drewyyz
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Brown Zucchini Leaves - Please Help Me

Hello,

Totally new to gardening and I would really appreciate your advice

I'm growing a zucchini in a pot. I've noticed some leaves turning yellow and then they get brown spots on them (see pictures). The brown spots were crunchy. I've cut off those leaves, but now the edges of the remaining leaves are turning dark brown. The brown is just starting on the edges, if you look really closely in the pictures you can see. I think there is also some white stuff (powdery mildew)? But it's very, very little white stuff. I'm mainly concerned about what's making the leaves so yellow and brown! I've already cut quite a few off or they have died...

I think my watering is adequate and I never let the put get dry, but at the same time, it is never soaking, dripping wet. There is good drainage at the bottom.

Any advice is greatly appreciated.
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TomatoNut95
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What has your weather been like? Have you fertilized the zucchini? Is the pot it's in big enough?

drewyyz
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Hi There! Weather is 20-30 degrees celsius during the day, with rain roughly twice a week, but I check if it needs water every day (and supplement with watering can). I fertilized it once on Saturday (3 days ago) with 20-20-20. I read on some forum that 20-20-20 would be good for zucchini plants in pots. It's in quite a large pot (I'm not sure the size in gallons), but it's the same pot that I bought it from the nursery, and it's sold as a "container zucchini". The nursery said I could keep it in the pot. I'm so confused what's happening :(

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TomatoNut95
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By the way, welcome to the forum. 🙂 Has it been humid? Excess rain and high humidity may entice powdery mildew. And when you water, try not to get the leaves wet. Is the zucchini near any other plants? I would separate it if so; powdery mildew can spread. Search for a fungicide spray to apply to the plant.
Last edited by TomatoNut95 on Tue Jun 09, 2020 9:33 pm, edited 1 time in total.

drewyyz
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TomatoNut95 wrote:
Tue Jun 09, 2020 9:23 pm
By the way, welcome to the forum. 🙂 Has it been humid? Excess rain and high humidity may entice powdery mildew.
Thank you so much! Today was 50% humidity, but I live in Toronto and normally it isn't particularly humid. The sun gets bright here, drying of any leaves and there isn't leaf crowding to prevent drying/air flow, so I didn't think powdery mildew.... If it were, what would I do? Can I buy a spray on amazon or something?

Do you think it could be nitrogen toxicity? Is 20-20-20 too strong for Zucchini? I only fertilized once since I've had it for about 3 weeks, but it's been 3 days since I fertilized and the leaves are the worst it's been....

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applestar
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What do the undersides of the affected leaves look like?

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TomatoNut95
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Yes, I would search for a fungicide spray that lists powdery mildew on the bottle. Amazon would be a good place to look if your local nursery doesn't carry any type of garden sprays.

As a matter of fact, 20-20-20 sounds a little strong in my opinion. If you could weaken it some, less than likely it would cause plant burn. Using a fertilize with less nitrogen might be better anyway, as excess nitrogen causes more foliage than plant production. I use the boxed water soluble Miracle Gro brand (I would use the kind for tomatoes or the Bloom Booster on veggie plants) and use at least every one to two weeks.

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Gary350
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I am having very good success with 2 teaspoons of baking soda & 1 teaspoon of dish soap, dissolved in 1 gallon of water to stop blight. Mold & mildew does not like the high PH of baking soda so it dies. My tomato plants turn out looking like they were bleached green. I use a 1 gallon hand pump sprayer. You need to spray both sides of leaves and stems and the whole entire plant once a week. If rain washes it off spray plants again. Pull off your, dead, brown, yellow, leaves get them away from the garden. This should work for zucchini squash too.

I use 15-15-15 fertilizer on my squash, I put 1 cup = 8 ounces in 5 gallon bucket of water stir well then use it to water, squash plants, peppers, corn, beans, cucumbers, herbs, potatoes, but not tomatoes. 1 quart for water is all each plant needs.
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drewyyz
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Gary350 wrote:
Tue Jun 09, 2020 9:58 pm
I am having very good success with 2 teaspoons of baking soda & 1 teaspoon of dish soap, dissolved in 1 gallon of water to stop blight. Mold & mildew does not like the high PH of baking soda so it dies. My tomato plants turn out looking like they were bleached green. I use a 1 gallon hand pump sprayer. You need to spray both sides of leaves and stems and the whole entire plant once a week. If rain washes it off spray plants again. Pull off your, dead, brown, yellow, leaves get them away from the garden. This should work for zucchini squash too.

I use 15-15-15 fertilizer on my squash, I put 1 cup = 8 ounces in 5 gallon bucket of water stir well then use it to water, squash plants, peppers, corn, beans, cucumbers, herbs, potatoes, but not tomatoes. 1 quart for water is all each plant needs.
Thank you everyone. I so appreciate your help and knowledge. I've ordered a fungicide and will also make the baking soda/dish soap mixture until it arrives (as I have this at home already).

