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About The gazette-times. (Heppner, Or.) 1912-1925 | View Entire Issue (July 30, 1914)
Diseases of Potatoes By H. L. Rees, Plant Pathologist of the State College of Wash ington. RHTZOCTONIA ot little potato dis ease, also known as roaette, is with the exception of the late blight the most serious disease of potatoes in "Western Washington. It is widely dis tributed in the United States, Europe and Asia and is of wide interest. It has been known in Europe sinee 1851 and was first described in America in 1891. It seems to be general on the Pacific Coast and is eortainly prevelant in Western Washington, causing losses last year as high as 50 per cent in some fields. Bymptoms There are several char acteristic symptoms of this disease, some of which however may be the result of some other cause. When the plant is attacked the stem is affected at the ground, showing as black discolorations and may girdle the stem for a half to an inch above the ground. A gray, moldy growth appears on this area. A discoloration exactly like this results from an attack of the black leg disease but is not accompanied by the gray, moldy growth. If the attack of the Bhizoctonia disease is serious the stem is rotted and the top wilts and dies early in the season exactly as is the ease with the black leg and Fusarium dis ease. However, with the latter the dis ease is not evident on the stem, the leaves roll and the plant may or may jrtot be killed at this time. When Attack Cornea Later. If the attack of Bhizoctonia is not Bevere enough to kill the plants, or the attack comes on later in the season as is usually the case in Western Washing ton, only the outer part of the stem will fee killed. In this case the discolora tion and the gray moldy growth appear but the plant remains alive. The tops usually develop peculiar twisted leaves with the leaves crowded together in a compact rosette-like appearance, not fonnd associated with any other potato disease. Aerial tubers small potatoes on the vines are formed and the pota toes in the hill are small and very numerous. This is caused by the gird fing of the outer part of the stem at the ground. The raw ford material from the roots ascends en the inside of the stem to the leaves where it is manufactured into starch. But because the starch can only deseend on the outside of the stem to reach the roots and tubers, and sinee this part is dead at the gronnd and prevents taedescent of the starch, the starch col leets on the vines and forms little po tatoes. Sine little food reaehes the tubers in the soil those developed there we small and numerous, Attacks of Xlack Leg. Attacks of black leg result in much the same way except that it kills the plant early and only a few tubers de velop either on the vines or in the ground, and those ia the ground are usu ally rotted at the stem end. If the plant is alive late in the season and Ue tubers ore numerous and not rotted at the stem end the Bhizoctonia disease has in all probability caused the trouble. This disease causes the formation of a network of fine, hair-like, brown threads on the surface of the tuber, which may or may not be large enough in diameter to be visible to the naked eye. These can only tie observed, how ever, as the tubers are maturing and not after digging. At digging time the dis ease shows as brown, superficial, elevat ed irregularly shaped masses, varying in size from a small dot to a spot as large as a quarter of an inch wide and half an inch long. These may be mistaken at first for soil particles but upon rub bing they will be found to adhere. If washed these masses are found to be dark brown and adhering with a tena city which necessitates hard scrubbing or picking to get them off. Either of these last two symptoms are peculiar to this disease alone and their presence is a positive means of identification. This disease as far as is known does not fur ther affect the potato except that there Bre indications that it may spread in Btorage, and most important its presence enables rot-inducing organisms to enter and rot the tubers. Parasitic Fungus. Cause This disease is caused by a parasitic fungus which lives, and may remain alive, in the soil for years. Pre viously it has been thought that the HOME ANT) FARM MAGAZINE SECTION of healthy plants, lose the bright glint ening appearance, become dull and roll up. the roots are found to be partly dead, are attacked early. Progress oi me un ease finally turns the leaves yellow or brown, and the top falls over. Frob ably this action on the part of the af fected plant has been the cauBO of not recognizing the presence of this disease as it is similiar to that of ripening. But only manner by which it became present was by being introduced on diseased seed, but investigations of Dr. Wollen- weber of the U. S. Department oi Agn- , .., .....i.,.,.., ...... ........... ........ ...... DET EOT Showing Appearance of Healthy and Diseased Tops. culture, in Western Washington indicate that it is possibly present even in the vir gin soil. When seed is planted in infec ted soil, this fungus infects them regard less of whether the seed have been treat ed, or not The" potato stems are at tacked and fungus spores are produced the ripening is premature and conse quently Tesults in a reduction of the vield. If the diseased plants are pulled up, the roots are found to be partly dead brittle and frequently bearing a white or pink mold. If the underground por tion of the stem is cut across, a pro DBT EOT Storage Bot Caused by This Fungus. nounced brown discoloration Is visible and can usually be found in the branch es leading to the tubers. External Evidence Bare. When the potatoes are dug there is rarely any external evidence of the dis- in the gray, moldy growth before noted. Later the fungus attacks the surface of the tuber and forms the irregularly shap ed masses described and known as scle rotia. These are very resistant to un favorable conditions and infect the soil if diseased tubers are planted. Control and Prevention There are three points connected with this disease which make the problem of control not an easy one for solution, i. e., 1) the possibility of the fungus being present in the virgin soil, (Z) tne possiDinty that the fungus may remain alive in the soil for several years even when other crops, if possible avoiding root crops and the present methods of seed disrarection used will not kill the fnngus as it exists in the sclerotia. But the following ree o.nmendations if carefully followed out, have been found to be valuable in elim inating and preventing this disease, Rotation of Crops If the soil is badly infected rotate for three years at least, with some other crops, if possible avoidng root crops and using cereals or grass. In any case at ways rotate crops, select the lignter typ es of soil for potatoes, avoiding heavy, noorlv drained soils, and maintain eood physical condition or tne son Dy deep preparation and culture. Keep down the weeds. Do not plant affected seed whether treated or not. Burn the diseased refuse potato ctop material, Clean culture methods are very import ant and highly valuable in the control of this disease. Potato Wilt or Dry Rot. Potato . wilt or dry rot, otherwise known as the Fusarium disease, is not equal in importance with the Bhizoc tonia disease in Western Wasnington, ai though the fact that it is present neces sitates a warning, This disease seems to be rather generally distributed over the United States and appeared in West ern Washington last year in widely sep arated regions. In the whole country the loss amounts to millions of dollars annually, but the loss in Western Wash ington is as yet unknown since many growers are not aware of the presence of the disease, Symptoms If the Infection is severe the disease first becomos noticeable when the plants are about a foot high, or if not, a little later. The leaves as sume a lighter green color thaa those ease. Occasionally the stem end may be rotted similiar to the rot caused by black leg, but when placed in storage and left the disease UBuaiiy dccoium apparent Beginning at the stem end the tuber shrivels, the inside becoming brown and rotted. The rot is not parti cularly soft nor does it possess a mater ially objectionable odor. But the pres ence of this fungus makes the entrance of rot inducing bacteria easy ana u these enter they will cause a wet rot accompanied by a very disagreeable odor. Affected tubers may be detected by slicing them, beginning at the stem end. If there is a brown discoloration underneath the skin and more or less parallel to the surface tins disease probably present. This discoloration may be in shape of a continuous ring or it may be discontinuous (See illustra tion!. The distance to wnicn me - coloration extends from the stom end depends entirely on the length ot time since infection occurred and the environ mental conditions. Cause This disease is caused by a ... I J- AVa parasitic fungus wnicn iivra .u soil, Low long is unknown. The fungus enters the plants tnrougn me roots and works upward in the vessels which conduct the sap. These vessels become filled and plugged with the fungus itself and the flow of sap is pre vented. This results in tho wilting and premature death of the plants. Rotate With Other Crops Control and Prevention After the soil becomes infected rotate with other . .... .. nnt crops for totiT or iivo yra". use manure, on which diseased tubers or vines have been thrown, for the potato land. This disease apparently aoes no oxist in the virgin soil and can only oe introduced by planting diseased seeo. Keep the disease out of the fields by planting only clean seed. This may be insured by using potatoes for seed which do not show a discoloration at tne stem end when eut. Treat as lor scbd s that all spores on the surface may do destroyed. Probably the best Method of control is to plant only white varieties of potatoes since in Western wasning ton the red varieties seem to be parti cularly susceptible while the white var ieties are either not susceptible or only slightly so. 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