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Turning up the heat on potato cyst nematode

21/03/2018

Article taken from Agronomist & Arable Farmer, March 2018.

Summer Vindaloo is a mix of the hottest mustard varieties and very hot rocket, which grows quickly and develops powerful biofumigation activity within three months of sowing, says Shropshire-based agronomist Andrew Wade.

The mix, using varieties developed by plant breeder RAGT Seeds, will appeal, especially on trickier land, to growers who prefer or need to complete their deep cultivations before winter sets in, he says.

"Provided Summer Vindaloo is sown early enough, in July or early August, it can be incorporated in October and deliver at least as powerful a punch as the more traditional over-wintered mixes," he explains.

Summer Vindaloo has been developed as a result of an extensive trials network and PhD research pioneered by Agrovista Agronomist Luke Hardy.

It has been developed with work by plant breeder Joordens Zaden (part of RAGT) in the Netherlands over the past three years.

Growers need to ensure they sow the mix on time, Mr Wade advises, to ensure it develops enough bulk to deliver a high enough dose of isothiocyanate (ITC) gas, which is released when the green material is macerated and incorporated into the soil, reducing the viability of the PCN cysts.

"Summer Vindaloo can follow crops like winter barley or early carrots. Whole-crop cereals or rye are also ideal and, as these are being grown more widely now with the advent and growth of AD (anaerobic digestion) plants, more farmers will have an opportunity to grow a summer­sown biofumigant crop," says Mr Wade.

The mix must be established well to ensure optimum results, he adds. "Alleviate compaction before drilling, and sow into a fine, firm seedbed. The crop may require fertiliser for maximum biomass -we would typically recommend 90kg/ha of N and 30kg/ha of sulphur. Trace elements should also be considered."

Flea beetle needs to be watched, but other pests like pigeons and slugs are likely to be less of a problem than with overwintered crops, he advises.

Provided it gets off to a good start, the crop can produce 80t/ ha fresh weight within three months, providing plenty of biomass to incorporate.

Following a few simple rules will ensure optimum results, says Mr Wade.

"The golden rule is to chop the crop thoroughly and as finely as possible. We've found machines fitted with knife flails do the best job."

Incorporation must follow immediately, to a depth of 15-20cm. "The best results come from a spading machine, but not everyone has access to one," he adds.

"Another option, which is nearly as good, is to rotavate the green material in -a tractor fitted with a front-mounted flail and a rear-mounted rotavator is ideal. Ploughing should then follow within five minutes to ensure the biomass is thoroughly incorporated throughout the soil profile, before finishing with a roll."

Time is of the essence, as ITC is produced as soon as the green material is macerated, says Mr Wade.

The gas is produced by the mixing of glucosinolates (the 'hot' compounds found to a degree in all brassicas, but which are present in very high concentrations in Summer Vindaloo) and an enzyme, myrosinase. These two compounds are found in separate areas of the plant cells but, once combined, produce ITC. The process requires moisture, so in dry conditions some irrigation may be required before chopping the crop for optimum results, says Mr Wade.

"Under the right conditions, gas will start to be produced in a few minutes and will have done its job in 12 hours. This is why it is important to incorporate macerated biomass quickly."

The summer mix tends to be stronger because it produces more glucosinolate than an overwintered one, says Mr Wade.

"Concentrations are higher and the plant material is also lush and softer, so cells crush more easily.

"Warmer soil also provides a better environment for the gas to work."

Trials history

Mr Wade and Agrovista colleague Mr Hardy started trialling biofumigants 12 years ago in Shropshire, in close association with Harper Adams University and more recently RAGT Seeds and Tozer Seeds.

"We are losing chemical active ingredients all the time, so we need to find non­chemical solutions or benefits to keep our crops healthy. Biofumigants are one of these developments," says Mr Wade.

"We decided we needed to investigate these in the same way we would a new molecule, comparing different treatments and combinations of treatments in replicated trials so we could put our research on a proper scientific basis to deliver proven results.

"We soon settled on three species that produced better glucosinolate content, and have been developing appropriate mixes and management practices since."

Further work in the Shropshire trials has revealed that biofumigation is best carried out a year or two before the next crop, not straight after a lifted one.

"Nematode cysts seem to be very tough in the first year, but appear to weaken as they age, possibly around the feeding point, which helps get more gas into the cyst. So we've moved away from fumigating newly formed cysts, preferring to wait for some cyst deterioration to take place."

The results are impressive, says Mr Wade. "Biofumigation has helped improve PCN control on trial farms, along with other measures such as wider, six-year rotations, improved incorporation of chemical 

granules and the use of soil sterilants.

"A few years ago, 60-70 eggs/g of soil were typical; now we are looking at five to 20 eggs/g. Given these results, I wouldn't be surprised to see over half the UK's potato area being treated with biofumigants within a few years."

Trap crops

Another new study in Agrovista's Shropshire trials is investigating trap cropping, using plants that produce a similar exudate to potato roots, fooling the PCN into hatching.

However, the larvae cannot enter the roots, so die without completing their life cycle.

"This can produce substantial reductions in numbers and could be very useful commercially," says Mr Wade.

"We have 10ha of trials in the ground this year, comparing three types of nightshade. Prickly nightshade is effective but very difficult to grow and needs to be established very early, in May or June, so we are looking at two alternative nightshades that might be easier to manage."

Growers can see examples of trap crops and biofumigant crops at an open day to be held on one of the Shropshire trial sites in September. Details will be available from local agronomists.

There will also be demonstration plots at Potatoes in Practice at the James Hutton Institute's Balruddery Farm, Dundee on August 9.

Other mixes

Hardy Mix -suitable for overwintering, mix of mustard + radish + rocket (15kg/ha)

Caliente 199 -summer option, high levels of glucosinolate - July sowing 9kg/ha October incorporation

Further biofumigant crop benefits

As well as helping to control PCN, green crops grown for biofumigation purposes deliver several additional benefits that can help produce higher yields of better quality crops.

  • Increased soil biological activity
  • Improved soil structure
  • Increased water holding capacity
  • Increased water percolation
  • Reduced runoff
  • Reduced diffuse pollution
  • Improved nutrient availability
  • Recycled nutrients overwinter
  • Better workability and timeliness of cultivations
  • Adherence to cross compliance

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