I will take pictures of the underside of the leaves tomorrow when it's light outside!

Just wondering: can I over-dilute the 20-20-20 fertilizer and still use it (just so I don't waste the entire package)? It's surprisingly hard to find a fertilizer where I am, so I was thinking I could use half the recommended fertilizer for the same amount of water, to weaken it. Would this work? Also, could I use this mixture of fertilizer for tomatoes too? I'm so confused by all the fertilizer and what is the best to use. There's so much info out there... I have zucchini , peppers, tomatoes, lettuce, carrots, onions and herbs.

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Gary350
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It will not hurt to mix 20-20-20 with more water or add less fertilizer to 5 gallons of water. I hope your not buying that over priced fertilizer from Lowe's, Home Depot & Hardware stores. You can buy fertilizer $20 for 50 lb bags at Farm supply stores. TSC has fertilizer too in 50 lbs bags. Also buy PELLET Lime $15 for 30 lb bag for plants that get BER, squash, melons, peppers, tomatoes. Pellet lime is nothing but lime stone dust formed into tiny round balls.

20-20-20 is not strong when mixed with 5 gallons of water. 5 gallons of water = 20 quarts = 40 pints = 80 cups = 1 1/4%. Mix 1 cup of 20-20-20 with 6 gallons of water then it = 1% strength fertilizer, less strong than many organic fertilizers.

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kayjay
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Hey Drew. Sorry you're having problems with the zucchini already.

I'm East of Toronto and I've conceded that the zucchini are just going to get both powdery mildew and downy mildew every year, it's just a matter of trying to slow it down until I get as much fruit off of them as I can. The weather so far this year has been junk - too many extreme temps. That hasn't helped... but I don't normally see those fungal diseases until July. I started my seeds a little too late and the plants are behind, but they're healthy so far.

Spraying hydrogen peroxide is another option to slow down the fungal diseases. That's what I've been doing every year.

Zucchini are heavy feeders and I doubt you over-fertilized them. I'm admittedly pretty lackadaisical about the fertilizer. They get compost from my bin in May when they go out, they get some generic cheap fertilizer once every two weeks; that's all that was available at my local hardware store at the time. They've been very forgiving.

(ETA) The generic fertilizer is for "flowering plants", 15-30-15. I also have Miracle Grow, 24-8-16 I'm pretty sure. I use the MG earlier in the season when I want everything to grow, then switch at flowering time. This year, I had a big brain fart and just started using the flowering plant fertilizer. Doh. We'll see what happens.

Good luck...

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TomatoNut95
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kayjay wrote:
Wed Jun 10, 2020 7:26 am

(ETA) The generic fertilizer is for "flowering plants", 15-30-15. I also have Miracle Grow, 24-8-16 I'm pretty sure. I use the MG earlier in the season when I want everything to grow, then switch at flowering time. This year, I had a big brain fart and just started using the flowering plant fertilizer. Doh. We'll see what happens.

That 24-8-16 stuff is what I kept using on my veggies until I learned it contained too much nitrogen causing my veggies to not produce as much. Then I switched to the Tomato food and the Bloom Booster which has less nitrogen than the other two ingredients. I guess the 24-8-16 stuff would be better suited for stuff that you WANT leafy, right? Like Basil, lettuce and other leafy greens.

drewyyz
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kayjay wrote:
Wed Jun 10, 2020 7:26 am
Hey Drew. Sorry you're having problems with the zucchini already.

I'm East of Toronto and I've conceded that the zucchini are just going to get both powdery mildew and downy mildew every year, it's just a matter of trying to slow it down until I get as much fruit off of them as I can. The weather so far this year has been junk - too many extreme temps. That hasn't helped... but I don't normally see those fungal diseases until July. I started my seeds a little too late and the plants are behind, but they're healthy so far.

Spraying hydrogen peroxide is another option to slow down the fungal diseases. That's what I've been doing every year.

Zucchini are heavy feeders and I doubt you over-fertilized them. I'm admittedly pretty lackadaisical about the fertilizer. They get compost from my bin in May when they go out, they get some generic cheap fertilizer once every two weeks; that's all that was available at my local hardware store at the time. They've been very forgiving.

(ETA) The generic fertilizer is for "flowering plants", 15-30-15. I also have Miracle Grow, 24-8-16 I'm pretty sure. I use the MG earlier in the season when I want everything to grow, then switch at flowering time. This year, I had a big brain fart and just started using the flowering plant fertilizer. Doh. We'll see what happens.

Good luck...
Thank you everyone for your replies. I'm such a newbie, so I really appreciate it. What ration of hydrogen peroxide to water do you use? Do you start when the mildew is just beginning or when it's bad?

