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INTRODUCTION.

HISTORY OF PRESENT INVESTIGATION.

The incident which, in part, initiated this investigation, was the receipt on February 24, 1913, of specimens of diseased onions from Mr. 0. L. Humphrey, manager of the Upton Storage Company's houses at Honeoye Falls, N. Y. A letter accompanying the specimens stated that the onions in the storage house were decaying rapidly and that the loss would be complete unless measures were at once taken to stop the spread of the disease. At the suggestion of Mr. F. C. Stewart, Botanist of this Station, an investigation was started. Upon visiting this storage house 700 bushels of yellow onions grown upon muck land were found stored in a rather damp basement. All of the onions were badly diseased, nearly every bulb showing the presence of large masses of black sclerotia encircling the necks, with an occasional specimen showing a gray, dense, close-growing weft of a fungus readily recognized as a species of Botrytis. The loss was practically complete. A visit to other onion storage houses in central and western New York revealed the fact that considerable storage loss was taking place because of this onion disease. It was evident that we were dealing with a disease of great economic importance and one whose etiology was obscure and control measures unknown. Further investigations and studies, herewith reported, were made during the years 1913, 1914, 1915, and 1916 from the Geneva Station, and during the fall of 1915 and winter and spring of 1916 at the Michigan Agricultural College. In Michigan, as in New York, the onion growers and storage house owners and operators had invariably the same experiences to relate. Their crops were apparently well cured and sound when stored; but a short time after storage began, about October or later, the stock became badly rotted, the rot increasing directly as the storage season advanced. The stock was sorted, but unless the apparently sound onions were marketed immediately the crop soon became an almost complete loss to the owners. Unusual care in curing and storing the crop did not appear to prevent the

disease.

ECONOMIC IMPORTANCE OF THE ONION.

The Thirteenth Census of the United States shows that 47,625 acres of onions, valued at $6,709,047 were produced in 1909, the onion holding third place among the truck crops of the United States. Every state is reported as producing some onions. Both as to acreage and value of onions produced, New York and Ohio were the leading states. In 1909 the largest onion acreage for any geographical division was reported from the East North Central States, including Ohio, Indiana, Illinois, Michigan and Wisconsin. The Middle Atlantic Division, including New York, New Jersey and Pennsylvania reported the second largest acreage. The writer feels confident that the onion acreage as reported by the census is low; at least this appears to be true for the states of Michigan and New York. According to Blair (1916) the area planted with onions in 1915 in the principal onion producing states was estimated by the Department of Agriculture to be 49,573 acres.

NEW YORK ONION DISTRICTS.

According to the Thirteenth Census of the United States, New York State in 1909 ranked second in onion production, having an acreage of 5,558 acres, valued at $954,610. Only seven counties in the State are reported as producing no onions. Orange County leads in onion production having approximately 2900 acres in the vicinity of Goshen, Florida, and Pine Island. Wayne County is second with 700 acres located near Rose, while Madison County is third with 570 acres in the Canastota region devoted to the production of this crop. The other important onion growing regions are in the counties of Queens, Monroe, Erie, and at South Lima in Livingston County.

MICHIGAN ONION DISTRICTS.

In Michigan the largest onion sections are in Allegan and Kent Counties. The Allegan acreage comprises the districts at Plainwell, Gun Marsh, Martin, Shelbyville and Wayland. The Kent County district is located between Byron Center and Ross. The other important districts are at Big Swamp in Lenawee County, Grant in Newago County, Zealand Township, Hudsonville and Vriesland in Ottawa County, Mentha, Van Buren County, and at Manchester in Washtenaw County. In the Thirteenth Census of the United States, Michigan is reported as having in 1909 an onion acreage of 1,130 acres, the crop being valued at $146,507.

THE DISEASE.

NAME. There are a number of common names applied to this disease. The list comprises Mold, Gray Mold, Storage Rot, Rot, Onion Rot, Onion Bulb Rot, Dry Rot, Black-neck Rot, Dry Neck-rot, Stem Rot, and Neck Rot. Of these names the last two seem to be more descriptive of the disease. The writer prefers the name Neck Rot since it more accurately describes the appearance of the disease in storage, a form which the grower readily recognizes. Furthermore, the term stem cannot be used, botanically, for the parts of the host plant above the bulb usually attacked by the fungus. Accordingly, the name Neck Rot will be used in this account.

PLANTS AFFECTED. The neck-rot disease caused by a parasitic Botrytis seems confined to Allium cepa, a broad species with many widely varying varieties. It has been found on perennial or tree onions, on seed onions, and growing or market crop onions. Schroter (1879) reported a Botrytis on Allium ursinum but gives no description whatever of the fungus. Frank (1896) stated that he also observed near Leipzig the Botrytis noted by Schroter.

