Fred Sinclair, CCA – ON, Product
Manager Pride Seeds
During the
last few weeks walking fields and plots, I have seen a lot of interesting
things happening. Most are positive,
but there are a few observations I thought would be worth passing on.
Corn Leaf Rust Update
Likely,
most of you have noticed that when you come out of a corn field your sleeves
are covered with brown rust. If you
have been in fields around London and areas north east from there you may have
observed your shirt to be quite dirty.
This is much less apparent in fields in Eastern Ontario and Quebec at
this point. Periods of warmer drier
weather will slow up the disease but will not totally eliminate it.
Leaf rust
does not over-winter in Ontario but instead originates from infected corn in
the southern United States and Mexico.
Rust spores are blown into Ontario from these infected corn plants. In most years, rust is of minor economic
importance, however sometimes spring weather fronts bring in spores that cause
early season infections. The disease
favours high humidity and cool evening temperatures (14 – 18° C) followed by
moderate daytime temperatures.
Early
symptoms of rust infection are yellow flecks or spots on either side of
leaf. These develop into small,
brick-red pustules that break through the surface (epidermis). The brick-red colour is the result of spores
being released from these oval or elongated lesions (2-10 mm long). Yellowing of the leaf occurs around these
lesions. Dead, brown (necrotic) areas
of the leaf develop, and in severe cases the entire leaf dies. The brick-red spores mature and turn black
as they mature, causing the lesions and the leaf surface to appear black.
Since
common rust does not survive or over winter in Ontario, cultural practices such
as reduced tillage and crop rotation do not influence disease development. Commercial corn hybrids have good tolerance,
whereas many seed corn inbred lines, sweet corn and specialty corn hybrids are
very susceptible to the disease. Foliar
fungicides in field corn are not usually needed or economical. Fungicide applications can be economically
justified in highly susceptible seed corn inbred lines or specialty corn
hybrids.
*Source in part: Agronomy Guide For Field Crops Publication
811
Crazy Top
Another
strange looking occurrence in a few fields (that received above average
rainfall during spring) is crazy top.
The tassel branches change to a leaf like condition, and in some severe
cases the whole top of the plant and ears are replaced with a mass of leaf like
structures.
This
disease is soil-born and is caused by a downy mildew fungus which gets into
corn plants only when infected soil or muddy water enters the leaf whorl.
Remember those heavy rains this spring and early summer before the 8 leaf stage
of corn? I have only noticed it this
year in areas of fields that seem to be waterlogged or flooded after planting. If the growing point is not submerged plants
will not become affected. At the time
when the tassel and ears are beginning to develop, the growth regulating
mechanism in the differentiating tissues is disrupted by the fungus and the
resulting organs become leaf-like instead of the normal male (tassel) and
female (ear) reproductive parts.
Providing
adequate soil drainage effectively controls this disease. But like we have seen this year, Mother
Nature can sometimes disrupt the system.■
*Source in part: Modern Corn Production