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Veggies, Grasses & Onion Maggots (again)

Time again to seed vegetables, and questions about ornamental grasses and onion maggots (again)!
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

August 7, 2005

One more glimpse of the Victoria Flower and Garden Show last weekend. This was called the Odzala Garden, and was inspired by a National Geographic Special about the Odzala National Park in The Congo rainforest basin. These clearings in the rainforest are made by elephants pulling down trees, uprooting shrubs and essentially planting desirable edibles through seeds in their excrement. They also create the ponds by digging in the mud to get at minerals and to have a place to bathe. The wondrous thing about these clearings is the wildlife they attract, from gorillas to deer and wild pigs. All of these animals benefit from the generations of labour performed by the elephants. This is a distinct ecosystem--a garden. Seasons ebb and flow and with them the floods that renew the land--land where the massive tread of the elephants give a light touch to the glory of nature. The garden was designed and created by Perry Mickle of the Pacific Horticulture College at Horticulture Centre of the Pacific, on the outskirts of Victoria. Author photo.

I haven’t written too much about vegetable gardening this year, and while I no longer grow veggies in anything but a small way, I still have a great interest in them, as that was how I started into gardening over 50 years ago.

The heat in eastern Canada, particularly most of Ontario, will likely preclude readers there from doing any seeding of vegetables for a week or two yet, but generally by the time mid-August comes along, there is a cooling period and that means it will be time to sow for fall salad crops such as all of the leaf and root crops, but not the fruiting crops. For example, you can and should sow: lettuce, endive, (‘Nataly’ is heat tolerant and a good alternative to lettuce), radicchio (a chicory, as well as other chicories), spinach (a few cultivars are mildew resistant if that has been a problem in your garden), Swiss chard (particularly ‘Bright Lights’, an AAS winner in 1998), arugula, cress, mustard, kale (don’t forget it’s use in the flower garden and containers as well), radishes (particularly ‘Summer Cross #3’), and turnips (the sweet summer type, not for winter storage). August sowings (once it cools a bit!) are less tricky than July, because the weather is usually milder, or at least we hope it will be!

While I was in Victoria, and our Flower and Garden Show, Dorothy Thurlow of somewhere in southern Ontario (I think) wrote as follows: “I heard on your program about a nursery in Brampton that specialises in grasses. We are looking for grasses that will grow to a height of about 4 to 5 feet. Could you please let me know where this nursery is if they have what we are looking for?”

The nursery is Humber Nurseries Ltd., located on Hwy. 50, just south of Hwy. 7, and just west of the end of Hwy. 427. They have, I am certain, the largest selection in Ontario, and if you ask, you will be able to go over to the residence part of the property where Franz Peters Sr. has many, many of the cultivars planted in various groupings in an ornamental garden setting. Do not miss seeing that, and the later in August, the better!

Another inquiry that came in while I was in Victoria was from Al Dixon in Northern Ontario, which really asked for a repeat of some earlier advice. Here’s what he wrote: “I'm am sending this on behalf of an elderly gardener here in my home town of Kapuskasing, Ont. He has recently mentioned to me about worms in his onions; small white ones, anywhere from 1/16" up to 1/4 " long. They are in the bulb of the onion. This has been happening for the last 4 or 5 yrs now and he does not know how to get rid of them and this is why I am writing you today!

“He has told me that he buys planting bulbs every year from a local seed store and this year is using all brand new premixed screened soil purchased in late spring. I read the article you have here from June White and mention how wrong she is to use salt! You mentioned that it was wrong to use which is ok, but I could not find an answer as to how you would eliminate them. If you could give me any information as to what kind of worm, reason for them or solution as to how to eliminate them it would be greatly appreciated.”

