Winter Rapeseed: Farmers Advised to Hold Off on Kerb Flo and Milestone Herbicides
A German crop protection adviser warns that propyzamide-based herbicides in winter rapeseed work reliably only in clear cold and with enough soil moisture. Spraying too early can sharply reduce control of blackgrass and other grass weeds.
Winter rapeseed growers in Germany are being advised not to treat the first ground frosts as a signal to spray herbicides. Nikolaus Schackmann, a crop protection adviser at DLR Eifel (a regional agricultural services centre in Germany), says the products Kerb Flo and Milestone lose effectiveness if applied in mild conditions. That can mean weaker control of blackgrass and other grass weeds, according to the farming outlet agrarheute.
Temperature and moisture
Both products contain the active substance propyzamide. It works through the soil and is taken up by the roots of grass weeds. At higher temperatures it breaks down faster in the soil, which can noticeably reduce its effect. As a guide, daytime highs should ideally stay below 5 °C and soil temperatures below 10 °C. The best window is the dormant period in late autumn or winter. A few frosty nights are not enough, and an early cold snap is no reason to hurry.
Soil moisture is the second deciding factor. Propyzamide has to reach the top soil layer to get to the weed roots, so the best timing is when rain is forecast and the soil is sufficiently moist. During prolonged dry spells it is worth waiting. Rainfall also washes the substance off the rapeseed leaves into the soil.
Differences between the products
Kerb Flo acts mainly against grass weeds, including blackgrass, loose silky-bent, brome, ryegrass and annual meadow-grass. Groove and Cohort also contain propyzamide. Milestone adds aminopyralid, so it also covers broadleaf weeds such as chamomile, corn poppy and cornflower.
Application conditions
Rapeseed should have at least four true leaves (BBCH 14). For still-sensitive grass populations without volunteer cereals, 1.25 l/ha is advised; for hard-to-control blackgrass and volunteer cereals, 1.875 l/ha. The valid approval conditions remain decisive. Water volume should be at least 200 l/ha. Mixing Kerb Flo with insecticides is not sensible, because the herbicide must reach the soil while insecticides must reach the plant.
If the crop has to be ploughed up in spring, maize, potatoes, peas and sunflowers are possible after Kerb Flo following ploughing, while after Milestone only maize, spring rapeseed and cabbage are named.
