Rapidly yellowing leaves on Zucchini plant

[Parnassus]

I had a healthy zucchini plant a few days ago. However, after I watered it with 1/2 strength balanced fertilizer along with some added cal-mag, the older leaves started yellowing the next day. 3 days later and the plant continues to rapidly yellow.

It looks like magnesium deficiency to me, but i just added cal-mag. The change was so sudden and dramatic that I was wondering if i could have created some sort of fertilizer burn, but I wouldn't think 1/2 strength fertilizer would do that (plus I watered other plants in the garden with the same mix without problems). Not sure about over fertilization, but I'd say that I only added a partial watering (enough to moisten but not soak the soil. I haven't noticed any pests either. I've killed a couple of squash beetles now and then, but that's about all i've noticed.

I coincidentally snapped a photo of it the day before fertilizing. Also including a photo of what it looks like 3 days after fertilizing.

Does anyone have any ideas what might be going on and how to fix it?

 

[Chuck]

I had a healthy zucchini plant a few days ago. However, after I watered it with 1/2 strength balanced fertilizer along with some added cal-mag, the older leaves started yellowing the next day. 3 days later and the plant continues to rapidly yellow.

It looks like magnesium deficiency to me, but i just added cal-mag. The change was so sudden and dramatic that I was wondering if i could have created some sort of fertilizer burn, but I wouldn't think 1/2 strength fertilizer would do that (plus I watered other plants in the garden with the same mix without problems). Not sure about over fertilization, but I'd say that I only added a partial watering (enough to moisten but not soak the soil. I haven't noticed any pests either. I've killed a couple of squash beetles now and then, but that's about all i've noticed.

I coincidentally snapped a photo of it the day before fertilizing. Also including a photo of what it looks like 3 days after fertilizing.

Does anyone have any ideas what might be going on and how to fix it?

Check around the base of the plant and up about a foot. Look for a sawdust like substance and for a hole in the stem. You may very well have been attacked by a squash vine borer. If not a SVB it appears that the plant is severely nutrient deficient. What liquid fertilizer are you using?

 

[Parnassus]

I don't see any sawdust-like substance or holes in the stem.

I've been using Jobe's organic fertilizer that's 4-4-4 about every 3 weeks. Recommendation is every 4-6 weeks, but i tend to give smaller doses more frequently. I occasionally give some of my heavier feeders a liquid boost in between and used a miracle gro 18-18-21 mixed at 1/2 strength. The liquid fertilizer doesn't have calcium though so I added a little cal-mag to the mix, esp since some of my peppers and tomatoes were showing signs of calcium deficiency.

I wouldn't think that I was using enough to over fertilize and it seems odd that the plant would dramatically turn nutrient deficient immediately after fertilizing. The organic fertilizer does have 8% calcium. Not sure if that extra little cal-mag could have resulted in too much calcium and locked out the magnesium. Other plants seem fine with it though. I just side dressed with some epsom salt yesterday evening in case, but I'm a little stumped.

Do I give it more fertilizer and hope it doesn't kill the plant?

 

[Chuck]

I don't see any sawdust-like substance or holes in the stem.

I've been using Jobe's organic fertilizer that's 4-4-4 about every 3 weeks. Recommendation is every 4-6 weeks, but i tend to give smaller doses more frequently. I occasionally give some of my heavier feeders a liquid boost in between and used a miracle gro 18-18-21 mixed at 1/2 strength. The liquid fertilizer doesn't have calcium though so I added a little cal-mag to the mix, esp since some of my peppers and tomatoes were showing signs of calcium deficiency.

I wouldn't think that I was using enough to over fertilize and it seems odd that the plant would dramatically turn nutrient deficient immediately after fertilizing. The organic fertilizer does have 8% calcium. Not sure if that extra little cal-mag could have resulted in too much calcium and locked out the magnesium. Other plants seem fine with it though. I just side dressed with some epsom salt yesterday evening in case, but I'm a little stumped.

Do I give it more fertilizer and hope it doesn't kill the plant?

I really don't think it is a nutritional problem. I think it is a squash vine borer. Nutritional problems do not come on this fast but if they did the leaf symptoms show nitrogen chlorosis. The cal-mag and epsom salts will not affect the plant, only the fruit. Is there any chance that the plant is root bound, thus depriving the roots of water? This would also manifest itself as your plant shows.

 

[Parnassus]

The squash vine borer would make sense given how fast the change in the plant's health has been. Is there any other way to detect them other than holes and saw dust? Also, if they burrowed in a few days ago, would the holes be heeled up by now? I'm attaching a couple of photos from each side of the main stalk in case I'm missing something.

