Dandelion infestations continue to plague some direct seeders. These weeds can really get established and those who are trying to get a handle on controlling them often refer to the "granddaddies" as the ones that are tough to get. Integrated weed control always looks at several ways to put pressure on weed communities. This is important for direct seeders to apply when controlling perennial weeds. A dandelion infestation will not likely be eradicated with one treatment. There are a number of herbicides that can be used that will pretty much control the seedling stage. There are a few combinations of herbicides and/or sequential applications along with proper timing that researchers and experienced producers are beginning to indicate may increase the pressure that can be placed on more mature dandelions.
Like all weeds, but especially perennials, there are times or plant stages when weeds are more susceptible to the various herbicides in the producer's arsenal. Like most perennials, better control of dandelions is achieved when applied after there is some new growth especially for those products, which need to be translocated. With moisture in the spring, dandelions, which have over wintered, have an early spurt of growth rapidly producing seed heads and then growth slows especially if moisture is limiting. When moisture conditions improve and/or other plant competition decreases such as the time that annual crops are senescing or are cut and removed, dandelions will become active again. This gives some clues as to when control options may work best.
Gord Pearse, who farms 15 miles north of Tisdale, has just recently come back to the farm full time to allow his father Terry to slow down. The Pearse's have been direct seeding for many years. Terry served as an SSCA director back in the early 90's and he had already been direct seeding for a few years then. They have also been growing forages for seed production including alsike clover. Perennial crops provide some good opportunities for dandelions to get established and get to the "granddaddy" size. When forages come out of production, it is not always so easy to kill these well established dandelions, especially in reduced tillage systems.
Gord says these big dandelions can certainly use a lot of moisture in the spring. He has found that one of the best methods to put significant pressure on dandelion populations is a ½ liter of Roundup in the month of Sept. He certainly also uses pre-harvest on their farm but Gord says that they have found that this often gives them mediocre results on dandelions. It gets the seedlings but not the established ones. They pre-harvest at 1 L/ac about 1 year in 4 on their wheat, flax, and canary seed acres. Gord feels that often the pre-harvest is too early to get good dandelion control. They are applying their post harvest application later in September, again on an average of about ¼ of their acreage. This means that, more or less, they are alternating between the pre-harvest and the post harvest every other year. Gord says he feels that although this program is not eliminating their dandelion problem, it is keeping them under control. When Gord came back to the farm, he left an agrologist position with Newfield Seeds. He used to encourage his growers to spray their forage seed fields for winter annuals and dandelion suppression by spraying in October. He has since decided that working until the last day before its too cold has more to do with luck than good management, and would now recommend spraying when possible, even if it is early Sept.
Some research and demonstration findings substantiate what Gord is saying about timing for dandelion control. Roy Button who was Sask. Ag. And Food's Soils and Crop Specialist in NE Sask. ran an ADF project in '93 - '94 spraying a number of different products in May and Oct 20 on 4 different dehy alfalfa fields in NE Sask. One of them was Terry Pearse's. He reported that the only reasonable control of the products he used was Roundup at 1 L/ac sprayed late in the fall. The 2 best treatments applied in the spring were Refine Extra and 2-4-D tank mixed with ½ L/ac Roundup. He said these treatments delayed the dandelions but did not effectively kill them.
Lyle Cowell, agrologist with the Sask. Wheat Pool, had a project on alfalfa termination and dandelion control. He sprayed a number of products on dehy alfalfa fields in May, July, and late September. He rated them the following August finding the best dandelion control by 10 to 20% where the treatments were sprayed in late September. The best product was 2 L/ac of Roundup.
The Crop Development Center at the U of S and Agriculture and Agri-Food Canada at Scott have had a dandelion control project the last few years. It was based on 2 sequential applications. One of these is in the fall followed up with a ½ liter of glyphosate burn-off in the spring. A third product in the sequence could in some cases be the in crop herbicide. Using a competitive crop will also place pressure on the dandelion population. The CDC fall treatments consisting of 4 product or product combinations were sprayed at 2 different times: late September and late October. Ken Sapsford reported on the project in their Weed Control Research - 2001. He suggests that the late October application showed poorer control because it was done after the dandelions had already been hit by a severe frost. Eric Johnson provided the numbers for this last season's ratings at Scott. The very dry conditions these last 2 years have made it impossible to have complete results, as the plots out of Saskatoon were not rated this past year but there are some interesting trends. See Fig. 1 and 2 for a summary of the four best products. It must be noted that these are only preliminary results and the CDC has hopes to carry on an expanded project so continue to monitor their results.
A new registration for dandelion control in the spring has been submitted by Dupont. It is for 4 g/ac of Express tank mixed with ½ L/ac of glyphosate. This is applied pre-seed for cereal seeding. For control of those rosettes larger than about 6" that rate can be increased to 6 g/ac. Watch for specific details after Nov.
Rob Ripley, Technology Development Representative with Monsanto at their Saskatoon research farm suggests that dandelion control is related to staging and growth that moisture induces. He observed in the late 90's that with moisture in the fall, pre-harvest Roundup was giving good dandelion control. See Fig. 3. The last few years have been drier, and there has not been sufficient moisture before pre-harvest to stimulate dandelion growth. Also crops matured earlier so pre-harvest was applied earlier and there was less time for dandelion re-growth. The in-crop herbicide may also have still been retarding re-growth more than when pre-harvest is applied later. The result has been poor pre-harvest control. After the crop comes off the canopy is opened up and dandelion re-growth is stimulated. The result is better post harvest control. Furthermore, Rob also suggests that dandelions seem to be more frost tolerant than other perennials. In conclusion, Rob reiterates that the options for dandelion control are pre-seed, using competitive crops in rotation, in-crop, pre-harvest, and post harvest.
