Lawn Grubs, Wisteria, Leaf Spot and Blight

More on the control of grubs in lawns; having Wisteria flower; pampas grass, Japanese maple problems; leaf spot or blight; and protecting the house foundation if raising the soil level!
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

May 14, 2006

Above, my Wisteria in East York at its best due to proper pruning; and below, two shots of leaf spot or blight disease (Entomopsporium) on the old and new foliage of Photinia fraseri. Author photos.

The first question(s) this week came from Connie Mallon in Uxbridge, back on April 26. I am not sure I have good answers for her, but here is her note and my response, in any case: “A friend of mine tells me he has a home recipe for the grubs and other insects in his lawn which he obtained from your talk show some time ago. The ingredients were, vinegar, I think vegetable oil and something else. He couldn't remember. I have white grubs in my garden and in my lawn and would like to use something other than Sevin to get rid of them. I have nematodes on order at Goodwood Gardens, but they have not come in yet, and I noticed last week that the grubs are already starting to hatch into June Bugs.

“I had a look at your garden on your website. It looks absolutely beautiful, I too have a front lawn which is now all garden except for the meandering paths, which are still grass. I would like to put mulch down but my husband likes the look of the grass, and I do too actually especially when it is lovely and green and the garden edges are all nicely dug. Would love your recipe as I worry about the birds that also eat from the grass and use it for nesting material in the spring.

“I have two wisteria vines, both about seven years old. Neither has bloomed yet, both are in full sun, planted on a fence and the wall of the garage which receives sun all day so is warm in winter as well. Both are in good soil, with excellent drainage. Any tips on how I can get it to bloom? Yours is absolutely lovely. My husband is disappointed in the wisteria, he is from NZ and used to prolific flowering everything. Would love to surprise him with a blooming wisteria this year. Thanks for any advice you can give me.”

Your friend is mistaken; it must have been another garden show. I do know a US garden broadcaster and book au-thor (who is not a horticulturist at all) who promotes those types of cures and solutions, but most of them do not work. For everyone who talks about them I can generally refer you to folk who have tried them and, like me, have found them not to work. In addition, many of the chemicals suggested for application to plants and soil with these ‘home remedies’ are far more negative to the soil than the registered chemicals. Vinegar (acetic acid) is a good ex-ample.

You are certainly too late now to try and control white grubs—the very tiny window for control in the spring is al-ways over by May, especially this year there with an early spring. The single best time for the control of white grubs is at the end of August when the new young grubs become active near the surface of the soil. At that time too, the soil is warm, and nematodes will have a better chance of working. However, let me advise you that, after having experience with nematodes for well over a decade, they do NOT work well on turf. The problem is getting them through the turf thatch. Good vendors will always advise aerating the lawn well first, and then the nematodes may have a chance to get to the soil to feed on the grubs. I do not recommend them for that use; but for control of black vine root weevil on such as yews, rhododendrons and other shrubs, or iris borer, they can be used quite successfully.

For my money, Nu-Gro’s Wilson GrubOut (Sevin) is the only product still on the market for consumers, which works reasonably well. Contract spraying companies can still get Merit which is an advanced form of the same chemical, but it is not available to homeowners. There is no pronounced danger to birds from those products.

As regards your two Wisteria, most important point is, were they flowering when you bought them? And, if they were not, that was a mistake. I never recommend buying any Wisteria that is not in bloom. An additional point is that some types are on their borderline of hardiness where you are in Uxbridge. However, my good friend Larry Sherk, horticulturist on the first Canadian plant hardiness zone map, says that one called Aunt Dee (Wisteria sinensis ‘Aunt Dee’) is likely among the hardiest.

That said, the pruning too is very important. In mid-summer you should cut back all the new long thin growths to about 30-40 cm (12-16”). And you can repeat that in late summer as well. Then in March next year (and every year) go back and prune back those growths even further, perhaps to about 20 cm (8”), and if possible, to just in front of a larger bud, wherever on the stem you may find that. You should see some bloom following such treatment. Two callers on my AM740 programme of last Saturday specifically called to advise that they had followed this advice from earlier years, and that it was working well for them.

This next question arrived the same day and requires a very short answer. Here is what William Peltomaa from the Niagara region asked: “I noticed you recently advised someone in my area about pampas grass, and having recently bought seed myself, I have a question, or rather, my wife has a concern. She's worried that the spread of seed might make it unmanageable, but since I am planting in submerged barrels and plan to cut the plumes off be-fore they start to drop, I think I'll be OK. From what I read, the plumes may not even develop for a few years, and I suspect that even in mild Niagara, the climate is still too cold for any rogue seeds to present much of a problem. How does my reasoning sound to you? And do you know of any difference in habit between the white and pink/purple varieties?”

