Pests/Diseases in winter cereals

When carrying out a monitoring for the economic thresholds of diseases in cereals, the sampling would be done in a diagonal or zig-zag pattern covering the whole field. It is desirable to check at least 100 plants.
Septoria triciti occurs mainly in wheat, but can also be present on rye and triticale. Water-soaked leaf patches turn brown in autumn and necrotic lesions may be evident by early December and throughout the winter on the lowest leaves. These lesions contain visible black pycnidia, which overwinter on leaves. Lesions are sometimes restricted by veins giving a rectangular appearance. It is recommendable to intervene with a fungicide in the following two scenarios, but only if the expected yield is >3000 kg/ha and when:
– 25% of sampled plants at the two-nod stage have at least 10% of the last two leaves´ surface covered by the disease.
– more than 40% of plant samples at the BBCH 51-59 (Inflorescence emergence, heading growth stage) have lesions.
If the disease is endemic in the area and/or the cultivars are sensitive to the disease, a preventive application is recommended if the expected yield is >3000kg/ha.
Powdery mildew produces a white to gray cottony fungal mass on the upper leaf surface in wheat (Blumeria graminis f. sp. Tritici) and barley (Blumeria graminis f. sp. Hordei), with the lesions mostly prevalent on the lower leaves. The conspicuous white to gray patches of fungus appear at BBCH 13-21. The white patches produce large quantities of small asexual conidia, which are easily dislodged by wind or rain. When powdery mildew is severe, the entire leaf turns yellow and dies. The fruiting bodies cleistothecia may appear on the lesion later in the season. Like with Septoria, chemical treatments are only recommended if the expected production is higher than 3000 kg/ha if:
– >30% of sampled plants (>50% in the case of barley) present symptoms on the last two leaves. This monitoring should be done from the two-node stage until the appearance of the ear.
– at the ear formation stage, >50% of sampled plants have lesions in the last two leaves and/ or in the ear.
The brown leaf rust (Puccinia triticina in wheat, Puccinia hordei in barley and Puccinia recondita in rye and triticale) requires at least three long periods of ROCIO at temperatures of around 20°C. In the spring, brown pustules scattered at random appeared on the leaves. Although symptoms are most common on leaves, in severe attacks pustules can also occur on the stem and glumes. In cases of severe infection, the rust infection might reach the glumes and produce a reduction in specific weight. When leaves begin to senesce, a green island develops around the pustules. At the end of the season dark teliospores might be produced. Regarding the thresholds, a chemical treatment is desirable when:
– 20% of sampled plants show pustules on the last three leaves from the two-node stage onwards.
– 50% of the plants present pustules on the last two leaves and/or the ear during the ear formation to flowering.
Autumn aphids (Rhopalosiphum padi, R. maidis and others) produce yellowing and curling of the leaves, but this damage is only relevant during mild winters. Nevertheless, the indirect damages through the transmission of viruses such as the BYDV is of great importance. Barley is the most sensitive cereal to viruses, followed by wheat and oats. The period for the thresholds´ assessment is from BBCH 11 to BBCH 22. Control must take place as soon as one aphid is seen, in the case of virus endemic areas, or when one aphid is found in 10 plants. Cultural methods such as crop rotation and the use of tolerant cultivars (such as Naturel, Cometa or Tudela) are desirable to prevent the use of pesticides. A seed treatment might be applied in high-risk areas. Foliar treatments can be done until BBCH 21.