Occurrence Dynamics and Countermeasure of Wheat Crown Rot in Weifang City

Hongping TIAN, Guocai LU, Xiuhua WEI, Hongxia TIAN, Miao ZHANG, Fujun LI*

1. Weifang Academy of Agricultural Sciences, Weifang 261071, China; 2. Weifang Vocational College, Weifang 2610412, China; 3. Weifang Agricultural Technology Extension Center, Weifang 261061, China

Abstract Wheat crown rot was first found in Weifang City in 2015, and now has become a major disease of wheat, showing an aggravating trend year by year. The author investigated the occurrence area and characteristics of wheat crown rot in Weifang City over the past 5 years, and analyzed the causes of the disease. The disease was mainly related to variety resistance and farming system. According to the occurrence regularity of the disease, a set of comprehensive control measures were put forward.

Key words Wheat crown rot; Occurrence characteristics; Influencing factors; Comprehensive prevention and control

1 Introduction

Wheat crown rot, known as the "cancer" of wheat, is a soil-borne disease caused by a variety of pathogenic fungi, and it occurs throughout the whole growth period of wheat[1]. The infection of wheat crown rot will lead to reduced tiller, weak and dwarf plant, decreased grain number per spike and reduced grain weight. In China, the disease was first discovered in Henan Province in 2012[2], and occurred in many provinces in 2016. The damage of wheat crown rot was first discovered in Weifang City in 2015[3]. In 2018, due to the influence of climate, seedling situation and farming methods, wheat crown rot occurred widely in Weifang City. The yield of the affected fields was generally reduced by 5%-10%, and was more than 50% in severe cases, or even the whole field failed to harvest. The occurrence dynamics, causes and control measures of wheat crown rot in Weifang City were briefly elaborated.

2 Occurrence dynamics

Since May 2018, Weifang City had organized plant protection technicians to investigate wheat crown rot. Through general investigation and key-point investigation, the occurrence and damage of wheat crown rot were basically mastered. As shown in Table 1, the occurrence area of wheat crown rot was increasing year by year. Meantime, through morphological identification and molecular biological identification of strains collected, it was found thatFusariumpseudograminearum,F.terinctum,Bipolarissorokiniana,F.asiaticumandFusariumsp. were the pathogens causing wheat crown rot, among which the former 3 species were dominant pathogens in Weifang City.

Table 1 Investigation of occurrence dynamics of wheat crown rot in Weifang City in recent years

3 Occurrence characteristics

There were significant differences in the incidence degree of the disease among wheat varieties. The plots with good water and fertilizer conditions had low incidence, while arid hilly land and barren plots suffered heavy damage. The plots suffered low damage if seeds were coated and treated with chemical agents. The plots with heavy occurrence of other diseases and insect pests (spider, leaf rust), or with occurrence of freeze injury suffered heavy damage of wheat crown rot.

4 Cause analysis

4.1 Poor disease resistance of varietiesAt present, the main wheat varieties in Weifang City are Zhongmai 578, Yannong 15, Yannong 999, Jimai 22, Jimai 44, Luyuan 128, Han 6172, Shannong 13, Jinan 17,etc.These varieties have poor resistance to wheat crown rot.

4.2 Framing systemWheat-corn continuous cropping is the main cropping pattern in Weifang City. According to the survey statistics, different previous crops also affected the occurrence of wheat crown rot. When the previous crop was corn, the incidence of wheat crown rot was the severest, with the average diseased plant rate of 21.60% and white head rate of 10.90%. When the previous crops were soybean, rice and Chinese medicinal materials, the white head rates were 4.40%, 1.50% and 0.50%, respectively (Fig.1). After wheat and corn were harvested, straw was returned directly to the field, resulting in a large number of pathogens remaining in the field. With the increase of years, the amount of straw returning to the field continued to accumulate, resulting in the continuous increase of pathogens in the soil. Meantime, rotary tillage was the major tillage method. Shallow tilling layer and poor land preparation quality not only resulted in the accumulation of pathogens in the surface soil, but also made wheat seeds easily suspended in the soil crevice after sowing, resulting in weak seedlings and decreased resistance to pathogens. As a result, wheat crown rot had been aggravating year by year.

Fig.1 The incidence of wheat with different previous crops

4.3 Lack of awareness, poor awareness of active prevention and controlWheat crown rot is a new disease occurred in recent years. Since the early onset symptoms are not obvious, it is difficult for farmers to identify. By the time symptoms appeared in the aboveground part and a large number of white heads appeared in the field, the optimal control period had been missed.

4.4 Less seed coating and seed dressingIn the early stage of wheat sowing, plant protection technicians propagandized and guided farmers on related crop pest control technique, but farmers did not pay attention to seed dressing and seed coating. Even some had carried out seed coating and seed dressing, they only used insecticides such as imidacloprid, with few fungicides.

5 Suggestions for prevention and control

5.1 Selection of resistant (tolerant) varietiesAccording to the identification results of variety resistance by Shandong Agricultural University and Shandong Academy of Agricultural Sciences, the varieties with resistance to wheat crown rot in Weifang City are mainly Handan 14-4610, Shannong 44641, Shannong 7506, Shannong 38,etc.

5.2 Rational rotationFor wheat-corn continuous cropping plots with severe incidence in previous years, according to the local situation, wheat should be rotated with soybean, cotton, peanut and other crops every 2-3 years to cut off the source of the pathogen and reduce the damage of wheat crown rot.

5.3 Deep tillage of soilWhen corn is harvested in wheat and corn continuous cropping field with straw returning to the field, fine straw returning or collection and baling is carried out to remove straw from the field. Before sowing, the soil is turned over to a depth of about 30 cm, and the surface straw or residue is turned over from the top layer down into the soil to reduce the initial quantity of pathogen. The soil should be deeply plowed every 3 years.

5.4 Precision farming and fine managementThe field management should be strengthened to carry out precision farming and health cultivation. After tilling, the plot should be finely raked and leveled, and seeds are sown uniformly in reasonable depth and suppressed after sowing. Fertilizers should be applied reasonably, while partial application of nitrogen fertilizer must be avoided. Dry and waterlogged lowland will be attacked by crown rot easily or aggravate the disease, and it is necessary to perform watering and drainage in time. Surface water should be irrigated in saline-alkali areas.

5.5 Late sowing in appropriate periodAccording to the occurrence of local wheat crown rot, climate conditions and cultivation practice, the sowing time of severely infected plots should be postponed appropriately, no later than October 20. In late sowing plots, the amount of sowing should be increased appropriately.

5.6 Seed treatmentThe seeds can be treated with pesticides containing fludioxonil, tebuconazole and difenoconazole. 27% difenoconazole·fludioxonil·thiamethoxam SD, 32% tebuconazole·imidacloprid SD, or 48% difenoconazole·imidacloprid SD can be mixed with seeds at the doses of 300, 500 and 400 mL/100 kg seeds, respectively. Besides, 2.5-5.0 kg of 100 million spores/gTrichodermaWDG can be mixed with seeds.

5.7 Pesticide application during regreening stageChemicals containing tebuconazole, phenamacril, pydiflumetofen, propiconazole and azoxystrobin can be sprayed on the base of wheat stem.