Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Wet seasons are always a challenge for potato growers. Several disorders are seen on potatoes when soils stay saturated.
Blackheart is often a problem in potatoes in wet years. This is a disorder related to low oxygen conditions. Heavy rainfall, especially on our heavier silt loam soils, sets up conditions for blackheart to develop. In soils that are flooded or that stay saturated for long periods of time, oxygen diffusion into potato tubers is restricted (oxygen diffusion is much slower through water than soil air spaces). Lack of oxygen to the tuber interior causes interior tissue to die and ultimately turn brown, purple, or black. When dug, tubers may appear normal on the outside, but when cut reveal the dead areas. This makes grading very difficult. With each truckload coming into the packing shed, a sample of tubers must be cut open and if a significant percentage show blackheart, the load is rejected.
Blackheart can also occur when soils are compacted, restricting air movement; when soils are hot and tubers are respiring heavily, using up more oxygen than can diffuse through the soil; and in storage or shipping when piled too high or stacked too closely for long time periods, again restricting oxygen. Managing low oxygen blackheart in the field requires attention to drainage, forming high loose ridges around tubers (avoid cultivating and ridging when soils are wet), managing field traffic to limit compaction, and harvesting in a timely manner, targeting fields with higher potential for blackheart to be dug first. Low areas in fields may have to be examined (samples cut open to see the percent of blackheart) and passed over during harvest.
Another wet weather disorder in potatoes is raised or enlarged lenticels. Lenticels are small openings in the tuber surface that allow for gas exchange necessary for tuber respiration. Enlarged lenticels occur where there is excessive soil moisture in wet seasons. This is a common problem in heavier soils, field bottoms, and compacted areas. In wet conditions, there is a proliferation of cells that form the lenticel pore making the pore larger. This cell proliferation will cause the potato to have raised white spots throughout the tuber surface. The area immediately surrounding the lenticels may also rise up, forming a “halo” around the lenticels. This is called halo disorder. Potatoes with raised lenticels may be subject to abrasion damage in packing. Raised lenticels can heal by forming suberin. However, the suberized closing layer can be ruptured when the cells beneath it proliferate under unfavorable conditions. Ruptured lenticel cells can be a point of entry and infection by bacterial soft rot organisms.
Raised lenticels on a potato tuber due to wet soil conditions.