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irrigated potato field

Tubercare

tubercare blue and white logo

Keeping Good Seed Healthy

The Tubercare initiative is an IPM approach to maximising seed tuber potential encompassing -

  • The understanding of diseases and the risk they pose.
  • When to use a fungicide seed treatment and how to get the best out them.
  • The cleaning, calibration and servicing of equipment and storage facilities.

All with the aim of keeping good seed healthy.

Read more in the ‘Disease Biology and Risk’ Tab

Potatoes spend more time in store than in the ground.

A seed tuber’s life can be split into 3 key Phases; at harvest, during storage and leaving store.

 

AT HARVEST

 

 

drawing of potato harvester

DURING STORAGE

 

stack of potato box store

LEAVING STORE

potato grading machine drawing

 

Resources

Open the ‘Resources’ Tab for: 

  • Downloadable content:

                 - Application and Calibration Guides

                 - Storage Guides

                 - Record Forms

                 - Product Labels

  • Potato Variety Information
  • Videos – calibration and best practice
  • Request FREE Treated Seed Labels
  • External Links; AHDB Store Managers Guide

Disease Biology and Risk

An understanding of the biology, life cycle and risk factors of unwelcome diseases - is the first step in the Tubercare initiative.

  • The Disease Profile Cards below explain the biology behind the common diseases seed tubers face. Helping identify which disease(s) are threats to a particular crop.
  • The IPM techniques indicated on the Disease Profile cards are the first steps that should be taken to help prevent these diseases occurring.  
  • As with most aspects of crop production, keeping good seed healthy is a matter of quantifying risk.
  • Certis’ fungicide seed treatments can be a vital tool in mitigating that risk.

Risk of disease should be assessed on a stock­-by-stock basis.

Some key considerations are:

Risk factor

Treatment threshold

What is the variety’s disease resistance rating?

Use an objective source such as the AHDB potatoes variety database.

If the susceptibility rating (resistance score) is low, consider a routine fungicide treatment.

Is the variety prone to damage during handling or is there any evidence of damage?

Varieties with longer more elongated tubers are more susceptible to damage when harvested and handled.

Damage, bruises, wounds and skin splitting can all lead to the ingress of disease through contact of disease inoculum on vulnerable exposed tuber flesh.

If damage is more than normal or skin set is poor, apply a fungicide seed tuber treatment.

Was disease present on the planted mother tubers?

Diseases like gangrene, dry rot, and skin spot are difficult to eradicate once established in a stock.  Even low levels in planted seed can cause severe disease in the harvested crop.

Does the farm have a history of particular disease issues?

If so, routine treatment may be required to suppress the disease.

Is the stock late harvested?

Late harvest increases the risk of most diseases except dry rot.

Are the conditions at harvest wet?

Wet harvest conditions make drying the crop more difficult and conditions favourable for infection, particularly by skin spot and silver scurf.

Assessing the risk of disease is often a challenge, and it is worth seeking specialist advice. If you suspect a particular disease issue, consult a BASIS qualified agronomist for a treatment recommendation. Professional diagnostic services are also available, and it is well worth checking what threats you are facing.

Table of variety disease resistance

Fusarium (Dry rot)

Dry Rot can cause loss of tubers both in store & in the field.

The fungal species responsible are from the Fusarium family. In Britain the most common fusarium pathogens ranked in order of prevalence are:

  • F. Coeruleum [Formerly F. Solani var coeruleum] 
  • F. Culmorum
  • F. Avenaceum
  • F. Sambucinum [Formerly F. Sulphureum]

    

Fusarium is a soil borne with infection occurring at harvesting and grading. It will infect any damaged tissue. Prevalence may well have increased in recent years, as many of the current popular varieties are considered to be thin skinned and therefore more prone to mechanical damage.

Alternative crop hosts should be born in mind when planning to grow susceptible varieties. Varietal resistance varies according to Fusarium spp. Some varieties are particularly susceptible.

DNA testing is available to help growers identify the fusarium species on their farm which can be helpful when managing susceptible varieties (as seen in the list below).

A good guide for managing dry rot is shown in the tables below. Click to enlarge. 

     

table of risk factors
Source: Originally BCP
Table of resistant potato species
Source: Originally BCP
Table of alternative fusarium hosts
Source: Originally BCP

Rhizoctonia

Otherwise known as Stem, Stolon & Root Canker/Black Scurf.

