Control Measures against Main Pinus koraiensis Diseases in Liaoning Province

Guanghan XIAO

Benxi Forestry Development Service Center, Benxi 117000, China

Abstract Pinus koraiensis, as the top zonal plant in Northeast China, is affected by external conditions and favorable environmental factors in nature, and grows through its internal contradictory movement. Under certain conditions, it is also affected by some adverse environmental factors, resulting in disasters. With the diseases infecting P. koraiensis in Liaoning area (bark rot, needle-shedding disease, pine dry blight, pine white rot and pine heart rot) as the research objects, the control methods against P. koraiensis diseases are explored, in order to provide reasonable technology measures for disease and pest control in Liaoning area.

Key words Pinus koraiensis; Bark rot; Needle-shedding disease; Pine dry blight; Pine white rot; Pine heart rot

1 Introduction

PinuskoraiensisSieb. et Zucc is affected by external conditions and favorable environmental factors in nature, and grows through its internal contradictory movement. Under certain conditions, it is also affected by some adverse environmental factors and causes disasters, among which pests and diseases are the most serious. The prevention and control of diseases and insect pests ofP.koraiensisshould follow the principle of "prevention first, integrated prevention and control", to minimize the damage as early as possible. In order to achieve the goal of rapid growth and high yield, the relevant personnel should promptly mater the occurrence regularity of diseases and insect pests, grasp the weak links in their life history, and take comprehensive control measures to timely eliminate diseases and insect pests according to local conditions. With bark rot, needle-shedding disease, pine dry blight, pine white rot and pine heart rot in Liaoning area as the research objects, the control methods againstP.koraiensisdiseases are explored, in order to provide reasonable technology measures for disease and pest control in Liaoning area.

2 Pinus koraiensis bark rot

2.1 Disease symptomsWhen the pathogen infects the stem and tip, they are often fully covered with spherical rash-shaped substances, namely the apothecia of the pathogen. In the initial stage of incidence, the apothecium is cup-shaped, light-colored, then become brown or black brown. The affected branches will dry up quickly and die. The bark of the diseased part is dark and rough. The infected lateral branches die and bend downward. Needles change from green to reddish-brown, and then gradually become yellow and shed. The drop-out rate of needles can reach 30%-40% when the incidence is high.

2.2 PathogenThe pathogenCenangiumferruginosumFr. causing bark rot belongs toCenangium, Helotiaceae, Ascomycetes.

2.3 Life history and invasion pathwayDue to drought, waterlogging, insect pests and various natural factors and mechanical damage, the growth of young trees is weakened, so the disease occurs. The pathogen is a weak parasitic fungus, which usually invades from various wounds in branches or shoots of weak trees and camps saprogenesis, making the trees wither and die quickly. Apothecium is formed in late autumn, which is the overwintering source of the pathogen. In May of the next year, the ascospore is the source of primary infection.

2.4 Control methodsYoung forest tending should be streng-thened, with reasonable pruning, and dry wood, suppressed tree and diseased tree should be removed to keep woodlands healthy. After canopy closure of young forest, translucent cuts, health cuts and prevention against diseases and insect pests on branches should be carried out in times, to promote robust growth of trees and enhance disease resistance. In early May, 2° lime sulphur and 50% anthracene oil emulsifiable paste (1∶5 emulsion) are used to spray the trunk and brush the affected part, which have good control effect.

3 Needle-shedding disease

3.1 Disease symptomsThe disease generally affects the needles ofP.koraiensisfrom late May to October, so that the needles gradually become yellow and dry and fall off from bottom to top. Generally, there are pale green faded spots on infected needles, which then become yellowish-brown to brown rash spots, namely the pycnidia of the pathogen. There are black horizontal lines between the interval of pycnidia, dividing diseased leaves into several sections, so that the leaves are yellow and will fall off quickly. In late autumn or the following spring, black spindle-shaped black matters with longitudinal fine slit in the middle are produced on infected needles, which are apothecia of the pathogen.

3.2 PathogenThe pathogenLophodermiumpinastri(Schrad. ex Fr) Ghev. causing needle-shedding disease belongs toLophodermium, Phacidiaceae, Phacidiales, Ascomycetes.

3.3 Life history and invasion pathwayThe pathogen survives the winter in fallen diseased leaves, and the ascospores are mature in the following spring or early summer. In the case of rain or wet woodland, the ascospores will split longitudinally in the middle and squeezed out, and then spread to needles by the wind, invading through the pores of pine needles. The brown rash spots appeared in June and July are the pycnidia of the pathogen, and monosporous pycnidiospores are produced, which have not re-infection ability. Therefore, the disease occurs once a year. The ascospores produced in fallen diseased leaves are the primary sources of the disease. The pathogen usually affectsPinusandPiceatrees, especiallyP.koraiensisforests that are overripe or grown in mixed forest with wet soil, overgrown weeds and poor sanitation, and the damage rate is about 10%. Moreover, it also damages young red forest.

3.4 Control methodsBuilding coniferous and broad-leaved mixed forest can alleviate the incidence. The operation and management should be strengthened, tending and thinning is performed timely, and health conditions are improved, to promote the growth of tree and enhance disease resistance. For newly planted young forests, 1∶1∶150 Bordeaux mixture or 65% zineb 500 times dilution can be sprayed in early May. For closed forests that have been infected, 621 smoke agent can be released in the mature and dispersing period of ascospores to reduce the damage.

4 Pine dry blight

4.1 Incidence timeThe disease generally occurs in the winter and spring when the sap just begin to flow and stop flowing, and it is the most severe from late March to April in early spring.

