8.0 PRSR 03-09-2017 - Laserfiche WebLink

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control (knapweed beetles--weevils) is recommended. Knapweed beetles (weevils) are released during the summer. Weevils can be purchased online and they are sent via the mail. Knapweed populations should be monitored each year to keep a record of the effectiveness of the bio-control. Weevils are effective for long-term control,but not a good short-term control option. Spot treatment with a systemic herbicide such as milestone or transline can be effective for short-term control. Applying herbicide to prairie restoration areas should be done with care. Remnants with high diversity should be spot treated,not broadcast-treated. It is recommended to treat first with the least impactful chemical,monitor to see if that works,and then try another if it does not work. Degraded and highly disturbed areas can be treated a little less gently,perhaps using broadcast applications. Always follow the product label when using any chemical for weed control. Treatment should be done before the target plants form seed,so late spring and early summer are best. Professional pesticide applicators are required for herbicide treatment. Canada thistle While native thistles are not generally problematic,exotics such as Canada thistle are clone-forming perennials that can greatly reduce species diversity in old fields and restoration areas (Hoffman and Kearns 1997). A combination of chemical and mechanical control methods may be needed. Chemical control is most effective when the plants are in the rosette stage and least effective when the plants are flowering.Where native grasses and sedges are present,use of a broadleaf herbicide such as 2,4-D is recommended,since 2,4-D only affects dicots. 2,4-D is most effective when applied 10-14 days before the flowering stems bolt. It is applied at a rate of 2-4 lb/acre using a backpack or tractor-mounted sprayer or in granular form. Dicamba could also be used,with the advantages that it can be applied earlier in the spring at a rate of 1 lb/acre. Another chemical that has been used for thistles is aminopyralid ("Milestone"),which can be applied at bud stage. Aminopyralid will affect other species and it has longer residual activity than some other chemicals, so use with caution—typically use it on large patches/clones of thistles and avoid areas of higher diversity. Plants that do not respond to treatment or that are more widely dispersed could be controlled mechanically. Mechanical control, involving several cuttings per year for three or four years, can reduce an infestation if timed correctly. The best time to cut is when the plants are just beginning to bud because their food reserves are at their lowest. If plants are cut after flowers have opened,the cut plants should be removed because the seed may be viable. Plants should be cut at least three times throughout the season. Late spring burns can also discourage this species,but early spring burns can encourage it. Burning may be more effective in an established prairie,where competition from other species is strong, rather than in an old field,where competition is likely to be weaker. Friends of the Mississippi River Bailey Point Nature Preserve NRMP 79