Symtoms are visible in various formats.

The Haulm: Brown or reddish lesions along the surface or at the end of shoots result in pruning of the stems as the lesion extends.

Extensive attack by the fungus can result in no, or delayed, emergence & uneven weakened plants. Further development of the disease can lead to cankers, girdling stem bases, premature death of smaller stems purple colouring of leaves & formation of aerial tubers.

potato plant stem showing sign of disease

Roots: Brown to reddish -brown lesions along or at root ends can result in pruning of roots, The disease reduces the root mass & function, preventing normal plant growth & development.

Stolons:  Again Lesions along the surface or at end of stolons result in pruning of the stolons. This phase of the disease causes malformed tubers & reduces number of tubers formed.

Tubers: Black Scurf is easily seen on surface of washed /soil free potatoes. The fungus produces black or dark brown structures called sclerotia .These can be of various shapes & sizes and can form or enlarge at and shortly after, harvest. Tuber symptoms do not cause damage to tuber tissue below the skin. After the start of crop senescence the rate of development is more rapid , as plants mature and soil conditions become less favourable for the fungus sclerotia are formed on the tubers.

Disease on plant roots, stolons & haulms can result in misshapen tubers, tuber cracking, skin pitting or netting.

Rhizoctonia occurs wherever potatoes are grown, and is associated with many crop & non-crop plant species. Several strains or anastomosis groups [AG] of the fungus exist in soils.

AG-3 is generally associated with the Black Scurf phase of the disease on potatoes. Diseased plants can usually be found in most fields of potatoes, but the disease incidence and severity vary greatly.

Rhizoctonia can survive for long periods on crop debris & in the soil as sclerotia & mycelium but also overwinters in a dormant state on potato tubers. Extending the time between crops of potatoes can reduce levels of the fungus.

Control

No  potato varieties are currently available with commercially acceptable levels of disease resistance. No single disease control method is highly effective. Planting seed with little or no fungus present will reduce disease risk. The use of Fungicides provide disease protection but not curative activity. Seed treatments are available as liquids & powders, however none of the currently available fungicides is 100% effective.

As the fungus also exists in the soil so this can also be managed, soil treatments can be used to reduce soil- borne inoculum levels.

The planting of sprouted seed, into warm, well drained soils and limiting the depth of the ridge will all help to reduce early season disease occurrence and severity.

Early harvest reduces black scurf especially when skins are mature. However, delaying harvest of tubers and storage of potatoes covered with soil can result in a higher level of black scurf.

Silver Scurf

Silver Scurf infection displays no obvious symptoms above ground or on the roots. However, lesions can be observed on Stolons soon after tuber initiation.

Silver scurf lesions primarily cause superficial disease of the tuber skin. New lesions may develop from spores present on the tuber surface a few weeks after planting, these can develop onto progeny tubers surface when in soil. Transmission can also be soil-borne.

silver scurf on potatoes

The lesions are usually small at harvest but enlarge during storage. Infection can occur in storage from spores present on the tuber surface after harvest or landing on the surface during storage.

The disease is most noticeable on red-skinned potatoes.

In severe cases the disease can cause skin freckling of the tubers, and has become an economically important disease through reduction in cosmetic quality of washed fresh-packed potatoes. Packers and retail grocery stores can reject infected consignments of potatoes.

Silver Scurf does not usually cause yield loss, but severe seed infection can affect vigor. The disease is also important in potato processing due to moisture loss from the tubers in long term storage.

Control

Once  the tubers are infected there is no effective control against silver scurf, especially in storage. Tubers treated with various fungicides at grading near to planting, at harvest, or at both times can reduce silver scurf infection. Imazalil applied at, or near to harvest can reduce the severity of the disease.  No cultivars carry high resistance to silver scurf.

The development of management practices that reduce silver scurf is a key element in control of the disease. These include:

  • Avoiding delay in harvest & exposure of tubers to the pathogen in the soil
  • Rapid drying of tubers after harvest, avoiding long periods of condensation on tuber surfaces in store
  • Good store hygiene such as Jet 5 disinfection.
  •  Storage temperature at less than 4C will help to control spread of the disease.

These measures can all help reduce infection and spread of disease. 

