Occurrence and Control of Pear Rust in Eastern Hebei Province

Longfei LI, Lijuan GAO, Jintao XU, Minghui JI, Baofeng HAO

Changli Institute of Pomology, Hebei Academy of Agricultural and Forestry Sciences, Changli 066600, China

Abstract In recent years, pear rust sometimes occurs in eastern Hebei area, resulting in early defoliation, fruit abscission and loss of fruit commodity value. In this paper, the incidence symptoms, regularity and causes of pear rust are summarized, and the comprehensive prevention and control measures of pear rust in eastern Hebei are put forward.

Key words Pear; Rust; Incidence regularity; Comprehensive prevention and control

1 Introduction

Pear rust (GymnosporangiumharaeanumSyd.), also known as brown spot, mainly harms young leaves of pear trees, as well as new shoots and young fruits, and it is an important disease of pear trees[1].

Eastern Hebei region is located in the northeast of north China Plain, adjacent to the eastern segment of Yanshan Mountains in the north and Bohai Sea in the south. It belongs to warm temperate sub-humid continental monsoon climate and is greatly influenced by the ocean. The region has four distinct seasons, abundant sunshine and a long frost-free period. With the increase of rainfall in spring in recent two years, pear rust occurred in large areas in some pear orchards in eastern Hebei Province. Through the interview survey, the author found that pear rust occurred severely in some "Anli" pear orchard in Sanchayushu Village, Qinglong Manchu Autonomous County in 2020; the diseased plant rate was about 50%, and the diseased leaf rate of some plants was up to 100%. There were multiple disease spots on the leaves, and the infected fruits were seriously malformed. In 2021, pear rust attacked the orchards of "Mili" pear and "Jingbaili" pear near the 261 Provincial Road of Liangshan Township, Changli County. Early defoliation occurred in infected pear trees, which affected the tree potential and fruit yield of pear trees. The hawthorn and begonia near the affected pear garden also suffered at the same time, and fruit farmers responded strongly. In this paper, the incidence symptoms, regularity and causes of pear rust were summarized, and comprehensive prevention and control measures of pear rust in eastern Hebei were put forward, in order to provide the reference for fruit farmers to control pear rust.

2 Incidence symptoms and regularity

2.1 Incidence symptomsIn the early incidence stage, orange dots about 2 mm in size appeared on young leaves, which then gradually expanded to nearly round small spots, with dense yellow grains on spots, and sometimes light yellow sticky fluids overflowed from the small grains. When the sticky fluids dried, the small grains became dark brown, and the pressure side of the leaf was depressed, but the back side was raised, and dozens of light brown hairs similar to the goatee grew out, about 3-5 mm in length.

After new shoots were infected, the tissue of the diseased part showed a yellow fusiform uplift, producing tiny black dots and hairs. In the late stage of the disease, the diseased part was bent and cracked, and the part above the disease was dead and easily broken by the wind.

In the early incidence stage, orange yellow spots and small grains were produced on the surface of young fruits, and then turned brown. In the late incidence stage, corkification was found in the center of lesions, covered with small black dots and hairs. The infected part stopped growing, and malformed fruits formed, mildewed and decayed, resulting in fruit abscission.

2.2 Incidence regularityPear rust is a fungal disease, andG.haraeanumforms galls going through the winter in infected tissues of juniper and other alternate hosts in the form of perennial mycelium. When the gall ruptures, it produces brown corn-shaped teliospore cirrus. The teliospore cirrus ofG.haraeanumappear in February and March in eastern Hebei, which will germinate after raining in March and April, producing a large number of basidiospores. The basidiospores spread to the young leaves of nearby pear trees with the wind. After 6-14 d of incubation, orange yellow spots appear on the pressure side of leaves, and the spermogonia grow. When the spermatia are matured, they overflow from the orificium of spermogonia, combine with the trichogyne of the opposite sex, develop into binuclear mycelium, and then expand to the dorsal surface of the disease spot. After 20 d, aecidium forms on the dorsal surface of the spot. The aecidiospores disperse from the orificium of aecidium, and spread to nearby juniper and other Coniferae plants with the help of wind to go through the summer and winter, no longer harming pear trees. Pear trees in eastern Hebei Province generally begin to be infected in late April, enters the peak incidence period in May and June, and will no longer be infected after July.

3 Incidence causes

3.1 Surrounding environment of pear orchardThe author found that most pear orchards affected by pear rust in eastern Hebei were close to national roads, provincial roads and other traffic roads. There were many evergreen trees such as juniper planted on both sides of the roads, and even juniper trees were planted in some pear orchards, which provided necessary conditions for the occurrence of pear rust.

