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Protecting crop from wireworm

1 August 2011

Timely and potentially very valuable advice to help growers protect their crops against the ravages of wireworm has been issued by the AHDB Potatoes.

The Wireworm Factsheet contains all the information growers need to
tackle this pest, including the effect of site and crop rotation on population size, how to assess risk to potato crops and preventing damage.

Crops hit by wireworms can quickly lose value, explains AHDB Potatoes technical executive Chris Steele. Even low populations of the pest can cause enough holing and tunnelling of ware tubers to render them unfit for market. A crop that was worth more than £100/t can quickly become
animal feed, he warns.

“Given the risk of total crop rejection, some growers consider wireworm to be a bigger threat to profits than potato cyst nematodes,” says Chris.

Wireworms are the larvae of click beetles, and reports of damage are increasing across the country. Potato crops following grass and set-aside are particularly at risk, especially on warmer, south-facing slopes. The pest is also becoming a major problem in some all-cereal rotations, with recent ADAS work suggesting that the minimum tillage boom is to blame.

Where possible, growers should avoid growing crops in infested fields, he advises. “Risk assessment is the key. With no new chemistry forthcoming, we have very limited means of control.

“Current choices like ethoprophos (Mocap 10G) and fozthiazate (Nemathorin) cannot be used later than planting and are expensive. A pre-planting assessment is therefore essential to determine the need for an application.”

This involves a range of techniques carried out at different times of the year. Pheromone traps, which capture the adult click beetles, should be used in the late spring or summer of the year before crops are planted. These devices release synthetic sex pheromones which attract male beetles, and if set up in the morning can be assessed later the same day.

Although these can produce a good estimate of population size, there is no recommended threshold. “The presence of just one click beetle can represent a significant risk to the following crop,” says Chris.

Soil sampling should follow in the autumn. However, the detection limit is 62,500 wireworms/ha, and significant damage can still occur at levels below this. “If any wireworms are found, that indicates a pesticide may be needed,” he notes.

The same advice goes for bait traps. These are used in late March just ahead of maincrop planting, and are filled with soaked grain, buried to about 20cm then left for 10-14 days. “Growers who have not carried out earlier tests on fields they intend to plant this spring can still get a useful indication of the threat by bait trapping,” he says.

Using these results, decisions to minimise wireworm damage can be made. This may include not cropping the field at all if the risk is high, or applying insecticides at planting and using early harvested varieties that are less prone to damage.

“It’s also worth considering other actions throughout the crop rotation,” says Chris. “Plough-based cultivations can help reduce numbers. And other insecticides, for example pyrethroids and neonicotinoids, have activity on wireworms. Using these as seed treatments in crops like cereals, sugar beet and oilseed rape will help reduce populations.”

For further information click here.

The factsheet will also be available at AHDB Potatoes grower meetings and technical days throughout the season.

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