Skin Spot

Skin spot is the occurrence of black or purple spots on the tuber surface. Spots can occur singly or in groups, around eyes and on damaged skin and sometimes raised from the skin surface.

Typical symptoms: Initially small light brown spots develop on Haulm, Stem bases, Roots & Stolons.

 

Spots are usually superficial and removed by a single stroke of a potato peeler, although can develop deeper into the tuber. Spots detract from the tubers appearance and can certainly reduce the value of washed pre-pack potatoes, King Edward & Rooster are known to be susceptible.

Disease prevalence is most common in cooler regions, particularly Northern Europe.

Perhaps the most important effect of skin spot is possible non-emergence or uneven emergence of seed tubers after planting, as a result of invasion of eyes and buds. Cool conditions that inhibit growth will allow the fungus to have a greater effect.

The fungus can survive in crop debris for up to 8 years, as well dust in store, and healthy seed can become contaminated. Survival of the disease is usually up to four years.

Typically contamination of tubers occurs via cool soils at harvest, through infection by wounds and abrasions. The fungus has a long latent period so typical symptoms will not develop for several months post harvest.

Varieties differ markedly in their susceptibility to skin-spot. On the whole , thin skinned varieties are more susceptible.

Control

A main control measure is to use disease-free seed.  Store hygiene during storage periods & between storage seasons is also very important.

Early lifting in warm, dry conditions minimizes tuber infection, dry curing for 10-14 days & preventing condensation will help to prevent spread in store.  Use of fungicides at or post harvest has been shown to give good control.

Gangrene

Presence of gangrene fungus is only easily detected when the haulm senesces or is killed. No distinct symptoms are normally seen on the Haulm, Roots & Stolons.

After infection small thumb-mark depressions develop on the tuber surface. The size area of this lesion on the tuber surface may give no indication of the extent of internal rotting.

The tuber rot is prevalent in cool, temperate climates such as Northern Europe. Low temperatures increase the risk of damage, delay wound healing & make it more difficult to dry tubers.

Infection usually occurs in susceptible cultivars after late harvest in cold, wet seasons.

Control

Early  haulm desiccation and harvest will reduce the build-up of inoculum around daughter tubers. A key element of a control strategy is to reduce damage at harvest and subsequent handling as much as possible.

Dry tubers rapidly and cure in warm atmosphere to create conditions favourable for wound healing.

Considering the use of fungicides such as Imazalil applied at, or as soon after harvest, combined with early harvest & dry curing can minimize the impact of gangrene.

Good hygiene in store can avoid spore contamination during multiplication and can minimise the build-up of the pathogen. The use a rigorous instore disinfectant such as Jet-5 can assist in the store hygiene regime.

 

Windows of Opportunity 

The management of seed potato diseases in store has to be planned to fit around the producer’s workflow constraints. The Table below suggests three core windows of opportunity when seed treatments, principally Gavel, can be applied conveniently.

For some diseases there are optimum timings for product application as colour-coded in the chart below. The darker the green the more effective the timing and financial benefit.

Windows of opportunity for using seed treatments

Gavel can only be applied once to Seed Tubers.

When is the best time?

For Storage Diseases

  • The optimum time to apply Gavel is in Phase 1. This offers the best protection from the full range of storage diseases including dry rot, the number one threat
  •  If facing practical constraints – availability of equipment, time and operators – plus the potentially unknown status of a harvested crop, Gavel can instead be applied in Phase 2. Whilst not optimal, it will still provide useful management of storage diseases.
  • If Gavel has not been applied in Phase 1 or Phase 2 it may still be used in Phase 3.
  • Treatment in Phase 3 offers significant benefits in managing silver scurf and skin spot which can be of great value to ware Growers of treated seed, reducing incidence of infection in the progeny crop.
  • Treatment in Phase 3 also suit seed producers that export by offering disease control for tubers that are damaged at final grading and subsequently shipped on longer, environmentally variable, journey.

For Field Diseases

  • Phase 3 is the opportunity for additional, Rhizoctonia control with Rhino Liquid: the only product approved with both black scurf and stem canker on the label.
  • With 185 days persistence Rhino Liquid can alternatively be applied earlier in Phase 2 to reduce the number of times tubers are handled
  • Rhino Liquid may be co-applied with Gavel in Phase 2 or Phase 3.

