Features Agronomy Diseases
Keep diseases off balance – ‘rotate’

High input costs, low commodity prices… What is a corn grower to do? The
answer for many is to reduce their corn acres in 2006. Although wheat acres
are up, the majority of these corn acres would likely switch to soybeans. The
problem and concern is that most of these soybean acres will be planted in fields
that have already had soybeans for one or more years. The result will most likely
be more soybean diseases. Short-term gain for long-term pain!

Soybean diseases have increased in southern Ontario as a result of reduced
crop rotations. Many of the diseases on the rise such as soybean cyst nematode,
phytophthora root rot, sudden death syndrome, stem canker and brown stem rot
thrive under these conditions. Therefore, to keep them off balance, it is necessary
that producers increase their rotation options by keeping corn, wheat or other
crops in the rotation.

Crop rotation is one of the most economical and oldest methods used to manage
diseases. There are many benefits to having a good crop rotation and some of
these include:

• increased yields,
• optimal utilization of nutrients,
• erosion control,
• insect and weed control,
• spreading labour and machinery requirements over a larger portion of the
  growing season and
• reduced disease risk.

A good method to limit the build-up of disease organisms or pathogens is by
using a rotation or crop sequence in which each crop is resistant to the diseases
of the crop grown the previous year. Most pathogens survive in crop residue,
but only for a limited time and most pathogens do not infect multiple crops.
For example, most soybean diseases (legume crop) do not infect corn or wheat
which are cereal crops. Crop rotation will reduce the potential for serious
infestations of pests associated with one specific crop or its residue. For
this reason, it is important that a good crop rotation is maintained over the
long-term. Try not to sway off course, since the consequences will be greater
economic losses from yield decreases due to pests (disease, insects, weeds)
as well as other factors and increased production costs (fertilizer, pesticides,
and so on).

Now is the time to sit down and re-contemplate how to keep corn and get more
wheat in your rotation. Over-use of any one crop will increase disease pressure.
By rotating, you minimize your potential for serious disease outbreaks since
each crop is resistant to the diseases of the previous year's crop. So take
full advantage of this very effective and time tested management tool and Rotate!
Rotate! Rotate! -30-

*Albert Tenuta is a field crop plant pathologist for the Ontario Ministry
of Agriculture, Food and Rural Affairs at Ridgetown.