What are the main pests of Fritillaria thunbergii? Detailed explanation of control methods

In terms of cultivation, Fritillaria thunbergii mainly suffers from the following diseases and pests: gray mold, black spot, soft rot, dry rot, white grubs, bean blister beetles, Pleonomus canaliculatus, and onion mites. Below is a detailed introduction to each, along with the corresponding control methods.

(1) Gray mold:

It is a disease caused by fungi. After infection, light brown spots first appear on the leaves, then expand into oval or irregular lesions with a distinct water-soaked ring at the edge, continuously enlarging to form large gray patches; after the flowers are infected, they shrink and dry up without blooming, and the flower stalks become constricted and shriveled, appearing light green; young fruits become dark green and dry up after infection, and larger fruits develop dark brown spots on the rind and fruit wings after infection, which continuously expand and gradually dry up. Under suitable temperature and humidity conditions, the infected parts grow gray mold. It generally begins to occur from late March to early April, breaks out heavily in mid-April, and causes severe damage. This disease overwinters as conidia on diseased plant residues or produces sclerotia that fall into the soil, becoming the source of primary infection the following year.

Control methods:

① After harvesting Fritillaria thunbergii, remove the infected plants and diseased leaves, preferably burning them, to reduce overwintering pathogens.

② Do not practice continuous cropping on land with severe disease incidence.

③ Strengthen field management, apply fertilizer reasonably, and enhance the disease resistance of Fritillaria thunbergii.

④ Before the disease occurs, spray Bordeaux mixture at 1:1:100 in late March, once every 7-10 days, for 3-4 consecutive times. In the early stage of disease, use 25% wettable powder carbendazim at 100 g per mu, sprayed as a 500-1000 times dilution; re-spray once after 7 days, for 2 consecutive times. Alternatively, spray 50% thiophanate-methyl at 1000 times dilution when the disease occurs. For soft rot and dry rot, attention should be paid during the summer to digging drainage ditches properly; soak seeds in 50% benomyl at 1000 times dilution for 15 minutes, dry them, and then plant; select bulbs free of pests, diseases, and wounds as seed. If damage from bean blister beetles occurs, spray 90% crystalline trichlorfon at 1500 times dilution or 40% dimethoate emulsion at 800-1500 times dilution.

(2) Black spot: A disease caused by a fungus. It starts from the leaf tip, the leaf color fades, and water-soaked brown lesions appear, gradually spreading toward the leaf base; some, due to environmental factors, do not develop deeply toward the leaf base and instead show wilting of the leaf tip, with a clear boundary between diseased and healthy parts. It generally begins to cause damage in late March and continues until the underground parts of Fritillaria thunbergii die. If there is continuous spring rain around Qingming, the damage is more severe. Black spot of Fritillaria thunbergii overwinters as mycelium and conidia on infected plants and diseased leaves, and re-infects and causes damage the following year.

Control methods: Same as for gray mold.

(3) Soft rot: A disease caused by pathogenic bacteria. The infected part of the bulb first becomes brown and water-soaked, spreads very quickly; after infection, the bulb turns into a mushy, tofu-dreg-like consistency, or becomes sticky and "snot-like"; sometimes the damage stops, and when the surface loses water, it becomes a cavity resembling insect damage. The boundary between rotten and healthy parts is distinct. The epidermis is often unaffected; after the interior soft-rots and dries up, an empty shell remains. Rotten bulbs have a distinctive sour, wine-like smell.

Control methods: For the control of dry rot and soft rot, comprehensive control measures must be adopted:

① Select robust, disease-free bulbs as seed. If dug up and stored over summer, they should be sorted by grade, spread out to air-dry, and then stored.

② Choose well-drained sandy loam for planting, and create good summering conditions.

③ Chemical control: Use various fungicides and acaricides in combination, soaking seeds before planting. For example, before planting, soak seeds in a mixture of 20% wettable tetradifon at 800 times dilution plus 80% dichlorvos emulsion at 2000 times dilution plus 40% kitazin emulsion at 1000 times dilution for 10-15 minutes; this has some effect, but further testing is needed to find safer and more effective chemical control measures.

④ Control mites, white grubs, and other underground pests, eliminate transmission vectors, prevent the spread of pathogens, and reduce damage.

(4) Dry rot:

It is a disease caused by fungi. From June to August, when the bulbs are summering, i.e., during the dormant period of Fritillaria thunbergii bulbs and when the soil is dry, the disease occurs. After the bulb base is infected, it becomes honeycomb-like, and after the scales are infected, they become brown and wrinkled. After such bulbs are planted, root development is poor, the plant withers early, and the new bulb is very small. In the suburbs of Hangzhou, the main manifestation of dry rot is that the base of the infected bulb turns bluish-black, the interior of the scales rots to form black spotted cavities, or dark brown and bluish cavities of varying sizes form on the scales. In some bulbs, the vascular bundles are affected, and brown dots are visible on the cross-section of the scales.

Control methods: During the summer preservation period of Fritillaria thunbergii, if intercropping on the ground is inappropriate or the bulbs are dug up too early -- rational intercropping should be practiced to create a cool, ventilated, and dry environment for dormant seed bulbs; control underground pests to avoid diseases caused by pest damage; for diseased seed bulbs, soak them in 50% carbendazim at 400-600 times dilution for 10-15 minutes before planting, let them dry slightly, and then transplant the seed bulbs.

Pests:

The main underground pests are white grubs, wireworms, etc. The damage period is during the dormant period of seed bulbs, and they can be controlled by drenching with 90% trichlorfon at 1000-1500 times dilution.

(5) White grubs: They are the larvae of scarab beetles, also known as "white silkworms." The body is white, and the head is yellow or yellowish-brown. The main pest damaging Fritillaria thunbergii bulbs is the larva of the copper-green scarab (Anomala corpulenta motschulsky). Other scarab larvae also cause damage.

The adult copper-green scarab has a body length of 1.8-2.1 cm, is copper-green in color, with earthy yellow edges; several basal segments of the legs are yellow; the outer side of the front tibia has two teeth; the claws have no teeth. The mature larva is 2.3-2.5 cm long, with a yellowish-brown head, milky-white thorax and abdomen, and an anal opening that is linear with one groove, with two bristles at the center front and many irregularly arranged bristles around it. The larva of the large black scarab has a three-cleft anal opening, with a cluster of flattened bristles with hooked tips at the front. The larva of the black velvet scarab has a longitudinally cleft anal opening, with a row of slightly arc-shaped bristles at the front.

White grubs begin to damage Fritillaria thunbergii bulbs in mid-April, with the most severe damage during the summering period of Fritillaria thunbergii, and stop causing damage after mid-November. Infected bulbs become pitted or have uneven cavities, resembling sweet potatoes gnawed by rats. Sometimes the bulbs are bitten into incomplete fragments. Adults appear in mid-May, are active in the evening, lay eggs scattered in relatively moist soil, and prefer to lay eggs on undecomposed barnyard manure.

Control methods:

① In winter, clear weeds, deep-plow the land, and eliminate overwintering pest populations.

② Apply decomposed barnyard manure and compost, and cover with soil after fertilizing to reduce adult egg-laying.

③ When preparing the land and turning the soil, pick up larvae to feed chickens and ducks.

④ Set up lights to trap and kill adult scarab beetles.