Wheat Bulb fly damage and egg-hatch update

This weeks Pestwatch indicates that egg-hatch is progressing in Suffolk, Cambridgeshire and Hertfordshire and has now started in Lincolnshire. Week-commencing the 17th January 2011, Wheat Bulb fly egg-hatch in Suffolk was reported to be 9.1%, in Cambridgeshire/Hertfordshire on mineral soils was 15.1%, in Cambridgeshire on organic land was 4.8% and in Lincolnshire 8.5%.

Explaining what this early egg-hatch means for growers, Sarah Hurry of Dow AgroSciences says that Wheat Bulb fly adults lay their eggs in exposed soils in July to August and these eggs hatch the following January or February. The eggs hatch into white legless larvae which move through the soil, bore into the base of the cereal plants and then eat out the central shoot. This causes the distinctive dead-heart symptom, resulting in loss of tillers and in some cases complete plant loss. The larvae can move from tiller to tiller and from plant to plant. Winter wheat, winter barley, rye and early sown spring wheat can be attacked. Backward, late-drilled or thin crops are especially at risk.

As some sort of measure if 20% of plants are attacked, yield losses can be of the order of 0.7 t/ha. At todays wheat price of 187/tonne this is equivalent to 130/hectare loss, she says.

Sarah Hurry reports that 40% of fields sampled in the HGCA 2010 autumn survey of Wheat Bulb fly egg incidence were over the treatment threshold of 250 eggs/metre. Overall the proportion of sites over threshold was the highest recorded since 2004 and the fourth highest since monitoring began in 1984. Growers with vulnerable crops in the high risk situations need to be ready to treat vulnerable fields with Dursban WG (chlorpyrifos). In any late drilled, struggling, backward or thin crops, it is worth considering an application of Dursban WG at the first available opportunity, as tiller survival will be very important in these crops.

Dursban is an effective soil insecticide and should be applied at egg hatch at 1 kg/ha in 200-1000 litres of water. Egg-hatch treatments are applied after eggs have hatched but before plant invasion by larvae takes place. Dursban WG is an egg-hatch treatment. It will give good control for 6 to 8 weeks under normal conditions which means that most larvae will be controlled if they hatch over a period of time. On organic soils a repeat application may be necessary.

Starting in mid January, results of the weekly soil sampling are issued by Dow AgroSciences and ADAS as Pestwatch reports. These reports reflect weekly data and provide advice on the timely application of the soil insecticide Dursban WG. Weekly information can be accessed at www.dowagro.com/uk/cereal/pest/htm.

For further information, please contact Sarah Hurry, Dow AgroSciences on the Dow Technical Hotline on 0800 689 8899.

Dursban WG (75% w/w chlorpyrifos formulated as a Water Dispersible Granule) is recommended for the control of Wheat Bulb fly as well as Leatherjackets, Frit fly and Wheat Blossom Midge. For Wheat Bulb fly, two applications at dose rates of 1 kg/ha maybe applied up until flag leaf sheath extending (GS 39). It is packed in a 1 kg pack.

Dursban is a trade mark of Dow AgroSciences LLC.