Tuber Bulking

Key Production Stages: Tuber Bulking to Plant Senescence

This usually is the longest stage in potato growth, covering from full bloom to senescence or vine death in determinate varieties. It extends from 8 to 14 weeks after planting (5 to 11 weeks after emergence) for early-season varieties and is longer for later season varieties.

Most Critical Actions = irrigation, pest control and stress avoidance.

Key Biological Activities = tuber growth.

Production Practices:

The most important practice in this stage is irrigation because the plant has its highest demand for water at this time. Depending on rainfall, application of 1½ inches per week is normal or a total of 12 to 15 inches of water is applied during this stage. Soil moisture needs to be kept between 80 and 90% field capacity. Avoiding plant stress is critical. In hot, dry climates, sprinkler irrigation also may help to cool the plants and soil.

Pest Control:

The key is to keep plants from being stressed. In many potato production areas, fungicides are applied to prevent early and late blight. In Nebraska, late blight occurs seldom, once every 10 to 15 years, and early blight usually occurs toward the end of the season. A pre-harvest treatment of certain fungicides will reduce tuber break down in storage due to leak and other diseases. Irrigation may help minimize tuber blemishes due to common scab and black scurf. Sulfur can be applied through sprinkler irrigation to assist healing of vines after hail or when early blight is present. Diseases such as early dying, wilts, and black leg cannot be chemically controlled but using certified seed and keeping the plants healthy usually will prevent them from being a problem.

The use of foliar-applied insecticides depends on insect populations. Often in Nebraska, an insecticide is applied only once during the middle or latter part of the season. Natural predators in Nebraska often keep the population of the Colorado potato beetle below injurious levels. And, the occasional migration of the potato leafhopper and green peach aphid (once in 4 to 5 years depending on the wind from the Gulf of Mexico) occurs relatively late in the season. Insect control is primarily important to the potato seed producer in Nebraska because of their potential for carrying plant viruses.

Weeds are not usually a problem after row closure. There are few herbicides available for post-emergence use on potatoes.

Plant Development:

Growth during this stage is totally centered on the tubers and final yield and quality depends on what happens here. The tubers will undergo a logarithmic growth pattern (Figure 2) which is characterized by a gradual growth increase, then a near doubling in size and weight and ending with a gradual slowing down of growth to a plateau level. During this period, the tubers are the food sink; sugars are transported from the leaves to the tubers and converted to starch. The transport of sugars in the reverse direction can occur if plants are under stress which may result in lower yields and poorer market quality. All plant stress should be avoided and so all steps should be taken to "keep them happy." Except for indeterminate varieties, there should be no or little vine growth. Vine growth will consume nutrients at the expense of tuber growth.


Comparison of stem length, tuber weight during season



Key Production Stages