This field lab will explore the viability of different cover crops and cultivation timing on wire worm population and the effect on following potato crops.
Concerns around wireworm damage and its effect on growers’ ability to grow crops has intensified in recent years, with a huge increase in the pest pressure seen across the country.
Processors are pushing towards more regenerative techniques in potato production. However, regenerative practices such as such as leaving stubble and providing green cover provide a food source for wireworm which leads to potato damage, yield losses and downgrading for a lower return. This can cause significant knock on effects for growers and packers in the following seasons and damage growers economically. Huge crop losses mean that this is not sustainable for growers or packers and therefore alternative non-chemical control methods need to be explored.
In this field lab, we are exploring control methods by harnessing the chemical properties of mustards and buckwheat in rotations to ward off the pest. The field lab group consists of potato growers, agronomists and researchers that will undertake core sampling to identify how buckwheat and biofumingant crops affect juvenile populations, compared with stubble. It is known that some species of cover crops have allelopathic effect on wireworm particularly in the juvenile stage.
It has been found that no-till systems increase the pressure of wireworm by providing a feed source (e.g. stubble, cover crops) during times where otherwise land would be fallow. Because of this, some farmers looking increase the use of regenerative techniques are cautious to do so, and organic farmers are left to rely on tillage for some control of the pest.
Whilst ploughing can reduce wireworm damage, farmers have found that it does not achieve sufficient control of the pest. Additionally, green manures and cover crops increase wireworm risk as they keep soils warmer and provide a food source.
However, some cover crops such as buckwheat are known to have allelopathic effects after incorporation into soils, meaning that during decomposition of the plant, chemicals are released which suppress weeds, pests and pathogens. Biofumigants such as hot mustard also contain naturally occurring compounds that may be toxic to soil pests and pathogens. It is known that wireworm are most vulnerable to these effects at the juvenile stage, so the particular focus of this field lab will be to assess the degree that population levels of juveniles are reduced.
Replicated trials will take place at Nick Taylor's farm in Shropshire. The site was chosen based on severity of damage and wet enough land to undertake core sampling. The site has had hundreds of adult beetle caught, and pre-sampling has taken place to ensure that wireworm are present within the plots.
Each treatment is 0.33ha, and there will be 5 replications of each treatment. There are 6 treatments:
Nick Taylor used a 6 metre drill.
Core sampling will be done by agronomist Richard Griffith,
To check for click beetles, Richard will lay traps and check once a week for 3 to 4 weeks.
10 core samples will be taken per plot to make up composite sample for analysis. A 4 inch corer will be used. Samples will be sent to ADAS undertake wireworm identification. Data will be analysed using ANOVA and post-hoc multiple range tests, possibly some regression analysis.
Support with trial design and analysis will be provided by Dr Ben Clunie, entomologist at HAU with a focus on IPM. Independent agronomist Martyn Cox is an expert on wireworm in the UK and a key partner in this project. Seeds are being provided by Hutchinsons Ltd.
There are six trial plots at the farm. This is the weed burner in action on the 'bare stubble, uncultivated' trial plot. This plot is designed to have minimum soil disturbance.
There is a discussion going on about when to incorporate the mustard. It needs to be done as soon as possible, but the mustard has not grown enough and rain over the weekend has meant the conditions are not right to incorporate. To have most impact as a biofumigant the mustard needs to be close to flowering and roughly 1m tall. It is hoped it will be incorporated next week.
Autumn is an ideal time for assessing wireworm in soils because the larvae are very active in the autumn as temperatures are perfect for their survival.
Last week Innovative Farmers ran a farmer workshop on wireworm at triallist Nick Taylor’s farm in Shropshire. The group discussed a wide range of issues and Martyn Cox at Blackthorn Arable led a session on risk management, the main points of which are outlined below.
1) Identify high-risk areas (e.g. grassy margins, permanent grass, nearby wet areas such as rivers and reservoirs, lots of cereals in rotation, weedy stubble)
2) Use bait trapping, pheromone trapping and soil cores to inform which control strategy to use. Just one wireworm in 20 soil cores of 10 cm in diameter (approximately 60,000 per hectare) can pose significant risk in the following crop.
Autumn is an ideal time for assessing wireworm in soils; wireworm levels can decrease a little during the summer but larvae are very active in the autumn as temperatures are perfect for their survival. Make sure your bait traps use organic seed; if not, the insecticide on it will repel pests, so it won’t be a useful test.
3) Create a plant free situation after a cereal crop for a month
4) Decide whether it will be worth planting potatoes in the spring
5) Isolate the areas for early harvest. Late lifted potatoes are associate with higher risk.
6) Grow buckwheat and brown/hot mustards to reduce populations. It is very important to incorporate these into the soil to increase effectiveness. Hot mustard incorporation should ideally happen when soils are above 10 degrees so that the gases can move through the soil, so ideally before Christmas.
7) Certain dressings, such as certain essential oils combined with entomopathogenic (i.e. insect killing) fungi show promising results for repelling wireworm, however these options may be expensive
8) Damage severity differs between potato varieties – see CUPGRA 2022 work on varieties. Consider dual purpose varieties
Granular nematicides have not been found to be very effective.
When assessing wireworm, be aware that stiletto fly larvae can be mistaken for wireworm larvae but are actually predators of wireworm.
Stiletto fly larvae have no legs and thrash around when disturbed. Other natural enemies include ground beetles for the larvae, and birds for the adult (click beetle).
The potato trial plots are being prepared for drilling with mustard and buckwheat tomorrow...
- Core sampling for wireworm carried out and sent to ADAS for analysis. 10 cores were taken per plot.
Late July 2023
26th September 2023
End October 2023
End October 2024