Fungicide use decisions for soybean must be made in the very near future, if not now.
I was reading an article on the Plant Management Network (http://www.plantmanagementnetwork.org/pub/php/news/2012/TimelyFungicideApplication/)
regarding the timely use of foliar fungicides to achieve maximum effect on soybean.
The article stated that the recent mild winter has resulted in an increased
disease risk that growers should take into consideration when making fungicide
use decisions. I am sure that some parts of the country probably do have an
increased disease risk as a result of the mild winter, but I do not believe
Kentucky is among them.
In most years, foliar, pod and stem (FPS) fungal diseases of soybean are
held in check by planting adapted varieties (mostly MG 4 varieties), avoiding
extremely early planting dates (full season crops) or planting late (doublecrop
soybean), crop rotation, limited-sporadic rainfall and high temperatures during
the summer months, and timely harvest. Typically, measurable yield losses
caused FPS diseases–the targets of foliar fungicides–are limited to certain environments
like river-bottoms, fields prone to extended periods of dew or fog, and continuous
soybean fields. Early maturing varieties (mainly group 3) are often impacted by
damaging levels of FPS diseases, especially when planted early. The same is
true for crops that are not harvested on time. However, FPS diseases are
usually not that destructive in Kentucky.
True enough, the winter of 2011-12 was very mild, even by Kentucky’s standards.
However, if anything, the mild conditions probably enhanced residue breakdown, thereby
reducing fungal survival in weed and crop residue, due to increased microbial
activity. Moreover, early planting may have been somewhat more common this
year, but the higher than normal temperatures and limited rainfall in April to
early-May likely negated the increased risk to FPS diseases normally associated
with early planting. I simply cannot reconcile how the mild winter might have increased
the potential for soybean FPS fungal diseases to occur in Kentucky. I will
concede that the mild winter may have increased the risk of insect-vectored
virus diseases, such as bean pod mottle virus (transmitted by bean leaf
beetles) and soybean mosaic virus (aphid-transmitted); however, these viruses
are not controlled by foliar fungicides.
Of course, the mild winter did favor survival of the soybean rust
pathogen in the deep South, but our winter, although mild, was still too cold
to allow soybean rust to survive the winter in Kentucky.
In summary, I do not believe that the mild winter of 2011-12 has resulted in
greater than normal potential for FPS fungal diseases to occur in Kentucky
soybeans. Dry, and now extremely hot and dry, weather across most of the state
has kept fungal diseases in check up to now. The soybean crop is very stressed
and if some relief does not come soon, yields will be seriously hurt by drought
and perhaps charcoal rot and soybean cyst nematode, but not by not by FPS diseases.
Strobilurin-based fungicides, such as Headline® or Quadris®, or
strobilurin-triazole products, such as Stratego YLD® are reported to impart some stress tolerance to
treated crops. Nonetheless, it is my
experience that stress tolerance benefits are simply overwhelmed when soil
moisture is limiting for an extended period of time (e.g., drought). It is anyone’s guess how the rest of
the season will play out, but it is my opinion that it may be difficult to
recover the costs associated with applying a fungicide this season unless July
and August turn wet. Many doublecrop fields are still not planted due to exceptionally
dry soil conditions. However, doublecrop
soybeans do not generally respond well to foliar fungicides even in a season
with decent moisture.
This may be a good year to consider leaving the fungicide sprayer in the barn.