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Yellow spots on leaves of otherwise healthy cucumber

Posted by viktoria5 5 (My Page) on
Tue, Aug 3, 10 at 11:56

I have four Marketmore cucumbers. They are my favorite in all of my vegetable garden, and that's saying a lot (I planted about two dozen different vegetables). They have been fruiting awesomely (I harvest a cuke on each every day) and two of them have main vines about 8 foot long, outgrowing the trellis. The cukes are sweet, tender and crunchy.

Now, about two weeks ago, small yellow spots appeared on the leaves literally overnight (they also appeared on a neighbour's cukes the very same day). Not all leaves are affected either: the problem is concentrated on a 2.5-foot section about two feet from the roots. The yellow, or I should say buff, spots have been slowly growing. The undersides of the leaves aren't affected in any way. No fuzz to be found anywhere, so it doesn't look like any kind of mildew so far.

Since the spots appeared, nothing else has changed about the plants. They still produce delicious cukes (I harvested five yesterday) and other than the affected leaves, everything else looks healthy. The main vines are going crazy and they look like they want to reach the roof. But the little spots are growing and they will most likely take over the entire leaf and the leaf will most likely die.

What should I do? I am not necessarily interested in knowing what exactly is wrong with my cukes, just in knowing in general whether I am dealing with insect damage, bacteria, mildew, etc., and consequently, whether I should spray, chop those leaves off, etc. Oh, and I also caught a few striped cucumber beetles, and they are mostly around the cukes, even though I have melons, zucchini and pumpkins as well. But there are not many and I am quite adept at catching and crushing them.

Between the cucumber plants, I have a watermelon with two tiny melons on them, one of which has been growing like crazy. The watermelon looks nice and healthy and I want to keep it that way, so I am afraid that whatever is wrong with the cucumbers might attack the watermelon. It is my only watermelon that definitely will produce mature melons by the time cold weather sets in (I have three more that may or may not have time to ripen).

Also, I feel I should mention that all of my plants have suffered a bad hail storm about a month ago. They all have little holes and tears in a limited amount of foliage. None of them seem to mind this (some of my bush beans have a lot of holes but they are still blooming away and producing delicious pods). I wonder if the spots on the cuke leaves may just be scars from that hail storm. The spots appeared about two weeks after the hail storm.

Sorry, I can't post a pic right now as hubby has the camera today. I'll post one tomorrow, though.


Follow-Up Postings:

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RE: Yellow spots on leaves of otherwise healthy cucumber

Do they look like the yellow spots I just posted?

My cucumber thread


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RE: Yellow spots on leaves of otherwise healthy cucumber

They look a lot like these! They are small round spots (when they first appeared, most were about half an inch in diameter, a few smaller and a few bigger), and they are very slowly growing, and they are now mostly 3/4 inch large. There is nothing dark in the middle of or around the spots, but the middle is paler, most likely because it is more dried out than the edge.

They appear just like on yours, not really concentrated on any particular part of the leaf. They also are really round and they don't seem to depend on the leaf's veining.

The difference with mine is that they are not punched out. No holes, just spots. Also, like I said earlier, they are still growing like crazy and producing many healthy, delicious cucumbers (no change in fruit whatsoever). I did notice though in your pictures that there is some yellowing of the leaves close to where the spots are. I don't have any kind of leaf discoloration, just the spots. All of the leaves have a nice, uniform green colour, except for a few leaves near the soil that just dried off entirely a long time before the spotting (lots of hot, humid weather most likely caused excess transpiration).

Did you have any adverse weather the last few weeks before the spots appeared? Is there any sick plant nearby? I am really thinking my cukes just didn't like the weather...

I will take a pic now and report back (I will take the occasion to harvest today's cukes as well). Thanks for your help!


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RE: Yellow spots on leaves of otherwise healthy cucumber

Hard to say what adverse weather is around here. We're having a very hot, often humid summer, with stretches of blazing sun followed by wicked thunderstorms.

No sick plants nearby that I know of. Donna suggested that my plants could have used more space, and that might be the problem.


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RE: Yellow spots on leaves of otherwise healthy cucumber

  • Posted by mjmarco Zone 6 Upstate NY (My Page) on
    Wed, Aug 4, 10 at 21:55

Could be a viruse like Mosaic viruse. Without picture it's hard to say but since you are seeing the stripped beetle they are know to spread the viruse. This virus will cause cukes to turn yellow any yellow in them is a cause. I don't think there is any fix and if it a mosaic those beetles will spread it to other vine plants. I have it this year too lost them all, good luck.
md


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RE: Yellow spots on leaves of otherwise healthy cucumber

I am happy to report I just got four more huge, delicious and healthy cukes. But in trying to take good quality pictures of the plants, I noticed some new development, which worries me.

