Symptom Identification and Control Methods of Peach Gummosis

Peach gummosis is a disease commonly occurring on peach trees today, and it can be severe; especially in peach orchards with extensive management and weakened tree vigor, the incidence 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, damage from pests and diseases, frost injury, freezing injury and others, or gummosis caused by physiological disorders of the tree resulting from extensive management, excessive pruning, excessive fruiting, improper fertilization, heavy clay soil and so on. The other is infectious pathogens, caused by fungi; the sexual stage belongs to the subphylum Ascomycotina, and the asexual stage belongs to the subphylum Deuteromycotina.

II. Symptoms and disease 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 semi-transparent, soft gum; gum flow is heavy after rain, and it later turns brown upon contact with air, becoming glistening 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 in older trees, and mild in young trees.

Any wounds caused by insect injury, disease injury, freezing injury, hail injury, sunscald and so on can cause non-infectious peach gummosis (without pathogenic bacteria). In addition, gummosis caused by physiological dysfunction of the tree due to heavy clay soil, poor drainage, excessive or insufficient irrigation and so on is infectious peach gummosis caused by fungi. The fungal spores of its asexual generation spread through wind and rain, invading through wounds and lateral buds. There are two disease peaks in one 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. When the pathogen invades the current-year new shoots of peach trees, tumor-like raised lesions centered on lenticels are produced on the new shoots, but no gum flows. In May of the following year, the tumor skin cracks and exudes a gum-like liquid, which is a colorless, semi-transparent viscous substance, later becoming a tea-brown hard mass. The diseased part becomes sunken into round or irregular patches, on which small black dots are scattered. 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 cankers and even death. When peach fruit is infected, brown rot occurs, densely covered with small granular dots, and when moist, white masses are exuded.

Infectious gummosis overwinters as mycelium and pycnidia in diseased branches. 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, a large amount of pathogen overflows from the diseased part, flows down along the branches and trunks or splashes onto new shoots, invading through lenticels and wounds, becoming the main inoculum source for initial infection of 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 flow points on the tree increases and the disease worsens. Infectious gummosis has two disease peaks in one year, the first from early May to early June, and the second from early August to early September, after which it no longer infects and causes damage. The most favorable time for pathogen invasion is when the cortical cells of the branches gradually become suberized and lenticels have formed. Therefore, preventing this disease is best done during the new shoot growth period.

III. Poor soil, such as being too heavy and clayey and relatively acidic. Poor drainage and excessive water accumulation on the ground. In addition, extensive management, excessive fruiting and so on can also cause weakened tree vigor and so on, all of which can cause gummosis.

IV. Comprehensive control measures. Based on the above symptoms and disease occurrence patterns, in actual production, the control of this disease should focus mainly on agricultural control and manual control, with chemical control as a supplement. Chemical control mainly controls the two peak periods of spore dispersal and spore invasion causing disease. The 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 later stages. Prune reasonably, manage the load reasonably, coordinate the contradiction between growth and fruiting, and maintain stable tree vigor. Do a good job of drainage in the rainy season to reduce humidity in the peach orchard. Carry out summer pruning at the right 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 wounds from pests and diseases and mechanical wounds.

2. Eliminate overwintering inoculum: from the coldest December to January, carry out orchard clearing and disinfection, scrape off hard gum masses and the rotten cortex and wood beneath them, gather them and burn them, then spray 5°Be lime sulfur mixture for disinfection, and afterward whitewash the trunk and large branches to eliminate overwintering inoculum 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, 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 sap begins to flow, that is, the end of March. At this time, it is exactly the initial stage of gum flow, with few affected trees and a small range of gum flow, which is convenient for control and reduces nutrient consumption of the tree. Afterward, apply powder for control whenever cases are found. Control on cloudy and rainy days is best, because at this time the gum liquid flowing from the bark is highly viscous and easily adheres to the quicklime powder. For fruit trees with severe gum flow or old and weakened trees, use a knife to scrape off the dried gum and old cracked bark, expose the tender bark, and then apply the powder for a better effect. This method is simple, convenient and effective.

5. Spray pesticides at the right time 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 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 disease peaks of infectious gummosis. Before each peak period, spray once every 7-10 days with 1000 times liquid Jundusha or Junduqing, Junlimie, etc., alternately spraying 2-3 times in succession, to eliminate the disease in the bud, and reduce the number of spray applications as much as possible according to the disease condition. Before the bud swelling stage, spray once with 4-5 degrees Baumé lime sulfur mixture. During the growing season, starting from leaf expansion in April, spray 50% carbendazim 1000 times liquid once every half month, for 4 sprays.

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

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