The Pathogenesis and Control Methods of Peach Tree Gummosis

Peach tree gummosis is a disease commonly occurring on peach trees today, and its incidence is severe. Especially in peach orchards with extensive management and weakened tree vigor, the rate of affected plants can reach over 90%. This disease severely weakens tree vigor, affects yield and quality, and in severe cases leads to dead branches and dead trees, threatening the production and development of peach trees. It is also one of the most troublesome diseases for fruit growers.

I. Causes of peach gummosis. There are two causes of peach gummosis: one is non-infectious pathogens, such as gummosis caused by wounds from mechanical injury, pest and disease damage, frost damage, freeze injury, etc., or gummosis caused by physiological disorders of the tree body resulting from extensive management, excessive pruning, excessive fruiting, improper fertilization, heavy clay soil, etc.

The other is infectious pathogens caused by fungi. The sexual stage belongs to the Ascomycotina, and the asexual stage belongs to the Deuteromycotina.

II. Symptoms and Occurrence Patterns of Peach Gummosis

1. Non-infectious gummosis mainly occurs on the trunk and large branches, and in severe cases small branches can also be affected. In the early stage, the diseased part swells slightly, then secretes a translucent, soft gum. After rain, gum flow is heavy. Subsequently, upon contact with air, it turns brown, becoming crystal-clear soft gum blocks, then dries into hard gum blocks ranging from reddish-brown to tea-brown. As the amount of gum flow increases, the cortex and xylem of the diseased part gradually turn brown and rot (but no pathogens are produced). This causes the tree vigor to become increasingly weak, and in severe cases causes tree death. The disease is severe in the rainy season, severe in older trees, and mild in young trees.

Any wounds caused by insect damage, disease damage, freeze injury, hail injury, sunscald, etc. can cause the occurrence of non-infectious peach gummosis (without pathogenic bacteria). In addition, gummosis caused by physiological dysfunction of the tree body resulting from heavy clay soil, poor drainage, excessive or insufficient irrigation, etc., is infectious peach gummosis caused by fungi. The pathogenic spores of its asexual generation spread through wind and rain, invading through wounds and lateral buds. There are two disease peaks per year, namely late May to early June and early August to early September.

2. Infectious gummosis mainly harms branches and trunks, and also infects fruit. The pathogen invades the current-year new shoots of peach trees, producing tumor-like raised lesions centered on lenticels on the new shoots, but no gum flows. In May of the following year, the tumor skin cracks and overflows a gum-like liquid, which is a colorless translucent viscous substance, later becoming tea-brown hard blocks. The diseased part becomes sunken into circular or irregular patches, scattered with small black dots. When perennial branches and trunks are infected, water blister-like swellings are produced, and brown gum liquid can seep from the diseased parts, which can lead to branch and trunk canker or even death. When peach fruit is infected, brown rot occurs, densely covered with small granular dots, and when humid, white block-like substances flow out.

Infectious gummosis overwinters in diseased branches as mycelium and pycnidia. From late March to mid-April of the following year, conidia are released and spread by wind, mainly invading through wounds, and can also invade through lenticels and lateral buds. Especially on rainy days, large amounts of pathogens overflow from the diseased parts, flow down along branches and trunks or splash onto new shoots, invading through lenticels and wounds, becoming the main source of primary infection for new shoots. The activity of latent pathogens in branches and trunks is related to temperature. When the temperature is around 15°C, gum liquid can seep from the diseased parts. As the temperature rises, the number of gum flow points on the tree body increases, and the disease worsens.

Infectious gummosis has two disease peaks per year. The first is from early May to early June, and the second is from early August to early September. After that, no further infection or damage occurs. The most favorable time for pathogen invasion is when the cortical cells of the branches gradually become suberized and lenticels have formed. Therefore, prevention of this disease is best done during the new shoot growth period.

III. Poor soil conditions, such as being too heavy and clayey or highly acidic, etc. Poor drainage, excessive water accumulation on the ground. In addition, extensive management, excessive fruiting, and other factors that cause tree vigor weakening can all cause gummosis.

IV. Integrated Control Measures for Peach Gummosis. Based on the above symptoms and occurrence patterns, in actual production, the control of this disease should focus mainly on agricultural control and manual control, supplemented by chemical control. Chemical control mainly targets the two peak periods of spore dispersal and spore invasion. Specific measures are as follows.

1. Strengthen cultivation management, enhance tree vigor, and improve the disease resistance of peach trees.

Apply more organic fertilizer to diseased trees, appropriately increase phosphorus and potassium fertilizer, and control nitrogen fertilizer in the middle and late stages. Prune reasonably, manage fruit load reasonably, coordinate the contradiction between growth and fruiting, and maintain stable tree vigor. Do a good job of drainage during the rainy season to reduce humidity in the peach orchard. Conduct timely summer pruning to improve ventilation and light penetration conditions, and at the same time control other pests and diseases, especially branch and trunk pests of peach trees, to reduce pest wounds and mechanical wounds.

2. Eliminate overwintering inoculum sources: During the coldest December to January, carry out orchard cleaning and disinfection, scrape off hard gum blocks and the rotting cortex and wood below them, collect and burn them, then spray 5°Be lime sulfur mixture for disinfection, and then whitewash the trunk and large branches to eliminate overwintering inoculum sources and insect eggs, while also preventing freeze injury and sunscald.

3. Before peach trees bud, spray 5°Be lime sulfur mixture on the tree body to kill active pathogens.

4. Quicklime powder control method: In recent years, quicklime powder has been used in experiments to control gummosis occurring on fruit trees such as peach, apricot, and plum, with very good results and a cure rate of 100%. The specific method is: apply quicklime powder to the gum flow site. After application, gum flow completely stops within 5-7 days, symptoms disappear, and there is no recurrence. The optimal period for applying the powder is when the tree sap begins to flow, namely the end of March. At this time, it is the initial onset period of gummosis, with few affected plants and a small range of gum flow, making it easy to control and reducing nutrient consumption of the tree body. Afterward, apply powder whenever discovered by mobilizing manpower for control. Control is best on cloudy and rainy days, when the gum liquid flowing from the bark is highly viscous and easily adheres to quicklime powder. For fruit trees with severe gummosis or senescent trees, use a knife to scrape off the dried gum and old cracked bark, exposing the tender bark, then apply powder for better results. This method is simple and effective.

5. Spray pesticides at appropriate times during the growing season: From late March to mid-April is the period when infectious gummosis releases conidia. Combined with the control of other diseases, spray 1500x thiophanate-methyl or 1000x Duoxiaoling, Guobingling, etc. for prevention. From early May to early June and from early August to early September are the two disease peaks of infectious gummosis. Before each peak period, spray 1000x liquid Jundusha or Junduqing, Junlimie, etc. every 7-10 days, alternating for 2-3 consecutive sprays, to eliminate the disease in the bud stage, and reduce the number of sprays as much as possible according to the disease condition. Spray 4-5 degrees Beaumé lime sulfur mixture once before the bud swelling stage. During the growing season, starting from leaf expansion in April, spray 50% carbendazim 1000x solution once every half month, for 4 sprays.

6. To control peach gummosis, it is necessary to spray pesticides in a timely manner to control pests and diseases and whitewash the trunk to avoid freeze injury, sunscald, and mechanical wounds.

7. Alternatively, first scrape off the diseased tissue at the gum flow site, then use a cotton swab or toothbrush to apply 43% Dashengfu diluted 30-60x to the wound. Generally, apply 2-3 times each in spring and autumn, and the diseased part can be cured after 1-2 consecutive years of control.