As they were this afternoon:
Image and video hosting by TinyPic

Spots in general:
Image and video hosting by TinyPic

This is the bottom face of the leaf to the right in the previous picture:
Image and video hosting by TinyPic

Ripening fruit:
Image and video hosting by TinyPic

So you have an idea of dimensions:
Image and video hosting by TinyPic

First off, I did find a few of these spots with greyish outlines. I only found these on one leaf so far, and other affected leaves still only have spots that are just tan.

I also found spots that are punched out like yours, alisande. Only a few once again, but it may just be the beginning.

Image and video hosting by TinyPic

I also found a kind of cobweb on the underside of one leaf, real close to one of these spots that seems this time to have been munched on by something. A flower real close to this leaf also seems to have been munched on. Could be the striped beetle (I have as yet not seen a single spotted one), I catch a few on occasion, but I only ever find one when I go hunting for them.

Cobweb kinda thing (notice grayish area on spot):
Image and video hosting by TinyPic

Another take of the cobweb thingy:
Image and video hosting by TinyPic

Signs of munching (grayish outline on holes along the bottom edge of the picture):
Image and video hosting by TinyPic

More munching:
Image and video hosting by TinyPic

So far, it really looks to me like something is eating my cuke plants (no sign of munching on the actual cukes). My nearby tomatoes are affected real bad by aphids, but somehow they seem to be very healthy all the same. Maybe those aphids are infesting my cukes? I tried to find some aphids in the cukes but could not see any, while the tomatoes are full of aphids and whiteflies. Ripening tomatoes look awesome, not a blemish.

Really, I am wondering if this is not simply signs of striped beetle munching without signs of illness. If that is the case, what should I do to halt the consumption of leaves? Kaolin? I did find another striped beetle today (I hate them, they always fly away when I approach, so they are difficult to pick).

Marketmore cucumbers are supposed to be resistant to scab, cucumber mosaic virus, and both downy and powdery mildew.

Am I missing something?


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RE: Yellow spots on leaves of otherwise healthy cucumber

  • Posted by mjmarco Zone 6 Upstate NY (My Page) on
    Thu, Aug 5, 10 at 15:52

mosaic virus has a yellow ring spot and yours are brown. looks like a chemical burn (maybe those cloths hanging above dripped some bleach on them)? Or a watering problem...I agree the aphids are eating that blossom. I'm not sure but the good thing is it does not look like a virus I would treat the insects and watch the leaves to see if it continues to spreed.
md


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RE: Yellow spots on leaves of otherwise healthy cucumber

Thanks for your hints, MD.

Yup, I think this is merely insect damage. However, I find those spots too large to be only from aphids. I am guessing it is a combination of aphids, striped beetles and maybe other critters as well.

I have Bug B Gon insecticide from EcoSense. I am trying to keep things organic (although I do think that chemicals are no big deal as long as you really want to care for a plant and they don't damage anything you don't mean to, like the neighbour's crop). It says here that it will control all stages of aphids, spider mites and whitefly, spittle bugs, adult and nymph stages of thrips, flea beetles, caterpillars, mealybugs, scale insects and sugar ants. It contains 0.5% pyrethrin and is lebeled as a skin irritant.

Here's the deal. I don't like that it is organic AND pretends to take care of all these bugs. If it were true, then nobody would have harmful bugs anymore, so I am suspicious. Somehow, I am thinking it may be damageable to the plants and may also kill beneficials (I am very lucky to have swarms of ladybugs). Do you think the benefits of using it would outweigh the risks?

If I indeed have striped beetle damage, this product wouldn't work. Can I do something against those that can be made at home or that is easily purchased?

Also, I have Bug B Gon insecticide soap (supposedly controls aphids, earwigs, mealybugs, spider mites, psyllids, pear and rose slugs [sawfly larvae], soft brown scale and whitefly--the soap 47% potassium salts of fatty acids and is lebeled as a skin and eye irritant), but I still don't understand the difference between insecticide and insecticidal soap. Both are used in the same concentration, applied the same way and at the same frequency, so what is the difference? Which one should I use? Should I use one this week and the other next week and alternate?

