As a result of the difficult growing year and late season, main crop potato desiccation and the harvest has been delayed. Over the coming weeks, the true extent of potential yield and quality reductions will become clear.
However, growers have an added worry this year. Diquat, the mainstay active of potato haulm desiccation, joins the list of key actives to come under pressure for re-registration in Europe without limited viable alternatives.
Importance of haulm desiccation
The timely destruction of the potato haulm is an important management tool for a host of reasons. As well as helping to stop potato bulking to optimise the yield of a marketable crop at the right specification, it is also important for:
Skin-set and stolon separation: burning down the haulm helps to induce and speed up skin-set on tubers to reduce bruising and damage at harvest and assists stolon separation from the tuber. Reducing late blight infection and virus spread: in a high blight pressure season, fast destruction of the haulm can help to slow the spread of the disease to daughter tubers, particularly important for crops going into storage.Weed control: in situations were weed control was inadequate, desiccation can also kill weeds that are likely to affect the speed of harvest. Ease of harvest: haulm destruction improves harvest ease, particularly where crop senescence hasn’t taken place yet. Diquat has for many growers formed the mainstay active in potato desiccation for decades. Once tuber size and dry matters are adequate, typical burn-down strategies consist of either one application when the crop is senescing or a split-dose application to initially open the canopy followed by main application seven to 10 days later.
SMART test
The hot dry weather this year has presented many challenges. While many areas have received adequate amounts of moisture, some areas still remain very dry. Applying products containing diquat, namely Reglone, on to crops in dry soil which are under pressure for moisture can lead to tuber damage.
The in-field Soil Moisture Assessment for Reglone Treatment (SMART) test allows growers to evaluate when there is sufficient moisture in the soil prior to application.
Simply dig down to the tubers and take a sample of soil from the middle of the drill. Gently squeeze the soil with one hand into a ball. If the soil remains in a ball, then it is sufficiently moist and it is OK to use Reglone. If the ball collapses then it is too dry for Reglone.
European pressure
Diquat came under pressure at EU level over concerns surrounding possible exposure to residents. Under a new exposure model, the issue centred on vapour pressure and concerns of the likelihood of the active vaporising post application.
Diquat was discussed for much of 2017 and the decision for reregistration came before the standing committee on plants, animals, food and feed members (SCOPAFF) in May 2018. When no qualifying majority was reached in favour of non-approval, the decision went to the appeals committee. There was no qualifying majority here either so the decision now lies with the European Commission.
If the Commission doesn’t explicitly vote for non-approval, diquat registration will expire on 30 June 2019 and follow the normal grace period under pesticide regulations of a six-month sell-out period followed by a 12-month use-up period. This would permit the use of diquat until 2020.
However, if the Commission decides in favour of non-approval due to concerns around resident exposure before the June 2019 expiry date, then the sell-out and use-up periods could be significantly reduced.
Diquat alternatives
Growers are advised to experiment with alternative desiccation methods while diquat is still available. If the alternative methods fail, diquat can be used as a fail-safe to mop up mistakes. There are a limited number of alternatives including mechanical and chemical desiccation.
Haulm flailing: flailing a green or senesced haulm is currently practised in parts and is effective at stopping bulking. It can prove difficult in a wet year, however, potentially spread disease and expose the crop to bird damage. Carfentrazone-ethyl (Spotlight Plus): this is currently used on crops. Growers report good results on potato stems but the haulm generally needs to be senescing naturally or defoliated first by another means before desiccation. It is also slower acting, meaning a fungicide may have to be applied post desiccation for blight control. However, in dry conditions, it can cause little damage to tubers compared with diquat. It is also more expensive than products containing diquat.Haulm burning: involves destruction of the haulm by gas flame or intense heat. This technique can be more successful after flailing. It is sometimes used in organic production. Grower concerns
Ned English
Castlecor, Co Cork
Ned has been growing potatoes in Castlecor for over 40 years and the potential loss of diquat represents a serious challenge for his business. He desiccates all of his main crop potatoes with diquat, which is important for skin set. “I’m very much concerned, there isn’t an easy alternative,” he explains. He states that stolon separation is slow when flailing alone and the crop can be exposed to bird damage. Diquat is quick, it stops the spread of blight and is safe on the tuber when used correctly, Ned explains.
John Carroll
Paughanstown, Co Louth
John has been growing potatoes in Paughanstown for over 20 years and explains that there is no direct alternative to diquat. “It’s always been there and it now just forms part of the management of the crop,” John says. He states that Carfentrazone-ethyl does work but the crop needs to be defoliated first. Flailing also poses a risk of spreading diseases, such as black leg or blight, if present in the crop. In a wet year, an extra pass with the tractor to flail the haulm may lead to reduced traction and create sticky conditions for the harvester.
Sean Ryan
Ballinadoney, Ballywilliam, Co Wexford
Sean has been growing potatoes in Ballinadoney for over 15 years and diquat has always formed the mainstay of his potato desiccation strategy. He generally lets the crops senesce as much as possible before burning down. He fears that in the absence of diquat, flailing the crop would expose the drills to bird attacks. Chemical alternatives such as Carfentrazone-ethyl can be effective but generally take longer to work. “This means that growers will have to try and pre-empt problems in the field earlier which can be difficult,” he says.
