Early drilling last autumn is thought to be behind the high incidence of gout fly damage being reported this spring.
Previous years have shown gout fly pressure to be highest in crops sown before mid-September, says Dr Steve Ellis, entomologist at ADAS. However, whether crop yield is subsequently affected by the pest may depend on its growth stage at the time of infestation.
If the crop is backward, the attack may occur before the crop elongates and attacked tillers remain short and never produce an ear but if the crop is well forward when attacked, damage will be less severe allowing the ear to emerge, but it might be poorly developed.
In general, crops at or beyond GS37 by mid-May in southern England or late May in the Midlands only suffer minor damage, says Dr Ellis.
Compensatory tillers
Todd Jex, Agrii agronomist covering Dorset and south Wiltshire, says: It is probably the worst gout fly pressure I have seen for a decade and generally anything that emerged in September is suffering with damaged tillers. Even some of the crops drilled into late September-early October have got a level of gout fly in them.
He adds that the worst-affected crop he has seen is an early planted hybrid barley seed crop that was planted in early September.
This crop was the earliest to emerge and near enough every plant has one out of four tillers affected, but I expect the crop to compensate with replacement tillers, so we are not expecting a yield drop, he says.
With minimal yield losses expected from the damage, growers are advised to front-load nitrogen fertiliser to ensure crops have the correct nutrition to allow compensatory tiller production.
Mr Jex recommends growers complete tissue testing and check key nutrients such as phosphorus and manganese are not deficient, reducing possible limiting factors for tillering.
Of the crops he has seen affected by gout fly damage, 90 per cent will not have a noticeable drop in yield at harvest, believes Mr Jex.
We are hoping to have negated the remaining 10 per cent by applying nitrogen slightly earlier and adjusting the splits to bring more of the total nitrogen earlier than we would in a normal year, he says.
Control threshold
Recent ADAS modelling work has tested use of shoot number to establish a control threshold for gout fly. The modelling confirmed that if infestations do not exceed 50 per cent of plants affected at GS12, yield is unlikely to be affected.
Kate Storer, ADAS senior scientist, says: It is important to note that this is theoretical and the shoot number model still needs validating in the field, but it is reassuring that the threshold appeared to be about right based on these estimates.
Is there a greater risk to spring sown cereal crops?
Gout fly attack in spring is different to that in the autumn and is mainly focused on the stem below the ear.
- Injury differs depending on the growth stage of the plant when it is attacked
- Damage is often done in the two to three weeks before the ear appears
- Damage is caused by the larva burrowing down the side of the ear to the first joint
- If the crop is backward, the attack may occur before it has started to elongate and the tillers remain short and swollen, never producing an ear
- If the crop is well forward the growth check is less severe and the ear emerges although it is poorly developed and the immature grains on one side are spoiled
- Shoots damaged by the spring generation can potentially lose 30% of grain yield
Source: ADAS
Actions growers can take
Early sowing helps to avoid damage by gout fly to spring cereals and is particularly important following exceptionally mild winters, when adult gout flies may emerge in late April.
In a forward crop, most of the ears emerge before the larvae have time to cause any damage and the most severe attacks occur when sowing late, for example in late April or if the crop is backward due to poor growing conditions.
If crops are beyond GS 37 by mid-May in southern England or late May in the Midlands, they usually only suffer minor damage.
Sow spring cereals as early as is practicable in areas where there is significant gout fly risk or where high numbers of infested winter cereals were seen.
