The main objective of the potato harvesting operation is to lift the crop with minimum damage to tubers as well as minimum amount of clay, dirt and stones. The first stage of potato harvesting is to desiccate or “burn-off” the foliage (haulms).
Potato Harvesting Desiccation
Good haulm desiccation is crucial to lifting and storing good potatoes. Number 1, getting rid of the foliage stops tuber blight by removing the source of zoospores. Secondly, stopping the plant growing and achieving good skin set means improved storage life and less damage at lifting, no matter how gentle you are with the tubers.
Thirdly, a good skin set means a bright potato with better marketability, and greater resilience against storage diseases such as Pink Rot and Gangrene. It is essential for controlling the tuber size for specific markets, and lastly detaching the stolons from the tubers means gentle lifting and easier sorting on the harvester.
There are many ways to achieve a fast and effective burndown. Growers are often told that there is a ‘right way and a wrong way’ but in reality if it works for you that is what matters. What are the options available?
|Flail||Safe, zero harvest interval Essential in dense canopies in varieties such as Asante, Melody or Shangi||Needs to be set up well to avoid ridge and tuber damage More wheelings through crop Tends to be less effective at detaching stolons. Avoid if Blackleg present in the crop.|
|Diquat||Fast, removes Blight risk. Good stolon detachment A small, early dose makes failing far easier and more effective. Kills weeds and prevents them seeding Can mix a fungicide such as fluazinam to reduce Tuber Blight.||Dry soil around tubers can shock the plant and cause vascular browning. Not available in every country.|
|Glufosinate ammonium||Given time, it is very effective on prolific varieties. Provides good weed control.||Only approved in some countries, NOT Kenya. Need to wait until crop is naturally senescing. Less relevant for smaller seed or salad crops.|
|Carfentrazone||Far less regrowth than Diquat.||Not available in Kenya as yet. Slow acting|
Stopping indeterminate varieties such as Markies can be quite a task in some years, and it starts with not over fertilising the crop.
But when the canopy is thick, a low dose of desiccant is a good start followed by the flail to cut the haulm. In crops that are smaller but still growing rapidly I prefer to spray first, then top to reduce the shock of cutting off the foliage. This is particularly important where you are looking for smaller tubers.
Where there is blight active in the crop, spraying diquat or paraquat first with a fungicide with zoospore activity such as Infinito or fluazinam is more sensible.
In dry conditions when bruising risk at lifting is particularly high, flailing early in the day is ver\y important. This allows the tubers to rehydrate overnight, so they are less prone to physiological shocks which can cause internal browning.
In wetter conditions regrowth is often rapid, so hitting with paraquat or diquat will likely need two and possibly three sprays to stop the crop.
Carfentrazone is quite effective on stems but less so on dense foliage and is relatively slow acting.
Flailing requires accurate driving to avoid ridge damage, which is why on ware crops many growers open the crop up with a low dose of diquat/paraquat with the final fungicide. The flail also needs to be set correctly – it is essential to leave 25cm of stem for the follow up chemical to work on, and make sure that the haulm is thrown into the furrow and not left on the ridge where it will stop the chemical getting to the stems.
Above all, keep monitoring – it will be different in every variety each season so stay flexible.
Till next time,
David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.