Pest control of lemon seeds

Fungal diseases of lemon fruits during storage mainly include black rot, sour rot, stem rot, green mold, anthracnose, physiological diseases mainly include dry scar and edema.

(1) Pedicle rot: divided into brown and black pedicle rot, the symptoms are similar, but there is no obvious boundary between brown pedicle rot spots and healthy tissues, and there is fermentation flavor in the later stage. There was a clear boundary between black stalk rot spot and healthy tissue, and there was foul smell in the later stage. The pathogen invades the fruit tissue from the fruit pedicle, the initial disease spot is water-stained, the disease spot expands continuously, gradually turns brown or black, and the rot passes through the center of the fruit faster than along the pericarp. It is especially severe in rainy and humid regions or years.

(2) Black rot: The initial symptom is that the fruit pedicle turns black, the pathogen develops downward along the fruit column, and wherever the hyphae reach, it turns black and decays. During fruit growth and development, black rot bacteria mostly existed in the fruit pedicle, and could not invade the lemon tissue before the fruit pedicle tissue was destroyed. Any condition that weakens the fruit, such as an uncomfortable environment, late harvest, or prolonged storage, increases the susceptibility of the fruit to black rot.

Green mold: refers to penicillium and green mold caused by two kinds of storage diseases. The disease process and symptoms are similar, the initial peel surface becomes soft, water-stained spots appear, white hyphae grow with the extension of the disease spots, and soon turn into green or green mold layer. It takes only 1-2 weeks from the beginning of the disease to the whole fruit rot. Pathogens are transmitted by conidia by contact or by air currents. Invasion from wounds and cracks, so the most fundamental prevention measure is to reduce mechanical damage. Green mold and green mold are the most common causes of postharvest decay in all commercial citrus producing areas in the world.

(4) Acid rot: The initial symptoms are slightly convex water-like pale yellow to yellow spots. The bacteria mainly grow inside the fruit. In the later stage, the internal tissues of the fruit are all decomposed into sour water-like glue. At 24-29℃, it takes only 5 days from infection to whole fruit decay, adjacent fruits will also contact infection, and the bacteria will invade from the wound.

Anthracnose: The disease starts at the pedicle end, and the initial external symptoms are gray to brown spots, which expand rapidly and sometimes extend to the whole fruit. Under wet conditions, pink spores appeared on the surface, and then the spore population turned brown to black, and the pathogen did not invade the deep part of the flesh until the late stage. It mainly infects broad-skinned oranges, lemon fruits occasionally occur, wet areas and years are seriously affected. The pathogen grows on dead branches or weak branches of the orchard and spreads from there to the fruit, entering the fruit through cracked pericarp or dead pedicles.

Control methods of the above diseases: in addition to post-harvest treatment, available drugs to control. The method is as follows:

Thiabendazole (Tekdo, TBZ) and benomyl (Benomyl): are the most effective postharvest fungicides, which can effectively control stem rot and green mold, and have certain effects on anthracnose, but have no effect on acid rot and black rot. These two fungicides are slightly soluble in water, often prepared into wax-water mixture or water suspension use, treatment must be constantly shaken suspension, in order to ensure uniform liquid medicine. The concentration of thiabendazole was 1? 000mg/L, benlaite 600mg/L, fruit soaking for 3-5 minutes after harvest.

2 sodium o-phenylphenolate (SOPP): can control stem rot and green, green mold, sour rot also has a certain effect, especially for orange more effective. 2% sodium o-phenylphenolate aqueous solution with pH value of 11.5-12.0 has the highest efficacy, so the commonly used formula is: 2% sodium o-phenylphenolate +0.2% NaOH +1% hexamine, or 1% sodium o-phenylphenolate wax aqueous solution can be used.

3. sec-butylamine: it can control green mold and green mold, has low efficacy on pedicle rot, and is ineffective on sour rot and anthracnose. sec-butylamine is liquid, boiling point 63℃, can be used as warehouse fumigant (25-200mg/L, V/V, 42h), can also be prepared into 1%-2% aqueous solution for fruit soaking treatment.

④ Biphenyl: can control stem rot and green, green mold, acid rot invalid. It's a vaporous disinfectant. The commonly used method is to impregnate the permeable fruit paper with biphenyl according to the ratio of 2.35g: 1 piece (27.9cm×43.2cm) to make biphenyl fruit paper. Biphenyl can also be dissolved in paraffin oil (or mineral oil) to make biphenyl-paraffin mixture, coated on paper to make biphenyl pad.

In China, the commonly used preservatives in production are thiophanate (1000-2000mg/L), carbendazim (800-1000mg/L), imazalil (500mg/L), sodium bicarbonate (2%), etc.

physiological disease

Brown spot disease (dry scar): mostly occurs in the middle to late storage period. The initial symptoms are light brown irregular spots, later the color becomes darker, the spots expand, and at low temperatures develop into irregular circular spots centered on the pedicle. Oil vesicles rupture at the lesion. The depression is dry and contracted, and the position is limited to the exocarp. Most people think that this is a physiological disease caused by hypothermia (Brooks & McColloch, 1936; Li Peiwen, 1977). The disease is especially serious when stored at low temperature and humidity. In order to control and reduce the incidence of brown spot disease, measures such as late harvest, high humidity, low O2 and high CO2 were adopted to avoid too low storage temperature.

(2) edema disease: the initial pericarp becomes pale, local pericarp appears irregular, translucent water-like spots, food has kerosene taste. After the disease is serious, the whole fruit is translucent water-stained fruit, soft, easy to peel, and has a strong alcohol taste. If it is stored continuously, it will be infected by other pathogenic bacteria and rot. A large number of experiments show that too low temperature storage and poor ventilation make CO 2 accumulate too much, which will lead to edema disease. As long as either of the two factors exists for a certain period of time, it will lead to edema, and when both factors exist at the same time, the onset is earlier and more serious. Therefore, in order to prevent lemon fruit edema disease, attention should be paid to preventing low temperature storage or excessive fluctuation, and at the same time strengthen management, pay attention to ventilation.