Mushrooms

by William Falconer

The mushroom grower has his full share of insects to contend with, and in order to overcome them one should acquaint himself with them, and know what they are, what they do, whence they came, and how to destroy them. One should study the diseases and mishaps of his crop and endeavor to know their cause. If we know the cause of failing health in plants, even in mushrooms, we can probably stop or devise a remedy for the disease or means to prevent its recurrence, and if we can not benefit the present subject we are forewarned against future attacks. But there is a deal of mysterious trouble in this direction in mushroom-growing. We are likely to know something about the depredations committed by insects or parasitic molds above ground, but I am sure there is a good deal of mischief going on under ground of which we know very little, if anything. The ills to which the mycelium is subject are not at all fully understood.

"Maggots."—This is the common name among practical mushroom growers for the larvæ of a species of fly (Diptera) which from April on through the warm summer months renders mushroom-growing unprofitable. It is unavoidable, and so far has proved invincible. It attacks the mushrooms in deep cellars, above-ground houses, greenhouses, or frames, and is often quite common in early appearing crops in the open fields. We sometimes read that it does not occur in unheated cellars, but this is a mistake, for in our unheated tunnel cellars, where the temperature in April does not exceed 55°, maggots always appear about the end of this month. But it is true that in the case of cool houses and where the beds are covered over with hay or straw maggots do not appear as early in the season as they do in warm houses and open beds. While rigid cleanliness, and care in keeping the house or cellar closed, no doubt have much to do in lessening the trouble, I have never been able to overcome it, and know of no one who has. We simply stop growing mushrooms in summer.

The maggots or larvæ are about three-sixteenths to four-sixteenths of an inch long, white with black head, and appear in all parts of the mushroom, but mostly in the cap and at the base of the stem, and perforate hither and thither leaving behind them a disgusting network of burrows. The tiny buttons, about as soon as they appear at the surface of the ground, are infested, but this does not check their growth, and when they become mushrooms large enough for gathering, unless it be for a dark looking puncture or tracing now and then visible on the outside of the caps and stems, there are but few signs to indicate to the inexperienced eye the presence of maggots. And this is why maggoty mushrooms are so often found exposed for sale in summer. But in large or full-grown mushrooms, and especially the white-skinned varieties, their presence is visible enough. Although very repugnant, however, and utterly unfit for food, maggoty mushrooms are not poisonous.

But all the mushrooms of summer crops are not maggoty, only a large proportion of them; the evil begins in April, and increases as the summer advances, until August, when it decreases, and in October completely stops—at least this is my experience.

A solution of salt, saltpeter, or ammonia sprinkled over the surface of the beds does not, in this case, do any good as an insecticide, pyrethrum powder diffused through the atmosphere, and tobacco smoke, have been ineffectual. Burning a lamp set in a basin of water with a little kerosene floating on the surface is a most doubtful operation. Multitudes of flies are destroyed by this lamp trap, but they are the poor little innocent "manure flies," and the atmosphere of the house is vitiated and rendered unhealthy for the crop. I have tried these lamp traps season after season, and never knew of their doing any good; that is, the maggots seemed just as numerous in the lamp-trapped cellar as in the other cellar in which no lamp trap had been used.

Regarding this "maggots" question, Mr. J. F. Barter, of London, writes me: "During the summer months the outdoor mushrooms get maggoty before they are big enough to gather, but of course they can be grown in cool cellars all the year round.... I know of no sure cure for them (the maggots); of course a slight sprinkling of salt with manure or mold does prevent, to a certain extent, but it must be used very carefully." Now my experience is, as I have already said, that it is impossible to grow mushrooms here in summer, even in cool cellars, without having them more or less maggoty. As regards the salt and loam preventive, I have tried it lightly and heavily, but without any apparent good effect.

Black Spot.—All mushroom growers are familiar with this disease, but unless it appears in pronounced form very little notice is taken of it, even by market men, for we see spotted mushrooms continually exposed for sale. It appears as dark brown spots, streaks, or freckles, on the top of the mushroom caps, and increases in distinctness and breadth with age. [Fig. 25]. It is caused by eel worms (Anguillulæ). These minute creatures enter the mushrooms when the latter are in their tiniest pin form and before they emerge from the ground. If a button arises clean it remains clean, if diseased it continues to be diseased, and it is a fact that if one mushroom in a clump has black spot we usually find that every mushroom in the clump has it. But mushrooms growing from the same bit of spawn and that come up an inch or two away from the spotted ones may be perfectly clean. Black spot has never occurred with me in new beds, and seldom in those in vigorous bearing, but it generally appears in beds that have been in bearing condition for some weeks or are declining. It does not confine itself to any particular spot or part of the bed, and sometimes it is much more plentiful than at others. Between October and March we have very little black spot, but as the spring opens this disease increases. During the winter season, with careful attention, perhaps not so much as one per cent will show black spot, but as the warm weather sets in the per centage increases until in May, when as many as twenty per cent may be affected by it.

Fig. 25. Mushroom affected with Black Spot.