How to control seed-borne diseases effectively and safely

Seed-borne diseases, such as bunt, loose smut and leaf stripe, have become a mostly forgotten threat to cereal production in the UK.

Bar a few instances each season, and a minor outbreak of loose smut in 2018, thought to have been caused by environmental conditions, these diseases are largely well-controlled.

The primary method of control is using fungicidal seed treatments – none of these diseases can be treated with foliar fungicide sprays, nor is there genetic resistance in today’s wheat and barley varieties.

Where outbreaks do occur, it usually arises from sowing untreated farm-saved seed.

Steps to reduce threat

There are some steps farmers can take to help reduce the threat of seed-borne diseases. For example, visually inspecting farm-saved seed crops for signs of loose smut infection prior to harvest and not using seed from infected crops is a good start.

Testing home-saved seed is crucial – most seed-borne diseases have thresholds for treatment, while buying certified seed reduces risk through its strict limits on seed-borne diseases.

Good farm hygiene will also help. For diseases, such as bunt, harvesting equipment contaminated by bunt spores can spread the disease into seed lots so good hygiene during harvest, storage and transport reduces the chances of the disease spreading to heathy grain.

Delaying drilling to give time for soil-borne bunt balls to germinate before the crop is sown will also reduce infection risk, while leaf stripe survives in crop debris after harvest.

Seed treatment

While all these measures will help reduce risk, seed treatment remains the most cost-effective methods of ensuring these diseases remain a forgotten threat.

They are also an environmentally friendly method of crop protection. Compared with sprays, seed treatments are applied to less than 0.6% of the field area. Each seed is treated individually to provide maximum effectiveness, which limits the effect on the soil around the seed and the environment above ground.

They are also applied at low doses in an enclosed environment by professional companies away from the field environment.

But they are still crop protection products and need to be handled and used carefully and safely to avoid risks to the user, environment, and wildlife.

On farm, there are three main risks from seed treatments:

• Accidental seed spills
• Seed not covered by soil during drilling that can be eaten by birds or mammals
• Dust abraded from seed

So how do you minimise these risks? There are things to concentrate on before, during and after drilling.

1. Preparing to drill

Much of this is common sense, but it is a legal requirement to use equipment that will adequately incorporate seed into the soil, minimise spillage and dust emission.

That means preparing good seedbeds appropriate for the crop and drill to make sure seed will be covered, ensuring the drill is properly maintained and calibrated, and checking drill components and coulters are set up correctly before drilling.

The risk of dust emission from seed has seldom received the same focus as spray drift, but especially when using a pneumatic precision drill with a vacuum-based sowing system for crops such as maize, dust can travel considerable distances on windy days.

Abrasion of seed before loading and by the drill can result in low concentrations of the seed treatment being emitted in the dust.

The risk is less with mechanical or pneumatic pressure drills, while older vacuum-type drills can be modified to discharge the drill’s air stream into the soil or close to the surface, minimising the emission of abraded seed treatment particles from the drill.

Low dust levels mean better adhesion of the product to the seed and reduced operator exposure, so regardless of drill type minimising dust is important.

Five tips to help avoid unnecessary dust:

• Check delivered seed is not obviously dusty; if it is return to supplier for exchanging or reprocessing
• Handle seed bags with care, especially when loading the drill
• When filling drills don’t drop seed from height but pour carefully
• Don’t tip any dust into a drill; leave it in the bag for safe disposal
• Don’t drill too fast, especially when the soil is dry, uneven or poorly prepared

Perhaps an even greater risk is seed spills, which are usually caused by poor operational practices, such as sloppy filling of the drill, poorly maintained machinery, not catching seed while calibrating or checking drill operation or allowing seed to be released while the drill is in transit or not working.

How to avoid spills:

• Take time and care when loading or emptying drills and when calibrating
• Load drill on field area to be drilled or in yard where spill can be easily collected. Ensure this is away from any drains or public access areas
• Do not fill drill or calibrate on grass or over other vegetation where spilt seed cannot be recovered
• Ensure no seed can be spilt while travelling outside the field
• Use the most appropriate drill for the task in hand

If you do spill any seed deal with it immediately. Small in-field spills should be buried where it is, while larger spills or any spills outside the field should be collected immediately and stored in the original bag for disposal.

A spill kit comprising of a spade, spare bag including label to save recovered seed and canvas sheet to be used when calibrating the drill should be part of every grower’s toolbox.

Appropriate personal protective equipment (PPE) including gloves and coverall should always be worn when handling treated seed – seed treatments are pesticides and should be handled as such.

2. Sowing the crop

Before starting sowing assess any risks that might leave seed uncovered, such as stony or cloddy soils or where there might be a lot of surface trash.

Drills cannot perform properly on poor seedbeds. If necessary, check drill set up and operation on a small part of the field yet to be sown to assess whether seed will be covered correctly.

Remember, it is not permitted to broadcast or autocast treated seed.

Even on better-prepared fields, conditions on headlands and especially in corners can be less than ideal, causing the drill to potentially leave seed uncovered.

The following five tips will help minimise the risk of leaving seed uncovered:

• Never drill around tight corners – this will force coulters out of the soil
• Select drilling speed according to the manufacturer’s guidelines – drilling too fast can leave seed uncovered
• Ensure the drill is moving forwards before lowering coulters into the ground
• Take care when lifting the drill in and out of work – shut off seed mechanisms a metre before the row ends so that no seed will spill from the coulters as the drill is lifted
• Sow headlands last – this minimises the number of row ends and incorporates any seed on the surface that has spilled as the drill is lifted

3. After drilling

Before leaving a field, check areas where seed could have been left uncovered – particularly cobbly areas, headlands, and corners. Also recheck areas where the drill was filled, set up and emptied, and bury any visible seeds.

The main body of the field should also be checked for areas of uncovered seed. If there are large areas of exposed seed, the only solution is to harrow and then roll as advised by product labels.

Use bird scarers where necessary to deter bird feeding soon after drilling.

When you have completed drilling, remove all seed from the drill, ensuring that all seed and dust has been collected for safe disposal. Never burn treated seed on farm – it is illegal.

Collect all empty sacks before leaving the field, and don’t reuse bags that contained treated seed for any other purpose than storing original treated seed.

Any leftover seed should be stored in original bags with labels. Seed should be used in the season of treatment and not stored for longer than three months unless the label states otherwise.

Storage should be in a dry secure store that prevents access by pets, livestock, birds and small mammals.