GROWING THINGS: Flea beetles burrowing into potatoes

Plus, how to condition soil for spring planting and when to prune your amur maple

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Q I am having a problem with my potato tubers. I hope you can help me identify what is causing the problem and what to do about it (I’m thinking ahead to next year).

Something is tunneling into my Yukon Gold potato tubers to a depth of about two mm. There’s also some scabbiness on the surface skin. I cook my potatoes without peeling and find these tunnels after I’ve cooked them and the skin falls off.  As the potatoes cool, the area around the holes becomes a little darker. I hope you can identify the pest and how to deal with it next year, organically, I hope.

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A The problem may be one of flea beetles. The larvae of this insect can feed on potato tubers causing the type of damage you describe. The larvae burrow into the tubers feeding just below the surface of the skin. The adult flea beetles overwinter in the soil in and around potato fields. The best way to control the problem organically is to rotate the crops. Do not plant potatoes in the same area for at least two years. 

Q When is it a good time to prune my amur maple? I read it should be done in the middle of July because that’s when the sap’s stopped running. Then I read a gardening article that says it can be pruned in February or March before the buds appear. Could you please clarify this? 

amur maple
Amur maple leaves are strikingly pale with green veins — a symptom of iron chlorosis. Photo by Donna Balzer /File

A I would prune the maple in mid-to-late summer, so July would be my first choice. By pruning in February or March, you run the risk of having the sap start running before the pruning wound has had a chance to heal. This ‘bleeding’ of sap could weaken the tree and it may even cause its death.

Of all the maples the amur maple (Acer ginnala) requires the least amount of pruning. All you need to look for are any dead or injured branches. Also, remove any branches affecting the appearance of the tree. This would include branches rubbing against each other or at unnatural angles. With my amur maple, I always like to remove the very long branches that reach skyward. I cut these back by a quarter to a third to encourage the plant to fill out.

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Q Every fall I turn over the soil in my garden and leave it in lumps. In the spring I have it rototilled. I like to add some organic matter but I never know when to apply it. Should I spread it put it before or after rototilling? I was thinking that after the garden is rototilled I could apply the manure and rake it in at the same time as raking the soil.  What would be better? Is there a preferred way to do this?

A I do both. How’s that for sitting on the fence? All joking aside, I do like to work the manure into the soil because it helps to break down our clay soils and I like to put a layer of manure on the top to act as a mulch as well. I use a 2.5-5 cm layer on top. It breaks down more slowly and every time you water you get the manure ‘tea’ seeping down into the root zone. Make sure that the manure is well rotted as manure that is still green can burn the plants.

I don’t know about you but I’ve had enough winter! I went looking for a quote to inspire us all as we begin to plan our garden for the upcoming season and want to share these words from May Sarton:

“Everything that slows us down and forces patience, everything that sets us back into the slow circles of nature, is a help. Gardening is an instrument of grace.”

Every week, Growing Things Outdoors runs online at edmontonjournal.com or, if you prefer an epaper format, epaper.edmontonjournal.com. Learn more by emailing your questions to [email protected], reading past columns at edmontonjournal.com or my book Just Ask  Jerry. You can also follow me on Twitter @justaskjerry01.

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