Fungicide Resistance

In high risk situations a combination of Gavel (Imazalil) and thiabendazole may be justified. Bear in mind thiabendazole resistance is present in some strains of silver scurf, Fusarium dry rot, and skin spot. Products containing different active substances do not mix well, so ensure constant agitation and mix with warm water. Alternatively, use a twin injection system.

Minimise Handling

If possible, apply tuber treatments at scheduled handling events, rather than adding an extra process.

potato harvester drawing

Phase 1 - At Harvest & Into Store

Early application of seed tuber treatments can be more effective at controlling disease infection and spread both during storage and in the following crop.

At Harvest

Although this is an ideal time to treat seed tubers, applying a fungicide safely and efficiently, while achieving adequate and consistent coverage can be a challenge.

Where the nozzles are positioned in the process affects coverage and there are health and safety implications for operators and pickers. Soil tare and environmental conditions also have a big impact on application.

Pros

- Treatment is as early as possible – fungicides work best as protectants

Cons

- Only possible when the whole crop is to be used for seed.

- Variable coverage with inadequate quantities of active substance contacting tuber surfaces caused by soil tare and wind diverting spray mist away from tubers.

- No purpose-made application kits available so set-ups tend to suffer from problems such as

  1. Application rate not linked to flow rate of crop.
  2. Incomplete coverage from stationary nozzles spraying stationery tubers
  3. Nozzle positioning not easily adjusted as conditions change 

- Limited chance for tubers to dry before loading into storage boxes so tubers remain damp in storage creating the ideal environment for disease.

Grading Into Store

This option suits lifting into bulk containers, rather than directly into boxes, and is the only Phase 1 option for dual purpose crops.

To optimise coverage and fungicide performance apply over a roller table with an air assisted canopy and rotating nozzles.

Pros

- Treatment is as early as possible – fungicides work best as protectants

- Ware fraction can be safely separated and marketed

- With a roller table uniform and accurate coverage of the seed fraction can be achieved

- Provides opportunity to apply a mix of products for fungicide resistance

- Flexibility if harvest conditions are wet or soil tare is high

Cons

- Double handling can increase the risk of damage

- High throughput at harvest requires applicators to be capable of treating large volumes per hour and be well calibrated and supervised during application

- Treated tubers need to be dried after treatment and cured if appropriate

Top Tips

  • Aim is to safely get complete coverage of tubers that are soil free
  • Nozzle choice

    • Misting nozzles – Extremely susceptible to drift so not suitable. However, these nozzles can be used to apply water to the separator in a dry season.
    • Flat fan nozzles – Less susceptible to drift and have a good breadth of coverage. However, the wide ‘fan style’ spray delivered from a single application point is only one dimensional.
    • Hollow cone nozzles – The best choice offering two points of application, at opposing angles, as the tubers pass beneath. Coverage may be further enhanced if the tuber is rotating e.g. on a separator or roller table.

  • Nozzle positioning

    • On an elevator or conveyor – The last point of handling, unlikely for damage or wounds to occur after the fungicide is applied. However, the tubers are often stationary and sometimes heaped on top of each other. With limited tuber movement or rotation, it may be difficult to achieve good coverage. The spray boom could also be in a vulnerable position, easily susceptible to damage.
    • Above a separator – On the last row or two of a separator, the tubers are rotating and they will be at their cleanest in the handling process. With the use of hollow cone nozzles, this may be the best opportunity to achieve good coverage. A spray boom above a separator may also be used in dry harvest conditions to apply water, preventing nipping and bruising.
    • Webbing – Here, tubers are more likely to be evenly spaced. Steady, even, horizontal flow, over a wide area is preferable. Larger, open, webbing gives the opportunity to have nozzles directed in opposing positions – from underneath and from above – to improve coverage, in the absence of tubers being able to rotate. However, be very conscious of the proximity to operators – always conduct a COSHH assessment. This set-up is also less vulnerable to spray boom damage.

  • Set application rate to flow rate of tubers under spray nozzles – usually possible with electronic control systems.
  • Ventilate treated tubers as soon as possible after harvest ideally using a positive ventilation system such as a drying wall.
drawing of stacked potato boxes

Phase 2 - During Storage 

Store hygiene is very important.

