JCL
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Sunburn Basil

Hi. My Basil seedlings just started turning yellow and spotty. I recently put them under a grow light a little closer than they were before. I assume they are sunburnt now. I have removed them from direct light hoping they will bounce back. Is this wishful thinking? I just want to know if I killed them or will they be ok further from the light source. Thanks

imafan26
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Re: Sunburn Basil

can you post a picture
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rainbowgardener
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Re: Sunburn Basil

Yellow and spotty does not sound sunburned; it sounds diseased (though imafan is right, a picture would help).

Sunburned leaves will be pale, cream to tan, only in the areas directly exposed, and in areas not spots. The burned area will be thinned and feel dry and crispy:

Image

These are basil leaves with cercospora leaf spot disease:
Image
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imafan26
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Re: Sunburn Basil

I was thinking it could be basil downy mildew which is seed borne and does show up early in sweet basil seedlings.

https://www.extension.umn.edu/garden/ya ... ny-mildew/

Basil downy mildew can be transmitted by infected seeds but is a oomycete or water mold. It does not live in the soil, but spores can travel in the air so plants need to be destroyed as soon as the disease is recognized. You can plant more seed but make sure the seeds are certified or steam sterilyzed. Basil seeds cannot be hot water treated. Sweet basil are the ones that are most susceptible and there are not good options. Research has been going on for years and traditional breeding has not yet developed a plant with good resistance that preserves the taste. Plant basil in drier weather and making sure it is spaced well. Plant in pots and bring them in when the humidity is high or it rains. You need to avoid the leaf staying wet for any length of time. Fungicides need to be used preventively but most fungicides approved are not readily available to the public and it does not work after the fact.
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JCL
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Re: Sunburn Basil

Here are pictures. They looked perfectly fine until I put them closer to the light source.
P1040782.JPG
P1040784 (Small).JPG
P1040783 (Small).JPG
This is a before shot.
P1040778 (Small).JPG

imafan26
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Re: Sunburn Basil

What do the undersides of the leaves look like? It does look more like disease than sun burn.
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JCL
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Re: Sunburn Basil

The underside looks just like the top side. So if these are diseased, should I dump them? Will they affect any of my other herbs? This is so sad for me. My first time growing from seeds and they were looking so good for a while. :(

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rainbowgardener
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Re: Sunburn Basil

Definitely not sunburn which makes pale areas not dark spots.

We are thinking maybe basil downy mildew. If so the underside of the leaves would look about like this:
Image

Dark dots but mainly on one side and mainly between the veins.

If that is the case, then unfortunately yes, you have to dump them. It is a deadly disease with no cure:
Remove Infected Plants
Basil that has become infected with Downy Mildew may have a yellowish appearance, similar to a nutritional problem.


The leaves turn yellow and fall off, while the stems wither, and the plant eventually dies. The most common symptom is the dusty spots, actually spores, that are located on the bottoms of the leaves. If you want a definitive diagnosis, you can bring an affected leaf to your local County Extension office for identification. Carefully pinch off a leaf and place it in a ziploc baggie for transport.

Once you are certain that it is Downy Mildew, cover the entire plant with a bag to prevent as much of the spores from being shaken off as possible. Pull up the entire plant and remove from garden area. Do not try to compost or try to remove only the visibly affected leaves. Both of these techniques can result in the spread of the spores. Do not save your basil seeds from any part of that year's crop. The spores can infect the seeds and affect the following year's plants.

Will It Stay In My Soil?
Yes.

The disease can stay viable for many years in the soil. Some experts say that the spores can stay viable for 8 years or more. If nothing else, rotate your crop of basil and plant in an entirely new location for the next season.
https://www.thespruce.com/what-to-do-fo ... ew-1762532

Very sorry to be the bearer of such bad tidings. :( Basil downy mildew has become an endemic problem in some areas, so much that people (like imafan) can't grow basil at all.