It is indeed unfortunate that your elderly friend has expended considerably money on planting stock, and soil, not to mention all the effort, only to have onion maggots ruin his results. Here was my original response, on May 15th, to the question: “Most other vegetable growers (it’s not just a problem with onion maggots and carrot rust fly, but also maggots ruining cabbage, broccoli and other brassicas as well) there is no easy answer now that the insecticide Diazinon is gone from our marketplace in Canada and the U.S.A. There simply is not an easy-to-use substitute. Let me explain first how these pests ‘operate’. That may help.

Shiny-green, yellow-headed flies (6 mm) lay eggs on soil surface near plants in late spring, early summer. The emerging larvae (maggots) dig down and attack tender roots. They pupate in the soil and emerge as adults in August or September. These mate and lay eggs which hatch into larvae that over-winter in the soil or in the roots (they are found in stored carrots).

The one characteristic these pests have in common is that the initial contact is made by the adult fly. The ‘old’ idea of putting the granular Diazinon into the soil was to get it into the area where the roots would develop and thus it would kill the larvae before they could do any damage to the roots.

One of the prime methods of preventing attack is moving the plantings of these vegetables to entirely different sections of the garden each year. Then, there are no lingering larvae to infest the young plants. However, that is often virtually impossible in small home gardens.

Now, there may still be an opportunity to use a similar method to that of the old granular Diazinon, only now using Doktor Doom House and Garden Insect Spray which contains 0.25% Permethrin, the water based chemical insecticide that was formulated as a copy of the naturally-occurring Pyrethrins. This product, like all Doktor Doom products, does not bear any ‘Poison symbol’ on its label and is safe to use.

In talking with the good Doktor Grigg, he told me that after checking various university Websites, he is suggesting that since the larvae mature on the soil surface at the base of the planted crops, there is a good possibility that Doktor Doom House & Garden Spray could take the place of the granular Diazinon. Apply the aerosol spray to the soil before planting the rows and treat the areas around the plant stems immediately after planting. “Given we have a residual in the soil and that the plants are treated early in planting--this should last for up to a month and it should work.”

Doktor Grigg emphasizes that you should be certain “to make the application to dry soil and stir it in after it is applied--and immediately follow up with planting (or seeding) and then apply at the base of the plants once they are in the ground, or if seeding, as soon as the young plants emerge.

You can be sure that this method will be being tried by many this season.

Now to some other ‘solutions’. Just as planting in areas ‘clean’ of larvae from previous years is helpful, it is likewise important to eliminate host-weeds like wild carrots (Queen Anne's Lace), wild parsnips and hemlock in the neighbourhood. Also, seeding early (mid-March) and harvesting in May or delaying seeding until June and harvesting early August will help due to the life cycles of these insects.

Another control that I have learned has been used in the past is to plant carrot rows between rows of leeks, sage or rosemary. These latter will repel the carrot rust fly. Also, in talking with Gord Nickel of the ‘Get Up and Grow’ TV programme, he recalls his father hanging cloths that were dipped in kerosene on sticks along the rows of the vulnerable vegetables. We have no experience with this, but I can well understand it working in much the same way as do the mentioned herbs.

Finally, perhaps the second-best solution, after the use of the Doktor Doom aerosol insecticide, is row covers. My friend Tom Thomson at Humber Nurseries has been suggesting the use of these for several years, because they are an economical, relatively simple, non-chemical solution to insect problems. The material used should be fine cheese cloth or muslin (possibly called re-may-cloth in the U.S.) and it should be applied over each row immediately after seeding, or planting of young transplants. The width of each row cover should be about 45 - 60 cm (18 - 24”) and the edges should be held down with soil to prevent the insects getting into the planted area. Ideally, each row cover should be slightly hooped up using flexible branches or the like (so that there is a clearance of about 15 cm in at the row centre to allow the plants to grow), but even if the material is flat on the ground with lots of spare material to allow the young plants to push it up as they grow, the row covers should work well. They can be removed after about three or four weeks. Keep in mind that cheesecloth allows penetration of full light and rain or irrigation.”

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