It doesn’t just apply to the store itself, it also applies to all associated equipment used to handle tubers;

harvesters, boxes, trailers, hoppers, grading lines, conveyor belts, roller tables, fungicide applicators, box fillers, bag fillers, forklift trucks, sweeping brushes, vacuums and even the farm yard.

All need to be clean and free from disease inoculum to reduce the chance of infection using disinfectants such as Jet 5.

Download - Certis Guide to Good Potato Storage

Infected seed potatoes with dry rot
This picture shows what can happen when store hygiene is neglected. This batch of seed left the store healthy, was subsequently graded on a Roller Table that had previously handled infected seed. The residual disease inoculum (Fusarium sp.) transferred from the Roller Table to the healthy seed and developed in further storage. No fungicides had been applied.

Click to download

At Grading

For growers that lift directly into boxes the main opportunity for seed treatment is at grading. The most important consideration here is timing as fungicides work best when applied as protectants. Delaying seed treatment gives pathogens an opportunity to become established so the sooner seed is treated, the better.

However, each time seed is handled the risk of damage and spread of disease is increased, so there is a balance to be struck. 

Early seed treatment achieves better results and is in the interest of both sellers and buyers of seed stocks.

To optimise coverage and fungicide performance, apply over a roller table with an air assisted canopy and rotating nozzles.

Pros

- Depending on machinery available, roller-table application may be possible

- With a roller table uniform and accurate coverage can be achieved

- Flexibility to await instructions from customers

- Opportunity to apply multiple treatments for both storage and field diseases

- For resistance management a second complimentary active substance can be applied

Cons

- Too late for the best control of storage diseases gangrene and dry rot

- The process of grading can increase the likelihood of sprouting. If seed is starting to chit, then early application of pre-planting treatments may be advisable. If the crop is totally dormant, there is an option to delay treatment until just prior to dispatch.

Grading out potatoes

Phase 3 - Leaving Store 

Seed treatment application may take place either grading out of store or on the receiving farm when transferring from seed bag to box for short-term storage. Seed should be dormant or with eyes just open.

To optimise coverage and fungicide performance apply over a roller table with an air assisted canopy and rotating nozzles.

Pros

Ideal time to treat for field diseases, principally Rhizoctonia

- With a roller table uniform and accurate coverage can be achieved

- Opportunity to treat seed when skins are cured and soil is more readily removed to expose cleaner skin

Cons

- Too late for good control of dry rot, gangrene and skin spot because wounds infected at harvest heal before coming out of store.

- Storage disease that have already taken hold in un-treated stock may contaminate the grading line and handling equipment spreading disease inoculum

sack of potatoes

Roller Table Application

Using a roller table is the best possible way to apply fungicides to seed tubers. Treating on a roller table offers much more control than treatment on other handling equipment.

A roller table can be used for applications in all 3 Tubercare Phases.

Of the various ways of applying seed treatments over a roller table, a rotating hollow cone nozzle(s) with an air assisted hooded canopy has been shown to give the most consistent, uniform spray pattern.

Certis has compiled a guide to help you get the best out of liquid seed treatments when applying over a roller table. Calibration Chart included.

Download - Certis Guide to Applying Liquid Seed Treatments with a Roller Table

Most consistent, uniform spray pattern achieved with a hooded applicator.

Click to download

Setting up your roller table

Potato seed treatment experts Paul Overton and David Turner give top tips for setting up a roller table. 

 

Roller Table Application Guide

Roller Table Calibration Chart

Treatment Record Form

Nozzle Flow Rate Charts

Gavel

Fungicides

A soluble concentrate containing 100 g/litre imazalil (9.35% w/w) for use as a protectant fungicide on potato for the reduction of silver scurf, gangrene, skin spot and Fusarium dry rot on seed potatoes.

See more…
Jet-5

Adjuvants and Sterilants

A powerful disinfectant (5% w/w) peroxyacetic acid, recognised as a food grade sanitiser with organic status, containing peroxyacetic acid, for the use in all areas of horticulture and agriculture for the disinfection of surfaces.

See more…
RhiNo

Fungicides

Seed treatment fungicide containing 460 g/litre (40.7% w/w) flutolanil for the control of black scurf and stem canker on potatoes.

See more…
RhiNo DS

Fungicides

A dust formulation containing 60 g/kg flutolanil for control of black scurf and some reduction of stem canker on potatoes.