Here's an article about the history and spread of this disease: https://vegetablemdonline.ppath.cornell. ... Downy.html
So far this year basil downy mildew has been reported in
Florida, South Carolina, Ohio, Louisiana, Pennsylvania, Massachussets, Connecticut, Georgia, but it is likely in other places as well and just hasn't been reported.
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rainbowgardener
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Re: Sunburn Basil

I remembered you are in Alaska, so I looked for that:

"States where this disease has not yet been reported and/or confirmed are Alaska, Arizona, Idaho, Nevada, Oklahoma, South Dakota, Utah, and Wyoming. Unknowingly distributing contaminated seed is a plausible way that the pathogen was first introduced into the USA and how it has been spread long distances between geographically-separated areas. The pathogen produces spores easily dispersed by wind that enable it to move during the summer growing season through regions where basil is grown widely, including the eastern USA." https://livegpath.cals.cornell.edu/exten ... ny-mildew/

So maybe it is something else, but still not sunburn...
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imafan26
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Re: Sunburn Basil

A big problem now is that basil seedlings that are infected with downy mildew are sold in places like the big box stores. The growers have treated the plants at the nursery but once in the stores they are no longer being sprayed and if the spores are in the air; especially when it is wet and humid, the plants get sick. Most of the people working in the store don't recognize the disease and people buy the plants; take them home and spread the spores around the neighborhood.

I had not planted basil for two years so I tried eleonora which has some resistance. It did fine with weekly fungicide treatments in dry weather. But once it started raining, and two weeks after Downy mildew started to appear on plants at Walmart which is less than a mile away, my basil started showing disease. I had to destroy all the basil. There are not many fungicides listed for basil and most are not readily available to the public. Fungicides are only preventive, once the plant gets the disease it usually cannot be cured. I had to bleach the pots and sterilize the soil. In my humid climate, the chances of controlling the disease is practically nil. I have been waiting 10 years now, and there is still no resistant sweet basil in sight. African and Holy basil appear to be immune to the disease. They have been around the other infected basils for years and still show no symptoms, but they have very different flavors.
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applestar
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Re: Sunburn Basil

I suppose in Alaska, you are probably growing in a green house -- warm, humid environment like imafan mentioned?

I don't know if you are going to try again, but I suppose one way to forestall the disease might be to grow the basils inside the house with probably low humidity air from all the heating during the winter (at least that happens in my house near end of winter/heater season).

Also, cowpots are interesting idea, but like peat pots, they hold moisture -- I never tried using them because I was never able to control the growing medium moisture properly using peat pots. You might have better luck with fungal disease-prone seedlings if you use plastic or terra-cotta containers that can be bleached or otherwise completely cleaned first. Use well-draining mix -- extra sand or perlite mixed in -- and sow seeds at least 1 inch apart to begin with so they won't be crowded as seedlings in the container.

There are many basil varieties besides the Genovese Sweet. You may like another variety even if not the same flavor. My current favorites are Lime and Sweet Dani Lemon and Thai for cooking. I like Cinnamon basil, too. I like Holy Basil for tea but the flavor is too different for cooking. I'm trying a few other varieties this year.


...just to be clear... when this happens, I'm pretty sure you can still sort out unaffected leaves from the obviously affected and "yuck I wouldn't want to eat THAT" leaves and harvest them for immediate use. They sometimes develop the fungal infested splotches if you try to store them in any way. Trim them away from the affected plants, wash with salty water, then chop up and use for cooking -- put in your pasta sauce or something. Even blending into pesto, with all the oil, salt, garlic, and cheese should kill the fungal spores. Then you can get rid of the remaining uglies with less compunction.
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JCL
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Re: Sunburn Basil

I germinated these seeds in my home about a month and a half ago using the paper towel method They have only been in my house under my grow lights until a couple of weeks ago when I started taking all my herbs out side a few hours a day for hardening them. The underside leaves have no visible spores, they are clean from what I can tell, you can just see the same brown or yellowing as the top. Perhaps using the cowpots are keeping them too wet. I will transplant them today in a plastic pot and trim off the ugly leaves and see if I can save them. I probably did over crowd them in their current pots. I am so very new at this. Thanks for all your help. You are teaching me things I was not aware of so thanks.

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rainbowgardener
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Re: Sunburn Basil

Good news! If there are no spores on the undersides of the leaves, it is probably not basil downy mildew. Maybe some other and less virulent fungus....
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JCL
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Re: Sunburn Basil

rainbowgardener wrote:Good news! If there are no spores on the undersides of the leaves, it is probably not basil downy mildew. Maybe some other and less virulent fungus....
Oh good, I can only hope. I picked off all the ugly leaves and I will transplant into bigger pots that are not cowpots. I think they may be allowing the roots to stay too moist. Trial and error for this first time gardener. Thanks!

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applestar
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Re: Sunburn Basil

Good luck! Gardening is definitely a learning experience. :-()
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