for over 100 years, and is effective. A few brands of copper based fungicides are Phyton 27, Dexol Copper Bordeaux Mix and Kocide DF. There are many other brands available.
Neem Oil: Neem oil is pressed from the nut of the Indian Neem Tree. It protects against and kills mildew by interfering with respiration and collapsing the cell wall. Some growers claim that plants grow more vigorously when sprayed with dilute neem oil twice a month. There are many brands of neem oil available. Many of them are listed as organic. Here is a resource on neem oil; https://www.peststrategies.com/pest-guides/chemicals/neem-oil/
Plant Shield: Plant Shield contains the organism Trichoderma harzianum strain T-22. This organism attacks fungi and mildews. It is used as a spray or dip. The organism seeks its food and forms a symbiotic relationship with plant roots, which it also protects.
Potassium Bicarbonate: Potassium bicarbonate collapses and desiccates the mildew hyphae. This is a very safe, very effective contact fungicide. Mildew do not develop resistance to it. The potassium in the formula is absorbed by the plant. Two brands are Kaligreen (registered in California) and Armicarb100.
Serenade: Is the fermentation product of a bacterium, bacillus subtillis, that inhibits cell growth of fungi and bacteria. It is very effective and easy to spray on or to use as a dip. It is a contact fungicide that kills only areas that it contacts. A wetting agent or spreader increases total contact.
Sodium Bicarbonate (baking soda): Baking soda leaves an alkaline residue on the leaves. The sodium collapses the powdery mildew cell wall and the alkaline environment discourages growth. Plants have a limited tolerance to sodium, so the residue should be washed off before more is applied. Used at the rate of 1/2 teaspoon per quart of water with a wetting agent.
Sulfur: Elememtal sulfur interferes with mildew cellular respiration. It has been used as a fungicide for more than 100 years. There are small packages available in the baking sections of supermarkets. Been using it. Basically it is holding the mildew in check, but consistent application is really hard with the hand sprayer. On the zukes, the mildew extends up the stem, and getting everything is really hard. Moreover, it only seems to “stall” the mildew growth.
I pruned the zukes so they would have good air flow. That helped some. There is healthy new growth coming up now and the new leaves seem a bit more resistant to mildew. The older, but still young, leaves should have better resistance.
The absence of silica in the hydroponic media versus the in-ground plants, is the probable reason for the delay of mildew in the in-ground plants. Since the ground plants are now affected, silica is unlikely to be effective enough to eliminate the condition.