See more…

Roller Table Application Guide

Roller Table Calibration Chart

Potato Storage Guide

SAC Good Practice Guide

Treatment Record Form

AHDB Storage Disease Resistance Ratings

Nozzle Flow Rate Charts

 

 

SAC Good Practice Guide

Certis have worked with SAC Consulting to create a good practice guide when using seed treatments. Click the options below to read more.

Post-harvest seed tuber treatments can form a vital part of Integrated Crop Management (ICM) for potatoes. Potato crops often spend longer in store than in the field, so it makes sense to apply the same attention to both situations.

A “one-size-fits all” approach to seed tuber management is not appropriate. Every seed stock, field, and season can lead to different disease pressures.  Underpinning disease risk are the different disease resistance ratings of varieties. Take time to identify what the risks are for the varieties you grow and what are the appropriate management responses. The decision to treat, or not to treat seed will depend on several factors.

Seed treatment is a component of good storage crop protection; it will not be effective unless it is integrated with other approaches. Seed treatments should only be applied when needed, in many situations non-chemical control measures will be sufficient. This document contains information specific to storage disease management, a more general overview can be found from sources such as the AHDB’s Store Managers’ Guide.

It is important to identify the cause of disease symptoms when they occur within a stock, as correct identification will ensure the most appropriate control measures can be applied.  Symptoms of various diseases can often be confused.  For example, dry rot pustules may develop on the surface of a rot primarily caused by watery wound rot.  Consult sources such as the AHDB, or seek expert advice.

Risk of disease should be assessed on a stock­-by-stock basis. Some key considerations are:

Risk factor

Treatment threshold

What is the variety’s disease resistance rating?

Use an objective source such as the AHDB potatoes variety database.

If the susceptibility rating is susceptible (rating of 1, 2 or 3), consider a routine fungicide treatment

Is the variety prone to damage during handling or is there any evidence of damage?

If damage is more than normal or skin set is poor, apply a fungicide seed tuber treatment.

Was disease present on the planted mother tubers?

Diseases like gangrene, dry rot, and skin spot are difficult to eradicate once established in a stock.  Even low levels in planted seed can cause severe disease in the harvested crop.

Does the farm have a history of particular disease issues?

 

If so, routine treatment may be required to suppress the disease.

Is the stock late harvested?

 

Late harvest increases the risk of most diseases except dry rot.

Are the conditions at harvest wet?

 

Wet harvest conditions make drying the crop more difficult and conditions favourable for infection, particularly by skin spot and silver scurf.

Assessing the risk of disease is often a challenge, and it is worth seeking specialist advice. If you suspect a particular disease issue, consult a BASIS qualified agronomist for a treatment recommendation. Professional diagnostic services are also available, and it is well worth checking what threats you are facing.

For full disease profiles, return to the 'Seed Potato Disease Biology' tab, at the top of the page.

Not all crops will require a seed treatment. If risk of disease is judged to be low and the variety has strong resistance characteristics, disease risk can be adequately controlled by store management (temperature and ventilation). This is an individual judgment call. Application of fungicide where it is not needed is wasteful and jeopardises both sustainability and product stewardship.

In situations that are judged to be high risk, using a combination of imazalil and thiabendazole may be justified. However, bear in mind that for many pathogens resistance to thiabendazole is present in some strains. Products that contain the different actives do not mix well, so ensure constant agitation or use a twin injection system.

If you are growing a crop where a large part of the crop will be sold as ware or you grow a seed-only crop but plan to sell over-sized tubers (‘tops’) for ware, fungicide seed treatment can only be applied after the ware fraction has been separated.  In addition, tubers discarded during grading of seed cannot be fed to livestock. Treated tubers cannot be used for human or animal consumption.

Determining how you plan to market your crop is the first step in the decision process. Tolerances for quality characteristics may be different for different customers, some export markets have high requirements for skin finish and very low tolerances for disease. Knowing what you are trying to achieve should frame your storage strategy.

If you are buying seed and are considering treating it, make sure you have a crop history and are aware of previous treatments (if any) so that maximum number of applications are complied with.

Treatment with fungicide within 2 days of harvest will give optimum control of infection by diseases during storage.

Regardless of when you treat, all equipment should be regularly checked and calibrated to minimize damage to tubers during operations.

