Questions on: Thistle
Ron Smith, Horticulturist, NDSU Extension Service
Q: I have a huge dog pen that I filled with gravel. The pen has been taken over by thistles. I've tried pulling them out and have used Roundup and bush killer. The pen stayed clean for about five days. Is there any way to control the thistles? Will a black tarp under the gravel help? I have 16 bags of weeds sitting in my barn because the city I live in won't take the weeds from the curb, so I have to take them to the dump for $10 a load. I'm going broke and they are driving me crazy. Any suggestions? My neighbors keep telling me to get rid of them before they flower. (e-mail reference)
A: If you cannot afford to hire a professional pest control operator to apply a restricted-use herbicide (the cost is about $50 to $75), then your only alternative is to shade them. Get a black tarp and lay it over the area and seal it with cinder block or stone. Leave it there for at least two weeks in the hot sun and see if that cooks them. They are tough to get rid of once established because of their root and rhizome system. I really think the best alternative is to contact a professional exterminator.
Q: I would like to know how late this fall I can spray for dandelions and Canadian thistle and still get effective control. (Lamoure County, N.D.)
A: Itís probably too late if youíve had a killing frost in your area. They will not respond when they have been shut down by cold weather.
Q: I would like to try to grow Niger thistle for bird feed in a corner of my home garden and at my son's home in Alberta. What are your recommendations in this regard? ( Victoria, B.C., Canada)
A: I'd say go for it and not pay out valuable Canadian dollars to the imported material that I'm sure is saturating your market as it is ours. There is a short-season cultivar known as early bird that we have successfully grown in the Northern Plains - specifically in the Carrington, Langdon, and Minot Research and Extension Centers. The crop was productive at all sites even when a delayed planting (June 13) took place at Carrington. The seeding rates were experimented with and it was found that the 9-pounds per acre rate consistently outproduced the 3- and 6-pound per acre rates. The yields ranged from as low as 300 pounds per acre to as high as 700 pounds. So, if you get something successfully going there, you might have yourself a small economic nest-egg!
Q: My landscaped beds are overridden with thistle and dandelions. There are certain areas of the beds that are infested with thistle and other areas with clumps of dandelions. What is the best way to get rid of these weeds? (E-mail reference)
A: That is a perpetual challenge! Since it is early in the growing season, I suggest the physical removal of them at this time. In other words, create a cleanly cultivated bed with nothing remaining but the ornamental plants that you want. There is a product known as Bio-Barrier that creates both a physical and chemical barrier between the soil surface and the germinating weeds. Place this in your landscape beds after the weeds are removed and cover with an organic mulch like bark or wood chips. You should be virtually weed-free for the next 10 years if everything is done correctly.
A: Confront is not listed as a restricted use pesticide, although it is not available to the general public. It is sold as a "speciality herbicide" to lawn care operators. Trimec is obtainable, and about as effective. Thistles are a pain to control because of their high seed release, and the fact that they are so viable!
A: It appears that you have a bull thistle. I would suggest applying Trimec directly to the plant--and do so as soon as possible! We don't want those plants to have any young ones sprouting up! Keep in mind the seed is very viable, blows easily in the wind and will establish just about anywhere. So maintain your vigilance!
Q. Could you please help me get rid of this weed. It has taken over places in my garden. I want it out because it chokes my produce.
Also in our pasture we have Russian thistles? Is there anything we can do? We used 2,4-D. Thank you. (Estelline, S.D.)
A. Your weed sample was of crabgrass, a warm season annual that is a prolific seed producer. This, along with many other weeds are controlled with Treflan, a preemergent you can spread before the weeds begin showing.
Q: What can be used to control sowthistle and wild morning glory in my strawberry and raspberry beds? (e-mail)
A: Two tough ones! You could try to spray Roundup carefully on them, trying not to get the spray on the strawberry foliage. Since it is not soil active, it
would not hurt the adjacent strawberry plants. There is nothing else I can come up with that you could use in a broadcast manner. Sorry!
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