Black spot is a disease, however, that can be controlled. Keep everything in and about the mushroom houses rigidly clean, and as soon as a bed has ceased to bear a crop worth picking clear it out, lime-wash the place it occupied, and make up another bed. Carefully observe that no old loam or manure is allowed to accumulate anywhere, or green scum forms upon the boards, paths, or walls; boiling water impregnated with alum poured over the boards, walls, and other scum-covered surfaces, will kill the eel worms, but it should not be allowed to touch the mushroom beds that are in bearing or coming into bearing. Much can be done to protect the bearing beds from the ravages of this pest: In gathering the mushrooms remove every vestige of old stump and fogged-off mushrooms, keep the holes filled up with fresh loam, and when the bed has been in bearing condition for a fortnight sprinkle it over with a solution of salt, and next day topdress with a half-inch coating of finely sifted fresh loam; firm it to the bed with the back of the hand, for it can not be pressed on with a spade on account of the growing mushrooms.
Is black spot unwholesome? I do not think so. I have never known any ill effects from eating it. The spotted parts are merely flavorless and tasteless. But it is a very disgusting disease, and no one, I am sure, would care to eat eel worms with their mushrooms. Until quite recently I used to regard the black spot as the mark of some parasitic fungus, and, acting under this impression, sent affected mushrooms to Dr. W. G. Farlow, Prof. of Cryptogamic Botany at Harvard University, for his opinion. He wrote me: "I find that the trouble is due to Anguillulæ, and I find an abundance of these animals in the brown spots." He advised me to submit them to an expert in "worms." I then sent samples to my kind friend, Mr. William Saunders, of Washington, D. C., who submitted them, for me, to Dr. Thomas Taylor, the microscopist to the U. S. Department of Agriculture, and who replied: "I recommend that you use a sprinkling of scalding water thoroughly over the entire surface of the bed, especially the portion next to the boxing. The scalding water should be applied before the buttons appear, but not penetrate more than one-eighth of an inch below the surface. Anguillulæ abound wherever decaying vegetable matter exists.... The green algæ on the outside of flower pots abounds in the anguillulæ."
Manure Flies.—This is the name we give to the little flies (a species of Sciara) that appear in large numbers in spring and summer in our mushroom houses, or, indeed, in hotbeds or structures of any sort where manure is used, as well as about the manure heaps in the yard. On account of their habits they are regarded with much ill-favor. They hop about the house and are continually running over the mushrooms, beds, and walls, in the most suspicious manner. But, notwithstanding this, I am inclined to regard them as perfectly harmless so far as injuring the mushroom crop is concerned, except the fact that they soil the mushrooms somewhat by their traveling over them with their muddy feet.
In attempting to get rid of the maggot fly I have destroyed large numbers of these little innocents, but without any apparent diminution in their numbers. Lachaume recommends: "These flies may be destroyed by placing about a number of pans filled with water to which a few drops of oil of turpentine have been added. The flies are attracted by the odor and drown themselves. They may also be caught with a floating light, in which they will burn their wings and fall into the water." I have found that pure buhach powder dusted into the air or burned on a hot shovel in the mushroom house has been more effective in destroying these flies than either the lamp or drowning process.
Slugs.—These are serious pests in the mushroom house, especially in above-ground structures, and they also occur in annoying numbers in cellars. Wherever hay or straw is used in covering the beds, or there is much woodwork about the house, slugs appear to be most numerous. They are very fond of mushrooms and attack them in all stages, from the tiny button just emerging from the ground to the fully developed plant. In the case of the buttons or small mushrooms they usually eat out a piece on the top or side of the cap, and as the mushroom advances in growth these wounds spread open and display an ugly scar or disfigurement. They also bite into the stems. But in the case of fresh, full grown mushrooms they seem to have a particular liking for the gills, and eat patches out of them here and there.
