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Clinton (1904) reported some spraying experiments designed to determine the value of bordeaux mixture as a preventive of neck rot on white onions. Three applications of the spray mixture were made, but since no neck rot developed in storage no data were obtained upon the relative keeping qualities of the sprayed and unsprayed stock.

FUMIGATION.

The fumigation of onions with formaldehyde gas, either just before or just after they are placed in storage houses, has been recommended by Selby (1910) and Humbert (1916) as an efficient method of preventing the neck-rot disease. In order to test the efficiency of the gas against the neck-rot disease, quantities of onions, varying from a few specimens to one bushel lots were subjected to the treatment for twenty-four hours. The fumigation chamber used was a wooden box of 21.56 cubic feet capacity constructed of matched lumber and painted on the inside. The fittings of the door, which was on one side, were perfectly tight and but very little odor of escaping gas could be detected during the experiments. The gas was generated by the permanganate method, using 30 cc. of formaldehyde solution and 14.25 grams of potassium permanganate for the 21.56 cubic feet of space. These quantities are equivalent to 23 ounces of permanganate and 3 pints of formaldehyde per 1000 cubic feet of space as recommended by Morse (1907) for the disinfection of potatoes. The details of all of the seven tests with gas will not be given. The results of one or two typical tests will suffice to illustrate the results secured. On October 2, 1913, a Georgia peach basket, containing about forty onions of both red and yellow globe varieties secured directly from the field where they were cured and made ready for the storage, was placed in the fumigation chamber. The charge of chemicals was prepared, mixed and the door closed immediately. The charge of gas was permitted to remain in the chamber for twenty-four hours when the door was opened and the basket of onions removed. Upon examination it was found that the gas had injured the onions where the outer dry skins had peeled off exposing the flesh of the scales. The injury was in the form of sunken areas or pits (Plate VIII, fig. 3) and in some cases appeared as distinct blisters. During the experiment the fumigation chamber stood in a storage barn where the conditions were practically identical with those found

in an onion storage house. After an examination was made the basket of onions was immediately taken to a potato storage cellar where it remained thirty-nine days. At the end of this period it was found that one bulb showed the typical black sclerotia at the neck end. The fungus mycelium must have been present in the bulb during fumigation. Cultures confirmed the macroscopical observation. Four out of six cultures, made from different places among the onions, showed that, in this case at least, the gas was not effective against the fungus. This lot of onions was kept in storage until April 2, 1914, when they were discarded. Slightly over 10 per ct. of the bulbs showed the neck rot at that time. In this connection the experiments of Massee (1913) are of interest. This investigator experimented with the Botrytis causing the lily disease and found that pieces of lily stem containing the hibernating mycelium, even when soaked for twenty-four hours in hydrogen peroxid and later cultured, showed abundant growth and fruiting of the fungus.

In another experiment twelve apparently sound onions were placed in the fumigation chamber and treated for twenty-four hours with twice the amount prescribed in the Maine formula. After twenty-four hours the injured areas on the bulbs showed as raised blisters and the scales had a greenish tint. After being in storage forty days one of the twelve bulbs showed the neck-rot fungus breaking thru the outer scales. Four months later two of the bulbs were infected, showing that double strength gas treatment was not effective in controlling the fungus.

In a third series of experiments, both single and double strength gas caused conspicuous injury to the freshly exposed scales. When using the gas treatment upon either the colored or the white varieties of onions no injury occurred to the scales which were completely enclosed by a dry skin.

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On October 6, 1913, a bushel crate of yellow onions was placed in the chamber and treated with the gas for twenty-four hours, after which it was removed and placed in a potato cellar along with another crate of onions from the same lot which was not fumigated. The storage conditions were perhaps typical of the average onion storage house in New York State. These were left. undisturbed until April 6, 1914, or six months later, when they were removed and examined. Both the fumigated and unfumigated

stock showed a large amount (about 65 per ct.) of neck rot. Many of the bulbs showed the sclerotia at both ends, and many of the bulbs had sprouted and the fungus had reduced the sprouts to a mass of soft, brownish tissue.

Conclusions. From these and similar experiments the writer is forced to conclude that fumigation of onions with formaldehyde gas against the neck rot is ineffective, mainly because it does not reach the mycelium in the bulbs. Furthermore, the average onion storage house is not tight enough to retain the fumes. The crates of onions usually contain a considerable amount of dry skins which prevents the penetration of the gas.

METHODS OF CONTROL.

