Teagasc tillage specialists have recently confirmed that spring barley crops are posing a challenge on multiple fronts. This is one of the key advisory themes addressed in the May issue of the tillage newsletter, which is available to the public. The crops fall into three categories based on the sowing date: early (February/early March); normal (early April); and the largest category of 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 have a higher risk of disease, but a very low risk of barley yellow dwarf virus (BYDV). The disease risk is lower in later sown crops. However, the risk of BYDV infection increases as sowing date is delayed. According to Teagasc advisors, the total nitrogen (N) rate should be reduced in later sown crops to match yield expectations. BYDV is a significant challenge for late-sown cereal crops. Aphid numbers also increase with temperature. This means that cereals emerging in May are at high risk of infection. Grain aphids are a major vector of BYDV. However, many have developed knock-down resistance to pyrethroid insecticides. As a consequence, 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 of aphid resistance at a local level. Late-sown barley crops present an opportunity to make savings on weed control due to faster development of the crop. As a consequence, 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. Any remaining N needs to be applied as soon as conditions are suitable.
Where lower yield potential is expected, growers should reduce the total N applied. A 6.5t/ha crop has a requirement for 135kg/ha (108 units). Growers should increase N by 20kg/ha for every tonne expected over 6.5t/ha. The average yield response from a two-spray fungicide program in Teagasc trials is 1.3t/ha. But this figure 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. Trials at Teagasc Oak Park have shown two half-rate fungicides (combined product), will give the maximum economic return.
The first fungicide should be timed before growth stage (GS)30. All fungicides have strengths and weaknesses, so it is important for growers 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 for growers to walk their crops beforehand. They can then decide on the fungicide of choice and rate in conjunction with the varietal characteristics.
It is important to note that crops sown in different periods face different challenges. Early-sown crops have a higher risk of disease, but a very low risk of BYDV. Late-sown crops have a lower risk of disease, but a higher risk of BYDV. Therefore, growers need to tailor their agronomy to match the sowing date. It is recommended that growers apply the correct herbicides and insecticides to their crops to ensure maximal yield. Additionally, it is important for growers to walk their crops and decide on the fungicide of choice and rate in conjunction with the varietal characteristics.