Why did that fungus kill my zinnias?

Question

It started growing about a month ago. I don't believe in using pesticides, so I didn't do anything to stop it. It finally killed the smaller plants, and is on its way to getting the larger ones.

What could I have done to prevent this? I grew zinnias last year (in the same spot) and they lasted a long time, without fungus.

Answer 1

From reading your question, I understand that you need two things. First, let’s determine the problem. Two, you don't like pesticides and you want to know how you could have prevented this problem without the use of pesticides.


PROBLEM: Zinnias can be affected by any number of fungal and bacterial pathogens. Though powdery mildew is common, so is Botrytis (gray mold) & Alternaria blight. Other pathogens we should consider are root and stem rots & bacterial leaf spots. Following is a brief description of the symptoms and signs for each disease. This list should aid you in determining your problem. No valid solution should ever be proposed without first identifying the causal agent.

POWDERY MILDEW: A white to light gray powder on the upper surface of the leaf. This powder is easily rubbed off with your fingers. http://www.ppdl.purdue.edu/PPDL/images/powdery_mildew-zinnia.jpeg

BOTRYTIS: A tan to gray, fuzzy mold. http://chatham.ces.ncsu.edu/growingsmallfarms/problemzinnia.html

ALTERNARIA BLIGHT: Reddish brown spots with grayish centers; round at first, then becoming irregular in shape. http://www.ces.ncsu.edu/chatham/ag/SustAg/zinnialeafspot.html

ROOT & STEM ROTS: Spots appear on the stem near the soil level or on roots; plants wilt & die. Sorry, no picture.

BACTERIA LEAF SPOT: Small brown spots surrounded by a yellow halo appear on the leaves. Bacterial leaf spot in on the right (Alternaria blight is on the left): http://www.mobot.org/gardeninghelp/images/Pests/Pest141.jpg


CONTROL: Now let’s talk about resolution. This is your second year planting zinnias in the same spot. You need to do good fall clean-up. Remove all old zinnia stems and leaves. This is where the fungal inoculum overwinters. Improve air flow around & through your zinnias. Do not plant as dense a stand of zinnias. At the first sign of a disease, remove the affected material from you zinnia’s garden bed. Burn, bury (at least 12” below ground) or discard this material in the trash. DO NOT let it multiply and spread. Do not work in the garden when leaves are wet, you spread the disease this way. Do not overhead water your zinnias. Water in the morning so soils have a chance to dry out before the evening.

POWDERY MILDEW: Plant mildew resistant varieties. Improve the drainage of your garden soil. Do not water late in the day so that the area is moist at night. Spray a mix of skim milk (1 part) and water (9 parts) every 7-14 days when weather favors powdery mildew formation (cool & humid). Baking soda works buts it’s a mess to mix. Potassium bicarbonate is safe, non-toxic and an organic bicarbonate like baking soda that you can purchase (Kaligreen).

BOTRYTIS: Like powdery mildew, botrytis is a disease of humid conditions, so improve the drainage of your garden soil. Do not water late in the day so that the area is moist at night. Remove infected leaves. Most fungicides that control botrytis will affect the blooms of zinnia; therefore, sanitation is your best control. Remove infected leaves and flower buds.

ALTERNARIA BLIGHT: Do not plant zinnias in the same spot year after year if you have Alternaria blight. Plant disease resistant varieties. Treat seeds in 125 degree water for 30 minutes, let cool and dry before sowing. Fungicides can be use to prevent.

ROOT & STEM ROTS: Improve the drainage of your garden soil. Do not use heavy layers of organic mulch. Do not keep soils excessively wet. Do not pile soil onto the stems. Avoid crowding plants. Make sure plants have balanced nutrient levels. Remove affected plants.

BACTERIA LEAF SPOT: Plant known bacteria free plants/seeds. Mulch to prevent rain water splashing. Do not overhead water. Water early in the morning. Remove infected plants.

Jim (AWLG)

Answer 2

Zinnia Leaves

Answer 3

Do you mean a black fungus or a white powdery mildew (looks like someone dusted the leaves with baby powder)?

You can get fungicides at better nurseries that are made out of neem oil (it's organic). At the first sign of infestation, spray the oil on (it comes in a spray bottle) to soak the leaves. For white powdery mildew, use a strong, fine spray of water (not so strong that it damages the plant) to wash the white powder off before applying the neem oil spray. You may have to reapply the spray every week or so. But, it should control the problem.

Also, before you replant anything in the affected area, remove all ground covering, mulch, leaves, etc., from the area. The fungus and mildew spores are still present and they can get blown up onto your plants. Scrape it all away, put it in a trash bag, and throw it in the garbage.

Answer 4

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Answer 5

You answered your own question. Are you talking about powdery mildew? (gray fuzzy fungus on leaves). This is what happens when conditions are right and when you don't believe in using fungicides. If you don't take precautionary measures with the plants and flowers in your landscape, eventually they will be overtaken by disease, fungus, or insects. There's just no getting around it. "If" you had treated them with a fungicide throughout the growing season, this wouldn't have happened.

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Answer 6

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Answer 8

You have powdery mildew.

Too much moisture, not enough air movement and probably light.
Plant correctly or use a fungicide.

Now go drink a beer and plan next year design.

Answer 9

It was likely the soil was too moist and the plants were too thickly planted (too close together)
I had a similar problem one year..it was basically like a mold..
lack of circulation between the stems

Answer 10

it didnt like em .