Thank you also for the reassurance re fertilizer. I'd ideally like one fertilizer for my entire vegetable garden. I have onions, carrots, tomatoes, peppers, and zucchini. Do you think I could use the 15-30-15 on the entire garden? I have 20-20-20 already, but could buy either the 15-30-15 or a 9-16-16 I found online.

drewyyz
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Gary350 wrote:
Wed Jun 10, 2020 6:25 am
It will not hurt to mix 20-20-20 with more water or add less fertilizer to 5 gallons of water. I hope your not buying that over priced fertilizer from Lowe's, Home Depot & Hardware stores. You can buy fertilizer $20 for 50 lb bags at Farm supply stores. TSC has fertilizer too in 50 lbs bags. Also buy PELLET Lime $15 for 30 lb bag for plants that get BER, squash, melons, peppers, tomatoes. Pellet lime is nothing but lime stone dust formed into tiny round balls.

20-20-20 is not strong when mixed with 5 gallons of water. 5 gallons of water = 20 quarts = 40 pints = 80 cups = 1 1/4%. Mix 1 cup of 20-20-20 with 6 gallons of water then it = 1% strength fertilizer, less strong than many organic fertilizers.
Thank you so much! I am sadly buying the over priced fertilizer from home depot :(.... sadly it's the closest store to me! Do you think I should switch to 15-30-15 from 20-20-20?

Oh ALSO, is it too late to transplant it into the ground? I was originally keeping it in the pot to save space in ground for other stuff, but I could pull up some random ground over plants and put it in the ground if you think it would do better. But I don't know if it's too late to put it in the ground (I already have 4 zucchini I picked from it) or if it's sick and it'll spread to other plants...

imafan26
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The white patches especially near the veins look like thrip damage. It can cause the edges of leaves to shrivel, but zucchini are pretty notorious for fungal issues. Downy mildew can also cause angular patchy discolorations on the leaf and one of your pictures does hint at that. The underside of the leaf will be more obvious.
https://www.growveg.com/plant-diseases/ ... ny-mildew/

I usually also accept that zucchini will die a fungal death. The best I can do is to remove the lower leaves that touch the soil and I use a potting soil bag with the white side up as a plastic mulch. It is better to water below the mulch and keep the leaves as dry as possible. Baking soda sprays help to keep the leaves dry and can be preventive. It is hard to control any fungal disease once it is entrenched. I usually just try to keep it going long enough to harvest as much fruit as possible.

I have had luck with Dunja and Parthenon which had unusually good resistance to powdery mildew and they are parthenocarpic which is a bonus since high temperatures do not favor female flower production. I don't have many issues with downy mildew since it more of a problem in cool wet conditions and It is near 90 degrees summer with high humidity, so powdery mildew is more of a problem. There are not a lot of resistance to downy mildew. Delaying planting till the weather is drier and planting in a controlled environment like a greenhouse are the best strategies.

MsDDC
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imafan, I'm with you and applestar...what do the undersides of the leaves look like? I get the same damage on plants from whiteflies, and they're just now showing up here after our cool spring. I use neem oil to control them.

imafan26
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Mildews both downy and powdery are common on "hairy" plants like melons, cucurbits (squash, cucumbers,) solanaceous (eggplant, tomato, pepper, ) gourds (bitter melon, upo, luffa). Also on geraniums. Downy mildew is more associated with cool, wet conditions and powdery mildew with warm and humid weather. The hairs on the plants were probably adaptive in their native climates which were relatively dry. The hairs allowed for maximum capture of water in the form of dew. In more wet climates, this can become a problem when wet conditions persist for weeks. Usually, where mildews are concerned, prevention is better than cure. Fungicides work better applied if you know the conditons that promote fungi growth are ripe and the fungicides can prevent the mildews from becoming established. It is much harder to control after the fungi have penetrated into the leaf cells.

Finding resistant cultivars helps, planting at the right time to avoid the wettest conditions, or planting in a controlled environment. Cultural practices like plant spacing, removing and destroying infested leaves and sanitation are options that usually don't resolve but can keep plants going long enough to get a harvest.

Powdery mildew is a white or grayish looking powdery dust on the top of the leaves. It usually show up 1-3 days after a prolonged period of rain has stopped and with the heat and humidity levels rising as the land dries up. In my case, it is more like steaming off.

Downy mildew starts on the bottom of the leaves but shows up as checkered patches in blocks bordered by the veins of the plant. It is more easily seen on the bottom of the leaf but will show up on the top of the leaf as well. It is more common in cold wet conditions.

There are some more disease resistant varieties that will produce longer as long as the plants are kept healthy.

https://vegetablemdonline.ppath.cornell.edu/NewsArticles/Cuc_Downy_Mar06.html
https://www.youtube.com/watch?v=sz0vZ-t0gyg
https://gardeningsolutions.ifas.ufl.edu ... downy.html
https://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_PM.htm



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