UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA CIRCULAR 287 May, 1925 POTATO PRODUCTION IN CALIFORNIA By J. T. KOSA CONTENTS page Foreword : 2 Present status in California 2 Potato growing districts of California 5 Varieties 9 Selection of seed potatoes 14 Factors affecting seed quality , 14 Appearance :. 14 Region of production 14 Irrigated vs. dry land 15 Maturity of seed 15 Storage conditions 15 Infection by diseases 16 Preparation of seed for planting 17 Planting 18 Irrigation practice 20 Fertilization practice 21 Harvesting 25 Insects of the potato 26 Stalk borer 26 Tuber moth 26 Aphids 28 Nematode 28 Diseases of the potato 29 Common scab 30 Rhizoctonia 32 Wilts 33 Stem-end rot : 34 Leak 35 Mosaic 35 Leaf roll, net necrosis, spindle sprout 37 Internal browning and heat necrosis 38 General disease control measures 40 Seed treatment 40 Crop rotation 42 Control of insects 42 Use of healthy seed 42 Production of certified seed 42 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION FOREWORD The Irish potato is one of our staple food crops, in the production of which California ranks as one of the leading states. As a quick maturing annual crop having high acre-value, it has played an im- portant part in the development of districts now almost entirely given over to other lines of agriculture. However, as new land is becoming scarce, the industry at present is being centered within certain districts which have proved their especial adaptability to this crop. The increased prevalence of certain diseases, the necessity in many places of using commercial fertilizers in some form, the advan- tages to be gained through the selection of proper seed, the require- ments of the markets as to variety, type, and quality of potatoes grown, and the increasing competition from other producing regions all make it necessary for the successful potato grower to have a con- siderable fund of knowledge of the potato plant, as well as of the culture of the crop. It is the purpose of this circular to discuss in detail certain phases of potato production, especially in the light of new information gained by scientific study in recent years. PRESENT STATUS OF THE POTATO INDUSTRY IN CALIFORNIA Table 1 shows the acreage, production, and car lot shipments of potatoes from California in recent years. Generally speaking, these have been years of heavy production in the country as a whole, and potatoes from other states have been shipped into California in increasingly large quantities. The rapid growth of the population of California cities has led to increased consumption of the crop by local markets, which partly explains the decrease in car lot shipments. TABLE 1 Acreage, Yield, and Car Lot Shipments of Irish Potatoes from California 1 Acreage Yield, bushels Car lot shipments 2 1920 95,000 3 13,015,000 10,108 1921 74,000 10,360,000 8,252 1922 76,000 9,880,000 7,765 1923 52,000 7,800,000 5,690 • * Weather, Crops, and Markets, 4:677, 1923. 2 For the crop year, May 15 to May 15. From Market News Service, U. S. D. A. 8 Yearbook, U. S. D. A., 1920. Circ. 287] POTATO PRODUCTION IN CALIFORNIA June Ju/y Aug 5ept. Oct Nor. Dec. Jon. Feb. Mar Apr Mac/. Fig. 1. — Car lot shipments of potatoes, by weeks, from Pacific Coast districts, for the season 1922-1923. 600 soo- Shipping Season /9£J -