Causes and Control Methods of Peach Gummosis

Peach gummosis is a disease commonly found on peach trees today, and it occurs severely. Especially in poorly managed orchards and those with weakened tree vigor, the incidence of affected trees can reach over 90%. This disease severely weakens tree vigor, affects yield and quality, and in severe cases leads to branch and tree death, threatening the production and development of peach trees. It is also the most troublesome disease for fruit growers.

I. Causes. There are two causes of peach gummosis: one is non-infectious pathogens, such as gummosis caused by wounds from mechanical injury, insect and disease damage, frost injury, freezing injury, etc., or gummosis caused by physiological disorders of the tree body due to extensive management, excessive pruning, excessive fruiting, improper fertilization, heavy clay soil, etc. The other is infectious pathogens caused by fungi, with the sexual stage belonging to Ascomycota and the asexual stage belonging to Deuteromycota.

II. Symptoms and Occurrence Patterns

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 translucent, soft gum. Gum flow is heavy after rain, and then turns brown upon contact with air, becoming crystal-clear soft gum lumps, then dries into hard gum lumps 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 pathogen is produced). This causes tree vigor to become increasingly weak, and in severe cases causes tree death. The disease is severe in the rainy season, severe on older trees, and mild on young trees.

2. Infectious gummosis mainly damages 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 bark splits and exudes a gum-like liquid, which is a colorless translucent viscous substance, later turning into tea-brown hard lumps. The diseased part becomes sunken into round or irregular patches, scattered with small black dots on them. 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 cause branch and trunk cankers or even death. Infected peach fruit develops brown rot, densely covered with small granular spots, and exudes white clumps when moist.

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 pathogen 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, the diseased part can exude gum liquid. As the temperature rises, the number of gum exudation points on the tree body increases, and the disease worsens. Infectious gummosis has two peak periods of occurrence in a year: the first from early May to early June, and the second from early August to early September. After that, it no longer infects and causes damage. The most favorable time for pathogen invasion is when the cortical cells of branches gradually become suberized and lenticels have formed. Therefore, prevention of this disease is best done during the new shoot growth period.

III. Integrated Control Measures. Based on the above symptoms and occurrence patterns, in actual production, the control of this disease should be based mainly on agricultural and manual control, supplemented by chemical control. Chemical control mainly controls spore dispersal and the two peak periods of spore invasion and disease occurrence. 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, maintain a reasonable load, coordinate the contradiction between growth and fruiting, and maintain stable tree vigor. Drain well in the rainy season to reduce humidity in the peach orchard. Carry out summer pruning at the appropriate time to improve ventilation and light 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 pathogen sources: Carry out orchard clearing and disinfection in the coldest December to January, scrape off hard gum lumps and the rotting cortex and xylem below them, gather and burn them, then spray 5°Be lime sulfur mixture for disinfection, and then whitewash the trunk and large branches to eliminate overwintering pathogen sources and insect eggs, while also preventing freezing 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 control experiments against 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, all gum flow stops within 5-7 days, symptoms disappear, and there is no recurrence. The optimal period for applying the powder is when tree sap begins to flow, that is, the end of March. At this time, it is the initial stage of gum flow, with few affected trees and a small range of gum flow, making control easy and reducing nutrient consumption of the tree body. Afterward, apply the powder whenever the disease is found, mobilizing manpower for control. Control is best on overcast and rainy days, when the gum liquid flowing from the bark is more viscous and easily adheres to the quicklime powder. For fruit trees with severe gum flow or old and declining trees, use a knife to scrape off dried gum and old rough bark, exposing the tender bark, and then apply the powder for better results. This method is simple, convenient, and effective.

5. Spray pesticides at the appropriate time during the growing season: Late March to mid-April is the period when infectious gummosis releases conidia. Combined with the control of other diseases, spray 1500 times thiophanate-methyl or 1000 times Duoxiaoling, Guobingling, etc. for prevention. Early May to early June and early August to early September are the two peak periods of infectious gummosis. Before each peak period, spray 1000 times liquid Jundusha or Junduqing, Junlimie, etc. once every 7-10 days, alternating for 2-3 consecutive sprays, to eliminate the disease in the bud. Reduce the number of sprays as much as possible according to the condition.