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I have three large zucchini plants in my garden, and all three have been producing nice fruits for a few weeks. The last couple days, one of them has started to turn yellow and sickly:

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I've never grown zucchini before, so I'm not sure if this is just the natural progression, and the plant's life is over... or if this is a sign of some damage or disease. If it is the latter, can I nurse the plant back to health? Or should I destroy it so it doesn't infect the remaining healthy plants?


EDIT

In response to @EdStaub's answer, here's a new photo of the base of the plant, at three magnifications:

enter image description here

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1 Answer

up vote 4 down vote accepted

Look at the stem, down near the base. Do you see some distinctive brown-orange sawdust-like material? If so, that's called frass, and your plant is being destroyed by one or more squash vine borers. The wikipedia article is really good, and shows pictures (at the bottom) of what to look for.

We've tried killing the grubs in the stem, with a hatpin and other things, with partial success.

Some varieties of squash have some resistance to borers. I don't know about zucchini, though.

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Thanks for the response. I have updated my question with a new photo. The base looks horrible... with brown-orange material. I think you diagnosed it. Thanks. –  Flimzy Jul 4 '12 at 18:22
    
Upon closer inspection, it looks like all of my zucchini plants are infested, just the one pictured is the worst off. I found one fruit with worms crawling out of it, too. sigh I'll probably rip most of it out. –  Flimzy Jul 4 '12 at 18:39
    
Don't rip them out quite yet! I just dealt with the same exact problem. I ended up ripping out a few plants, but I think I managed to save some as well. For plants that don't look like a total loss, you can look for possible entry points on the stems. Make a lengthwise slit a few inches above the highest visible sign of damage. You'll often end up getting the vine borer using this method. Start with the plants that look like a total loss, so you can get some practice on making the cuts. Then when you move on to the healthier-but-still-infected plants, you have a better chance of saving them. –  Doresoom Jul 5 '12 at 20:25
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Also, if your other squash is under attack as well, you can bury portions of the vine to encourage rooting. Then a vine-borer attacking the base of your plant won't kill the entire plant. bstpierre gave me a pretty good answer on my related question: gardening.stackexchange.com/q/4634/6 –  Doresoom Jul 5 '12 at 20:26
    
@Flimzy, see Doresoom's comments here - I agree - we've gotten squash from plants where only a small portion of the stem remained. –  Ed Staub Jul 6 '12 at 0:13
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