South: Beware choosing diquat for desiccation

The atrocious weather shows no signs of letting up and the lack of sunshine and high disease pressure will surely limit grain fill. I recently went to look at some very interesting fungicide trials.

The fungicide treated plots looked reasonably well, but the untreated trials were awful. Most varieties had virtually been defoliated by either rust or septoria, except for Relay, Grafton, JB Diego and Tuxedo. These four varieties looked relatively clean and I suspect trials like these this year will lead to a shake up on the recommended list to some of the resistance scores!

Rape desiccation is now under way and the debate about Reglone (diquat) versus glyphosate on lodged crops has surfaced again. It is true that if plant stems are kinked then translocation of glyphosate around the plant will be limited but would reglone do a better job?

Firstly you need 300-400 litres of water/ha for reglone to work effectively, and it works by contact only, so in a tangled lodged crop how on earth will the chemical penetrate the first layer of pods and desiccate the stems? In practice it never has done and it never will.

Talk to any combine driver who has experienced harvesting lodged crops desiccated with Reglone and you will hear tales of sap wet haulm, blocked concaves, clogged sieves and high seed losses. For these reasons I will only be using glyphosate and always advise the addition of a pod sealant.

Fortunately, most of my crops have stood well and the few that have lodged have done so at the stem base as a result of saturated soils and poor anchorage and therefore have not kinked the stem. I am going to keep rates of glyphosate high and advise using 150 litres of water. If a pod sealant is being used don’t use much more water than this, as trials work indicates that efficacy reduces the more water you use.

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