Read more
Ruling the roost in Carlow
IFA potato report: growers' attention turns to main-crop harvest
As a result of the difficult growing year and late season, main crop potato desiccation and the harvest has been delayed. Over the coming weeks, the true extent of potential yield and quality reductions will become clear.
However, growers have an added worry this year. Diquat, the mainstay active of potato haulm desiccation, joins the list of key actives to come under pressure for re-registration in Europe without limited viable alternatives.
Importance of haulm desiccation
The timely destruction of the potato haulm is an important management tool for a host of reasons. As well as helping to stop potato bulking to optimise the yield of a marketable crop at the right specification, it is also important for:
Skin-set and stolon separation: burning down the haulm helps to induce and speed up skin-set on tubers to reduce bruising and damage at harvest and assists stolon separation from the tuber. Reducing late blight infection and virus spread: in a high blight pressure season, fast destruction of the haulm can help to slow the spread of the disease to daughter tubers, particularly important for crops going into storage.Weed control: in situations were weed control was inadequate, desiccation can also kill weeds that are likely to affect the speed of harvest. Ease of harvest: haulm destruction improves harvest ease, particularly where crop senescence hasn’t taken place yet. Diquat has for many growers formed the mainstay active in potato desiccation for decades. Once tuber size and dry matters are adequate, typical burn-down strategies consist of either one application when the crop is senescing or a split-dose application to initially open the canopy followed by main application seven to 10 days later.
SMART test
The hot dry weather this year has presented many challenges. While many areas have received adequate amounts of moisture, some areas still remain very dry. Applying products containing diquat, namely Reglone, on to crops in dry soil which are under pressure for moisture can lead to tuber damage.
The in-field Soil Moisture Assessment for Reglone Treatment (SMART) test allows growers to evaluate when there is sufficient moisture in the soil prior to application.
Simply dig down to the tubers and take a sample of soil from the middle of the drill. Gently squeeze the soil with one hand into a ball. If the soil remains in a ball, then it is sufficiently moist and it is OK to use Reglone. If the ball collapses then it is too dry for Reglone.
European pressure
Diquat came under pressure at EU level over concerns surrounding possible exposure to residents. Under a new exposure model, the issue centred on vapour pressure and concerns of the likelihood of the active vaporising post application.
Diquat was discussed for much of 2017 and the decision for reregistration came before the standing committee on plants, animals, food and feed members (SCOPAFF) in May 2018. When no qualifying majority was reached in favour of non-approval, the decision went to the appeals committee. There was no qualifying majority here either so the decision now lies with the European Commission.
If the Commission doesn’t explicitly vote for non-approval, diquat registration will expire on 30 June 2019 and follow the normal grace period under pesticide regulations of a six-month sell-out period followed by a 12-month use-up period. This would permit the use of diquat until 2020.
However, if the Commission decides in favour of non-approval due to concerns around resident exposure before the June 2019 expiry date, then the sell-out and use-up periods could be significantly reduced.
Diquat alternatives
Growers are advised to experiment with alternative desiccation methods while diquat is still available. If the alternative methods fail, diquat can be used as a fail-safe to mop up mistakes. There are a limited number of alternatives including mechanical and chemical desiccation.
Haulm flailing: flailing a green or senesced haulm is currently practised in parts and is effective at stopping bulking. It can prove difficult in a wet year, however, potentially spread disease and expose the crop to bird damage. Carfentrazone-ethyl (Spotlight Plus): this is currently used on crops. Growers report good results on potato stems but the haulm generally needs to be senescing naturally or defoliated first by another means before desiccation. It is also slower acting, meaning a fungicide may have to be applied post desiccation for blight control. However, in dry conditions, it can cause little damage to tubers compared with diquat. It is also more expensive than products containing diquat.Haulm burning: involves destruction of the haulm by gas flame or intense heat. This technique can be more successful after flailing. It is sometimes used in organic production. Grower concerns
Ned English
Castlecor, Co Cork
Ned has been growing potatoes in Castlecor for over 40 years and the potential loss of diquat represents a serious challenge for his business. He desiccates all of his main crop potatoes with diquat, which is important for skin set. “I’m very much concerned, there isn’t an easy alternative,” he explains. He states that stolon separation is slow when flailing alone and the crop can be exposed to bird damage. Diquat is quick, it stops the spread of blight and is safe on the tuber when used correctly, Ned explains.
John Carroll
Paughanstown, Co Louth
John has been growing potatoes in Paughanstown for over 20 years and explains that there is no direct alternative to diquat. “It’s always been there and it now just forms part of the management of the crop,” John says. He states that Carfentrazone-ethyl does work but the crop needs to be defoliated first. Flailing also poses a risk of spreading diseases, such as black leg or blight, if present in the crop. In a wet year, an extra pass with the tractor to flail the haulm may lead to reduced traction and create sticky conditions for the harvester.
Sean Ryan
Ballinadoney, Ballywilliam, Co Wexford
Sean has been growing potatoes in Ballinadoney for over 15 years and diquat has always formed the mainstay of his potato desiccation strategy. He generally lets the crops senesce as much as possible before burning down. He fears that in the absence of diquat, flailing the crop would expose the drills to bird attacks. Chemical alternatives such as Carfentrazone-ethyl can be effective but generally take longer to work. “This means that growers will have to try and pre-empt problems in the field earlier which can be difficult,” he says.
Read more
Ruling the roost in Carlow
IFA potato report: growers' attention turns to main-crop harvest
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