The plant is in a 16", 10 gallon fabric pot. It's the first time I've grown zucchini so I'm not sure if the pot size is big enough for the zucchini to be happy, but I use fabric bags because they air prune the roots which avoids the roots running around the edges and strangling themselves. I grew fairly large tomato plants, cucumbers and even watermelon in 5 gal fabric bags last year. They didn't love the container size, but they grew and produced.

 

[Chuck]

The squash vine borer would make sense given how fast the change in the plant's health has been. Is there any other way to detect them other than holes and saw dust? Also, if they burrowed in a few days ago, would the holes be heeled up by now? I'm attaching a couple of photos from each side of the main stalk in case I'm missing something.

The plant is in a 16", 10 gallon fabric pot. It's the first time I've grown zucchini so I'm not sure if the pot size is big enough for the zucchini to be happy, but I use fabric bags because they air prune the roots which avoids the roots running around the edges and strangling themselves. I grew fairly large tomato plants, cucumbers and even watermelon in 5 gal fabric bags last year. They didn't love the container size, but they grew and produced.

When I have had SVB the hole is where the orangish colored sawdust was expelled. And the way the plant has gone downhill so fast would lead one to believe that the borer is the culprit. I see zero evidence of a borer. That leaves a lack of water as the cause. A zuc has what is basically a taproot. It goes down deep but if it cannot go deep it must bend or curl. I have never grown squash in a container but if this taproot has curled it would be basically the same as encircling roots on a tree, causing a mass or a ball of roots that would be difficult to water. I have never used a grow bag either but if it is not impervious to water I would stick the entire plant, bag and all into as deep of water as you can and let the plant soak up moisture from the sides and bottom of the bag. I don't know if you could remove the plant from the bag or not but if you could it would be a lot faster in knowing what is happening.

 

[Parnassus]

I checked out the roots this evening. They don't appear to be root bound at all. In fact, there was a lot more loose soil than I expected.

Is there any chance that over watering could do this? I thought it was pretty tough to over water in a fabric container since they have drainage everywhere. The reason I ask is that I had noticed that the container had been a little heavy leading up to this. Even though the top layer was drying out, I could feel a lot of weight in the bottom half. I actually had removed the drip irrigation after fertilizing to let the container dry out some. It never did though. The plant started turning yellow the next day and on day 3, it rained all day.

 

[Chuck]

I checked out the roots this evening. They don't appear to be root bound at all. In fact, there was a lot more loose soil than I expected.

Is there any chance that over watering could do this? I thought it was pretty tough to over water in a fabric container since they have drainage everywhere. The reason I ask is that I had noticed that the container had been a little heavy leading up to this. Even though the top layer was drying out, I could feel a lot of weight in the bottom half. I actually had removed the drip irrigation after fertilizing to let the container dry out some. It never did though. The plant started turning yellow the next day and on day 3, it rained all day.

I don't think so. From a strong vigorous healthy plant to a severely chlorotic plant in 3 days? I just can't see it from too much water. It would have to been slopping wet for an extended period of time, perhaps 7-10 days and the changes in the plant would not be sudden like this. The only thing that makes sense is a borer. Is the plant wilting at all?

 

[Al H]

I had a healthy zucchini plant a few days ago. However, after I watered it with 1/2 strength balanced fertilizer along with some added cal-mag, the older leaves started yellowing the next day. 3 days later and the plant continues to rapidly yellow.

It looks like magnesium deficiency to me, but i just added cal-mag. The change was so sudden and dramatic that I was wondering if i could have created some sort of fertilizer burn, but I wouldn't think 1/2 strength fertilizer would do that (plus I watered other plants in the garden with the same mix without problems). Not sure about over fertilization, but I'd say that I only added a partial watering (enough to moisten but not soak the soil. I haven't noticed any pests either. I've killed a couple of squash beetles now and then, but that's about all i've noticed.

I coincidentally snapped a photo of it the day before fertilizing. Also including a photo of what it looks like 3 days after fertilizing.

Does anyone have any ideas what might be going on and how to fix it?

Is the mix you sprayed on the plant recommended as a foliator? I’m sure I spelt that wrong. It is possible you burnt the leaves with the mix. Another thought is did you spray them in the heat of the day. I don’t know where your from but spraying even with water in the heat of the day will blister the leaves and they will look like you picture with yellow leaves. A close friend of mine killed his tomato patch spraying the plants with straight water when it was 95’. Within a week his plants were bare.