As far as I have ever noted, you should have no problem with the pampas grass over-producing from seed even in Niagara. Humber Nurseries has grown these for well over a decade and I don’t see them overcome with seedlings. I have taken several groups of Australian gardeners through the Humber Nurseries gardens and had a number of comments on the fact that it is a terrible plant in their country because of the spread of the seed. But, we are a lot colder. Even here in British Columbia, it is widely grown and I don’t see any sign of run-away seedlings.

Doug Sly wrote from hometown Parksville almost two weeks ago as well. Here were his questions: “Our home is 13 years old and had a beautiful Japanese maple tree when it was built. Last year for the first time a number of branches died and leaves shriveled up. This year there has been no sign so far of any leaves coming to bud. We are thinking of replacing the tree with another one but wonder if there is anything we can do with to revive this one. We have heard that there are several brands of these maples but don't know what brand this one is. The other mat-ter is the question of what to do once moss killer has been applied to areas of the lawn affected by it. Do we rake it out and plant more grass seed?”

The problem with your Japanese maple could be one of several. For example, during hot, dry summers they often suffer leaf burn as a result of not enough moisture in the soil. That is probably less likely in your case with an old tree. They also die of Verticillium wilt (Verticillium albo-atrum), sometimes over a period of years, and sometimes quickly. There is always a distinguishable olive-green colouration in a circular pattern within the sapwood when this is the problem. Something else that seems to be hitting maples recently is a leaf spot known as Cristulariella depraedens. Some control of this may be possible with a copper fungicide generally available at garden centres. With these diseases it is important to rake up all the leaves that fall, at any time, and place them in the garbage, not the compost.

In case Verticillium is your problem, I would change the type of tree; i.e. anything but a maple. Visit Shirley, Heather or Perry at Cannor Nurseries in Parksville, and give them your wish list (i.e. height and spread, flowering, leaf colour, fall colour etc.) and see what they have.

Yes, do rake the old, dead moss out vigorously, but you may not need to re-seed; an extra application or two of fertilizer should encourage the existing grass to fill in, which is far superior to applying bird feed!

Another Vancouver Island resident (I think), Barbara Tesluck, wrote on the final day of April, about a common problem which often occurs in Ontario as well as here, although the plant about which she in inquiring does not grow in Ontario. Here was her question: “We have a Photinia fraseri that is not doing well. It has dark brown spots on the old leaves, and now even the new growth has spots. Is there anything that we can do or do we replace it with another. If we replace it can we put in the same type or is there something in the soil that will wreck the new one as well. We watch you quite regularly and enjoy your hints.”

Barbara’s problem, and that of thousands of other gardeners, is a leaf blight or spot disease, Entomosporium mespili, which also occurs frequently on hawthorn trees and bushes, hence my reference to the same problem in On-tario. We have it on the one Photinia we have here near the sea in Parksville. We did move it a little further away from the sea and it now seems to be slightly better. The area where it is planted (both before and after the move) receives considerable wind, and this is likely helpful.

Cultural practices are important to control Entomosporium leaf spot. Infection is favoured by free moisture on the leaves so you should avoid wetting the foliage when watering. Selective pruning can increase air circulation through the plant and reduce disease incidence. Severely infected leaves on the plant and those fallen on the ground should be removed and thrown away (not composted). Susceptibility to leaf spot development varies by cultivar. Infection occurs primarily in the milder weather of the spring and the fall. Fungicides are most effective during this time. The trouble is so few are available. As I recommended above, a copper fungicide will help, ap-plied periodically.

If you decide to remove it, rather than spraying, I would look at a different shrub—your choice but certainly not a hawthorn (Crataegus) or Indian hawthorn (Raphiolepsis indica).

Finally this week, Susan Keegan from Collingwood, Ontario wrote with the following question, which might have been better left to Paul Napolitano of Royal Home Improvements, my bi-weekly guest on AM740: “Before starting this project of a raised flowerbed, I decided it was best to obtain the advice of an expert, so I'm e-mailing you with my question. Since the raised bed will be two feet above the ground surface and up against the house foundation, do I need to put a waterproof material between the soil and the house brick? About one foot of the soil will be covering the house foundation, the other foot will actually cover the bricks and I don't want any water/moisture problems down the road. If I need a barrier, what material is best to use? Regular listener.”

Whenever I hear about the use of raised beds, I always like to question the person who is thinking of using one or a number. I believe the concept is over-done. Yes, I believe you should put some sort of waterproof barrier between the house foundation (and especially the brick) and the soil in the bed. I would go for some sort of heavy roll roof-ing or similar. Perhaps the ‘rubber’ pool liner (such as Firestone Pond Gard) that every garden centre sells for ornamental pools could be ideal. I say heavy, because you certainly do not want to have something thin that is easily damaged while you are digging in the bed because if it is damaged it would be difficult to replace once the soil is in place.

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