Ben Hill County Ag

August Peanut Disease update

Disease Management is Critical in August for Peanut Farmers
Bob Kemerait

There is not a peanut farmer in the state of Georgia, at least a successful one, who doesn’t
recognize the threat from diseases and nematodes to his or her crop and who doesn’t recognize
the importance of a good management program. Still, growers often have many questions in
August, primarily because they are uncertain on best disease management strategies. Below
are some points to consider.

1. Why are diseases such a threat in August? There are several reasons. First, weather
how is typically very warm and, this year, quite wet. Hot and wet weather adds up to
near-perfect conditions for development of fungal diseases. Second, the peanut crop
has developed to a point where it is increasingly vulnerable to disease. The growth of
the foliar canopy traps humidity and extends leaf wetness creating perfect conditions for
pathogenic molds to grow. This thick blanket of leaves also inhibits movement of
fungicides from the top to the plant to the crown of the plants where they are needed to
protect against important diseases. Third, protecting pods and pegs from disease is
important, but getting a fungicide to them is very difficult. Last, diseases have likely
been developing slowly since soon after the peanut crop was planted. By August, there
are more spores present to cause significant disease and, also, small amounts of
disease that may have been invisible to the grower may suddenly “explode” and be
readily visible.

2. How should management programs in August differ from programs earlier in the
season? There are four main differences between fungicide programs in August versus
earlier in the season. First, white mold and Rhizoctonia limb rot control is very important
in later-season fungicide applications and much less important earlier in the season.
Second, selection of fungicides with some level of “curative” or “systemic” activity
becomes more critical later in the season when disease is likely present in the field.
Third, with the thick blanket of leaves that has likely developed, it becomes increasingly
important to use water from either rainfall or irrigation to help translocate the fungicide
from upper leaves to the lower limbs and crown of the plant. Last, given weather
conditions and amount of disease in the field, growers may need to tighten (shorten)
spray intervals to improve chances for adequate disease control.

3. Should I change I change up my fungicide program? Two of the most common
questions I receive this time of the year are, “What should I spray next?” and “I have
been on one spray program but should I change to a new fungicide program?” Growers
are understandably nervous this time of year to ensure that the fungicides they use are
appropriate for controlling important diseases. This is especially true when they find
some leaf spot or some white mold in their fields. Growers need to be reminded that
none of our programs are “Bullet Proof;” with conditions we have now even the very best
programs are likely to have some disease in the field. Growers who use an “ala carte”
program should carefully scout their fields and select fungicides for upcoming
applications based upon risk and what is present. Growers who are on a specific
fungicide program may consider modifying their program if a) an unexpected amount of
disease is developing in the field, of b) if conditions, e.g., weather, change and increase
risk beyond what was initially expected.

4. The most important management practices to minimize diseases in the peanut crop are
to a) be timely with your fungicide applications, b) tighten spray intervals when
conditions become more favorable for disease, c) use irrigation or rainfall to help
translocate fungicides from the upper leaves to the crown of the plant to better manage
diseases like white mold and d) consider use of a more effective (and likely more costly
fungicide) with greater efficacy and perhaps systemic activity IF disease control seems
to be less than expected. No fungicide program will absolutely keep disease out of the
field; appropriate fungicide programs (timing, selection, water) will help a peanut grower
to be profitable this season and into the future