DISTRIBUTION. That the neck-rot disease of onions, or what appears to be this disease, is widely distributed is indicated by reports from nearly every onion growing region. Sorauer, as early as 1876, reported a Botrytis disease of onions from Germany, while a few years later Frank (1880) reported it from the same place. Bruck (1907) also mentioned this disease as being common in Europe. Voglino (1903) stated that he found what appears to be this disease in Italy and France in 1892. An onion disease caused by a Botrytis was noted in England in 1894 according to Massee. Halsted (1890) appears to have been the first in America to report a neck rot of onions due to a Botrytis. Clinton (1903) reported this disease from Connecticut; Jarvis (1909) also reported it from that state. The disease was recorded by Selby (1910) as being abundant in Ohio, while Jackson (1914) stated that it is a serious storage trouble of onions in Oregon. Humbert (1916) reported heavy storage losses from this disease upon white onions in Ohio districts.

In the fall of 1915 the writer noticed the neck-rot fungus upon some large white onions in crates in the Grand Trunk Railway freight house at Lansing, Michigan. These onions were consigned to a Lansing dealer and were shipped from Bermuda. Isolations in pure culture confirmed this observation. Again, in 1916 and 1917, the Botrytis neck-rot fungus was found upon, and isolated from, large white onions shipped from Bermuda and also from Texas.

In a letter from Dr. Johanna Westerdijk of Amsterdam, Holland, addressed to Professor H. H. Whetzel of Cornell University and dated January 4, 1917, an interesting reference is made to a disease of the onion. Dr. Westerdijk supplied Professor Whetzel with a culture of a Botrytis which she stated caused a severe disease of the leaves of onion. A critical study of transfers from the culture furnished to Professor Whetzel showed the fungus to be identical in every particular with the cultures of the onion Botrytis secured from various places in America. Dr. Westerdijk also stated that she had described the disease in a brief paper. Unfortunately, no further information regarding the disease could be obtained from this source at this time.

A report based upon the records l of the Plant Disease Survey (Bureau of Plant Industry) show that the Botrytis neck rot of onions has been reported by collaborators as being serious in the states of Connecticut, Illinois, Maryland, Massachusetts, Michigan, New York, Ohio, Oregon, Pennsylvania, Washington and Wisconsin.

ECONOMIC IMPORTANCE.

The margin of profit on storage onions is usually small, and unless a marked increase in price takes place a small amount of neck rot will offset the gain from storage. The neck-rot disease has practically prevented the growing of white onions in many onion sections in New York and Michigan. Figure 1, plate V, shows one of a number of white onions taken from an upland field early in the season of 1915. Their condition indicates the virulence of the fungus upon these tender, thin-skinned varieties.

1 These data are from unpublished records of the XJ. S. Dept. Agr. Bur. Plant Indus., Plant-Disease Survey. They include reports from states where Sclwotium cepivorum is believed to be the cause of the disease, also Botrytis cinerea, Botrytis vulgaris, Sclerotinia fuckeliana, Sclerotinia sp., and Sclerotinia (bulb rot) are reported as causing what is believed to be this disease of onions.

A study was made of the losses due to the neck-rot disease occurring in the retail trade of grocery stores dealing in southern onions. With the flat white onions from Texas a loss of about two per ct. occurred, this increasing slightly as the spring season closed. Frequently, one finds a badly diseased specimen among the large, white bulbs sold as Spanish and Bermuda onions. These are usually sold by the pound and the losses are correspondingly greater. The records of the Plant Disease Survey as furnished by collaborators in the states mentioned in the preceding section show that the losses vary from 7 or 8 per ct. to as high as 50 per ct. of the crop. In two instances it is reported that the acreage devoted to onion growing has been materially decreased because of the ravages of this disease. The highest losses are plainly associated with seasonal conditions which are termed "poor seasons for onions." Neck rot is plainly one of the limiting factors in onion growing.

ESTIMATE OF LOSSES IN MICHIGAN AND NEW YORK

For these states as a whole it is difficult to obtain any accurate data covering the losses in the yellow and red varieties of onions. The estimates must be limited to individual storage houses. During the storage season of 1912-13 the losses in some poorly ventilated houses were almost total, while in some houses of the better class the average loss was approximately one crate out of every ten at the time of sorting before shipment. During the storage season of 1915-16, following an exceedingly unfavorable growing season for onions, the storage losses were enormous, being practically total in many storage houses. In Michigan, early in the winter of 1915, the loss from neck rot in several storage houses was averaging one crate out of every six sorted, while by January 4 the losses were slightly over 50 per ct. of the total stored crop. Some definite, accurate data furnished by one prominent onion grower are as follows: Owing to a poor onion year this particular grower harvested about 25 per ct. of a crop. This gave 2200 bushels which were put in storage. The neck rot appeared in a severe form in less than six weeks after the stock was placed in storage. Of the 2200 bushels stored, 1200 were dumped out on the fields. The owners were able to realize upon but 1000 bushels. Of the entire crop only two bushels of bulbs were fit to save for producing a seed crop.

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