Key Production Stages: Emergence to Tuber Initiation
The key characteristics of this stage are rapid vine growth, continued root growth and tuber initiation (enlargement at the ends of rhizomes). This growth stage covers from emergence to pre-bloom, the period from 3 weeks after planting (emergence) to 6 weeks after planting (or 3 weeks after emergence) for a short-season variety such as Norgold Russet. This period is similar for mid-season varieties but longer for long-season ones.
Most Critical Actions = disease and insect monitoring for treatment, gradually increasing irrigation and second application of nitrogen.
Key Biological Activities = healthy and rapid vine growth, root growth and development of tubers on the rhizomes.
Soil moisture should be at least 65% field capacity; 70 to 80% is preferred. Therefore, irrigation can be kept infrequent in the beginning and intensified as the plants get larger. Additional application(s) of fertilizer, primarily nitrogen, are made during this period.
In the early part of this stage, cultivation and hilling can be done. Remember cultivation or hilling after placement of certain pre-emergent herbicides may interfere with their weed control activity and may injure the plants. Care must be taken to avoid root pruning. Remember the roots are in the soil at the side of the hills and between the rows.
The use of certain herbicides labelled for early post-emergence application at this stage is not generally recommended due to possible injury to the plants. This caution depends on the varietal sensitivity to these materials which is not known for all varieties. There is minimal use of fungicides and insecticides under the Nebraska climate. On the East Coast and in Southern states where high humidities and warm night temperatures are common, applications of these materials is important at this stage to avoid plant damage.
The major characteristic of this stage is rapid vine growth; the canopy may double in height every week for the first three weeks. Although the seed piece is still a key food source in the beginning of this stage, as the foliage develops and grows, food production (photosynthesis) increases until the leaves become the only food source.
Rhizomes are underground branches; when exposed to light, they will turn green, form leaves and secondary branches. From 3 to 6 weeks after planting, the rhizomes are in the "hook" stage (Figure 1A) which is characterized by tiny leaves at the end of the rhizome forming a hook-like appearance. From the hook stage, the rhizomes will go into the "swelling" stage which is characterized by an oblong swelling that forms behind the hook and a slight "bowing" of the tip into what looks like a "parrot" profile (Figure 1B). From the swelling stage, the rhizomes initiate tubers.
The duration from planting to tuberization depends on planting date, variety, temperature, quality of seed piece, and nitrogen fertilization.