Risk of damage to turnip rape from certain herbicides used in the previous crop
Turnip rape is more sensitive than rapeseed to many herbicides and it has been shown that recommendations for following crops sometimes underestimate the risks. I especially want to warn of risks with products containing the active substances florasulam and pyroxsulam when the following crop is turnip rape. Florasulam and pyroxsulam belong to the group of ALS inhibitors and are common in many products used for weed control in cereals. Some products are Broadway, Broadway Star, Gullviks Prima, Gullviks Grande, Flurostar XL, Primus, Saracen and Starane XL. For several of the products, it is stated that any crop can be grown after the treated crop, but I have several times had severe damage to especially winter turnip rape grown after a crop treated with florasulam and pyroxsulam.
Some examples:
Year 2018
Previous crop was winter wheat treated with Broadway in the spring of 2018. In August, the field was prepared with shallow cultivation and then winter turnip rape was sown. Many plants died soon after emergence. In patches, turnip rape plants survived but had slow growth.
Year 2022-2023
Previous crop was spring barley treated with Starane XL and Harmony 50 SX in the spring. Also in 2021 there was spring barley with the same treatment and the field was plowed in the fall of 2021. The field was cultivated and sown with winter turnip rape in August 2022. There were no clear symptoms in the fall, but in May 2023 the lower leaves of the turnip rape turned yellow. Many pods were poorly filled and the yield was low.
Year 2023-2024
Previous crop was winter wheat treated with Gullviks Prima in the spring of 2023. In August 2023, the field was plowed and then winter turnip rape was sown. The winter turnip rape was growing very well in the fall and overwinters 100%. But in the spring the lower leaves turned yellow and the crop was growing poorly. Seed set was greatly reduced and the yield was about 10% of normal. The symptoms were the same as in 2023, but much more severe.
Picture 1. Yellowing of the lower leaves of winter turnip rape in the spring of 2024.
Year 2024
Previous crop was spring barley treated with Starane XL and Nuance in the spring. In 2023 there was winter wheat that was treated with Gullviks Prima in the spring. The field was plowed in autumn 2023 after the winter wheat harvest. In August 2024, the field was plowed after the spring barley, but because it was dry and hard, the plowing became shallow on some parts of the field. At the end of August, winter turnip rape was sown. In the parts that were plowed deeply, emergence was poor and the plants that emerged died after a few days. Where the plowing was shallower, the plants survived but grew slowly.
It appears that florasulam and pyroxsulam degrade slowly if the field is plowed after the treated crop. Turnip rape that is established afterwards can grow well at first but is affected when the roots reach deeper. Plowed-down residues of the herbicides can also be plowed up after another year and then cause damage. In some cases, I have seen symptoms of damage 24 months after treatment with Broadway.
Not everyone agrees that any crop can be grown after a treated crop. For the herbicide Florasulam 50, which is sold in Australia, 8 months is specified as the limit before you can sow canola, field beans and peas. In Ontario, Canada, there is a limit of 11 months before you can sow canola after a treatment with pyroxsulam. The Swedish Agency for Agriculture's publication " Kemisk ogräsbekämpning " mentions that in 2018 there was secondary damage to winter rape from Broadway products.
Jerrestad Agro AB supplies varieties of winter turnip rape and spring turnip rape and I recommend not using florasulam and pyroxsulam 24 months before establishment of turnip rape. The time can possibly be reduced if you do not plow after the treated crop. Low doses can also reduce time. For example, a full dose of Broadway provides 5 g of florasulam and 15 g of pyroxsulam per hectare, while a full dose of Starane XL provides 1 g of florasulam.
What possibilities do you have for chemical weed control in cereals when you want to sow turnip rape afterwards? ALS inhibitors (Group 2) can cause damage at very low levels, but thifensulfuronmethyl and tribenuronmethyl break down quickly and seem to be safe to use. Fluroxypyr (group 4) also seems to work well. It does not exclude all others, but these are the ones I have experience with.
