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Hibiscus Plants

Q.Question For Mary Dyer Based On Her Article On “How To Use Copper Fungicides In Gardens”.

Zone Anthem, AZ 85086 | baum00 added on June 22, 2021 | Answered

I live in the Phoenix, Arizona metro area and have been plagued by “Black Spot” fungus on my “Hibiscus” flowering plant and “Snail Vine” (Cohliasanthus Caracalla, a Leguminous Vine) in my back yard garden. For the past few weeks locally, we have been suffering daily through 115+ temperatures even though on the calendar it was technically still Spring. This fungus attacks the Snail Vine leaves very aggressively and literally destroys them within a matter of days. The Hibiscus leaves end up drying out and turning yellow at a slower but still progressive rate. After trying and totally failing with Ferti-lome’s liquid Systemic Fungicide and then Neem Oil, Bonide’s liquid Copper Fungicide RTS showed some better degree of effectiveness. In your subject article, you write that I need to wait 7 to 10 days before reapplying the Copper Fungicide. Why? What will happen to the leaves if I reapplied at a shorter frequency (perhaps even the following day)? You state that your concern is that the fungicide will “Degrade”. I am concerned that that my plants won’t survive the fungus attack without another interim “booster shot” of fungicide “medicine”. You also write “Never apply copper fungicide on very hot days” (well, “Hot” weather is what you are used to in your local geographic area) but varying degrees of “Hot” temperatures appears to be all we have here in Phoenix’s so-called “Valley-of-the-Sun” for half the year. So, what am I supposed to do wait until Winter time – everything will be long gone and dead by then! You write “Never over-apply fungicides” (how much, specifically, is “over-applying” and what, specifically is your prediction as to the probability of the outcome if I didn’t adhere to the “7 to 10 day rule” and “over applied” on a more frequent schedule? You write “Never mix copper fungicide with other chemicals” Not having read your article at the time, I applied that Neem Oil spray the next day after spraying with Bonide’s Copper Fungicide (under the thinking that it would “complete” the job of totally curing the plant from the fungus) and all I achieved was to make it a lot worse with many more leaves turning yellow than the day before’s application of Copper Fungicide. Please help before it is too late. Thank you.

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Certified GKH Gardening Expert
Answered on June 22, 2021

She does not answer questions, here, but I can do my best to help you.

Unfortunately, it sounds like there were too many "mistakes" made prior to finding the article.

In your area, it is common to see infections from overwatering. Many people make the mistake of watering too much in compensation for the heat, rather than choosing plants that are suited for their environment. When this happens, pathogens get introduced to the area.

Black spot is, particularly, aggressive. It can only be controlled once established. Curing is relatively difficult. Though, in your area, using native species and not watering at all would probably rid the area of disease, permanently.

Now, Let's address a few things.

Neem oil is a very poor choice for your area. It will burn, just about, any plant while in direct sun. Add heat, and that is a recipe for a plant's death. Azadirachtin would have been a better choice. This is the active ingredient in Neem oil, and it will not burn plants.


As for overlapping fungicides- That will leave the soil a toxic mess, as the ingredients within each fungicide bind together to form, unintended, chemicals. (Some of these chemicals are highly illegal to release into the water shed, and doing so can land you in some trouble) Waiting the full rest period according to the instructions will be necessary to let the products degrade in the soil. For, very obvious, reasons- It is important to wait this long so that the soil does not become toxic from overlap, as well as so that the fungicide does not lose efficacy.

Other questions can be answered by reading all instructions on the fungicide of your choice, VERY CAREFULLY, as all of these questions are answered within the included pamphlet on each fungicide bottle.

Otherwise, it is important to keep your soil healthy, rather than having to treat when it is sick.

Keeping soil healthy includes proper beneficial microbe content, proper watering, and proper disease management at the first signs of illness.

Here are some more articles that will help:








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