"Bullet" or "Shot" Holes.—My attention was first called to these by Mr. A. H. Withington, of New Jersey. They are little holes cut clear through the mushroom caps, as if perforated by a buckshot, and are evidently the work of some insect. He had, before then, submitted some of these perforated mushrooms to Prof. S. Lockwood, who sent them to Prof. C. V. Riley for his opinion. Prof. Riley replied that: "It is quite likely that the damage was done by some myriapod, possibly a Julus, or some of its allies. Only observation on the spot will determine this point." As I never had any trouble with myriapods attacking mushrooms and had seen nothing of this "bullet hole" work in our own beds I was much interested in the question and determined to look out for it, so I marked off a part of a bed and left that uncared for. I soon found out the trouble. These holes are the work of slugs which I have found and watched in the act of eating out the holes. To find the slugs at work, one has to take his lantern and go out and look for them at night. And to find out about plant parasites—be they fungus, or insect—one has to let them alone and watch them. Had we kept up our unsparing hunt for slugs, probably we should not yet have known what caused these "bullet holes," for no slug would have been left alive long enough to eat a hole through a mushroom cap.
Slugs must be caught and killed. We can find them at night by hunting for them by lamp-light; their slimy track glistens and reveals their presence. A few small bits of slate or half rotten boards with a pinch of bran on them laid here and there about the beds are handy traps; the slugs gather to eat the bran, hide beneath the rotten wood, and can then be caught and killed. Fresh lettuce leaves make a capital trap, but lettuces in January or February are about as scarce as mushrooms themselves. A dressing of salt is distasteful to slugs, and not injurious to mushrooms. Strong, fresh lime water may be freely sprinkled over woodwork, pathways, walls, or elsewhere where slugs might gather and hide themselves; but this solution should not be used upon the mushroom beds. Rigid cleanliness, however, about the mushroom house, and an ever-alert eye for slugs, should keep them under.
Wood Lice.—These are sure to be more or less abundant in every mushroom house, even in the cellars. They crawl in through doors, ventilators, or other interstices, and are brought in with the manure, and find shelter about the woodwork, manure, or any bits of dry litter that may be around. They attack the pinhead and small button mushrooms by biting out little patches in their tops and sides; and although these patches are small to begin with, the blemish spreads as the mushroom grows, and is an objectionable feature. Trapping and killing the insects is the chief remedy. Put part of a half boiled potato (for which no salt had been used) into a little pasteboard box, and cover the potato with some very dry swamp moss, lay the box on its side, and open at the end on the bed. The wood lice will gather to eat the potato, and remain after feasting because the dry moss affords them a cozy hiding place. Several of these little boxes can be used. Go through the house in the morning, lift the little traps quickly, and shake out any wood lice that may be in them into a tin pail (an old lard pail will do), which should contain a little water and kerosene. These traps may be used for any length of time, merely observing to change the potato now and again to have it in appetizing condition. Hot water or strong kerosene emulsion may be poured about the woodwork, walls, and pathways, to destroy the wood lice, but should not be allowed to touch the beds. Poisoned sweet apples, potatoes, and parsnips have been recommended as baits for these pests, but I must discourage using poisons of any sort in the mushroom house. Six or eight inch square pieces of half rotten very dry boards laid in pairs, one above the other, also make capital traps; the wood lice gather there to hide themselves; these traps should be examined frequently and the insects shaken into the pail containing water and kerosene.
Mites.—Two kinds of mites are very common about mushrooms in spring and summer; one is whitish and smaller than a "red spider" (one of the commonest insect pests among garden plants), and the other is yellowish and as large as or larger than a "red spider." But I do not think that either of these mites is worth considering as a mushroom pest. The yellow mite (probably Lyroglyphus infestans) is extremely common in strawy litter on the surface of hotbeds, and I have no doubt finds its way into the mushroom house as manure vermin rather than a mushroom parasite. They are the effect and not the cause of injury to the crop. When mushrooms are wounded or cracked, particularly about the stem, the crevices often become abundantly inhabited with these mites, but they do no material damage.
Mice and Rats.—These rodents are very fond of mushrooms, and where they have access to the beds are troublesome and destructive. Both the common house mouse and the white-bellied fence mouse are mushroom destroyers, but, so far, the nimble but timid field mouse (among garden, open air, and frame crops generally) has never yet troubled our mushrooms, but I can not believe that this immunity is voluntary on its part. The mice bite a little piece here and there out of the caps of the young mushrooms, and these bite-marks, as the mushrooms advance in growth, spread open and become unsightly disfigurements. In the case of open mushrooms, however, the mice, like slugs, prefer the gills to the fleshy caps. Rats are far more destructive than mice. Trapping is the only remedy I use, and would not use poison in the mushroom houses for these creatures for obvious reasons. But we should make our houses secure against their inroads.