What are the control methods for jujube witches' broom? A detailed explanation
1. Symptoms
Jujube witches' broom, also known as witches' broom disease, broom disease, and fire dragon disease, is a devastating disease. Fruit growers call it "mad jujube tree" or "male jujube tree." The jujube tree can be infected both above ground and below ground. Above-ground infection mainly manifests as flower organ degeneration, abnormal bud germination and growth, ultimately leading to clustered branches and leaves, elongation of the fruiting branchlet tips, clear veins, yellowing, or spoon-shaped curling of young leaves, with occasional ear-shaped leaves. Below-ground infection mainly manifests as clustered root suckers. In diseased trees, the entire flower organ degenerates into vegetative organs, and the flower stalk elongates, being 5-7 times longer than the flower stalk of healthy flowers, showing obvious small branches, and the sepals, petals, and pistil can all become small leaves. In severe cases, the flower disc also degenerates, the sepals become dark green and enlarged, turning into small leaves, and sometimes the axillary buds of these small leaves sprout small branches again. The petals become enlarged, longitudinally wrinkled, and also turn into small leaves; the pistil retains its original shape, but the ovary becomes enlarged, thickened, and extends in a columnar shape, and some stigma tips also turn into two small leaves. Another type is that the stamens become small leaves, and the ovary becomes a short branch; but the axillary buds germinate, producing short and thin new branches and new leaves that continue to grow. Diseased flowers generally cannot bear fruit; only flowers with elongated stalks can bear fruit, but most drop prematurely. Infected fruit becomes smaller, thinner, and tapered at the end. In some varieties such as Yuanling jujube, the fruit surface is uneven, with red on the raised parts and green on the sunken parts, appearing mottled; the internal tissue is hollow and unfit for consumption. There are two types of abnormal bud germination. One is the small-leaf type symptom. That is, most of the true buds on the current-year vegetative branches and the latent buds on perennial vegetative branches of the diseased plant germinate into vegetative branches, and the buds on them continue to germinate and produce branches, and so on level by level, until the main buds of the fourth-order jujube heads no longer germinate, forming clustered branches. Most of the fruiting mother branches of diseased trees extend into vegetative branches, and these branches also produce clustered small branches. Diseased branches are slender, with shortened internodes, and the leaves become smaller and yellow. In autumn, the clustered branches dry up but are not easy to fall off. The other is the mosaic type symptom, which is uncommon and mostly occurs at the tips of tender branches, slightly smaller than healthy branches, with yellow-green mottled spots on the leaf surface; sometimes the veins lose chlorophyll and become clear-veined, the leaf margins curl inward into a spoon shape, the leaf surface is uneven, and sometimes yellowing appears, and they are not easy to fall off in autumn. After below-ground infection, adventitious buds germinate in large numbers, forming clusters of short mad branches; multiple clusters can appear on the same lateral root. After emerging from the soil, the branches and leaves are small and yellow-green; they stop growing at about 0.3 m, then all scorch and die in a brush-like manner, leaving only remnant branches. Finally, the cortex of the diseased roots turns brown and rots, the phloem easily falls off, the fruit is lost, or the entire plant dies.
2. Occurrence pattern
2.1 The pathogen is a mycoplasma-like organism. Under electron microscopy, mycoplasma-like organisms of varying shapes, 80-720 nm in size, were observed in the sieve tube cells of leaf veins. In mature mycoplasma-like organism particles, nucleic acid fibrous substances are clearly visible. The pathogen can first move to the roots of the jujube tree, and after multiplication, spread from the diseased part to the whole tree.
