Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
I have seen a considerable amount of tomato blotchy ripening, yellow shoulder, graywall and white tissue in market tomatoes recently. The discolored tissue is often hard even when the rest of the tomato is ripe. These are physiological ripening disorders and not diseases. Symptoms often appear during stress periods or when the environment changes rapidly. The recent hot weather after the previous period of cloudy, rainy weather may have been a contributing factor to the onset of these tomato fruit ripening disorders.
There are several keys to controlling blotchy ripening, yellow shoulder, and other tissue ripening disorders in tomato. First is variety selection. Some tomatoes are more prone to develop yellow shoulders than others, especially those with dark green shoulders without the uniform ripening gene. Other varieties are prone to excess white tissue development. Review local tomato trial results for ripening disorder ratings. Second is to manage crop canopies — yellow shoulder is more prevalent in open canopies; blotchy ripening is more prevalent in dense canopies. Try to have a canopy that allows for air circulation with adequate fruit cover but without excessive vegetation. Third, and probably the most important, is to manage potassium nutrition. Tomatoes are heavy users of potassium and a shortage of potassium during fruit development and ripening can lead to increased problems with ripening disorders. Tomatoes require close to 200 lbs of K2O to grow a heavy crop. In our commercial vegetable recommendation guide even at optimum soil levels we recommend 100 lbs of K2O (300 lbs K2O in soils with low K2O levels) for a crop of tomatoes.
To reduce ripening disorders during the growing season, apply additional potassium through the drip system under plastic or as a sidedressing in bare ground production. Foliar applications of potassium can also be of benefit to reduce symptoms but should not take the place of soil applications.