4.2 Disease symptomsThe victims ofPinusspp. often includeP.koraiensis,P.sylvestrisandP.tabuliformis. The infected needles change from green to yellow, and the terminal buds are dried up or the new shoots are withered, or even the whole tree dies becauses all needles are dried up. The disease occurs mostly in the tip and makes terminal bud sticky and dry, so it generally affects tree height or causes bifurcation.

4.3 Incidence reasonThe disease is a non-infectious or physiological disease. Due to the lack of rain and snow in winter and spring, and the sudden rise of temperature in early spring and the influence of drought wind, the above ground sap ofP.koraiensisseedlings and saplings begin to flow prematurely, while the underground part is still in a dormant state. As a result, the above ground part loses too much water, forming physiological drought. According to the investigation, part of pine dry blight is also caused by nest roots of afforestation.

4.4 Control methodsOverwintering measures, such as soil cover, grass cover or wind barriers, can prevent seedlings from being harmed. In early November, the seedlings are sprayed with lime liquid to implement physical drought prevention and sunscreen, which not only can reflect the sun and prevent temperature upheaval, but also play the role of blocking leaf stomata and inhibiting transpiration, protecting seedling from blighting caused by spring dry winds. Nest root phenomenon should be avoided in seedling bed change or afforestation. The selection of forest land should be paid attention, andP.koraiensisforest land in frequently affected areas should be selected in the leeward place rather than in tuyere. Mixed forest is created so that youngP.koraiensistrees can get lateral shade from other mixed species to protect wind damage. When tending young forest, some weeds and shrubs should be properly retained at a certain distance from young trees to play the role of lateral shade, increase snow cover in winter, moist the environment, and also weaken the influence of drought wind.Pinusspecies in highway, parks and surrounding areas can be timely irrigated in the occurrence season of dry blight after mid-late March in early spring.

5 Pine white rot fungi

5.1 Morphological characteristicsFruiting bodies perennial, low horseshoe-shaped, quite rigid, almost lignified, sessile, lateral to the trunk, pileus dark brown on upper surface, dark black, with radial fissures and obvious lamellar concentric grooves, woody, hard, yellowish brown; tubule short (0.2-0.9 cm), with unobvious hierarchy.

5.2 Disease symptomsPine white rot fungi affect the heartwood of standing trees, which usually invade from trunk dead sections, broken branches and other wounds, and spread from central part of the trunk to the sapwood. Small white honeycomb spots appear in the cross section of the heartwood, causing typical white honeycomb decay. There are no obvious symptoms in the appearance of standing trees in the early stage, but the cavity is formed in the late stage of decay, with sparse crown and weakened tree vigor. Because this decay is concentrated in the middle or base of the trunk, so the use value of timber is lost greatly. The disease occurs in low-lying, shadyP.koraiensisforest with poor drainage, poor ventilation, heavy humidity and poor sanitary conditions, and the older the tree, the heavier the incidence.

5.3 Control methodsThe forestland is cleaned in combination with forest management, while tending and main cutting must pay attention to the direction of falling trees and try to avoid injuring the retained trees, so as not to infect the pathogen. For the forest stand that has been severely attacked, sanitary cutting should be carried out, and decayed wood or pressed wood are removed. Meantime, the fruiting bodies in the forest should be collected and treated immediately to eliminate the source of infection.

6 Pine heart rot

6.1 Morphological characteristicsFruiting bodies annual, with lateral stalk if grown at the root of the tree, or sessile if grown on the trunk, imbricate overlapping, lateral; pileus flat, funnel-shaped, surface yellowish brown, russet, with unobvious concentric grooves, densely shortly tomentose, spongy; tubule short, hyphal hole polygonal. The pathogen mainly invades standing trees ofP.koraiensisandL.gmelinii, and the damage rate is very high.

6.2 Disease symptomsThe pathogen usually invades from all kinds of wounds in the root and stem, or from the dead place. The decayed xylem becomes russet and forms fissures, causing typical brown block decay. The decay spread from the root to the top, which can reach 7 m high, but generally is 1-2 m high. It severely harms the xylem of the trunk, and a cavity is formed in late stage of decay. The infected trees become windthrow or often wither due to root decay.

6.3 Control measuresReasonable operation and management should be implemented to enhance the growth vigor of trees and improve the ability of resistance to disease and rot. Tending cutting or sanitary cutting is performed, to thoroughly remove diseased rotten wood, rotten wood and dry wood, and fruiting bodies of the pathogen are collected, deeply buried or burned to eliminate the source of infection. Mixed coniferous and broad-leaved forests are built to improve the growth conditions ofP.koraiensisand control and isolate the spread of the pathogen. The investigation of the relationship between differentP.koraiensisforests and the incidence shows that steepP.koraiensisforest and slope shrub broadleavedP.koraiensisforest have robust growth and strong disease resistance because of good drainage and moderate soil and air humidity, soP.koraiensisis mildly infected by heart rot. On the contrary, because of the low-lying terrain and moist soil in the valley fern picea-abiesP.koraiensisforest, the growth of trees is not prosperous, and the incidence is more serious. Therefore, the suitable conditions for tree growth should be taken into account when constructing artificial forest. The trees infected by the pathogen of heart rot increase with the age and diameter class, and the agedP.koraiensistrees over 130 years old are often damaged, especially those about 200 years old. Therefore, the overripe trees with declined growth should be cut, so as to avoid the serious loss caused by the invasion of heart rot pathogen. The mechanical damage ofP.koraiensistrees caused by various activities should be avoided as much as possible to reduce the way of pathogen invasion.