How to prevent and control garlic heart rot? Occurrence patterns and integrated control techniques

In recent years, the garlic industry in Pizhou City has developed rapidly, with the planting area growing from 3,333 hectares in the 1970s to 33,000 hectares in 2004, making it the largest garlic production area in the country and a national standardized high-quality garlic production demonstration county (city). However, with the expansion of garlic cultivation area and the extension of continuous cropping years, various pests and diseases have become increasingly severe, especially the damage from garlic heart rot, which has worsened year by year and seriously affects garlic yield and quality.

1 Occurrence patterns and damage symptoms

① Occurrence patterns In late February 2002, it was found sporadically in Chefu Mountain and Suyang Mountain townships; by 2003 it had spread to 5 townships, with an affected area of 1,667 hectares; by 2004 it reached 5,333 hectares, occurring to varying degrees in all garlic-planting townships. Generally, the disease begins to appear from after garlic planting to late February of the following year, with the peak incidence in mid-to-late March, and the late peak in early April. In some fields, the disease appeared as early as early November of the previous year, and affected plants die entirely if not controlled promptly.

② Damage symptoms Initially identified as a bacterial disease. After garlic is infected, it shows physiological growth disorder, with leaf tips turning dark brown inward; the whole plant becomes stunted and does not extend upward; the growing point (base) softens and rots, the base swells and becomes soft, rotting from the inside out, emitting a foul fishy odor.

2 Analysis of disease causes

① Sufficient pathogen sources are the basic condition for disease occurrence It took only 3 years to rise from sporadic occurrence to a major disease, indicating that pathogen sources in the field are abundant. In particular, during the entire garlic growing period in 2003, rainfall was sufficient, and field temperature and humidity favored disease occurrence. The garlic market remained sluggish throughout, and garlic farmers did not take control measures, allowing pathogen sources to accumulate in the field. Combined with the garlic bulbs themselves carrying pathogens, the disease became even more severe in 2004.

② Climatic factors such as rainfall are the main cause of disease occurrence According to observations, the pathogen can grow at 4-39°C. The main cause of disease occurrence is humidity. From late February to early March, there was abundant rain. After 2-3 consecutive days of heavy rain in the field followed by sunny days with rising temperatures, the disease began to appear in the field and spread rapidly, with the diseased field rate and diseased plant rate increasing by 8% and 1.9% respectively within one week. In addition, irrigation after the New Year aggravated the disease. According to a survey on March 20, 2004, there was a significant difference in disease severity between irrigated and non-irrigated fields of the same type.

③ Other factors From the analysis of survey results, excessive application of nitrogen fertilizer or excessive application of organic fertilizer resulted in more severe disease; among garlic varieties, large white garlic was more severely affected than red-skinned garlic; early-season garlic was more severely affected than late-season garlic; garlic without seed soaking was more severely affected than garlic with seed soaking.

3 Integrated control techniques

3.1 Agricultural control

① Rejuvenation and cultivation of strong seedlings Garlic is prone to degeneration. After 2-3 years of planting, select areas with large differences in geographical conditions and cultivation conditions for seed exchange. When selecting garlic seeds, remove damaged cloves, rotten cloves, soft cloves, sproutless cloves, and diseased cloves. Select large garlic bulbs and cloves as seeds to cultivate strong seedlings and improve disease resistance.

② Cultivation measures Use high ridges and deep furrows to ensure smooth field drainage during the flood season. Sow at the appropriate time, apply more decomposed organic fertilizer, and increase phosphorus and potassium fertilizer. Apply 3,000-4,000 kg of high-quality decomposed farmyard manure per 667 sq m as base fertilizer.

3.2 Chemical control

① Garlic seed disinfection Use 80 ml of garlic virus-removal agent mixed with 100 kg of water to soak 200 kg of garlic seeds for about 6 hours. Remove and air-dry for 2-3 hours before sowing. At sowing, apply 3-4 kg of garlic continuous cropping agent mixed with 30 kg of fine soil per 667 sq m for soil sterilization treatment.

② Field spraying In the early stage of disease occurrence, first remove diseased plants, then spray 60-90 g of 20% Longkejun (thiazole copper suspension concentrate) mixed with 40-60 kg of water per 667 sq m. Apply continuously 2-3 times. If rain occurs after application, re-spray immediately after the rain. Spray evenly on both upper and lower surfaces for good control efficacy.