Crops notes April 2007

Most of us involved in growing cereals agree that early sowing (if soil conditions allow) is a major factor in maximising yields and therefore profitability of spring barley. We should complete spring barley sowing as soon as possible using seed rates between 160 KG per ha (10.2 stone per acre) and 180 KG perha (11 stone per acre). As crops begin to emerge look out for signs of leatherjacket damage, especially in crops following grass or grassy stubbles. If a problem is suspected, treat the crop with chlorpyrifos (for example, Dursban).

Growth stage 31 (first node detectable) is the best time to apply the main nitrogen top dressing in winter cereals. However, the mild, wet weather means that many winter barley crops have passed this stage, so, applying this top-dressing without delay is essential to maintain yields.

All cereals, especially those on light, sandy or free-draining soils, will be at risk from sulphur deficiency so they should receive 15 to 25 KG S/ha in spring. This can be done most conveniently by applying a sulphur-containing nitrogen fertiliser.

The key growth regulator timing in winter wheat crops is early stem extension (GS30 to 31). A chlormequat or trinexapac-ethyl based product (e.g. Moddus) is most effective, applied at this time, to all but the thinnest crops as a precaution against lodging.

Wet soil conditions in the autumn may not have allowed the timely application of residual herbicides to winter cereals. If you find yourself in this situation it is probably too late to control most grass weeds. However, broad-leaved weeds, especially cleavers, can still be easily controlled and will need attention as soon as possible. The range of cleaver herbicides has expanded in recent years. Where conditions are warm and weeds are actively growing, Starane will provide effective control. In colder weather, or where a wider weed control spectrum is required, alternatives (for example, Boxer, Chekker, Eagle, Lotus or Starane XL) should be considered.

Having judged cereal competitions for several years I am aware of the problem wild oats have become on many farms. These prolific weeds are very competitive and expensive to control so every effort should be made to eradicate them from our farms. If there is a wild oat infestation that can’t be rogued, specific herbicides should be used. Consult product labels for latest timings.

Rhynchosporium in barley and Septoria tritici in wheat are the two main disease threats for these crops.

Winter barley should be sprayed at GS31 (first node detectable) with a mixture containing, a robust rate of triazole and a strobilurin in crops with higher yield potential. Suitable options include: Acanto + Opus or Punch C; Mobius or Fandango, Punch C or Landmark. Where symptoms of mildew are found, the inclusion of a morpholine such as Corbel will be required.

Winter wheat should receive its first fungicide spray as soon as leaf three has emerged. This normally coincides with GS32 (second node detectable). A triazole (for example, Opus or Proline) should be the linchpin of this spray.

Early sown crops are likely to have a relatively long interval between their first and second fungicide treatments. In this situation the persistence of the first spray can be improved by the addition of chlorothalonil (for example, Bravo).

As planting time approaches, it is important to maintain seed in good condition until it is required. If seed is not to be pre-sprouted it is best held in cold store until close to planting. Once delivered, the seed needs to be kept in a cool, airy and well-lit area and protected from frost. This is to prevent the growth of long weak sprouts that are easily damaged at planting and thus provide an entry point for disease.

We can assess seed for disease by examining washed samples. Some diseases such as silver scurf and black scurf are significant problems in pre-pack potatoes and can be reduced by applying appropriate fungicide seed dressings. Although it may be past the time for applying many liquid treatments, dust formulations can still be used at planting. Growers must refer to the manufacturer’s label recommendations before applying seed dressings, as incorrect application of some products may affect crop emergence.

Although early planting means an earlier harvest we should wait until ground conditions are suitable before cultivating. Compaction caused by ‘forcing’ a seedbed in poor conditions restricts root growth, leaving the crop susceptible to nutrient deficiencies, drought and lower yields. Aim to produce a fine tilth that retains moisture and assists the performance of residual herbicides.

For rapid emergence and growth, potatoes need to be planted into warm soil, with temperatures consistently 8 degrees Celsius or higher. This is very important for some varieties such as Pentland Dell, which are sensitive to cold temperatures and may display the disorder ‘little potato’, in which tubers are initiated before foliage has emerged. If soil temperatures are low, it is especially important that the seed is held in cool conditions prior to planting.

Your questions and comments are very welcome so that we can address the issues that are important to you. Please email the author directly at james.knox@dardni.gov.uk