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Harvested Crops

7 August 2019

Ensuring stores are clean and free of pests is essential to prevent any problems after all the hard work of growing and harvesting the crop.

Bear in mind that no pests of grain come in from the field – they are all loitering in the store or on associated machinery, trailers, pits, ducts just waiting for grain to arrive.  They keep themselves ticking over on spilled grain, which can be found in crevices, on ledges, in pits and ducts.  Consequently, giving the store a thorough cleaning can reduce the risk of pests such as weevils, saw-tooth grain beetle, mites and psocids (book lice) in particular being a problem.  Don’t forget to treat associated machinery as well as the walls of stores.  The use of bait bags to see what may be present in the store now is highly recommended, and if any pests are present insecticide treatments can be applied to the store to get rid of them.  Any suspicious insects or bait bags can be sent to the Crop Clinic for rapid identification of any insects present.

Ideally, once the grain has been harvested, the moisture content should be reduced to 14% or lower. Getting the moisture down in-store is the key to stop grain pests such as mites, beetles and weevils from breeding and surviving.

The presence of blue-black beetles in harvested oilseed rape seed or seen on the trailers is an advance warning that there could be a problem in the next winter oilseed rape crop from cabbage stem flea beetle.  The beetles won’t harm the seed in the store and will be desperate to get out of the store and find an oilseed rape crop to feed on.  We would welcome any reports of cabbage stem flea beetle at harvest as this provides information that impacts the management of this pest on the next crop of winter oilseed rape.

Pre-harvest and desiccation options for cereals

With the more changeable weather this year, it may be beneficial to treat crops pre-harvest, particularly if there are un-controlled weeds that will slow harvesting, or there are secondary tillers.  Where there are secondary tillers or there is annual meadow-grass in the base of the crop, a low dose of glyphosate is sufficient because it is particularly effective against annual grasses.  Where broad-leaved weeds or couch grass are present the dose should be increased as specified on the product label.

Minimising the dose will lead to reduced residues in the grain. Care is needed because glyphosate is detected in routine residue testing carried out each year on products from shops and supermarkets. Cereal-based products such as bread, breakfast cereal etc. often contain traces of glyphosate – generally well below the MRL.  Results of the PRiF surveys are published online

In order to minimise residues, it is good advice not to routinely treat crops pre-harvest with glyphosate – only pre-harvest spray crops where it will be cost-effective and there will be a benefit from treatment.  Use the lowest appropriate dose and adhere to the recommended timings.  It is important not to apply before the grain moisture has fallen below 30% as applying earlier increases the risk of residues.  It is also important to comply with the harvest interval (7 days in cereals).  Check with the end user before using pre-harvest glyphosate and do not apply to seed crops.

Be aware of the risk to neighbouring sensitive crops from drift when treating pre-harvest.

Winter and spring wheat

Trials by SRUC and in England by NIAB have consistently shown that in wheat there is little benefit from pre-harvest glyphosate treatment of weed-free crops that have no secondary tillers.  In these clean crops, it does not increase grain or straw dry matter or improve combine performance.  In weedy crops or those with secondary tillers, there is a proven benefit in reduced grain moisture and improved combine performance.

Glyphosate can be used on feed and milling crops and crops due for distilling – but check with your merchant first.  Do not use on seed crops.  The wheat must have less than 30% grain moisture – the ‘hard-dough’ stage.  This can be confirmed by collecting a representative sample of grain then cutting each grain in half.  If 75% of the grains have a dark brown pigment strand in the crease, grain moisture has reached 30%.  If all grains have a dark brown pigment strand in the crease, moisture is below 30%.  Glyphosate cannot be used to speed up the ripening of crops not at the hard dough stage.

Winter and spring barley

It is only worth treating winter barley if it is weedy or has secondary tillers.  Most crops are now past the stage for treatment and are being harvested.

In spring barley, SRUC trials have shown a small decrease in grain moisture and improved combine performance in the absence of weeds, so if the weather continues changeable there may be a case for treating clean crops.  Weedy crops or lodged crops with secondary growth may also benefit from treatment.  If the crop is to be sold off-farm, check with the end user before treating.  Grain must be below 30% moisture before treatment.  This can be checked by looking at the peduncle immediately below the ear.  When the peduncle, situated at the top of the stalk immediately below the ear starts to lose its green colour and turns brown the moisture level should be ideal for spraying.

Winter and spring oats

Glyphosate can be used as a harvest-aid in milling or feeding oats, but check with the end user before treatment.  Oat grains vary considerably in maturity according to position on the panicle; so make sure that the least mature grains are below 30% moisture content before spraying pre-harvest glyphosate.  Due to the later maturity of spring oats compared with other cereals, long-term control of perennial weeds may not be as good where the weeds have started to die back when treated.

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