past two weeks, purple corn has been observed in several
fields throughout southern and western Minnesota. Although
corn that is deficient in phosphorus has a purple color,
it is doubtful that phosphorus deficiency is responsible
for the observations this spring and early summer.
coloring this year, as was the case in 1997, is probably
caused by a situation called the “fallow syndrome.” This
situation usually occurs in areas where a crop was not grown
last year or following sugar beets.
of the “fallow syndrome” involves an understanding
of a symbiotic relationship between the corn plant and a
group of fungi called mycorrhizae. It’s a “ You
scratch my back, and I’ll scratch yours” relationship.
The mycorrhizal fungi grow and develop around corn roots
and assist the root in taking up nutrients. The mycorrhizal
fungi are usually associated with uptake of phosphorus and
zinc. The fungal growth is stimulated by excretion of sugars
and other organic compounds from the root system. So, the
mycorrhizal fungi and the corn plant help each other – a
of the mycorrhizal fungi reaches a minimum following a non-host
crop or where no crop has been grown. The sugar beet crop
is not a host for these fungi. Therefore, the “fallow
syndrome” is frequently observed when corn follows
a sugar beet crop. Likewise, repeated tillage of soil where
a crop was not grown last year can produce a “fallow
syndrome.” For example, the “fallow syndrome” may
appear where heavy rains flooded soybean fields and the flooded
area was tilled repeatedly to control weeds.
no management practices that are appropriate for correcting “fallow
syndrome” this year. As temperatures warm and soils
dry, the purple coloring usually disappears.
application of phosphate fertilizer near the seed at planting
can prevent the problem. Broadcast applications of phosphate
are not effective. A banded application of 20 lb. P2O5 per
acre at planting is suggested.
syndrome” does not appear every year. A banded application
of phosphorus is good insurance to prevent the problem. This
is especially true when corn follows a sugar beet crop.