How to control mite damage in oyster mushroom cultivation in spring

Oyster mushroom is a popular edible fungus with a broad consumer base, high biological efficiency and good economic returns, so its cultivation area is relatively large. However, the raw materials used for spring cultivation of oyster mushrooms are generally left over from last year and often carry mites. As temperatures gradually rise, conditions become suitable for mite growth and reproduction, and they multiply quickly. They mainly feed on oyster mushroom mycelium and fruiting bodies, causing reduced yields and, in severe cases, total crop failure.

1. Distribution, morphology and biological characteristics of Acarus siro and Tyrophagus putrescentiae

1. Acarus siro

(1) Distribution and damage: This mite is a cosmopolitan species. In edible fungus production, flour mites often occur in environments contaminated by competitor microorganisms; through their activity they spread the contaminants, causing healthy fruiting bodies to become damaged and rot. Flour mites can also feed directly on oyster mushroom mycelium, causing reduced yields or even total crop failure.

(2) Morphological characteristics: Adult male mites are 320-240 μm long, adult female mites are 350-650 μm long. The body is colorless, the chelicerae and legs are pale yellow to reddish brown, and the posterior end is bluntly rounded. The legs are relatively thick, with 4 pairs of short legs, each divided into 6 segments. The first pair of legs in males is thick and large, with a larger spine-like projection on the femur. The tarsus of the fourth pair of legs bears two suckers. On both sides of the anus there are anal setae and anal suckers. The first pair of legs in females is weaker than in males, with no spine-like projection on the femur; the tarsus of the fourth pair of legs has no suckers, and the genital opening is located between the coxae of the fourth pair of legs. The hypopus is about 200 μm long, pale reddish brown, broadly oval and arched-concave, pointed at the front and rounded at the rear.

(3) Life history and habits: Acarus siro often enters mushroom houses with culture material that has not undergone high-temperature fermentation or thorough disinfection, or is carried to mushroom beds by insects, wind, tools and the like. After edible fungi are inoculated, if competitor microorganism contamination occurs, they quickly gather and become active in places with abundant mold. Under suitable temperature and high humidity, they reproduce rapidly; at 23°C and 87% humidity, they need only 9-11 d to complete one generation. When populations are large, large amounts of cast skins and excrement remain on the culture material or mycelium, giving off a musty odor. Acarus siro has strong cold resistance, but its drought tolerance is very poor; eggs can hardly hatch at all at 60% relative humidity, and under dry conditions a hypopus can form between the first and second instars. The spread of this mite in mushroom houses or on mushroom beds occurs not only by its own crawling but mainly by attaching to other pests and mites.

2. Tyrophagus putrescentiae

(1) Distribution and damage: This mite is a worldwide pest mite and is commonly distributed throughout China. It often occurs mixed with Acarus siro and also causes relatively serious damage to fungal materials. Affected stored materials often carry an unpleasant odor. In addition, materials carrying Tyrophagus putrescentiae can cause rash disease if eaten by humans, and skin contact with this mite can sometimes cause dermatitis.

(2) Morphological characteristics: Adult male mites are 280-350 μm long, with a smooth, glossy cuticle; on the ventral surface of the body, on each side of the anal opening, there is 1 circular sucker, and a pair of mating suckers is borne at the middle of the tarsus of the fourth pair of legs. Adult females are 320-415 μm long; body shape, setal length and arrangement are similar to those of males; the genital opening is located between the bases of the third and fourth pairs of legs; the anus extends almost to the end of the body and is surrounded by 5 pairs of anal setae. Eggs are about 115 μm long, elongate oval, slightly pointed at the front, milky white; larvae are milky white with 3 pairs of legs; nymphs are milky white with 4 pairs of legs and can be divided into the first nymph and the second nymph.

(3) Life history and habits: As long as environmental conditions are suitable, they can grow, develop and reproduce throughout the year. In China, the peak outbreak period of mites during the year is the plum rain season. This mite moves quickly, prefers to be active in dark places, often gathers on surfaces to cause damage, and likes moisture while fearing dryness; eggs can hatch only at a relative humidity above 70%.

2. Occurrence patterns

1. Causes of pest mite occurrence

Mushroom houses for cultivating oyster mushrooms are close to warehouses, feed rooms, chicken coops and places storing coarse bran, cottonseed hulls, rapeseed cake and the like, or mites are carried to mushroom beds by insects and so on; during disinfection of empty rooms, mites and their eggs hidden in cracks are not killed; spawn carrying pest mites; culture material carrying pest mites that is not thoroughly treated; and soil used for casing that has not been disinfected and carries pest mites.

2. Damage symptoms

(1) In spawn affected by mite damage, the mycelium at the bottle mouth is not dense enough and shrinks and degenerates, and in severe cases no mycelium can be seen in the spawn medium.

(2) When oyster mushrooms are damaged by pest mites during the mycelial growth stage, the white mycelial mass turns black and gives off an unpleasant musty odor.

(3) On the caps or stipes of young or mature fruiting bodies, brown or yellow spots of varying shapes appear; in the early stage the spots are sunken or become holes, with dark brown edges and slightly lighter centers or hollow centers, but the fruiting bodies do not rot.

3. Control methods

1. Mushroom houses should be fitted with fine-mesh screen doors and screen windows, and ventilation openings should also be fitted with screen mesh; the surroundings and cracks of the house body should be sealed tightly with mud to prevent insects from flying in and bringing mites to the mushroom beds.

2. Culture material should undergo secondary fermentation or high-temperature disinfection to kill pest mites in the material.

3. Do a good job of environmental sanitation and reduce competitor microorganism contamination, so as to reduce mite infestation and damage.

4. Absolutely ensure that spawn and the spawn-running room are free of mites. Carefully inspect spawn; if mites are found in spawn bottles, they must be discarded, or spawn suspected of having mites should be spawned in separate rooms. The spawn culture room should be built far from livestock sheds, poultry houses and warehouses, and it is strictly forbidden to pile up culture materials such as sawdust and cottonseed hulls and miscellaneous items indoors; the culture room and mushroom house should be disinfected frequently, and the surroundings of the house, the floor and the cultivation bed frames should be sprayed with chemicals to eliminate mites and insect pests.

5. When pest mite damage is found on mushroom beds, chemicals should be used as early as possible to eliminate the pest mites. First, chemical spraying: use propargite at 2000 times dilution, or lime sulfur mixture at 0.5-1.0 degrees Baumé; second, use trapping methods: (1) Spread fresh tobacco leaves flat on the surface of culture material damaged by mushroom mites. When many mushroom mites have gathered on the tobacco leaves, gently remove the tobacco leaves and burn them; if mites are still found, continue as before until there are no more mites. (2) Take 100 mL boiling water, 100 mL vinegar and 10 g white sugar, mix well, stir until dissolved, and after cooling add one drop of dichlorvos and mix well to make sugar-vinegar liquid. Soak gauze in the prepared sugar-vinegar liquid until thoroughly wet, then lay the soaked sugar-vinegar gauze on the culture material or mushroom bed damaged by mites. After attracting the mites onto the gauze, remove the gauze and scald the mites to death with boiling water. Repeat many times until the mites are basically killed.