Why Do Bayberry Trees Decline? Cause Analysis and Rejuvenation Technical Measures

Causes of Bayberry Tree Decline and Rejuvenation Technical Measures

The northern mountainous area of Chao'an currently has about 1,173.3 hm2 of bayberry, an important fruit tree in the mountainous and semi-mountainous areas of Chaozhou City. The 'Dongkui' bayberry introduced at the end of the last century has significant benefits due to its large fruit and excellent quality, and planting bayberry has become an important source of agricultural economic income for towns such as Wenchi and Guihu. However, starting from 2010..., bayberry trees began to show dead branches, decline, and even death, and the area gradually expanded. More than 800 hm2 have severely declined, affecting the development of the bayberry industry in Chaozhou City, with great losses. In response to this phenomenon, since 2014, through in-depth investigation, experimentation, and research, the author selected targeted pesticides for prevention and control, combined with scientific supporting cultivation measures, effectively inhibited the decline of bayberry. The mortality rate of bayberry trees was controlled below 2%, costs were reduced by 40%, and normal growth was restored within 3 years, achieving good results.

1 Analysis of the Causes of Bayberry Tree Decline

1.1 Caused by Root-Knot Nematodes

With the support of higher-level scientific research departments, agricultural technicians from the Agricultural Work General Station of Chao'an District, Chaozhou City, tested the soil and fine roots of some declining bayberry orchards in Guihu Town and Wenchi Town. The test results showed that the main root cause of large-scale decline and even death of bayberry was bayberry root-knot nematode disease. Bayberry root-knot nematode disease, which had long been ignored, has become the most serious hazard, directly causing bayberry tree decline and even dead branches and death.

After bayberry is damaged by root-knot nematodes, in the initial stage, the leaf tips at the ends of the main branches show yellowing, shedding, and branch death. Dead branches gradually increase until dead branches cover the whole plant. When the root system is dug out, the root ends can be seen turning black and rotting, and sometimes root-knot-like lumps can also be seen, spreading from branch roots to the main root system. The root system is severely damaged, and its ability to absorb and store nutrients declines, so the tree body cannot receive the necessary nutrient supply, thus affecting the growth of the bayberry tree. In the later stage of damage, diseased trees even wilt and die. At the same time, it can also induce other diseases such as root rot and wilt disease.

Because root-knot nematodes are small and cannot be seen with the naked eye, and the initial symptoms after bayberry trees are damaged are not obvious, combined with fruit growers' weak awareness of prevention and control, after the disease occurs it is often confused with lack of water, lack of fertilizer, or other diseases, thus delaying the best time for prevention and control.

1.2 Unscientific Management Measures

1.2.1 Abuse of herbicides, especially glyphosate types. Heavy use directly harms the root system and destroys soil structure. Frequent weeding leads to soil erosion, causing relatively dry and water-deficient soil. In the high-temperature seasons of summer and autumn, shallow roots are damaged.

1.2.2 Unscientific fertilization methods. Most fruit growers use chemical fertilizers for a long time, applying only nitrogen fertilizer and phosphate fertilizer, rarely applying potassium fertilizer, and basically not applying organic fertilizers, resulting in increased soil acidity. This is an important reason for inducing the spread and damage of root-knot nematodes.

1.2.3 Abuse of plant regulators. In order to bring fruit to market earlier, fruit growers heavily use plant growth regulators, seriously disrupting plant growth patterns. New shoots grow chaotically, inducing large outbreaks of pests such as leaf roller moths (hanging worms) and scale insects. Disorderly growth affects normal flowering and fruiting, leading to unstable yield and decreased quality.

1.3 Climatic Factors

Due to global climate warming, the annual accumulated temperature has risen, which is the main reason for the large-scale damage by root-knot nematodes. The suitable temperature for nematode growth and reproduction is 25-30°C, and they stop activity below 10°C. The time when the temperature in Chaozhou City is below 15°C is relatively short, and root-knot nematodes often maintain relatively strong reproductive capacity.

2 Rejuvenation Technical Measures

2.1 Control Root-Knot Nematodes and Promote New Root Growth

If nematode damage has already occurred widely in the bayberry orchard, promptly use 1,000-fold solution of 10% "fosthiazate" mixed with organic liquid fertilizer to drench the roots, trying to drench the root system thoroughly, especially the areas where fine roots are dense. This can eliminate most nematodes and promote new root growth. In the 1st year, drench 2 times, with an interval of 4-6 months; in the 2nd year, determine the number of control applications according to the situation. After more than 2 pesticide applications for prevention and control, bayberry trees can basically recover their vitality. If there are similarly damaged bayberry trees above the orchard, prevention and control must be carried out at the same time; otherwise, measures should be taken to isolate them to avoid rainwater spreading root-knot nematodes. Adjacent orchards must also carry out unified prevention and control at the same time to prevent rainwater transmission.

2.2 Protect Vegetation, Control Grass Without Removing It

Good vegetation can reduce soil moisture loss, maintain relative soil humidity, and benefit bayberry root growth. Except for small shrubs, generally annual grasses should be retained. A mower can be used to control weeds, or a lower concentration of herbicide can be used to simply control growth speed. During winter orchard cleaning each year, 50 kg of lime can be broadcast per 667 m2.

2.3 Pruning and Shaping, Rebuilding the Canopy

When dead branches are severe, retractive pruning and reshaping must be carried out to recultivate the canopy. For severely declining bayberry trees, the damage from root-knot nematodes should first be controlled, and the first pruning and shaping should be carried out after new shoots sprout and turn green again. For bayberry trees with few dead branches and not severe decline, pruning can be carried out at the same time to promote new shoot sprouting. For some particularly severe bayberry trees, after heavy short pruning, wrap the branches and trunk to prevent sunscald.

2.4 Reasonable Fertilization to Restore Tree Vigor

When tree vigor has just recovered, the root system is not well developed, so the amount of fertilizer applied should be controlled. For mature trees, apply 200 kg of organic fertilizer per 667 m2. Each time new shoots emerge, apply 1 topdressing, with 10 kg of NPK compound fertilizer per 667 m2 each time. In the 2nd year, when tree vigor has recovered, compound fertilizer with higher potassium content can be applied additionally to promote flower bud differentiation.

2.5 Integrated Pest and Disease Control, Protect Branches and Leaves

Declining trees need enough green leaves to restore growth, so protecting branches and leaves is very important. The main insect pests of bayberry include carpenter moths, leaf roller moths, inchworms, and scale insects. Carpenter moth larvae mainly damage branches and trunks. Control methods are cultivating robust trees, whitewashing trunks, and manual capture. Whitewashing trunks in April each year and brushing the main trunk and main branches white is the best measure to prevent damage from carpenter moths, longhorn beetles, and others. Leaf roller moths, inchworms, and scale insects mainly damage new shoots and tender leaves. The control method is to use 22.4% spirotetramat 4,000-fold solution in the early stage of occurrence. This pesticide is selective toward many natural enemies such as ladybugs and parasitic wasps. Using it in the early stage of pest occurrence can protect natural enemies to the greatest extent. Orchards with a good ecological environment have many biological natural enemies, such as Charops bicolor and Goryphus basilaris, which are hosts of leaf roller moths, carpenter moths, and inchworms; Synharmonia conglobata ab. geminopunctata, Menochilus sexmaculatus, Chrysopa septempunctata, and Chrysopa sinica are natural enemies of aphids and scale insects, so attention should be paid to protecting and utilizing them.