Garlic Diseases and their Integrated Control techniques

In recent years, with the expansion of garlic planting area, farming system and cultivation environment change constantly, garlic plant disease resistance also decreases year by year, garlic disease caused by more and more losses. Especially, new diseases appear constantly, some diseases even show a sharp upward trend, which intensifies the harm to garlic. According to investigation and analysis, the damage rate of garlic disease to garlic is generally 20%-30%, and the serious year and plot can reach more than 50%, or even higher. For example, investigation in 1993 showed that the rate of garlic rust in Zhongmu County was as high as 80%, and the affected area reached more than 65% of the planting area. The affected garlic was seriously degraded, affecting export and foreign exchange earning, and greatly dampening the enthusiasm of garlic farmers. At present, there are more than 20 kinds of garlic crop diseases known, which are caused by fungi, bacteria, viruses and nematodes respectively. In addition, physiological diseases have attracted more and more attention. Disease occurrence and damage has become a major obstacle to garlic production. The main diseases of garlic and their integrated control techniques are introduced as follows.

1. The main diseases of garlic and their occurrence rules

1. Garlic virus disease occurs in different degrees every year in the main garlic producing areas. The disease can cause garlic head to become smaller, and the yield reduction is between 20% and 50%. It is the most important disease of hidden yield reduction in production at present.

Sowing garlic cloves with poison can cause disease after emergence, generally in the case of high temperature and drought, large number of aphids, or dry soil, lack of fertilizer, overgrown plots, heavy disease and onion or lily family other crops continuous cropping, adjacent to the field is also easy to cause disease.

2. Garlic rust is an epidemic disease of garlic in China, which occurs every year. The annual incidence of disease is more than 10%, and the year of heavy occurrence can reach more than 80%. Generally, the yield is reduced by about 10%, and the serious plot reaches more than 30%. The disease mainly damages leaves, followed by pseudostems; the head of the diseased garlic plant obviously becomes smaller, easy to crack and respect petals, and the commodity value obviously decreases. According to the investigation in Zhongmu County from 1993 to 1995, the disease caused early leaf death 15-20 days.

Garlic rust pathogen likes warm, cool and high humidity, spring temperature rises quickly, more rainy, especially from March to May, there is more rainfall, and there is breeze, which is conducive to the spread and invasion of pathogenic bacteria. The disease is serious in the land with high groundwater level, heavy soil and low lying.

3. Garlic leaf blight is one of the most serious diseases in garlic growing areas, which is widely distributed in Henan Province and seriously damaged. The disease mainly injures leaves and garlic sprouts. In severe cases, the diseased leaves dry up, garlic sprouts cannot be extracted, or they break from the diseased parts when extracted, and the color is yellow and white.

The pathogen develops in a wide temperature range and needs a large humidity. The onset time depends on the temperature, and the severity depends on the humidity. There are two peaks in November-December before the year and April-May in spring. Continuous cropping of fields, especially the accumulation of diseased plant residues in fields and fields, occurred seriously.

4. Garlic leaf spot diseases include purple spot disease, black spot disease, blight disease, gray spot disease, coal spot disease, etc., which are divided into garlic main production areas. The disease occurs heavily in the years with more rainfall from March to May. The annual incidence rate of sick plants is about 5%. The disease rate of sick plants in heavy years can reach about 15%. This kind of disease mainly damages leaves, causing leaves to die, and when it occurs seriously, it causes the whole garlic plant to die.

This kind of disease pathogen temperature adaptation range is wide, requests the air relative humidity to be higher, if appears in spring pours fragrant cold, in addition April rainfall many then occurs seriously. Along the Yellow River basin, rainy, foggy and light weather often occurs from November to December, and peak incidence can also occur. High planting density, lack of soil organic matter, partial application of nitrogen fertilizer field often serious disease; general late-maturing varieties, purple garlic light disease.

5. Both sclerotinia sclerotiorum and white rot occurred in garlic area of Henan Province, the former occurred intermittently, the latter occurred all the year round, the incidence of both diseases was low all the year round, and the incidence of some plots reached more than 30% in serious years. Generally, the yield is reduced by 30%-50%, and the heavy ones will not be harvested. Sclerotinia sclerotiorum damages pseudostems, yellow brown rot, lodging, or slow growth on the ground, early plant death. Garlic white rot starts from the outer leaf tip, yellow brown vertical stripe appears, plant grows slowly and yellows, then develops to pseudostem, soft rot occurs when humidity is high. Underground garlic is small, and the garlic dug out has no leaves and loses its commodity value.

The occurrence of two diseases is mainly related to the climate from April to May. When the temperature is 20-25℃, the disease is serious or even disastrous; the disease is heavy in the upper quality, low-lying in the field, or in the field under the forest, the disease is heavy in continuous cropping, ponding, high density or partial application of nitrogen fertilizer; the disease is light in the field covered with complete plastic film.

6. Other important diseases such as garlic bacterial soft rot and penicillium are also important diseases that can not be ignored. Garlic bacterial soft rot occurs sporadically in general years and tends to worsen in recent years. Penicillium is a disease which is easy to occur after harvest and storage period. If it rains during harvest, does not dry in time after harvest, and stores under humid conditions, the disease will be serious and the infection rate will be high.

