Wednesday, July 16, 2014

Saying Goodbye To Basil...For This Year Anyhow


A couple of weeks ago I started to notice some bronze type patches on my basil:

Bronze Patches on Sweet Basil Leaves
 
I didn't think too much of it at first.  I assumed it was a bit of sunburn.  And even though basil is a sun loving plant, I had read that they can become sunburned if they get too little water and too much sun.  I'm not the most conscientious when it comes to standing their, spraying a bed, so I bumped up the watering a bit.

But the basil didn't get better.  In fact it got worse with each passing day and dark brown patches began to appear.


Basil with Bronze Patches and Brown Spots

At first, only the sweet basil was affected, but in the last few days, I began seeing signs of the same thing on the Thai basil.  Yesterday I turned over a leaf and that is when I realized that this was definitely not a simple case of too much sun & not enough water.  Off to the computer I went and, after a bit of research, I discovered that it was Basil Downy Mildew.

Basil Downy Mildew Spores on Undersides of Leaves

I have never encountered downy mildew in the garden before, so it was a bit of a surprise.  And I was even more surprised when I discovered that there is a form of downy mildew that is specific to basil.

Basil Downy Mildew is caused by a parasitic organism - Peronospora belbahrii - yeah, I can't pronounce it either.  It thrives in warm, humid conditions - which basically describes the typical Southern Ontario summer.  And apparently there is a bit of an outbreak this year.

The spores are usually carried through both infected seeds & wind.  I have no idea how my plants became infected - it could have been either of these sources.  If it was through the seed, that means that at least one of the three packets I sowed was infected.  I'm pretty confident that the Thai basil seed is fine as it was the last to show any signs of infection.  I am going to toss both Genovese basil packets, just in case, and purchase fresh sweet basil seed next spring.  Downy mildew does not survive winters in the north, so next year, I will still be able to plant basil in my herb bed.

If you want to find out more about Basil Downy Mildew, there is a very extensive article on the Cornell University Vegetable MD website that was just posted in February 2014.

All of my plants were pretty much goners, so I have pulled them up.

Genovese Basil Infected with Downy Mildew
- Just before I pulled them all up -
 
Thai Basil - Also Infected & Pulled Up

The pictures actually make them look a lot better than they were.  Practically every leaf had mildew spores underneath.

The best way to avoid or minimize future episodes is to keep the plants dry.  Ideally, they should be planted in a nice sunny spot with good air flow and drip irrigation.  The first two conditions were present in my garden.  But, unfortunately, I don't have drip irrigation installed in the herb bed yet, so my overhead watering likely made the infection progress significantly faster than it otherwise would have.  There is little that can be done once the mildew is evident on the plants.  I don't use fungicides, but even if I did, they are ineffective unless you use them before the plants show signs of infection (the Cornell article has quite a detailed section on the use of fungicides).

I'm not yet sure what I am going to do with the newly vacated section of the herb bed - I may sow some more dill and/or cilantro.  But even though my basil is done for the year, I'm thankful that I was able to get in a few good harvests before the mildew took over.

This post was shared on Green Thumb Thursdays.

Till next time...

“Enjoy the little things, for one day you may look back and realize they were the big things” ~~ Robert Brault

14 comments:

  1. Oh, that's a bummer. What is summer without basil?

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    1. You said it. I had yet to make a batch of pesto this summer - bummer indeed!

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  2. What a shame--it seems there is always something.
    That was a real loss there. Sorry about that.
    : (

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    1. Thanks Sue - I had been holding off on picking the Thai basil until it got a bit bigger so I didn't get more than a taste of that one...sigh.

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  3. That happened to me last year. I know it wasn't the seed because I had used the same seed the year before and I had no trouble. I've just got my fingers crossed this year. It really does take the whole planting down once it gets in.

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    1. I just hate to throw out seeds that are viable but what can you do? Better than nursing the seedlings for a couple of months just to find out they are infected again. I'm definitely going to start saving my own basil seed from now on - at least that takes one variable out of the equation. I hope that your basil does well for you this year.

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  4. How disappointing to lose your basil! When I transplanted my basil in the spring, the plants looked sickly and I thought I might lose some. Thankfully, they survived, but now I feel compelled to check the undersides for mildew.

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    1. I had never seen this before, so it never occurred to me to check for mildew when the leaves started to take on a bronze tint...but now it will definitely be the first thing I do.

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  5. That is a shame! Thankfully I have not seen it yet in my garden. but I will read the Cornell article and do some preventive actions. Thanks for sharing the info!

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    1. What's that old saying about forewarned is forearmed? Had I been aware of basil downy mildew beforehand, I would have been much more careful when watering & may have gotten a few more harvests (& pesto!) before my plants went kaput.

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  6. This is another pox (along with late blight) that was introduced into the New England area by plants sold in the big box stores. All I can say is buy local or grow your own, but meanwhile we all have to deal with this stuff.

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    1. So true. The unfortunate thing about this mildew is that it is often airborne and it can, apparently, travel quite the distance. Most people, unfortunately, don't start their plants from seed & big box stores are an all too easy convenience for picking up a plant or two. All it takes is one neighbor with an infected plant....sigh.

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  7. Love this post! Thankfully, it hasn't happened to me....but I'm pinning for future issues! lol

    Thanks for joining Green Thumb Thursday last week. I've chosen you as my featured post this week at www.FeathersInTheWoods.com. Please stop by and grab the featured button for your blog!

    ~Lisa M

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