Also, I think right now would be a good time to spray. It is a bit windy, but otherwise, we have nice cloud cover. There is a risk of rain later on and all through the week. Would spraying these products during a cloudy day (daylight but cool and no sunshine) be a problem? I don't want to miss my chance.

Please, help as this is about my first bug challenge and I am pretty much a noob.


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RE: Yellow spots on leaves of otherwise healthy cucumber

  • Posted by mjmarco Zone 6 Upstate NY (My Page) on
    Sat, Aug 7, 10 at 21:24

Well...I never used Bug-b-gon so I can't help you there. I'm not a organic person...don't believe you can be and I also don't think you have to over spray to wipe out every bug on the plant.

With that being said, I think you have aphids and you need to spray for them. Since your seeing the stripe beetle I would spray for them and use one product that kills both...however...WHATEVER you spray will kill the Ladybugs...you have no choice. At this point if the stripe beetle gets a hold of your cukes, say goodbye.

Remove any cukes that are ready to be picked and read the lable for the timing of the harvest. Don't spray today and eat tomorrow,if you know what I mean.

But I'm not sold that those spots are insect damage or a fungus...so I went back to your first post and missed this,

"I have suffered a bad hail storm about a month ago".

Depending on the size of that hail those spots could be damage from the hail. If the hail was small it could take that long to show like wind damage on tree leaves. You also said they are growing like mad...so what fertilizer are you using and could you have spilled it on the leaves?

Again you need to spray for the aphids and the stripe beetle since your seeing them around...I lost all my cuke to them (I didn't catch it in time) and my zucchini from squash vine borers...so watch those watermelon plants at the stems where the plant comes out of the ground for the borers.

Hope this is helpful...good luck
md


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RE: Yellow spots on leaves of otherwise healthy cucumber

Thanks for your helpful suggestions, MD.

No, the clothes on the clothesline are not dripping any chemicals onto my plants as the closest clothesline is at least twenty five feet away. The only thing ever touching my plants that doesn't come from me is when the neighbour waters her plants (chemicals are now illegal in Montreal, and they are also very hard to find).

I have no idea where those spots are coming from, but I do know that striped cucumber beetles are munching on my cuke leaves (they have been trying to reproduce, which is the best time to catch them as they are then off guard). Whether this is related to those spots or not is a mystery to me. One thing I do know is that other than a mild case of powdery mildew, all of my gardening misadventures are attributable to that damned cucumber beetle (looks like they are after my tomatoes now that the last of my cucurbits is running out).

Next year, I will try kaolin clay (Surround WP), and I will release a few bugs that supposedly parasite cuke beetles among others. I will also keep zucchini plants under row covers and hand-pollinate. Finally, I will also use the big bright yellow bucket full of water to try and trap them so they drown. I trellis my cukes and so I think I will even hang some yellow plastic cups on the trellis.

I realize now that in my area, the cuke beetle is the most serious threat to veggie plants, and that is really what I need to worry about. I didn't have squash bugs, no vine borers, and the aphids and whiteflies I do still have aren't a threat to any of my plants (toms are tasty, juicy and plant leaves are nice and healthy). So, next year will be full on war upon the cuke beetle.


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RE: Yellow spots on leaves of otherwise healthy cucumber

Just to let you know the diagnosis: bacterial wilt from striped beetles. The spots were marks from their munching, and then they moved on to flowers, and finally to the actual cukes, most of which ended up having blotches of brown sap on them (good to eat, though). Most of the leaves totally curled up and dried out.

I initially had four plants. I just pulled two of them. Another one has the wilt but is still healthy enough to produce on the upper part of the vines. One surprisingly doesn't have the wilting at all, has many beautiful, spotless leaves (which at this point is truly a miracle) and is now going crazy. It also looks like the striped beetles are gone as nothing is deteriorating now and I haven't seen any beetles for a few weeks now. So, that one plant seems to be safe now and it has half a dozen cukes that are pollinated and growing, as well as another half dozen whose pollination I am crossing my fingers for (the flowers are nice and yellow, so things are looking up).

I guess the lesson to be had is to plant more than you need, spend part of the summer looking for people who can never have enough cucumbers and by late summer, you should have just enough crunchy cukes for your own needs. I am still thinking of wrapping my trellis in row cover next year...


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RE: Yellow spots on leaves of otherwise healthy cucumber

Will 7 dust be ok?


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RE: Yellow spots on leaves of otherwise healthy cucumber

Will 7 dust be ok?


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