|
Seedling Diseases
Compliments
of Agronomy Services Department
Seedling diseases vary among crops,
from state to state, from year to year, from field to field and even from one area of a
field to another area. Factors contributing to disease include the stage of growth when
the plant is infected, cultivator damage, herbicide injury and environmental stress. The
most common groups of diseases are fungi, bacteria and viruses. Several disease pathogens
are present in the soil waiting for a susceptible host to appear. A susceptible host,
pathogen, and favorable environment must occur at the same time for disease infection to
break out. If one of the three factors is missing, then a disease will not occur.
Although we are aware of yield
losses occurring from seedling diseases, it is often difficult to determine how much is
actually lost. Controlling seedling diseases once the infection has occurred is not a
viable option at this time; therefore preventing the diseases through good management
practices is most beneficial. Generally, seedling diseases are controlled or reduced by
management decisions and practices made prior to planting. Some examples include
artificial drainage, proper soil pH and fertility. Some of the most critical environmental
factors influencing seedling diseases beyond the control of the producer are air and soil
temperature, rainfall and soil type.
Another means of controlling
diseases is through plant resistance. However, hybrids and varieties vary in their degree
of resistance to any specific disease, and those with adequate resistance to one disease
may or may not have resistance to another. Some hybrids and varieties are specifically
resistant to a disease, meaning they are highly resistant to that disease. Other hybrids
and varieties are not highly resistant to a disease but still have some resistance,
although they appear susceptible. This is known as field resistance. Additionally, some
other hybrids and varieties are disease tolerant, meaning they will continue to function
even though they become diseased.
A third method for controlling
seedling diseases is crop rotation. At least every other year rotation is necessary if
this practice is used. Even then, rotation is not always effective because the level of
inoculum may be very high in the soil.
The incidence of certain specific
diseases may be lessened or increased by the effects of tillage. Some diseases favor high
soil temperatures and low soil moisture (i.e. conventional tillage), while others are more
likely to occur in cooler and wetter soils (i.e. no-till).
Fungicide treatment of seed corn is
a common practice to reduce seedling blight diseases. Today, all seed corn is treated
prior to purchase. However, not all crop seeds are treated by the company. Soybeans, for
example, are not treated with a fungicide, because many years of research have not shown a
consistent yield advantage to treatment. Therefore, it is left up to the grower to treat
their own soybeans if they choose to do so.
Many seedling diseases are
difficult to identify, and laboratory examination is often required to make a positive
identification of the disease. Until you are familiar with the field symptoms of a
disease, it is best to submit the sample to a lab. Most Land Grant Universities have a
plant diagnostic lab. Be sure to contact the lab prior to sending the sample to obtain
specific instructions on packaging and shipping the sample. |
