Key Production Stages: Tuber Initiation to Full Bloom and Tuber Bulking
As the name implies, tubers form at this stage. Tuber initiation covers the period from the rounding of the ends of rhizomes into spheroids and the appearance of the first flowers (in most varieties) to full bloom and the start of tuber bulking, lag phase of tuber growth. For short-season varieties, this period is from 6 to 8 weeks after planting (3 to 5 weeks after emergence).
Most Critical Actions = irrigation, and pest monitoring and early control.
Key Biological Activities = initiation of tubers and row closure.
Irrigation becomes increasingly important during tuber initiation due to high rates of transpiration (water movement within plant) and may aid in common scab control. Optimum soil moisture is 80 to 90% field capacity. Fertilizer is not applied during the rest of the season except by commercial growers. These growers may use petiole-nitrate analysis to indicate whether nitrogen levels in the plant have fallen below that suggested for the variety being grown. Nitrogen, if required, needs to be added in small amounts through the irrigation system to maintain tuber quality. Note that excess nitrogen at this stage may inhibit tuber initiation and could leach into the ground water.
Herbicide residual activity should carry to the end of this stage when the rows close (that is, when plants in adjacent rows touch each other between the rows across the furrows). In comparison to many other potato production areas, foliar application of fungicides and insecticides is usually low in Nebraska. However, this may vary widely based on the intended market; for instance, growing seed potatoes requires higher pesticide input than growing tablestock. Also, pesticide use greatly varies from year to year depending on weather conditions during and prior to the growing season, such as winds from the Gulf of Mexico bringing in leafhoppers and aphids. In areas with high humidity and warm night temperatures, disease and insect problems are much more severe and occur earlier than in Nebraska. The cold winters (-30 to -40 degrees F), little snow cover and arid climate in Nebraska help to keep pest populations low.
This stage is identified by the formation of tubers at the end of the rhizomes. Tubers are initiated when the tiny leaves at the end of the rhizome disappear and the tip becomes oval ("egg-shaped") or spherical ("ball-shaped") (Figure 1C). The tubers although formed grow very little for a couple of weeks while the vines continue to grow.
Toward the end of this stage, vine growth slows and the plant is in full bloom. Varieties differ in the amount of flowering. Most varieties are determinate and thus vine growth ends with flowering. However, some long-season varieties are indeterminate and vines continue to grow after flowering. The most notable example of the latter type of potato is the Russet Burbank. Note that flowers may be pollinated and produce small, round, green fruit containing true seed. Row closure occurs during this stage assuming healthy vine growth. This stage is a transition from a time of vine growth to a period of tuber growth or bulking.
Key Production Stages