2.2 Transmission routes and occurrence conditions The disease is transmitted through various grafting methods, such as bark grafting, bud grafting, branch grafting, and root grafting. In nature, leafhoppers are the transmission vectors of the disease, mainly including the Chinese rhombic-marked leafhopper, orange-banded rhombic-marked leafhopper, concave-margined rhombic-marked leafhopper, and red-flashed small leafhopper, all of which are transmission vectors. Once the concave-margined rhombic-marked leafhopper ingests the jujube witches' broom mycoplasma-like organism, it can carry the pathogen for life and can successively infect many jujube trees. As for soil, pollen, seeds, sap, and contact between diseased and healthy roots, none can transmit the disease. The direction of movement of the pathogen in the host is consistent with the direction of nutrient movement in the tree: upward from below during germination, and downward from above after branch growth stops. After graft inoculation, the incubation period is as short as 25-31 days, with symptoms appearing on newly emerged buds; the longest incubation period reaches 382 days. Factors affecting the length of the incubation period include inoculation time: inoculation before the end of June can cause disease in the same year; inoculation after the end of June shows symptoms at flowering the following year; inoculation at the roots can cause disease very early in the same year; the more bark graft pieces, the faster the disease develops; in addition, it is also related to the growth of new shoots and the size of the inoculated plant, and seedlings show symptoms faster after inoculation than mature plants. The occurrence of the disease is related to the terrain, soil quality, management, and variety of the jujube orchard. In soils that are dry and poor, with poor fertilizer and water conditions, extensive management, severe pests and diseases, and weak tree vigor, the disease is severe; otherwise it is mild. Saline-alkali land rarely develops the disease, possibly because saline-alkali land affects the metabolism of the jujube tree and enhances its resistance to jujube witches' broom, or possibly because the local area lacks vector insects. There are certain differences in susceptibility among jujube varieties. Artificial inoculation tests have shown that Jinsi jujube is highly susceptible, Tengxian red jujube is relatively resistant, and Jiaocheng vinegar jujube is immune. In addition, small jujube and round red jujube are highly susceptible, and the entire plant dies within 1-3 years after onset; long red jujube is next, and can survive for about 5 years; maya jujube, changling jujube, huiling jujube, and suanling jujube are relatively resistant.
3. Control methods
3.1 Quarantine. Strengthen quarantine at the place of origin to prevent diseased seedlings from entering jujube-growing areas. Select disease-free mother plants for collecting scions, cuttings, and propagating root sucker seedlings. Strictly prohibit jujube witches' broom seedlings from entering jujube-growing areas.
3.2 Select disease-resistant sour jujube varieties and disease-resistant large jujube varieties with jujube kernels as rootstocks.
3.3 Scion disinfection. For diseased scions, soak in 1000 mg/kg tetracycline hydrochloride solution for half an hour to disinfect and eliminate the disease.
3.4 In disease-free jujube areas, collect scions, graft buds, or divide roots for propagation; cultivate disease-free seedlings; once diseased seedlings are found in the nursery, immediately pull them out.
3.5 Eradicate diseased trees to prevent infection. Promptly and thoroughly dig out diseased trees to eliminate the source of infection at an early stage; when digging out diseased trees, the large roots should be dug out completely to avoid sprouting. Removed diseased trees, diseased branches, or diseased roots should be burned promptly.
3.6 Strengthen jujube orchard management. Apply more organic fertilizer and alkaline fertilizer. During the budbreak and leaf expansion stage, flowering and fruit setting stage, and rapid growth stage, the jujube tree needs increased water and fertilizer; combine with spraying 1-2 times of 300-fold urea solution for foliar topdressing. This can improve soil physical and chemical properties, increase soil fertility, and enhance tree vigor.
3.7 Control vector insects that spread the disease in the field. From May to September, spray 50% parathion emulsifiable concentrate + 50% dimethoate emulsifiable concentrate each at 250-fold solution, or 50% dimethoate emulsifiable concentrate + fenvalerate each at 250-fold solution, spraying thoroughly on the tree canopy and surrounding weeds to control the transmission vectors.
3.8 Trunk girdling. Because the pathogen conducts in a directional manner within the trunk, this method is effective. The method is: before sap flow in spring, perform ring peeling on the middle and lower parts of the main trunk of the jujube tree, with a width of 0.3-0.5 cm.
3.9 Pour medicine to eliminate the disease. From April to August, drill 2-3 holes on the same side of the trunk as the diseased branch, deep into the xylem, grind 50 g of mint water, 100 g of dragon bone powder, and 50 g of copper green into fine powder, mix well, and pour into the holes using a paper tube, 3 g per hole, then drive in wooden wedges tightly, seal with mud, to kill the pathogen and cure the disease.
3.10 Apply Qufengling. Before budbreak in spring, open a small ring-shaped groove at the base of the trunk, half as deep as the phloem, pour the medicinal solution into the groove, wrap tightly with plastic film, and apply a second time after 1 month. For a tree with a trunk diameter of 20 cm, apply 8 g; for 40 cm, apply 16 g, with good efficacy.