Some growers choose to treat at harvest, although treatment on an indoor roller table is preferable. In most cases at harvest treatment is very difficult to do well. Early applications post-harvest can be more effective at controlling pathogen infection and spread both during storage and in the following crop. However, achieving adequate and consistent coverage may be very difficult. Applying fungicide on the harvester safely and efficiently is a difficult task.

Producers who treat at harvest often have a bespoke system, adapted from separate components. Where the nozzles are positioned will affect coverage, and clearly there are health and safety implications if there are pickers on the harvester.

Soil tare and environmental conditions will have a big impact on “harvester” application. High soil tare may lead to poor coverage by the fungicide treatment. High wind may divert spray mist – even a canopy cover will not fully prevent this.

For these reasons higher water volumes (3 – 6 L/t) are usually used for on harvester treatment. If this is the case, it is important that treated tubers are well ventilated as soon as possible after harvest. A positive ventilation system is recommended.

This is an option if you lift into bulk containers rather than directly into boxes. Separating the ware fraction and soil away from the target tubers means that (1) ware can be marketed and (2) much more uniform coverage of the seed fraction can be achieved.

Treating on a roller table offers much more control than on a harvester, and a much better chance of achieving good coverage and performance.

One disadvantage is that split grading into store can involve double handling and increased risk of damage.

For growers that lift directly into boxes the main opportunity for seed treatment is at grading. The most important consideration here is timing. Fungicides work best when they are applied as protectants. Delaying seed treatment will give pathogens an opportunity to become established.

That said, each time a crop is handled risk of damage and spread of disease is increased, so there is a balance to be struck here. Some growers delay treatment until well into the New Year as they wait instructions from customers.  This means that disease development during storage will not be controlled.  Thus, the sooner a seed treatment, the better. Early seed treatment will lead to the bester results and is in the interest of both sellers and buyers of seed stocks.

If your risk assessments indicated a seed treatment is justified, or if it is requested by a customer it is important that good coverage is achieved. This contributes as much towards efficacy as the product itself. Whenever you apply a fungicide ensure that the label instructions are followed, and that appropriate health and safety measures are in place.

There are two fungicide options available for post-harvest (storage) treatment in seed potatoes: Gavel (imazalil) and Storite Excel (thiabendazole). Of these, Gavel has the wider range of target diseases with a label claim for reduction. These include silver scurf, gangrene, skin spot, and Fusarium dry rot.

Only two chemical classes are used as storage seed potato treatments in GB: imazalil (FRAC Group 3) and thiabendazole (FRAC group 1). Resistance issues are well known for group 1 fungicides such as thiabendazole, and have been detected in pathogen populations affecting potatoes in the UK (including silver scurf, Fusarium dry rot, and skin spot). It is important to follow fungicide resistance management guidelines. For thiabendazole, where resistance is known to occur for some pathogens, excessive use should be avoided. If used, it should be integrated with other measures and preferably applied in conjunction with imazalil.

Once you have identified which disease(s) are threats to a particular crop, the condition of the tubers should be assessed. If damage is present a curing stage will likely be required. As storage fungicides are protectant, it is generally better to treat seed prior to curing. Fungicide sprays will not reach the tuber surface where tubers have a heavy covering of soil.

Seed treatments are most effective if the following conditions are met:

  • Skin set is complete
  • Damage is minimal
  • Tubers are still dormant
  • Tuber skins have low soil adhesion
  • Tubers are dry

In practice, it may be very difficult to achieve all of these conditions and trade-offs may have to be made.

Large improvements have been made in tuber seed treatment technology in recent years. Older systems such as the spinning disc and fixed hydraulic nozzle applicators are still in use, but their efficiency is lower than a modern rotating nozzle system.

The CTC 2 applicator and canopy combination produced by Team Sprayers is the gold standard for seed treatment, and if you have an older system it is a worthwhile investment to upgrade. Some models include two nozzles and roof fans to aid distribution of seed treatment spray. These can be useful when throughput is high.

Even with a modern system fitted over roller tables, it is still possible to apply seed treatments poorly if calibration and supervision are inadequate. The most important factors are throughput and rotation of tubers. Flow of tubers through the treatment area should be uniform with complete coverage of the rollers with tubers. This is helped if tuber size is uniform (often difficult in practice) and if there is a buffering system in place to smooth flow.  In practice, this may mean utilising variable roller speeds if your system has this capability. In addition, tubers should be rotating under the spray mist to ensure that tubers achieve maximum coverage.