3.2 Climatic factorsThe temperature before germination of pear tree, the frequency of rainfall and the amount of precipitation in leafing and young fruit stage are important factors affecting the occurrence of pear rust[2-3]. In April 2021, the average temperature in Changli County of Qinhuangdao City was 8-17 ℃, and the highest temperature on April 19 was 26 ℃. There were 9 times of rainfall from March to April, and continuous rainfall from April 21 to 23 met the conditions for the germination of teliospore cirrus. Meantime, the rainfall was often accompanied by strong wind, which led to the occurrence of pear rust in some pear orchards.

3.3 Variety factorsPear orchards in eastern Hebei are dominated by old local varieties, such as "Anli" pear, "Mili" pear and "Jingbaili" pear, which have poor resistance to pear rust, so they are vulnerable to pear rust.

4 Control methods

Severe damage of pear rust and not timely prevention and control can cause the failure of harvest in pear orchards, to which enough attention should be paid. The prevention and control of pear rust in eastern Hebei Province is dominated by prevention, supplemented by treatment. Agricultural and chemical control measures should be comprehensively adopted, to realize unified prevention and control.

4.1 Agricultural control

4.1.1Cutting off the infection cycle. Cutting off the infection cycle between pear tree and alternate hosts is the most thorough and effective method to control pear rust. If juniper and other alternate hosts are planted within 5 km of pear orchard, the alternate hosts should be cut down completely or replaced with other non-Coniferae garden tree species. It is not suitable to plant pear trees in areas where alternate hosts can not be completely cleared due to the limitation of conditions.

4.1.2Strengthening the forecast of pear rust. Through the analysis of incidence regularity and cause ofG.haraeanum, it can be seen that the occurrence of pear rust requires certain climatic conditions. From March to April every year before pear tree germination and leafing, relevant units should cooperate with local meteorological departments to timely monitoring weather conditions and disease status of alternate hosts near pear orchards, and provide accurate prevention suggestions for fruit farmers, so as to determine the best prevention period and improve the prevention effect.

4.1.3Selecting disease-resistant varieties. Pear varieties have great differences in resistance to pear rust[4]. The disease-resistance varieties suitable for local cultivation can be selected to reduce the occurrence of pear rust. "Yuluxiang" pear, "Wujiuxiang" pear and "Xinshiji" pear have certain resistance to pear rust, and are suitable for planting in eastern Hebei Province. The pear orchards affected by pear rust can be appropriately replaced by high quality resistant pear varieties.

4.1.4Strengthening the management of pear orchard. Pear orchards built in flat areas can effectively reduce the occurrence of pear rust if the conditions are available to use greenhouse for sheltered cultivation of pear trees. The pear orchard under the condition of open cultivation should strengthen management. The organic fertilizer and microbial fertilizer can be increased in spring, and reasonable pruning will enhance the tree potential and improve the pear tree resistance. Drainage in rainy season should be paid attention, to reduce the humidity of pear orchard. The whole orchard bagging after fruit thinning can effectively prevent pear rust from harming pear fruit, reduce early fruit dropping, improve fruit appearance quality and reduce pesticide residues.

4.2 Chemical control

4.2.1Control of alternate hosts. In spring, the bacterial galls of juniper and other alternative hosts near pear orchards should be manually cut off before germination and leafing of pear tree. In early March in eastern Hebei Province, 4-5°Be lime sulphur could be sprayed on alternate hosts to reduce the initial overwintering quantity of the pathogen and infection source. From July to August, 20% triazolone EC 1 000 times dilution is sprayed on alternate hosts to eliminate the source of infection. The control of alternate hosts of pear rust can reduce the use of chemical agents in pear orchards, which is suitable for the production of green pollution-free fruits, and will save labor and chemical agents.

4.2.2Control of pear trees. The time of spraying is the key for the prevention and control of pear rust. In eastern Hebei, pear trees are sprayed with 3-5°Be lime sulphur once before germination in late March, or sprayed with 1-2°Be lime sulphur once before leafing, in order to prevent the infection ofG.haraeanumbasidiospores. The occurrence of pear rust can be basically controlled by spraying once within 25 d after leafing in April and once again after 10-15 d. 25% Triazolone WP 1 000 times dilution, 10% difenoconazole WG 6 000 times dilution, 65% mancozeb WP 500 times dilution, 10% flusilazole EW 1 200 times dilution can be selected, which all have better prevention and control effects on pear rust, and can be used alternately.