dates for the main commercial crop from November in southern Florida and Texas to June in Maine depending on regional climate and latitude. It is desirable to plant at such date as will allow the period of blossoming and tuber-setting to come in relatively cool weather. In regions subjected to late blight infection, the early planted crop is most likely to escape while at the same time it may be correspondingly more subject to injury from flea-beetles and leaf hoppers. High labour cost has resulted in the extensive use of machine planters in America during recent years. Probably over two-thirds of the commercial acreage is now so planted. Two types of planters are employed : a picker type requiring only one man, and a platform or automatic feeding type requiring two men. These machines can be adjusted to space the hills at desired distances in the row. Straighter rows and im mediate covering of the seed pieces are additional advantages of machine planting over the hand method. Four inches is the depth of planting recommended, the best depth being shallower on heavy soils and deeper on light soils. Planting is done either in check rows to allow of cross cultivation for effective weed control or in drills with the hills close together in the row. The latter method is used by the majority of growers, requires somewhat more seed, and usually results in higher acre yields. The average amount of seed used is approximately 1 2 bu. to the acre, the range being from six to 25. Experiments indicate that for most conditions of soil fertility and moisture, larger amounts of seed up to i8 or 20 bu. can be profitably used. Cultivation for weed control is impor tant as the potato plant is very subject to weed competition. On the contrary, the plant may be seriously checked in growth and yields reduced when harsh, deep, late season cultivation results in cutting off the extensive, lateral, fibrous root system and disturbs the developing tubers between the rows. Thorough seed-bed prep aration and early season cultivation rather than late is therefore recommended. Moisture conservation is not one of the prime func tions of cultivation after the plants become well established be cause the extensive surface root system of the potato intercepts the rising soil moisture which has heretofore been thought to be conserved by the maintenance of a surface soil mulch. Shallow cultivation of heavy soils to break the crust which forms after heavy rains is desirable, however, to provide soil aeration and permit absorption of later rains. Ridging of the rows is commonly practised, especially on heavy soils. This affords an effective means of weed control, easier digging of the crop, run-off of excess surface water and a degree of protection of the tubers from late blight spores which might otherwise be washed through the soil from the plant. Sulky or riding cultivators for early season cul tivation and killers or horse-hoe ridgers for "laying-by" are used.
These are very numerous. The diseases are classed as fungous, bacterial and virus. The most serious fungous disease is late blight (Phytoph thora infestans), this being prevalent throughout the northern and north-eastern States where warm muggy days and cool nights dur ing the late growing season are conducive to its development. In wet years, the crop is seriously reduced by this disease through a reduction in the foliage growth and rotting of the tubers. It is controlled by application of Bordeaux mixture to the foliage either in wet spray or dry dust form. Several applications under high pressure throughout the growing season are necessary for good re sults. This treatment is also the principal means of controlling early blight, flea-beetles, leaf-hoppers and tip burn. Other fungous diseases of importance are early blight, wilt, rhizoctonia and corn mon scab. The two last-named reduce the market value of the
crop by their effect on the appearance and culinary quality of the tubers. Their control is by seed treatment, already referred to, and by crop rotation. Black-leg is the most important bacterial dis ease, its name being derived from the blackened soft-rot which it causes in the base of the stalk and the stem-end of the tuber. Several virus diseases cause marked losses throughout the United States by their effect in reducing foliage growth. The principal ones are mosaic, leaf-roll, and spindle tuber. Yields are reduced from one-fourth to two-thirds depending on the disease and its severity. These are most easily avoided by the use of seed which comes from plants free from virus the previous year. Certified seed ordinarily contains a minimum of these diseases. They are spread from plant to plant, principally by sucking insects such as aphis and leaf-hoppers. The four principal insect pests are Col orado potato beetle, flea-beetle, leaf-hopper, and aphis. The first two are biting or leaf-eating insects and are controlled by applying arsenical poisons such as Paris green, arsenate of lead, and arsen ite of soda to the upper leaf surface. The last two are sucking in sects which work on the under surface of the leaves and must be controlled by contact sprays. Bordeaux mixture containing nico tine sulphate (Black-leaf 4o) is applied to the under surface of the leaves for control.
The labour costs involved in har vesting potatoes comprise an important item in the cost of produc tion. Most of the commercial crop is now dug by chain-elevator diggers some of which are equipped with small gas-engine attach ments and many of which are hauled by tractors. To a very limited extent, combined digger and picker machines are used where the acreage is large and the soil is free from large stones. In the South the crop is gathered by negroes who are paid according to the number of barrels gathered. In the northern States, extra day labourers are employed on a daily wage basis. Slatted crates holding one bushel are commonly used for gathering the crop in most of the late crop States. In Maine it is customary to use small veneer baskets to fill barrels to be hauled to the storage or warehouse on underslung wagons locally known as "jiggers." Much of the crop in the North is still immature when killing frost ends the growing season. Such immature tubers should be allowed to dry or cure an hour or two on the ground before being handled. This reduces the peeling and surface injury of the tubers which would otherwise result. Approximately one-half of the late crop is put into storage at harvest time, the remainder being marketed at once. The lack of storage facilities and the need for cash return on the crop makes this necessary. The Southern crop is marketed at once or at least never stored in any but very temporary storage. House cellars and barn basements are used for storage in most States except Maine where specially constructed bank storage buildings are used. Potatoes should be stored under conditions of low, even temperature and medium humidity. The actual freezing temperature is about 28° F, but both seed and culinary quality of the tubers can be maintained best within a temperature range of
to
Fahrenheit. Higher temperatures increase the respiration rate, hasten the tubers into sprouting and thereby increase shrinkage. In commercial storage struc tures, ample wall and ceiling insulation is necessary for protection against freezing and to provide against condensation of moisture. Sufficient ventilation to remove excess moisture and foul air is also necessary. The tubers are most commonly stored in piles. Storage in bags is not recommended.