II. Integrated control techniques of garlic diseases

(i) Before and after sowing

Control strategy: based on agricultural control, in order to cultivate strong seedlings for the purpose of optimizing the appropriate counterpart varieties.

1. agricultural control

(1) Selection and selection of garlic seeds before sowing, virus-free garlic, disease-resistant garlic, disease-free garlic as far as possible, and selection of large-petal garlic. It is a good way to transfer seeds from other places. For example, Zhongmu County transfers a large number of Cangshan garlic from Shandong every year.

(2) Choose sandy loam with dry and flat terrain, convenient irrigation, rich organic matter and strong ability to keep fertilizer and water to plant garlic. Avoid continuous cropping or continuous cropping with onion and garlic.

(3) Fine leveling of land, watering of soil moisture, timely ploughing and harrowing, creating a soil environment conducive to root growth and development, in order to improve disease resistance.

(4) Timely sowing to minimize the occurrence of freezing damage. For early-maturing bolting garlic, it is necessary to strengthen the seedling stage before winter to reduce the degree of freezing injury.

(5) Scientific and rational fertilization, application of sufficient base fertilizer, organic fertilizer must be fully decomposed, increased application of phosphorus and potassium fertilizer, cake fertilizer, can promote the healthy growth of seedlings, improve the disease resistance of garlic before the year. Formula fertilization or garlic fertilizer can reduce the occurrence of physiological diseases.

(6) Plastic film mulching can effectively reduce the chance of pathogen spreading by rain, watering and border irrigation, improve soil temperature, preserve moisture, reduce irrigation times, and prevent disease occurrence.

(7) The pathogens of garlic leaf blight, leaf spot disease, white rot and sclerotinia sclerotiorum all overwinter and oversummer in soil with the residues of diseased plants. The residues of diseased plants should be thoroughly cleaned up and rotation should be carried out for more than 3 years.

2. chemical control

50% Thiophanate-methyl WP or 50% Carbendazim WP or 70% Mancozeb 0.5-1kg to water 5- 7.5 kg can be sprayed evenly on garlic seeds, then air dried and sown, good control effect can be obtained.

b) During the growth period

This period spans a long time, from seedling emergence after sowing to harvest in late May, which is the occurrence period of diseases such as leaf blight, leaf spot disease, gray mold, rust and epidemic disease. The following measures are mainly taken.

1. agricultural control

It is strictly prohibited to irrigate with heavy water, drain water in time after rain, clean up the residues of diseased plants in combination with field management, and take them out of the field. The top dressing should be applied at the drying and shrinking stage of garlic stem, the elongation stage of garlic stem and the expansion stage of scale bud. 5~10kg urea or 10kg ammonium nitrate should be applied every 667m2, and 10kg ammonium sulfate should be applied as "head fertilizer". Potassium dihydrogen phosphate can also be sprayed to improve the disease resistance. Plant ash or gypsum powder can be applied to the stem base of garlic white rot and sclerotinia sclerotiorum to reduce the chance of pathogen invasion. Timely harvesting, try to avoid excessive scratches.

2. chemical control

(1) Control garlic rust, in case of heavy rainfall years, check the disease center in early spring, timely prevention, generally select 15% triadimefon WP 1000 times solution, or 15% triadimefon WP 1500 times solution plus 70% mancozeb WP 1000 times solution in early April to control the first time, 10~15 days later to control once, generally according to the disease control 2-3 times.

(2) To control garlic leaf blight, leaf spot, gray mold, etc., choose 800 times solution of 75% chlorothalonil WP, 500 times solution of 64% sandufan WP, 500 times solution of 50% copper succinate WP or 1500 times solution of 50% prohydantoin WP, depending on the field condition, start to control at the end of November or late March, and control twice in spring.

(3) To control virus disease, virus-free garlic is the best method. Plants are strong and leaves are dark. Secondly, spray 1.5% Zhibing Ling 1000 times solution, or 20% virus a500 times solution, 5% Jundu Qing 300 times solution in the early stage of disease.

(4) To control bacterial soft rot, spraying 72% agricultural streptomycin soluble powder 4000 times solution at the early stage of disease, 77% can kill 500-800 times solution of wettable particulate agent, once every 7 days, and continuously controlling 2-3 times depending on the disease condition.

(iii) Post-harvest and storage period

Mainly to control penicillium, gray mold, purple spot and other storage diseases, the main measures taken at present are as follows:

(1) Stop irrigation 5 days before harvest to prevent garlic skin rot and storage intolerance.

(2) Try to avoid mechanical damage when harvesting, clean up the residues of diseased plants in time, take them out of the field, concentrate on high temperature stacking and composting, which is helpful to reduce the source of disease and reduce the chance of disease occurrence.

(3) The harvested garlic should be dried in time, peeled off the skin according to the requirements of commercial garlic, and rotten garlic, green garlic, etc. should be picked out.

(4) Ray treatment and cold storage can effectively prevent the further damage of late stage and storage diseases to garlic.