A Comprehensive Introduction to Common Pests and Diseases of Morinda officinalis

The main pests and diseases of Morinda officinalis arestem base rot,root-knot nematode disease,purple root disease,sooty mold,white grubs (scarab beetle larvae) and mole crickets,scale insects, whiteflies, aphids and red spider mites. The following is a detailed introduction to the symptoms of these pests and diseases and their control methods.

I. Diseases of Morinda officinalis

1. Stem base rot: This is the most widely distributed and most serious destructive disease. The stem base, roots and seeds of Morinda officinalis can all be infected by stem base rot. The pathogen belongs to the genus Fusarium, Fusarium oxysporum (var. aromaticum). The fungus has strong parasitic specialization. It can occur at all growth stages of Morinda officinalis. It mostly occurs in large numbers on plants 2-3 years after planting. The initial onset period is from late March to early April (when the temperature rises above 15°C), the widespread outbreak period runs from early April to mid-May, and two peak periods occur from mid-May to late October.

Control methods: Choose an ecological environment similar to that of wild Morinda officinalis for planting, use aged burned soil and superphosphate as base fertilizer, and do not apply nitrogen fertilizer as a top dressing. To prevent the pathogen from invading through wounds, avoid cultivating and loosening the soil; it is best to pull weeds in spring and autumn, and use grass for shading in summer to lower the surface temperature and protect the root cortex from damage. During the rainy season, excess water should be drained promptly. Severely diseased plants should be pulled up and burned, and the diseased planting holes disinfected. At the initial stage of the disease, spray the stem base with a 60% carbendazim 800-fold solution or apply it as a drench once, then apply 2-3 more times during the peak period. Alternatively, apply 1:1 yin-yang ash (plant ash and lime); applying sulfur powder (1-1.5 grams per plant) also gives good control of stem base rot.

2. Root-knot nematode disease: It occurs fairly commonly and causes damage slowly. After the plant is affected, it grows poorly, and the aboveground parts wither or die. After the roots are affected, round galls of varying sizes with a rough surface form on the main and lateral roots. When the galls are cut open, white granular matter can be seen inside; under a microscope, pear-shaped female adults can be observed. This disease is caused by root-knot nematodes. Root-knot nematodes overwinter in the roots or in the soil, infecting the young tissues of the roots, especially the root tip tissues. They are mainly spread by seedlings, fertilizer, farm tools and water flow.

Control methods: Morinda officinalis is a deep-rooted plant, so using chemical agents to control root-knot nematode disease is difficult, costly and yields little effect. The main approach is to eliminate sources of infection and carefully select the site. For seedling raising, choose virgin land or land with rice as the previous crop. For the planting site, choose virgin land of red soil or yellow loam soil with relatively good fertility. Seedling quarantine should be strengthened, and diseased seedlings should be culled to stop the spread of the damage.

3. Purple root disease: Also known as violet root rot, it causes serious damage in some areas. The surface of affected roots is purple. When the root surface is surrounded by a dark purple short-velvety mycelial mat, the cortex rots and peels off very easily, and the xylem initially turns yellowish brown and becomes wet rot. This disease is caused by Helicobasidium purpureum. The pathogen survives in the soil through its mycelium and sclerotia on diseased roots. Moist soil or poor drainage favors the growth of the pathogen.

Purple root disease

Control methods: Use healthy seedlings for planting; pay attention to drainage at the planting site to promote vigorous growth of Morinda officinalis. Diseased plants should be dug out and burned promptly. The soil around diseased plants can also be disinfected by drenching with 20% limewater or 2.5% ferrous sulfate. For newly reclaimed land, remove tree roots, dead branches, fallen leaves and other debris. Purple root disease

4. Sooty mold:It is caused by sooty mold fungi of the order Dothideales in the class Ascomycetes. The mycelium, conidia and ascospores of the pathogen can all overwinter and become the source of primary infection the following year. It mainly damages leaves and tender branches, forming a black mold layer on the host that resembles soot. In severe cases, the surface of leaves and tender branches is completely covered with black soot-like material, hindering normal photosynthesis of Morinda officinalis and, in severe cases, causing the entire plant to wither. Its occurrence is closely related to damage by aphids, scale insects, psyllids and others; the more insect pests, the more severe the disease. Therefore, insect pests should be eliminated promptly.

Control methods: After the disease occurs, spray with 0.3-0.5 degree Baume lime-sulfur mixture, or an 800-1000-fold solution of amobam.

II. Insect Pests of Morinda officinalis

White grubs (scarab beetle larvae) and mole crickets: Both are common underground pests. A 1000-fold solution of trichlorfon original powder of 90% or above can be used to drench the soil. To make a poison bait, mix 50 grams of 90% trichlorfon with 0.5 kg of bait (rice bran or wheat bran stir-fried until fragrant, then add trichlorfon and mix well); it is best to place 2 granules at the burrow entrance on the evening of the first clear day after several days of rain, or use pine needles, vegetable leaves or bamboo shoot husks dipped in a little peanut oil, then coated with insecticide and inserted into the burrow entrance, so that the pests are poisoned and die after feeding.

Mole cricket

White grub

Scale insects, whiteflies, aphids and red spider mites: All damage the leaves. For scale insects at the young stage, spray with a mixture of 0.5 kg of 40% dimethoate emulsion, 0.1 kg of kerosene and 750 kg of water, or 0.2 degree Baume lime-sulfur mixture, once every 7-10 days for 2-3 consecutive times. For aphids, spray with a 1500-fold solution of 40% dimethoate emulsifiable concentrate. Whitefly larvae suck leaf sap; control is the same as for scale insects. For red spider mites, spray with a 500-1000-fold solution of 25% chlordimeform or a 1000-1500-fold solution of 40% dicofol emulsifiable concentrate, once every 7 days for several consecutive times.