Zucchini leaves are yellowing from the bottom up (w/pic)

redmoss(7)June 3, 2007

Hello

I planted a Zucchini in the garden, and it was doing very well until around 2 weeks ago. At that point, I started noticing a yellowing of the bottom-most leaves, starting at the tips. Over about a week, the affected leaves would get yellower and yellower until the only remaining green was along the leaf veins. The rest is dried like parchment, almost a bronze color, and curled up.

The plant as a whole seems to be doing well right now, flowering and producing new leaves. However, it looks like whatever was affecting the older leaves also strikes new leaves about a week after they emerge. The pattern is the same: yellowing around the tips of the leaves, spreading to the base of the leaf over several days, and eventually resulting in a curled-up, dried leaf.

I took a dried leaf to the local garden center to elicit a diagnosis and/or suggestions to fix the problem. Three people looked at it, and none of them knew what the problem was. They said maybe inadequate sunlight, which couldn't be it since the plant gets full sun from around 10 AM to around 6 PM. They thought maybe the soil was too wet, but I don't think this is the problem since the soil feels neither soggy nor powdery when I stick my finger into it (I'm using "square foot gardening" technique: 1/3 vermiculite, 1/3 peat moss, 1/3 assorted composts in a 4' x 4' x 6" raised box). They looked up plant diseases and guessed maybe Cucumber Mosaic virus, but the leaves are evenly dried, there are no dark blotches, and there is no slimy liquid when I cut off a leaf. They said maybe a grub had gotten in and was siphoning off the plant's liquid, but the "trunk" of the zucchini looks pretty healthy to me.

I will attach a picture to give more information.

So, can I cure the plant? If not, should I just tear it out now instead of wasting several weeks waiting for it do completely die and planting a new one? Is it a soil/fungus problem? If so, should I avoid planting a replacement in the same spot?

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Kimmsr(4a/5b-MI)

What is the soil like this is planted in?
When was the last soil test done?
This is a nutrient related problem, but you need to know what is going on in the soil before determining what can be done.

    Bookmark   June 4, 2007 at 7:32AM
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ronalawn82(z9FL)

redmoss, I take it that the roots of the zucchini are in a comparatively small area and the vine is spreading out. And that you are checking for moisture etc. in the root area. A certain amount of leaf loss like you describe can be quite normal, especially as the plant flowers and sets fruit. I would be concerned about the young leaves. I would look back to two or three weeks ago and see if any cultural or environmental condition occured to account for the change in the plant. Try the garden center or extension service but this time take one healthy young leaf, one young leaf with early symptoms and two or three others that will show the progression of the symptoms. If you do decide to remove the plant, do it carefully and perform a post mortem or 'CSI Plants'. Examine the roots, the stem at ground level and split the stem lengthwise to see if anything has been ambushing your efforts.

    Bookmark   June 4, 2007 at 11:11AM
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botanybob(Northern Idaho)

These symptoms are not by themselves diagnostic. It does look like a nutrient deficient plant, but that could have a number of causes. What are you using for fertilizer? You might try giving it some extra and see what kind of response you get. Your soil mix has a lot of organic matter which, if it isn't adequately decomposed, can rob nitrogen from the soil as it decays. What kind of compost did you use?

    Bookmark   June 4, 2007 at 7:27PM
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redmoss(7)

kimmsr: the soil is 1/3 vermiculite, 1/3 peat moss, and 1/3 compost. The compost was bought from the garden center and is approximately 1/3 composted cow manure, 1/3 composted mulch, and 1/3 composted... something else, which I can't remember. I have not done any soil tests yet, though I have a home-testing kit that I am now preparing. Am I looking for a particular nutrient deficiency? My home kit tests pH, N, P, and K levels.

    Bookmark   June 4, 2007 at 9:02PM
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redmoss(7)

botanybob: Would the nitrogen deficiency also be affecting the surrounding plants? I have eggplant, tomato, pepper, and pole beans next to the zucchini. They all look happy and are presumably tapping into the same soil/nutrients.

    Bookmark   June 4, 2007 at 9:10PM
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redmoss(7)

It would appear that it was some kind of nutrient deficiency. I applied some of my home-made vermicompost, and the "rusting" stopped on the new leaves. I have now gotten several new zucchini off the plant.

Thanks for everyone's help pointing me in the right direction.

    Bookmark   July 20, 2007 at 8:38PM
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Kimmsr(4a/5b-MI)

Many people think first that yellowing leaves indicates a Nitrogen deficiency and depending on how the leaves yellow that is one of the nutrients that can cause yellowing. The others are Potassium, Magnesium, Zinc, Iron, Sulfur, Boron, Copper, Manganese, and Molybdenum. Looking at the soil mix I am thinking multiple nutrient deficiencies. 1/3 vermiculite would make for a soil that really drains well and that could mean the water soluble nutrients are being washed right out of the soil.

    Bookmark   July 21, 2007 at 7:15AM
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