Sunday, April 1, 2012

Blight On!

Hopefully you will already be doing the basics of today's post, but I thought it would be a good idea to tell you WHY you should do it and make sure that you ARE doing it.
It has been a pretty warm Winter, no complaints here, so this could be a bad year for this topic, Camellia Petal Blight.
Here in my Zone 8 Camellias have pretty much petered out, but there are still things to do to alleviate headaches for next year.
Let's start with the basics.
Camellia petal blight is caused by the fungus Ciborinia camelliae. All cultivars of camellias are equally susceptible to this disease. Camellia sasanqua is less so because it's bloom time is in the Fall. This disease only affects the flowers, not the roots, stems or leaves.
The development is favored by frequent rain showers, high humidity, and mild temperatures during bloom. Kind of sounds similar to the Winter we had this year, doesn't it?
Usually the disease is introduced into the landscape on already diseased plants.
The simple scoop is, Camellia petal blight causes blossoms to rot and drop prematurely.



I know what you are thinking, "Flowers rot and drop off after a certain length of time and that is all that this is". And you would be right, except that this happens right after opening and they should stay on the plant for days. Another difference is, the blighted petals are dry and leathery but do not crumble when handled. Petal blight can also be confused with cold injury, but cold injury is usually found on the outer petals, which become dry and crumbly and do not fall from the plant. Flowers from the same plant can have petal blight and cold injury.
The disease is first seen as brown spots on the expanding flower petals. In the early stages of the disease, veins within the spots appear darker than the surrounding tissue, giving some blooms a distinctive netted appearance.
That looks like this:



These spots, which began as small brown specks, enlarge rapidly during warm weather as the fungus invades and kills the flower tissue. A gray or white fuzzy growth may be observed at the base of the flower where it attaches to the stem. (See the base of the flower in the first picture) Eventually the fungus invades to the flower base where a hard, black structure called a sclerotium forms. (Again see the first picture, lower right hand corner) These sclerotia can persist in the soil for several years. Under favorable conditions (cool weather followed by warm, wet weather), the sclerotia germinate to produce tiny mushroom-like structures. The “mushrooms” produce airborne spores that land on nearby camellia flowers, starting a new cycle of disease.
Once introduced it is almost impossible to rid your landscape of this disease. There are things you can do to slow it down. Make sure you don't introduce it to begin with. Check the plant you are buying. If it is flowering, look for the brown specks on the flower. If not, look at the soil and see if you see any of the sclerotium laying there.
If it is has been introduced and you are already dealing with it, watch carefully and collect and destroy all diseased blooms on and beneath the plant.
Each Spring, remove the old mulch. Then spread a layer of about 1 inch of fresh bark, pine straw or whatever your favorite mulch is around the base of each Camellia. The mulch will interfere with the spread of spores to the flower buds. Be sure not to over-mulch the Camellia; burying the root system under 2 or more inches of mulch may kill the plant. Also remember to keep it away from the trunk of the plant to stop other problems from arising.
Along with these sanitation practices, you can apply fungicides. Make sure you read the label and it has Camellia listed. Follow the directions to the letter, this is the law! There are also some soil drench fungicides that can be applied to get any of the spores that may be hiding there.
The fungus may also be spread by the distribution of diseased flowers. This is the reason that at Camellia shows ALL flowers are suppose to be destroyed at the end of the show. You will want to remember not to add camellia petals or leaves to any compost that will be used around Camellias. Most home composts do not get hot enough to kill these sclerotium and you could just be re-infesting your Camellia bed.
Hopefully you have been practicing these types of sanitation tips already. This actually can apply to many kinds of fungus and diseases of plants. If a plant dies and you are not sure why or know that it died due to some illness, better play it safe and burn it or dispose of it in some other manner OTHER than your compost bin.
SO, If you look under your Camellia bushes and you see this:



You might be asking for trouble and end up with this:



Happy Growing!
Darren

1 comment:

  1. Interesting, I didn't realise this was a blight, just thought it happened as the flowers aged. Will remember the tip about compost.

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