Occurrence and Control Methods of Major Diseases, Insect Pests and Rodent Pests of Lilies

Lily, also known as night lily, mountain lily, Zhongpeng flower, etc., is a plant that combines medicinal, edible and ornamental uses, with a large market demand. Lily is also a traditional export specialty of China and is planted throughout the country. However, with the expansion of lily planting area, diseases, insect pests and rodent pests have become increasingly serious, becoming the main factors restricting stable and high yields of lilies. The occurrence and control methods of the main diseases, insect pests and rodent pests of lilies are introduced as follows:

1 Main diseases and control

1.1 Main diseases There are many kinds of lily diseases, but fungal diseases such as gray mold and Fusarium wilt are the main ones. In addition, viral diseases and bacterial diseases also occur rather seriously in some areas.

1.1.1 Gray mold, also known as lily leaf blight, mainly damages the aboveground parts. After the leaves are infected, small brown spots first appear, then gradually expand into round spots; when humidity is high, a gray mold layer can be seen on the spots on the underside of the leaves, and the spots easily spread and merge, causing the entire leaf to turn brown and rot. After flowers are infected, small brown spots appear. When the stem is infected, long brown streaks appear, and the plant shrinks and falls over. The pathogen of this disease is Botrytis cinerea, and the primary infection source is mainly the sclerotia that overwinter in the soil with diseased plant residues. When the temperature rises above 10°C in spring, the sclerotia produce conidia, which are transmitted to the plants by rain and other means, causing primary infection. Generally, suitable temperature and high humidity in May to June are conducive to the epidemic spread of the disease, which is the peak period of incidence.

1.1.2 Fusarium wilt can damage all organs of the plant. Affected plants are dwarfed, and the leaves yellow and then wilt and dry up; the underground bulbs develop brown rot, and the scales often fall off from the stem plate. This disease is caused by Fusarium, and the mycelium overwinters in the seed bulbs or in the soil with diseased plant residues. The disease begins to occur the following spring when the temperature is around 12°C, with the peak period from mid-April to mid-May.

1.1.3 Phytophthora blight, also known as lily foot rot, can damage all organs of the whole plant. After flowers and leaves are infected, water-soaked brown small spots appear, then gradually expand, with a white mold layer on them. Stem lesions can continuously expand into long strips and rot, causing the plant to die. When the bulb is first infected, water-soaked brown spots appear, then it gradually rots. This disease is caused by Phytophthora cactorum, which overwinters in the soil with diseased plant residues as chlamydospores or oospores, and produces hyphae for infection the following spring when conditions are suitable. Generally, temperatures of 22 to 26°C and rainy, humid conditions are conducive to the occurrence and spread of this disease.

1.1.4 Soft rot This disease is a bacterial disease and mainly damages bulbs during storage. After the bulb is infected, irregular water-soaked lesions first appear, then expand, causing the entire bulb to rot. The pathogen of soft rot is the carrot soft rot variant of Erwinia, and it can be transmitted by seed bulbs and soil.

1.1.5 Viral diseases mainly include mosaic disease, rosette disease, ringspot disease, etc., which can cause symptoms such as leaf yellowing, plant dwarfing and deformity, and necrotic spots on stems. These diseases are mainly transmitted by virus-carrying seed bulbs or by insects (mainly aphids) as virus vectors.

1.2 Control measures

1.2.1 Combining the selection of disease-free good varieties with soil disinfection Most pathogens harmful to lilies can overwinter in the soil with diseased plant residues (gray mold, Fusarium wilt, Phytophthora blight, etc.), and seed bulbs can also carry pathogens (soft rot, Fusarium wilt, etc.); therefore, broad-spectrum fungicides such as carbendazim can be used to disinfect the soil and seed bulbs before sowing, and tissue culture methods can also be used to cultivate virus-free seedlings (to control viral diseases) for planting. This is the basic step in preventing disease occurrence.

1.2.2 Crop rotation and timely cleaning of fields Most fungal diseases harmful to lilies are soil-borne diseases, and continuous cropping provides conditions for the accumulation of pathogens in the soil; therefore, it is best to rotate with different crops, and diseased plots should stop planting for 2 to 3 years. In addition, diseased plant residues should be promptly removed, centrally burned or used for biogas, so as to reduce the base number of pathogen sources.

1.2.3 Applying sufficient base fertilizer, controlling planting density, and improving plant resistance Lily is a fertilizer-loving plant, so sufficient base fertilizer should be applied, and attention should be paid to the reasonable combination of nitrogen, phosphorus, potassium fertilizers and organic fertilizer, which can make the plants grow robustly and improve disease resistance. Overdense planting will cause insufficient light for plants, poor air circulation in the field, and increased humidity, which is conducive to disease occurrence.

1.2.4 Biological control According to reports, microbial preparations such as Bacillus and Streptomyces have good effects on Fusarium wilt and gray mold, and the control effect can last for many years.

1.2.5 Chemical control In the early stage of disease occurrence, spraying with 50% Shukeling, 70% thiophanate-methyl (to control gray mold), 20% Junduqing (to control viral diseases), 40% fosetyl-aluminum (to control Phytophthora blight), etc. can effectively inhibit the further development of the disease. Before the bulbs are put into storage or refrigerated, treat them with 50% carbendazim and then dry them, which can prevent the occurrence of soft rot during storage.

2 Main insect pests and control

2.1 Aphids Aphids can occur for more than 10 generations a year, with the peak damage period in April to May. Adults and nymphs gather on stems and leaves to suck sap, causing leaves to curl and plants to become dwarfed, while also transmitting viral diseases, causing greater damage.

Control method: Spray 20% fenpropathrin emulsifiable concentrate 2000-fold solution, or 2.5% lambda-cyhalothrin emulsifiable concentrate 2000-fold solution, or 80% dichlorvos 1000-fold solution onto the aphid bodies on the plants, which can achieve a good control effect and, accordingly, also reduce the occurrence of viral diseases.

2.2 White grubs White grubs can directly bite off the roots and stems of seedlings, causing dead seedlings, and also gnaw on bulbs.

Control method: Before planting, isofenphos-methyl emulsifiable concentrate can be mixed into poisonous soil for hole application. When damage occurs during the growing period, isofenphos-methyl can be used for root irrigation. During autumn plowing, white grubs can be captured manually to reduce the overwintering population base.

2.3 Cutworms The larvae can bite off the stems of seedlings near the ground, causing the whole plant to die, and can also damage bulbs in the soil.

Control method: Promptly remove weeds at the field edges. Preventing adults from laying eggs is the key to controlling cutworms. Chenopodium album, alfalfa and other foods favored by cutworms can also be piled up to attract and trap them, or combined with chemicals for poisoning. They can also be controlled by spraying 20% fenvalerate or 90% trichlorfon, or treated by root irrigation with methamidophos.

2.4 Mites Adult mites and young mites gather on the young and tender parts of plants, piercing and sucking sap, causing leaves to become stiff and yellowish brown, and in severe cases can lead to dead seedlings.

Control method: Crop rotation. Promptly removing weeds at the field edges can reduce the occurrence of mites. In addition, propargite and isocarbophos can be used for spraying control.

3 Main rodent pests

Zokors and moles are the main rodents harmful to lilies and can bite and eat underground bulbs. Control method: Manual capture with mousetraps (traps), or bait made from foods favored by rodents mixed with rodenticide placed at the burrow entrance for lure feeding and killing.