Detailed Explanation of Control Methods for Peach Gummosis

Peach 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 trees 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 the disease. 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 injury, freezing 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, with the sexual stage belonging to the Ascomycota and the asexual stage belonging to the Deuteromycota.

II. Symptoms and disease patterns

1. Non-infectious gummosis mainly occurs on the trunk and large branches, and in severe cases small branches may also be affected. In the early stage, the diseased part swells slightly, then secretes semi-transparent, soft gum. Gum flow is heavy after rain, and subsequently the gum turns brown upon contact with air, becoming crystal-clear soft gum blocks, then drying into hard gum blocks ranging from reddish-brown to tea-brown. As the amount of gum increases, the cortex and xylem of the diseased part gradually turn brown and rot (but no pathogens are 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 in older trees, and mild in 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 without gum flow. In May of the following year, the tumor bark cracks and exudes a gum-like liquid, which is a colorless semi-transparent 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 appear, and brown gum liquid can seep from the diseased parts, which can lead to cankers on branches and trunks or even death. Infected peach fruit develops brown rot, densely covered with small granular dots, and exudes white block-like matter 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 pathogens overflow from diseased parts, flow down along branches 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 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 peak periods per year: the first from early May to early June, and the second from early August to early September, after which it no longer causes infection. 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 carried out during the new shoot growth period.

III. Comprehensive control measures. Based on the above symptoms and disease patterns, in actual production, the control of this disease should focus mainly on agricultural 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 load reasonably, coordinate the contradiction between growth and fruiting, and maintain stable tree vigor. Drain well during the rainy season to reduce humidity in the peach orchard. Carry out summer pruning in a timely manner 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 blocks and the decayed cortex and wood beneath 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 trials 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 sites. After application, gum flow stops completely within 5-7 days, symptoms disappear, and there is no recurrence. The optimal period for powder application is when 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, which facilitates control and reduces nutrient consumption of the tree body. Afterwards, as cases are found, manpower can be mobilized to apply powder for control. Control is best on cloudy 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 senescent trees, use a knife to scrape off dried gum and old rough bark, exposing the tender bark, and then apply powder for better results. This method is simple and effective.

5. Timely spraying 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 1500-fold thiophanate-methyl or 1000-fold Duoxiaoling, Guobingling, etc. for prevention. From early May to early June and from early August to early September are the two peak periods of infectious gummosis. Before each peak period, spray 1000-fold liquid of Jundusha or Junduqing, Junlimie, etc. once every 7-10 days, alternately spraying 2-3 times continuously, to eliminate the disease in the bud stage, and reduce the number of sprays as much as possible according to the condition of the disease.