Mid-summer is always a good time to watch out for crop pests. Take a quick pass around the farm to look for one of the most obnoxious weeds around, leafy spurge. My co-worker, Graig Reicks (SDSU Extension weed ecology field specialist), wrote this article focusing on leafy spurge that I want share with you.
In June, leafy spurge, one of our most problematic rangeland, pasture, and roadside weeds, displays its yellow bracts. This is also one of South Dakotas noxious weeds that landowners are required by law to control. Leafy spurge spreads through underground rhizomes and by seeds that are often viable by mid-July. Short-term control of leafy spurge is often achieved with a combination of 2,4-D and picloram (Tordon), both synthetic auxins (group 4 herbicides). As weve learned over the years, repeated use of herbicides that target the same site of action can cause the weed to become resistant to those herbicides.
Even though theres been no reports of group 4 herbicide resistance to leafy spurge, we should still consider incorporating other herbicide modes of action into our leafy spurge management strategies. Two underutilized modes of action include imazapic (Plateau), which belongs to the ALS inhibitors (group 2) and saflufenacil (Sharpen, Detail), which belongs to the PPO inhibitors (group 14). Saflufenacil kills above-ground foliage on contact, but has little to no impact on the roots. Since killing the roots is essential for controlling perennial weeds, saflufenacil should be mixed with systemic herbicides, such as Plateau, Tordon, and/or 2,4-D that are translocated throughout the plant.
Research from Nebraska (Datta et al., 2013) has shown that when Plateau is tank-mixed with and applied during flowering, it can provide three years of control from a single application, as opposed to only two years of control from a fall application of Plateau. SDSU research has also shown that adding saflufenacil to herbicide tank mixes can increase the performance of both Tordon and Plateau at one year after application (Figure 1).
However, when Tordon was tank-mixed with 2,4-D ester, there was no benefit to the saflufenacil addition. If herbicides have already been purchased, its best to apply them soon, if they havent already been applied. If they havent been purchased, consider diversifying herbicide modes of action by applying Plateau plus saflufenacil.
As a downside, Plateau applications made after green-up can suppress growth of desirable grasses, especially the cool-season species of smooth brome and Kentucky bluegrass. For this reason, its often applied by transportation departments to reduce mowing costs in right-of-ways.
The Nebraska study reported a 30% reduction in cool season grass production for up to six weeks after application after a 9 fl oz/acre Plateau application.
To reduce the chances for temporary grass production decline, apply Plateau at 6 fl oz/acre instead. Refer to the label to determine whether the grass species present on your land may be susceptible to growth suppression.
Since leafy spurge may exhibit regrowth from underground rhizomes, continue to monitor regrowth and expect to make more than one application to fully-control this weed. Since weeds can quickly become resistant to ALS inhibitors, do not repeatedly apply Plateau. Mowing, hand weeding, and releasing leafy spurge beetles can have utility as well.
When youre not controlling summer crop pests or tending to livestock, come visit us at one of our summer events happening in your area. We look forward to seeing our clientele each year and hope we can provide you with useful information and networking opportunities.
Upcoming agronomy-related events
Please see extension.sdstate.edu/events for more info/registration on all events.
- Northeast Research Farm Field Day July 10; 4 p.m.-dusk at 15710 455th Ave., South Shore. Supper provided.
- Oak Lake Field Station Field Day July 10; 9 a.m.-4 p.m. at 19862 483rd Ave., Astoria. Lunch will be provided. Registration is preferred.
- Integrated Pest Management (IPM) Field School July 22; 9 a.m.-4 p.m. at the SDSU Volga Research Farm, 21200 464th Ave. Volga. Lunch is provided no registration cost.
- Cover Crop and Organic Vegetable Production Field Day at Haroldson Farms July 22; 10 a.m.-1 p.m. at 20044 464th Ave., Bruce. This co-hosted event with SDSU Extension, the SDSPA, and Haroldson Farms. A light farm-to-table lunch will be provided.
- Cut Flower and Pumpkin Field Day July 25; 9 a.m.-3 p.m. beginning at Eden Acres near Alpena Lunch will be provided, and registration is preferred.
- Cottonwood Field Station Field Day Aug. 13; 9 a.m.-noon at 23738 Fairview Road, Philip.
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