Occurrence and Control Methods of Common Diseases in Oyster Mushrooms

In recent years, with the expansion of oyster mushroom cultivation areas and the increase in cultivation years, pest damage has become increasingly common, showing a trend of early and rapid occurrence, and in severe cases, entire flushes of mushrooms are lost. Because oyster mushrooms are relatively sensitive to pesticides and prone to phytotoxicity, applying chemicals after pest outbreaks makes it difficult to achieve the effect of eliminating pests while protecting the mushrooms. Therefore, identifying the damage characteristics of various pests and reducing infection sources are effective measures to avoid and reduce pest occurrence.

I. Pest Species

1. Sciarid flies, also called dark-winged fungus gnats, commonly known as small black mosquitoes, small flies, or white maggots (referring to larvae). They belong to the order Diptera, mosquito-like insects. Adults are 2-3 mm long, brown or grayish-brown, with hair on the body surface, one pair of membranous forewings and one pair of hindwings specialized into halteres. The compound eyes are well developed, pointed at the top, extending over the head and meeting left and right to form an eye bridge. The antennae are filiform, with 16 segments. The female's abdomen tip is slender and pointed, while the male's abdomen tip has a pair of pincer-like claspers. Larvae are white and transparent or milky white. Newly hatched larvae are 0.75 mm long and 0.1 mm wide, and later reach 5.5 mm long and 0.5 mm wide, with 12 segments in total, legless, with a black, sclerotized head and well-developed chewing mouthparts.

Adults are active and good at flying, phototactic, fond of humus, and often gather in unclean places (such as mushroom roots, weak mushrooms, rotten mushrooms, and garbage) to mate and lay eggs. Larvae prefer to live in groups in the substrate, moving and feeding, damaging mycelium, primordia, and young mushrooms, and are suitable for feeding on senescent mycelium. At this time, if too much water is sprayed, it further favors larval growth and development, causing disaster in a short period. Therefore, mushroom sheds that produce some mushrooms in autumn and winter and then produce mushrooms again in spring suffer severe damage; in mild cases yield is affected, and in severe cases total loss occurs.

2. Gall midges, also known as mushroom gnats, with larvae called fungus maggots. They are mosquito-like pests of the order Diptera. Adults are relatively small and delicate, about 1-2 mm long, pale yellow or orange-red. The head is small, and the compound eyes are large. The antennae are bead-like, with 11 segments, with obvious hairs on the segments, and the male's antennae are longer than the female's. The forewings are membranous, transparent, and hairy, with 3 longitudinal veins and 1 cross vein, and the hindwings are reduced to halteres. The 3 pairs of legs are similar. The female's abdomen tip is slender and pointed, while the male's abdomen tip has a pair of pincer-like claspers. Larvae are small, about 2 mm long, initially milky white, later orange-yellow or orange-red, elongated or spindle-shaped, with an underdeveloped head, 1 pair of short antennae, the body divided into 13 segments, and the integument transparent and legless. There is a prominent forked sternal spatula on the mesothoracic sternum, which is the main characteristic of gall midge larvae.

Adults are poor fliers, gregarious, strongly phototactic, and lay eggs in mushroom bed materials or compost yards. Gall midges mainly damage as larvae. Larvae prefer moisture and can live in water. During the spawn-running period, larvae damage in the substrate; during the fruiting period, they damage the substrate surface, young buds, and mushroom stipes. Damaged mushroom buds turn yellow, wilt, and die. After mature mushrooms are damaged, large numbers of larvae gather on the stipes and the underside of the caps, and in severe cases the substrate surface shows a layer of orange-red powdery material, affecting the marketability and yield of oyster mushrooms. Because they mainly reproduce by paedogenesis, their reproductive cycle is short, and they can outbreak in a short time.

3. Phorid flies belong to the order Diptera. Adults are small, pale brown to black. The antennae are short, with 3 segments, aristate. Larvae are transparent to milky white, with a pointed head, not sclerotized, and a blunt abdomen tip.

Poor ventilation and excessive humidity in the mushroom house, and failure to promptly handle dead and rotten mushrooms, often cause phorid fly adults to lay eggs and reproduce and cause damage. Larvae move quickly, invade from the base of mushroom buds, and bite and feed on tender tissues, turning the mushroom tissue into a loose, spongy mass, and finally hollowing out the entire mushroom bud. The greater the humidity of the casing soil layer, the more severe the occurrence.

