Roots, Shoots, Fruits & Flowers: Fire Blight, Bacterial Leaf Spot, Edible Mushroom, and Phosphorus Deficiency

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A pear tree with symptoms of fire blight in red circles. Photo: Carol Martinez.

Fire Blight

Laurie called the AgCenter and asked AHA to examine her pear tree. Upon arrive, AHA saw a tree resembling one in the photo.

Laurie’s pear tree had the classic symptoms of a bacterial disease called fire blight. The leaves looked scorched and had the classic shepherd’s hook at the end of the branch. An article on the AgCenter website, “Control Fire Blight Early” recommends these treatments next spring during the bloom, “While spraying the tree is not a sure cure it can help to prevent the spread to other susceptible plants which include pear, apple, crabapple, quince, loquat, mayhaw, hawthorn, Indian hawthorne, cotoneaster and pyracantha.

The control method would be to spray either streptomycin or a copper fungicide. Cooper can be purchased as Kocide™, Tri-Basic Copper Sulfate and Bordeaux™ mixture. Streptomycin can be found in products such as Agri-Mycin™ and Bonide Fire Blight Spray™.

Start your spray when 10% of the pear blooms are open. Repeat your spray every 4-7 days until the blooming period is complete but pay attention to and follow the number of sprays allowed and interval between sprays that are listed on the individual product label.

Your only other choice for fire blight control is to prune out the dead limbs making sure to dip your shears in a 10% Clorox™ solution between cuts. This type of pruning will make a mess of the form and shape of the trees but will help control the disease if visual appeal is not a goal.”

Claudia has a similar complaint about her apple trees, “I’m trying to find out about [fire] blight. I have been told my apple trees (2 about 5 years old) have it. I was told there is no cure and they will die. Is this true? [Is] there is nothing that can be done? Some is on the limbs, but it is also on the main tree trunk [, and it is] like a black stripe around the middle of it. It is black and peeling the bark off.”

Branches with the cankers from fire blight can be pruned out. However, if the main trunk of the tree is infected and has cankers, then the tree will likely succumb.

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A zinnia with infected leaves. Photo: Susan McReynolds, LA Master Gardener.

Bacterial Leaf Spot

Susan asks, “Can you tell me what’s going on with my zinnia? “

Dr. Raj Singh, the AgCenter’s “Plant Doctor”, examined the image and made both a diagnosis and a recommendation, “It’s bacterial leaf spot. Copper spray may help but do not [spray] above 85-degrees F. [because of leaf burn.]

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A species of chanterelle. Photo: Lea Kimbrell.

Edible Mushroom

Lea sent a clear image and was interested in this mushroom.

AHA consulted with Mr. David P. Lewis, President, Gulf States Mycological Society, and he shared this note about Lea’s mushrooms, “These are probably a species of chanterelle, most likely Cantharellus cinnabarinus, The underside should have blunt gills with cross veins. They are common and a good edible.” Before eating any mushroom, consult with a mycologist, or fungi specialist, for positive identification to avoid accidental poisoning.

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A hydrangea leaves with symptoms of a phosphorus deficiency. Photo: LaVone Boyd, LSU AgCenter.

Phosphorus Deficiency

LaVone asked, “Would you happen to know what might be going on with the leaves on my Hydrangea? I just planted it a few months ago.”

Lavone’s hydrangea has leaves with purple coloration, and this purpling is consistent with symptoms of a phosphorus deficiency. Recommendations for fertilizing included in soil test results will help to correct this deficiency.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or khawkins@agcenter.lsu.edu. Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“Before you buy or use an insecticide product, first read the label, and strictly follow label recommendations. Mention of trade names or commercial products in this article is for informational purposes only and does not constitute endorsement by Louisiana State University AgCenter.”

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

8/10/2020 1:45:08 PM
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