Over the last three years, potato growers lost the approval for the most commonly used herbicides: linuron (in 2017) and diquat (in 2019), AHDB Potatoes says in a news release. It says weed control management has become a challenge, which experts are now trying to resolve by researching alternative options at the Strategic Farms trials.
During the trials at the AHDB SPot Farms, two herbicide options have come forward: Emerger (aclonifen), a product manufactured by Bayer Crop Science UK, and Shark (carfentrazone-ethyl), manufactured by FMC Agriculture.
Emerger is a residual herbicide and it was investigated as a potential replacement for linuron.
The efficacy of Emerger, which is a residual herbicide, was studied in trials at SPot West (Heal Farms, Shropshire) and SPot North (RJ and AE Godfrey, Brigg, North Lincolnshire) in 2019. Last year’s herbicide trials investigated the effect of Emerger with different combinations of residual herbicides on weed counts and phytotoxicity. The varieties included in these trials were Maris Piper and Sunita.
Emerger was applied alone at the approved rate of 1.75 l/ha and then in two-way combinations with Shotput, Praxim, Stomp Aqua, Gamit 36 CS and a three-way combination with Praxim and Defy. When applied alone, Emerger showed good weed control results.
However, the best results were noticed when applied in combination with another herbicide. For both SPot West and SPot North, no phototoxic symptoms or differences in crop vigour were observed on any of the varieties.
The weed burden has to be taken into consideration when herbicides are applied. Emerger showed good results against fat hen, mayweed, stinging nettle, annual meadow grass, blackgrass, runch and charlock. Full control of oilseed rape was seen across all treatments. Emerger alone provided partial control of knotgrass and bindweed, but it was felt that this was not sufficient enough to give commercially acceptable control.
“Emerger has to be applied in an even layer, while the product is maintained in constant agitation, and the soil should not be disturbed after spraying in order to achieve good weed control,” said Edward Hagues, Campaign Manager for Potatoes and Industrial Crops at Bayer.
Shark, which is a contact herbicide, was observed in trials as a potential replacement for diquat. The trials took place in 2019 at SPot South-West (Dillington Farms) and SPot East (Elveden Farms).
Trials and application
Two varieties were planted at SPot South-West, Georgina and Lanorma, and four at SPot East, Nectar, Maris Piper, Jelly, and Sovereign.
Shark label instructions state that the product should not be applied later than 10% emergence, which is a major difference to diquat, which could have been applied up to 40% emergence.
“When Shark is applied in a tank mix with a residual herbicide, it would be best to apply it before cracking of the ridge of the potato crop, rather than catching any emerging leaves of the plant as it comes through the ground,” said Jeff Fieldsend, Commercial Agronomy Manager at FMC.
In the trials conducted at the SPot Farms, Shark was applied at one of three timings: pre-emergence, 10% and 50% emergence. Severe symptoms of phytotoxicity were seen when the product was applied at 50% emergence. The crop vigour was also badly affected. Jelly showed the most severe symptoms, with a 50% reduction in crop vigour at the final application timing with Shark. Maris Piper was the least affected variety, with 40% reduction at the final application timing with Shark.
During application, the full ridge should be sprayed in order to achieve the best results: “Water volumes should never be reduced, a minimum of 200 litres is required to assure good ridge coverage. Another aspect potato growers should take into consideration is the wind. Windy conditions and crosswinds could result in certain parts of the ridge not being properly treated,” said Jeff.
Fat hen, common fumitory, , common groundsel and stinging nettle were weeds present at SPot East, which were fully controlled by this treatment. “Shark has good results on a large spectrum of broad-leaved weeds, but it has very little activity on grass weeds currently,” added Jeff.
AHDB concludes that Emerger and Shark have shown good weed control during trials. Factors such as weed spectrum, variety resistance and soil type and moisture have to be taken into consideration before deciding on which weed management programme to follow.
To improve results when applying Emerger, a mix tank with another chemical will have to be applied; in this case, the price of application will also have to be considered.
Shark label timings have to be followed carefully as the difference between 10% emergence and 50% emergence can be a matter of days, and if applied later, this herbicide will have a negative impact on crop vigour and yield quality.
AHDB points out that with less chemicals available than before and the resistance of the weed spectrum to herbicides increasing over the last years, growers will have to follow an IPM strategy as well as looking at non-chemical weed control methods, such as mechanical, hand or laser weeding in-crop.