Wednesday, July 4, 2012

Tomatoes: Yellow Shoulder Disorder

What’s wrong when tomatoes don’t ripen evenly? For example, most of the tomato will turn red, but the stem end, known as the shoulder, remains green or yellow, and even whitish. This is a physiological disorder known as yellow shoulder, also known as green shoulder.  The shoulder area may also be noticeably harder than the rest of the fruit.  

Scientists have been working on this problem for many years.  They have finally come up with three potential causes.  1) Environmental – the disorder can occur when high temperatures, above 90 F, remain for a prolonged period, and the fruit receives too much direct sun exposure.  2) Nutritional – it can be triggered by insufficient potassium and a soil pH above 6.7.   3) Varieties – although no specific research has been conducted to conclusively identify the better varieties, there seem to be certain varieties that are less prone to the yellow shoulder disorder. The problem is more prevalent in heirloom varieties because many hybrid tomatoes have been bred to alleviate this problem.  

What to do – first, try some other varieties, especially the newer hybrids. In addition, you may need to increase the amount of potassium you are applying and adjust the soil pH.  If there is a heat wave, create some partial shade cover for the plants.   Letting the fruit hang longer on the vine in order for the fruit to color does not help and can increase the potential for rot.