From the data and experimental evidence at hand it is evident that the control of this disease lies mainly along the line of careful cultural measures and storage house control. Since it is evident that the greater part of the neck and bulb infection takes place late in the season, especially when the crop is curing, every precaution should be exercised to have the crop mature and die early. Late maturity may be prevented by avoiding the very late application of fertilizers and manures, especially fertilizers of an incorrect formula, and also by careful selection of the seed stock, being careful to avoid the types of onions with a thick neck. Air drainage has been found to have an indirect effect on the amount of neck rot and also an important bearing upon the prevention of onion mildew. The growing of onions in fields surrounded by hills and dense woods should be avoided when possible. Removing the tall weeds along ditches, or still better, by replacing the ditches with covered tile. drains has been found to materially lessen the amount of neck rot, mainly by facilitating better drying of the crop. However, it is often necessary to provide wind-breaks of arbor vitae or picket fences along one side of the field to prevent wind injury to the crop. Care should be exercised in handling the crop since infection occurs thru bruises, shovel, fork and topper wounds. As far as possible prevent bruising the stock while running it over the topping machine. The onions should be topped fairly short 1 to 2 inches. The removal of excess soil, screenings, and tops by screening in the field will facilitate drying in crates. After a thoro drying

in the windrows the crates of onions should be kept in the cribs and drying sheds as long as possible. The bulbs should be stored in slatted crates of standard size. The use of bags or bins cannot be too strongly condemned. The full crates should be stacked with 1 x 3 inch binders between them, to facilitate ventilation. Onions stored in large, loose piles undergo a sweating process which aggravates the neck rot. The regulation of the onion storage house is most important. The neck rot cannot be controlled in storage unless good air circulation is provided by means of ventilators at top and bottom which can be opened and closed at will to control the temperature. The temperature of the storage house should be carried as low as possible without freezing the bulbs. A temperature just above 0° C., or 34°-36° F., is desirable. After the onions are thoroly chilled the storage should be kept closed to hold the temperature down. The storage house should not be opened for any considerable length of time especially during warm, damp, rainy or foggy days. If this is done the damp outside air will rush in and the entire stock will become covered with moisture and severe bulb rotting will follow. A relative humidity of 65-70° is very detrimental to keeping quality. Artificial heat, when needed, can best be supplied by stoves, or, at least, by dry heat. Steam heating is conducive to considerable rot since the steam pipes when not in use in cold weather become covered with frost and then, if steam is passed thru them, the humidity of the house is raised to a high degree.

Storage houses with a low, flat roof and poor top and bottom ventilation are to be avoided for onion storage. They should be constructed double thruout, using a good quality of lining for the walls. Concrete houses must have double walls with a dead-air space and must be sheeted up on the inside. The roof should have a steep pitch with large ventilators at the extreme top. The floors should be of heavy material with spaces of about one-half inch between each narrow piece of flooring. This is especially essential when onions are stored below the first floor.

The old, rotting onions should not be used as a fertilizer on the onion fields since it has been proved that they are a means of carrying the fungus to the fields and to the growing crop thru the mycelium and the sclerotia. Piles of decaying bulbs should not be permitted to remain in the vicinity of onion seed fields.

Especial attention should be given to the selection of sound, healthy seed or "mother bulbs" for the seed crop, since a few diseased bulbs may serve as a dangerous source of infection for the entire seed crop if the season is a wet one.

The treatment of the seed used for sowing the market crop by soaking it for 20 to 30 minutes in a solution made by adding 1 ounce of formalin to 2 to 3 gallons of water is being used by a number of onion growers. This is used as a preventive of onion smut and also as a precautionary measure against onion blight. Altho spores of the neck-rot fungus have been found on the seed, the possibilities of seed treatment for this disease have not been fully worked out experimentally. Seed treatment appears to be a safe precautionary measure. The light seed floating on the surface of the disinfecting solution may be skimmed off.

Spraying the crop with 5-5-50 bordeaux mixture or resin bordeaux, beginning early in July, and making 3 or 4 applications, has been found to be of some value in preventing neck rot, but extensive data on the value of spraying are not at hand. It has been practically demonstrated that the prevention of onion blight has a marked influence upon the amount of neck rot which may follow when poorly cured, soft, blighted stock is placed in storage.

Fumigation of yellow and red varieties of onions with gas either before or after the bulbs have been placed in storage cannot be recommended as a precautionary measure. In the first place onion storage houses are, as a rule, not tight enough to retain the fumes; furthermore, it has been found that the mycelium of the fungus is already within the necks of the bulbs before they go to the storage house. Any disinfectant which would kill the fungus in such cases would necessarily destroy the onions.

Aderhold, Rudolf.

BIBLIOGRAPHY.

1896 Die Fusicladien unserer Obstbaume. Landw. Jahrb., 25:875-914. Allen, C. E.

1901 On the origin and nature of the middle lamella. Bot. Gaz., 32:1–34. Ames, Adeline.

1915 The temperature relations of some fungi causing storage rots. Phyto pathology, 5:11-19.

de Bary, A.

1863 Recherches sur le développement de quelques champignons parasites. Ann. Sci. Nat. Bot., IV. 20:5-148.

1866 Neue Untersuchung ueber Uredineen II. Monatsber. d. Akad. d. Wiss. z. Berlin, p. 205.

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