Plants be­hav­ing badly

Se­nior hor­ti­cul­ture ed­i­tor Stephen West­cott-grat­ton de­clares a pox on will­ful botan­i­cal in­vaders.

Canadian Gardening Annual 2016 - - Stephen Speaks -

I prob­a­bly should have writ­ten this col­umn a year ago, but to be hon­est, when I first heard about the re­cent pro­lif­er­a­tion and spread of wild parsnip (Pasti­naca sa­tiva), I pretty much dis­missed it as just an­other weed du jour. Af­ter 25 years of gar­den­ing, I’ve seen sev­eral epi­demics come and go: First there was pur­ple looses­trife (Lythrum sali­caria), which threat­ened to car­pet the coun­try and crowd out na­tive species with its pretty pur­ple flow­ers. Al­though it’s still a men­ace in some ar­eas, the de­lib­er­ate in­tro­duc­tion of two Euro­pean leaf-eat­ing bee­tles has done a great deal to re­strict its range. Nev­er­the­less, gar­den­ers should never plant pur­ple looses­trife in their bor­ders, in­clud­ing the sup­pos­edly ster­ile cul­ti­vars that still oc­ca­sion­ally show up at lo­cal plant swaps. The next in­va­sive species I re­call caus­ing a me­dia frenzy wasn’t a plant, it was a bug: mag­no­lia scale (Ne­ole­ca­nium cor­nu­parvum). I re­mem­ber do­ing a seg­ment about it on Ci­tytv’s Break­fast Tele­vi­sion about 20 years ago and watch­ing the host re­coil from the in­fested branch I bran­dished at the cam­eras. Su­per-yucky mag­no­lia scale was a se­ri­ous prob­lem for sev­eral years, but as is of­ten the case, na­ture re­stored a bal­ance, and now it’s just an­other gar­den­va­ri­ety in­sect pest (you can knock adults off branches with a strong jet of wa­ter, and au­tumn ap­pli­ca­tions of dor­mant oil will kill any over­win­ter­ing nymphs). Where I live, the last furor was over gi­ant hog­weed (Her­a­cleum man­tegazz­ianum), and I was both amazed and de­lighted to see how quickly lo­cal mu­nic­i­pal­i­ties jumped all over this flo­ral thug. Gi­ant hog­weed – along with pars­ley and car­rots – is closely re­lated to our most re­cent plant plague, the wild parsnip. A few months ago, I had cause to take wild parsnip se­ri­ously when I saw what it did to a neigh­bour’s teenaged son; in short, it made the worst poi­son ivy look like a day at the beach. As with gi­ant hog­weed, the above ground parts of the plant con­tain a sap that re­acts with out­door UV rays to cause se­vere burns, blis­ters and scars – if it gets in your eyes, per­ma­nent blind­ness can re­sult. Sur­pris­ingly, “wild” strains be­long to the same species as our cul­ti­vated veg­etable types (de­li­cious ‘Al­bion’ and ‘Gla­di­a­tor’, for ex­am­ple), so it’s pos­si­ble that they’re just agri­cul­tural es­capees that have re­verted to their un­do­mes­ti­cated form. Nev­er­the­less, parsnips have been grown in North Amer­ica for more than 200 years, so it’s a mystery why they’ve gone rogue so swiftly. Wild parsnips have been re­ported in ev­ery prov­ince and ter­ri­tory ex­cept Nu­navut. Small in­fes­ta­tions (less than 100 plants) can be dug up in spring, but you’ll need gog­gles, heavy rub­ber boots and gloves and haz-mat-style cov­er­alls. It’s the sort of job that’s gen­er­ally best left to pro­fes­sion­als. But de­spite the bad be­hav­iour of the wild parsnip, I’ll still be eat­ing my share of sweet roast parsnips with Sun­day din­ner.

Wild parsnips are bi­en­nial, so pre­vent­ing sec­ond year flow­ers from set­ting seed is an im­por­tant con­trol strat­egy. Left alone, the plant can form large colonies, crowd­ing out na­tive species and se­ri­ously re­duc­ing bio­di­ver­sity.

Wild parsnips are a re­minder that kids must never pick or eat any plant With­out adult su­per­vi­sion.” stephen West­cott-grat­ton, CG se­nior hor­ti­cul­ture ed­i­tor

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