How to prevent and control barley yellow leaf disease? Detailed explanation of occurrence and control measures

In recent years, barley yellow leaf disease has become increasingly serious in the northern Jiangsu region, often leading to reduced yield and quality, and in some areas even severe seedling death, forcing plowing and replanting. From 1992 to 1995, the author conducted organized surveys of 1466.7-1866.7 hectares of two-row barley planted in the coastal reclamation area of northern Jiangsu and carried out trials of planting disease-resistant varieties, analyzing the relationship between the occurrence and spread of yellow leaf disease and factors such as variety, sowing date, tillage and cultivation, and climate. The report is as follows:

1 Main factors affecting the occurrence of barley yellow leaf disease

1.1 Disease resistance and tolerance of varieties

1.1.1 Test results of different varieties Gangpi No. 1 (KA-4B), 7111, 7113, and 6605 showed mild disease, strong resistance, and relatively strong tillering. For 91-Dan 2, Gang 2, and Suyinmai No. 3, the disease incidence before winter was 40%-50%, but they recovered quickly after green-up and jointing, showing relatively strong disease tolerance. Su Pi No. 1 was relatively susceptible, with severe seedling death, and the number of productive ears per 667 sq m was 193,000, which was seriously insufficient.

1.1.2 Large-area disease survey In 1993, with Su Pi varieties as the main planted type and Gang 2 as a companion variety, 178 fields of Su Pi varieties were surveyed (each field about 8 hectares; 29 fields were diseased, accounting for 16.3%), and 78 fields of Gang 2 were surveyed, with 5 diseased fields, accounting for 6.4%. In 1994, planting of Gang 2 was expanded and Su Pi was reduced. Of 109 fields of Su Pi, 37 were diseased, with an incidence rate of 34%; of 187 fields of Gang 2, 9 were diseased, with an incidence rate of 4.8%. In 1995, resistant and tolerant varieties such as Gangpi No. 1 (KA-4B) and 91-Dan 2 were planted across the board, Su Pi varieties were eliminated, and no yellow leaf disease occurred.

1.2 Sowing date. The main transmission vector of barley yellow leaf disease is Polymyxa gramini in the soil. The susceptible period is mainly the 30-40 d seedling stage after sowing. The earlier the sowing, the higher the probability of virus infection and disease occurrence. In 1992 and 1993, the area sown before mid-October reached 50.8% and 60.1%, respectively. Statistics on disease occurrence over the 2 a showed that 38 fields sown early before October 20 were diseased, covering 14.8 hectares; only 8 fields sown at the appropriate time from October 26 to 31 were diseased, covering 1.56 hectares; and late-sown wheat in November had extremely mild disease. In 1994, a large amount was sown in mid-to-late October, 5-10 d later than in previous years, and in 1995 there was almost no disease.

1.3 Previous crop and tillage

1.3.1 Long continuous cropping years resulted in severe disease. For example, in fields 5N10# and 22S9#, susceptible varieties such as Su Pi were planted continuously for 4 a, and the disease was relatively severe, with a diseased area of 30%-40%.

1.3.2 Dry-crop fields with reduced or no tillage were more severely affected than rice-stubble fields. Polymyxa gramini is distributed in the shallow soil layer of 5-20 cm. Cotton-barley intercropping, relay seeding, and soybean-stubble fields mostly adopted reduced or no tillage and shallow plowing and shallow harrowing sowing methods, which had little effect on Polymyxa gramini. In cotton-stubble and soybean-stubble fields, the incidence of barley yellow leaf disease accounted for 41.5% and 31.7% of diseased fields, respectively, while rice-stubble fields, after long-term irrigation and pre-sowing deep plowing, suppressed the number of Polymyxa gramini, with diseased fields accounting for 20.80%, so the disease was relatively mild.

1.4 Climate

The soil temperature suitable for the activity of Polymyxa gramini zoospores is 1.0-15°C. Locally, the average 5 cm soil temperature falls below 10°C around late November, while the barley sowing period is late October. The pre-winter vector activity coincides with the period of wheat seedling infection. Therefore, the key meteorological factor determining the epidemic of yellow leaf disease is rainfall at autumn sowing. For example, within 40 d after autumn sowing in 1993, the local daily average temperature was 13.7°C and rainfall was 224.1 mm, respectively 3.3°C and 165.9 mm higher than normal, with continuous overcast rain; waterlogged tillage and sowing were favorable for the vector to spread with rainwater, waterlogging damage was severe, wheat seedling resistance was weak, and yellow leaf disease spread severely. In contrast, within 40 d after autumn sowing in 1992 and 1994, rainfall was 1.1 mm and 21.5 mm, respectively, with drought and little rain, and yellow leaf disease occurred only mildly.

2 Control measures to control the occurrence and damage of yellow leaf disease

2.1 Plant resistant and tolerant varieties. Select resistant and tolerant, high-yield, high-quality brewing barley varieties adapted to local planting, such as Gangpi No. 1 (KA-4B), 91-Dan 2, and Gang 2. Plot trials and large-area application have proven that they have strong tillering ability, resistance to lodging, stable 1000-grain weight above 38 g, germination rate above 90%, and a yield of about 400 kg per 667 sq m. Yield and quality are highly favored by planting units and malt manufacturers.

2.2 Avoid sowing too early. For example, locally delaying sowing from mid-October to after October 25 can both ensure that wheat seedlings overwinter with 5 leaves and green up in 70 d, and also reduce viral disease. For cotton-stubble wheat, reduce relay-seeded area as much as possible, promote late-sowing cultivation techniques after cotton, and increase the ear-bearing rate.

2.3 For dry-crop fields (relay seeding, intercropping, soybean stubble), pay attention to deep plowing 20-25 cm, and promptly dig ditches and beds to drain water and reduce waterlogging, thereby suppressing the spread and diffusion of the Polymyxa gramini vector.

2.4 Rotation and crop change. Avoid continuous cropping of brewing barley, implement paddy-upland rotation or switch to planting @#@245@#@ to reduce disease occurrence.

2.5 Reasonable dense planting and fertilization. Apply the two-promotion fertilization method of heavy base fertilizer and light ear fertilizer. For diseased fields, increase nitrogen fertilizer or spray phosphorus and potassium fertilizer and ABT rooting agent on the leaves to promote rooting, quickly produce new leaves, and increase plant disease resistance.