Key production practices: Planting to Emergence
The planting to emergence period usually ends at 3 weeks after planting and is lengthened by cooler soil conditions; it ends when sprouts emerge from the soil surface.
Most Critical Actions = weed control and fertilization.
Key Biological Activities = root, sprout and rhizome growth.
Seed pieces should be planted six to eight inches deep. Do not plant seed pieces in soil with a temperature less than 50oF. Soil moisture in the top foot should be between 65 and 80% field capacity. Irrigation during this period, i.e., "irrigating the plants up," is not recommended. There is enough moisture and nutrition in a healthy and acceptably-sized (1½-2 oz) seed piece to sustain the plant to emergence. Also, irrigation during this planting to tuber initiation may promote seed decay before emergence and early dying (Verticillium wilt) later when the tubers are rapidly enlarging.
Fertilization can be applied successfully during this period. Nitrogen, phosphorus and potassium (N-P-K) can be added as a side-dress two inches beside and at the same depth as the seed pieces. Row spacing is usually between 32 and 36 inches, the latter being most common. Recommended plant spacing within the rows varies with the intended market and variety; narrower spacing as low as 6 inches for seed tuber production and further apart as much as 16 inches for "bakers" and long french fries.
A systemic insecticide may be added into the furrow during the planting operation by commercial growers, but home gardeners should use foliar insecticide as needed during the season. In-furrow application involves placing the material after the furrow-opener and before seed piece placement. When properly done, some soil will cover the material before the piece falls due to the motion and vibration of the planter.
Pre-emergence herbicide application is the most critical pest control operation during this period. Most potato herbicides are labelled for pre-emergence application and are not recommended for post-emergence use on many potato varieties, especially white-skinned varieties, because these may be injured by the herbicide. Most pre-emergent herbicides used in potatoes have a six to eight week active residual period in the soil. When applied at recommended rates between one to two weeks after planting, they will suppress weed growth until five to seven weeks after emergence. By then, healthy plants should have closed the rows and the potato plants themselves will keep down any newly emerged weeds by shading them. Cultivation is also used during this period as a mechanical weed control practice. By itself, however, cultivation will have little residual effect and weeds will appear until row closure. Also note that after some pre-emergent herbicide applications, cultivation would have a negative impact by breaking the herbicide layer and throwing treated soil against the newly emerged plants. The use of herbicides by home gardeners is not recommended due to sensitive garden plants grown nearby, the small areas treated and possible exposure of pets and children. In this case, the operative phrase is "a-hoeing we will go."
The seed piece itself is its own principle source of food and water during this period, and must be healthy from the start. After planting, the seed piece will sprout and grow toward the surface. Usually, more than one sprout will grow from a seed piece and often more than one stem will appear from a sprout. The additional stems from a sprout are actually branches.
During this period, plant resources are devoted to root and shoot growth and will reach 18 inches in length on the average, some varieties longer. Potato roots tend to be relatively shallow. Rhizomes, or stolons as they are commonly but erroneously called, do not appear until around emergence. Rhizomes are the structures on which the next generation, the daughter tubers, will form.