Spring barley update

Spring barley fits into three distinct sowing categories this year: early (February/early March); normal (early April); and, the largest category, late-sown crops (mid to late April).

Each category presents distinctly different challenges, and agronomy should be tailored to match the sowing date.
Early-sown crops will have a higher disease risk, but a very low risk of barley yellow dwarf virus (BYDV), whereas disease risk is lower in later-sown crops, but the risk of BYDV infection increases as sowing date is delayed. The total nitrogen (N) rate should be reduced in later-sown crops to match yield expectations.

Management of BYDV in spring cereals

BYDV is a major challenge for late-sown cereal crops. Aphid numbers increase with temperature, which means that cereals emerging in May are at high risk of BYDV infection. Grain aphids, a major vector of BYDV, have developed resistance (knock-down resistance (KDR)) to pyrethroid insecticides (Karate Zeon, Decis Protech, etc.); therefore, insecticide use needs to be planned and targeted to achieve the best effect.
Teagasc research on late April-sown spring barley has shown that one application of a pyrethroid insecticide at the four leaf stage will give the best control of aphids. Multiple applications do not increase the level of control and will exacerbate the problem at a local level.

Weed control

Late-sown crops present an opportunity to make savings on weed control due to faster development of the crop. Low rates of herbicides can be effective, but successful control is dependent on applying herbicides to small weeds that are actively growing. For late-sown crops, this can be done with an aphicide following a period of good growth.

Fertiliser

Any remaining N needs to be applied as soon as conditions are suitable. Where lower yield potential is expected, reduce the total N applied. A 6.5t/ha crop has a requirement for 135kg/ha (108 units). Increase N by 20kg/ha for every tonne expected over 6.5t/ha.

Disease control

The average yield response from a two-spray fungicide programme in Teagasc trials is 1.3t/ha, but can range from 0.5-2.75 t/ha, depending on the season. The expected response will be lower on late-sown crops, meaning that the spending on fungicides can be reduced. Oak Park trials have shown two half-rate fungicides (combined product), will give maximum economic return.

The first fungicide should be timed before GS30. All fungicides have strengths and weaknesses, so it is important to match the correct fungicide with the varietal characteristics. All current spring barley varieties contain Mlo resistance to barley powdery mildew, so the inclusion of a specific mildewicide is rarely warranted. It is essential to walk the crop beforehand, then decide on the fungicide of choice and rate in conjunction with the varietal characteristics.

For example, in Table 1, RGT Planet is susceptible to net blotch and the fungicide programme should contain a strob (e.g., Comet) with good activity on net blotch, whereas the risk to varieties like Geraldine and SY Amity is much lower. A mismatch of fungicide and variety can lead to either poor disease control or unwarranted fungicide use.

Table 1: Department of Agriculture, Food and the Marine (DAFM) spring barley disease ratings.

*limited information

This article was first published in the Teagasc Tillage Newsletter May 2023, read the full publication here.