Even with roller tables at full capacity a proportion of spray will not be intercepted by tubers.

Over-wetting* is also a potential issue if calibration is poor. If this occurs tubers may not roll correctly through the spray mist, compromising coverage. Also, over wetting increases the risk of bacterial soft rot development.

Use hollow cone nozzles rather than standard flat fans. Cone nozzles with a fine bore produce mist with small droplets that improves coverage. Like any equipment in frequent use, these can wear and droplet size change over time. They can also be prone to blockage. Check and change nozzles on a regular basis.

 

*Optimal coverage is usually achieved with 1 – 2 L/t.  Water volumes > 2 L/t rise over-wetting.

 

  • Has a risk assessment been conducted to ensure seed treatment system complies with H&S regulation?
  • Is the operator qualified (PA12)?
  • Has the sprayer been recently calibrated?
  • Can throughput be consistently maintained?
  • Keep records of all treatment operations.

Finally, a few general points to keep in mind with stored potatoes:

  • Handle them as little as possible. Any operation where tubers are handled risks damage and disease spread.
  • Several diseases are helped by wet tuber surfaces – this includes after seed tuber treatment with liquid. Remember that seed treatment will only be effective against target pathogens. Products currently on the market will not control bacterial diseases. After treatment, dry tubers.
  • Even when treated, tubers are not invulnerable. Monitor stocks for condensation, disease development, and sprouting. Make sure they stay dry. If you identify a specific issue, it may be worth.

On the following pages a decision tree can be found. This tree has been designed to help you decide the most appropriate course of actions for your seed potato stocks.

 

 

 

FREE Treated Seed Labels

Currently, all treated potato seed lots should be labeled with information of the chemical treatment used.

To help make things simpler, Certis can provide free printed labels for your treated seed if using Rhino liquid or Gavel.

Complete the form below, indicating how many labels you need and Certis will post them direct to you. 

By ticking this box I agree to the Certis Europe Privacy Policy in line with GDPR and to receiving topical emails from Certis UK.

example of treatment label

Recent Articles

Interpreting In-Field Crop Knowledge for Better Storage 

The Vegetable Farmer November 2021

Potato specialist Dr Stuart Wale, SAC Consulting, offers advice on limiting the risk of rots and other diseases from developing post harvest. Click on the images to largen. 

article taken from vegetable farmer
second page of vegetable farmer article
screen shot of article

Dry rot risk is high in Scotland this year and seed potato growers are being urged to apply tuber treatments as early as possible to prevent disease progression in store.

Read the article >

We asked Scottish Agronomy’s Eric Anderson for a personal take on the three most significant behaviour changes needed to achieve the paradigm shift of flushing virus out of the system.

Read the article >

Virus has dominated potato industry headlines recently, as levels of non-persistent PVYN, in particular, have increased dramatically. Certis talks to two differing Yorkshire Highland Seed Potato Growers’...

Read the article >

Virus has dominated potato industry headlines recently, as levels of non-persistent PVYN, in particular, have increased dramatically. Certis talks to two differing Yorkshire Highland Seed Potato Growers’...

Read the article >

Product Information 

Click on the products for key information; Label Text and MSDS.

Gavel

Fungicides

A soluble concentrate containing 100 g/litre imazalil (9.35% w/w) for use as a protectant fungicide on potato for the reduction of silver scurf, gangrene, skin spot and Fusarium dry rot on seed potatoes.

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Jet-5

Adjuvants and Sterilants

A powerful disinfectant (5% w/w) peroxyacetic acid, recognised as a food grade sanitiser with organic status, containing peroxyacetic acid, for the use in all areas of horticulture and agriculture for the disinfection of surfaces.

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RhiNo

Fungicides

Seed treatment fungicide containing 460 g/litre (40.7% w/w) flutolanil for the control of black scurf and stem canker on potatoes.

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RhiNo DS

Fungicides

A dust formulation containing 60 g/kg flutolanil for control of black scurf and some reduction of stem canker on potatoes.

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Useful Links

AHDB Guide to potato storage diseases.

 

SAC Consulting - Potato Services. 

 

Scottish Agronomy - Potato agronomy services.