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Weed Killer, Garlic, Spraying Trees & Osteospermum

Chemical that kills everything vs selective weed killer; harvesting garlic; prevention is best for insects on fruit trees; a discussion of whether or not to spray large shade trees and if the Asters fail, plant Osteospermums!
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

June 19, 2005

I have just one Osteospermum in a pot in my garden this year, although the City of Parksville has what seem to be thousands planted in various beds around the city. Author photos.

Daphne Walters wrote a week ago: “I enjoy your show every Saturday morning on 740. I have a problem hope you can help. I bought a weed killer for my lawn and did not realise that it was a grass killer also. I have several ugly dead patches of grass. How do I remedy this situation?”

This is not an easy-to-solve problem, but nevertheless, a very common one! All users of chemicals and so-called natural products, should always be careful to read the full directions on all packages before using the product. In this case Daphne, and perhaps the clerk who sold it to her, have confused two quite different products. Products such as Glyphosate and Glufosinate Ammonium (sold under the brand names of Roundup and WipeOut, respectively) will kill almost all vegetation, including grass. They are ideal to kill weeds in pavement and driveways, or even to kill annoying weeds in the garden, by using my method of painting a strong solution on the foliage you wish to kill, and at the same time, being sure to keep it off the foliage of plants you wish to keep. These chemicals are inert as soon as they hit the soil. But, Daphne found out, they certainly do kill grass as well as weeds!

The other products are called selective weed killers in that they generally only kill broad-leaf plants, and not grasses. Products such as 2,4-D, Mecoprop and Dicamba, sold under brand names such as Lawn WeedOut and Killex are what Daphne should have used. These are quite safe, used according to directions.

Now what does she do. That depends how large the bare spots on her lawn are. I would suggest if the “ugly dead patches” on her lawn are 20 cm (8”) in diameter of less, that a couple of heavy applications of fertilizer to the lawn, and good watering through the next two months will cause the grass to grow in. If the patches are larger, grass seed, or sod should be used. The problem is that seed applied during the hot summer season is often not successful because it dies off due to lack of water. You must keep it moist at all times! The best way to do that is to purchase a bag of patching grass seed that comes mixed with a mulch to retain the moisture better.

Gerry Christie posed two questions: “I have a question, last fall I planted garlic for the first time, well now it is about 2 feet high. When and how do I know when it is ready to pull up and then what do I do with it? Do I have to hang it to dry or is it ready to use right away? Also I planted a peach and a pear tree last fall, they are coming fine, should I be spraying them with something, the leaves seem to have some small holes in them. Any help is greatly appreciated, thank you.”

Garlic should be considered a specialized crop--it is relatively fussy. Garlic requires soil nutrients and moisture to be almost perfect, needs regular fertilizer, doesn’t grow well if surrounded with weeds, is easily damaged with a hoe, must be dried properly to assure keeping quality and tends to pick up diseases unless the plants are renewed from a new source (i.e. not your own kept-over mini cloves) each year.

They should generally be harvested when at least the top half of the plant turns brown and dries up. There is no ‘absolute date’ at which to harvest, the drying of at least half the plant signals harvest time. If it should be particularly wet at the time just prior to harvesting it does not hurt to harvest a little early, and then dry them either out-doors in the sun (if it is not too strong), possibly given a little shade, or indoors, say in the kitchen. Prior to drying, wash off the bulbs, particularly the roots and then dry. Once dry, peel off the outer skin and then braid the bulbs together for indoor storage.

Keep in mind there are two or three distinct types of garlic, all under the botanical name Allium sativum. Each has varying requirements, and, of course, there are varying flavours. One of the major garlic growers in Canada is Ted Maczka (Munchka), the Fish Lake Garlic Man, R.R. #2, Demorestville, ON K0K 1W0; 613-476-8030. He will send you a catalogue is you send him $3.

Regarding your fruit trees, it is quite important to spray fruit trees, first before the leaves emerge with a dormant spray, mixing the two (natural) chemicals (lime sulphur and a light oil), together usually in a 2:1 ratio as directed. If this is done just as (but not before) the growth buds show no more the two or three millimetres (1/4 inch) of new growth, good control will be achieved. Most growers also apply a good insecticide such as Doktor Doom Residual Insecticide Spray just before the flower buds show colour (called the pre-pink stage) and just after they turn brown (post-pink). If insects show up later in the season they can be controlled using the same product when and where needed.

Bev in Edmonton wrote twice recently with these two questions about trees: “Our Aspen trees are getting rolled leaves. When we unroll, there are tiny black spots (eggs I guess). Some have developed into a small green worm. The largest trees are about 30 ft. (3 years old), the others were planted last year and this year we planted more. What can we do to get rid of these pests and what should we do in the future to prevent this infestation? I hope this is not common of these trees as we were counting on them for privacy.” And, more recently, “Two-year-old Linden. Planted by builder on each Brass III Property. Finding many dead branches. The leaves seem stunted rather than large as they are supposed to be. Many have tiny holes on them and almost a rust spot around the holes. What is it and what do you suggest we spray with. These trees are about 20 ft. tall with trunk about 10 inches around. Waiting for an answer. Thank you.”

Generally speaking, the same response applies to both of Bev’s questions. There is a consensus among urban arborists currently that unless a particular insect is literally totally defoliating a tree or group (a particular species) of trees, and such attacks are happening or are likely to happen in successive years, that spraying should not be carried out. Chemical spraying within urban and suburban areas, it is agreed, presents more problems than solutions.

Personally, I think we’ve gone too far, but nevertheless the pros in the International Society of Arboriculture and its affiliates and other parallel organizations have gone along with the pressures of the activists and we just have to live with that until another view is presented and through reasons of what may happen down the road, causes society to take another look.

If you wish to spray the trees yourself you may still be able to find some form of wand sprayer that attaches to your hose and shoots the spray up a reasonable distance. Even if that is not the entire height of the trees, the fact you kill off a large percentage of the pests will certainly reduce the amount of damage done to the trees. Do keep in mind that many pests come and go from year to year, and weather conditions (i.e. wet spring vs. dry spring) play a large roll in the presence of most pests in any one year.

And, lastly this week, Maureen wrote as follows: “Hello can you tell me how I can successfully grow asters and dahlias in Regina Saskatchewan. They both seem to acquire a rot of some kind. Is there something I can dust them with or ....??”

I have talked to a number of horticulturists and we see no reason you should not be able to grow dahlias (generally) in your climate. Asters are an entirely different question. They have, for decades, suffered from a (or several) virus disease(s). If you are attempting to grow them in the same place each year, even close by an area you grew them previously, it is not surprising you are having problems. Simple answer always is to try something different--in this case I would suggest some of the new Osteospermum which have a similar look, but do not attract the diseases that Asters do.

The presence of a rot indicates too much water to me. Try planting both in drier areas.

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