4. Springtails, also known as ash worms, belong to the order Collembola. Springtails are wingless lower small insects, 1-2 mm long. Nymphs and adults are blue-purple, with scattered grayish-white small spots on the body, hairs and waxy powder, and can move on water. The head has thick, short antennae. There are 3 pairs of legs, thick and large, and there is a pair of furculae on the fourth abdominal segment. Larvae are whiter, similar in body shape to adults, molt after dormancy, and gradually darken in color. Most are saprophagous, and some feed on oyster mushroom fruiting bodies, boring into stipes and caps to feed, causing holes and reducing market value. After a major outbreak of oyster mushroom springtails, large numbers gather at the junction of the stipe and cap, damaging the gills and causing reddish-brown spots. Once disturbed, springtails jump off the mushroom bed and hide in moist, dark corners, even forming clumps. Springtails can also carry pathogens and viruses.

5. Mites belong to the class Arachnida, order Acari. They are minute, with 8 legs, like spiders. The main mites damaging oyster mushrooms are pyemotid mites and acarid mites.

(1) Pyemotid mites are minute, oblong to oval, pale brown, with short hairs on the body wall, slow-moving, fond of group living, and infest mycelium, young buds, and fruiting bodies. Under conditions of spawn running and fruiting and high humidity, they reproduce very quickly. After reproducing to a certain extent, they migrate in groups to the casing soil on the surface of the mushroom bed, appearing like a layer of earthy-yellow powdery material. If control is not carried out promptly, they can destroy the entire mushroom house in just a few days, eat all the mycelium, and cause total loss.

(2) Acarid mites are larger than pyemotid mites, round, white, with several long hairs on the body wall. They move individually, feed on mycelium, and are saprophagous. When they outbreak on mushroom beds, they can cause mycelial decline, but do not cause total loss.

II. Control Methods

Control of oyster mushroom pests should focus on prevention, with treatment as a supplement, using integrated control.

1. Do a good job of mushroom yard environmental sanitation. Livestock and poultry sheds, manure, grain warehouses, weeds, waste materials, sewage ditches, and the like around the mushroom house are all major habitats and breeding places for pests. Spring each year is the revival period for various pests. A clean environment inside and outside the mushroom house should be maintained, and waste materials, sewage, and crushed stone should be cleaned up promptly. Whether new or old mushroom houses, before use it is best to fumigate with formaldehyde plus potassium permanganate, and during the fruiting period hang medicinal cotton in the mushroom house to achieve pest prevention.

2. Install insect-proof equipment. Install 60-mesh screen doors and screen windows in the mushroom house, which not only facilitate ventilation and light transmission but also prevent pests from entering.

3. Prevent pests in the substrate. The raw materials for cultivating oyster mushrooms carry more or less pests. Generally, fresh, non-moldy raw materials of the current year are selected, and before use they are treated to kill insects, such as sun exposure and mixing with chemicals. For raw materials with many pests, short-term fermentation can also be used, generally stacking for 5-7 days, turning the pile 2 times, and controlling the material temperature at about 60°C, which can kill insects and eggs in the material. Material treated as above can reduce pest damage from the spawn-running period to the early fruiting period.

4. Avoid pest-carrying spawn. Do not use fruiting bodies carrying pests to make spawn; use cooked material as substrate to produce spawn.

5. Use light traps to kill adults. Install light bulbs or tubes in the mushroom house, place a water basin below, and drip in used engine oil. Pests such as flies and mosquitoes will come toward the light, stick, and die. If conditions permit, installing black light lamps gives a better trapping and killing effect.

6. Use sugar-vinegar liquid to control pests. For phototactic pests such as sciarid flies and gall midges, mix 3 parts sugar, 4 parts vinegar, 1 part white liquor, 1 part dichlorvos, and 91 parts water, then soak cloth or cotton balls in the solution, take them out, wring them dry, and cover the substrate surface. Pests that crawl onto the medicated cloth or cotton are poisoned to death. Mix 1 part honey, 10 parts water, and 2 parts 90% trichlorfon evenly to trap and kill springtails.

7. Management should be appropriate. In the process of oyster mushroom cultivation management, especially during the pest reproduction period, control measures should be appropriate; otherwise, it can also lead to pest invasion. The main management points are: during the spawn-running period, the mushroom bed should be tightly covered with film, and when ventilating, care should be taken to prevent pest invasion; during the fruiting period, the one-time water application amount should be strictly controlled to prevent water accumulation on the mushroom bed; and as far as possible, each batch of mushrooms should be harvested by flush, avoiding leaving the mushroom bed exposed for too long, so as to reduce the number of eggs laid by pests on the mushroom bed; if pests are found during the fruiting period, spray 25% permethrin-ester mixture at 2000 times dilution; after harvesting, clean the mushroom bed promptly and cover it tightly.