Brown Zucchini leaves from SVB?

Troutslayer · Tue Jun 30, 2015 2:46 pm

This is my first year of gardening since constructing my raised garden bed. My zucchini plant has been growing very well and producing several fruits. It has recently started to turn brown on the leaves. In reading on this forum I have seen some scary information about squash vine borers (SVB). When I went out to take a picture of the leaves, I happened to see what I think is a SVB based on internet pictures. Can someone confirm this, and also comment on whether this is what is causing my brown leaves? I have a drip system set on a timer, so the watering is consistent. Is there any turning back or is my zucchini done?

Peter1142 · Tue Jun 30, 2015 6:09 pm

That does look like a borer to me (I am no expert), but IMHO I do not think that it related to the brown leaves. No idea what it is though.

SVB damage can be slow and mild and is not a guaranteed death sentence. It depends. No reason to write off your plants as dead tomorrow. But you should take action and thoroughly inspect the stems looking for damage and eggs.

Of course, there is the issue of the brown leaves....

applestar · Tue Jun 30, 2015 6:49 pm

Does that look like downy mildew? I'm more familiar with powdery mildew so I'm not sure.

Peter1142 · Tue Jun 30, 2015 9:07 pm

I only have experience with PM also, but I don't think so.

Thrips? https://ask.extension.org/questions/200930#.VZM84E3bLgA

rainbowgardener · Wed Jul 01, 2015 12:12 am

That is the squash vine borer moth, so it is likely you soon will have the borers. Keep checking the base of the stem for chewed looking areas, with little piles of sawdusty looking stuff outside them.

But so far that is NOT what is going on. The borer chews up the stem from the inside, disconnecting the plant from all the circulation channels that bring water and nutrients from the roots.

So soon it looks like this:

https://migardener.com/wp-content/upload ... -borer.jpg

and very soon after like this:

https://www.mofga.org/Portals/2/Agricult ... -borer.jpg

see the dead piles of nothing behind the inset photo of the borer?

That all happens in a very few days after the borer attacks.

thrips or a mosaic virus sound like good guesses about what you have now, but watch out for that moth you pictured....

Peter1142 · Wed Jul 01, 2015 8:14 am

Oh geez. I don't know why people deliberately stoke anxiety on web forums like this.

I had the borer in all my plants last year. At the end of the year I was finding them in the fruits.

Only 2 of my plants out of about 15 were completely taken down by the borer before they were a heaping pile of PM. They all made fruit, and it took at least a month for the plant to go down from first seeing the frass.

I understand maybe some SVB are more virulent than others, but I feel confident in saying that saying your plant will be a pile of dead nothing "a very few days" after the borer attacks is a major exaggeration and will lead people to needlessly pull good plants, especially plants like zucchini that are constantly producing.

rainbowgardener · Wed Jul 01, 2015 8:20 am

I am reporting on my experience. I'm glad to hear some people have different experience. A few days from a big beautiful plant just producing its first zucchinis, to a wilted pile of nothing is not an exaggeration in my garden. (I will say I am not always good about doing daily inspections for problems like little holes in the stem - when I was last growing zucchini before I gave up on them because of the borers I was still working full time - so the few days is from when I first noticed the first signs of wilt to total collapse of the plant, not necessarily from when the hole first appeared.)

But I wasn't suggesting and wouldn't suggest anyone pull their plants before it happens. And if you do a search here on SVB you will find a ton of information on them, including how to make a slit in the stem and remove the borer larvae, which sometimes can save the plant. Not always, if they have already destroyed the circulation channels; that's why I said keep an eye out. The sooner you can get them the better.

Peter1142 · Wed Jul 01, 2015 8:39 am

Yes, better yet scout out for eggs... they take a week to hatch.

I am going to try the inject BT approach this year.

rainbowgardener · Wed Jul 01, 2015 8:55 am

That is definitely true, but not easy. Unlike squash bugs which lay big clusters of eggs on undersides of leaves, which are easy to spot, SVB moth lays small eggs in ones or two near the base of the stem, and they are difficult to spot.

https://www.bigpumpkins.com/Gallery/Gall ... pic_81.jpg

Peter1142 · Wed Jul 01, 2015 9:00 am

I found a few this year. They make a satisying popping noise when squished with a fingernail.

Of course impossible to find them all probably, but it can't hurt.

Troutslayer · Wed Jul 01, 2015 1:00 pm

Thank you all for your replies. I have done a "thorough" check for any larvae and have come up empty. Still wondering what is causing the spots on the leaves since it seems to be independent of the SVB. The picture within the link that Peter1142 posted looks very similar, but I have not seen any bugs on the underside of the leaves.