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Late Season Disease Management and Harvest Issues

Late Season Disease Management and Harvest Issues
By Bob Kemerait
Disease management late in the peanut season can either be very easy or it can be quite
confusing. In fields where these is little disease, growers can generally “coast” to harvest with
confidence that there is little (or nothing) to be done to finish the crop. Where disease is
present, growers must decide what measures should be taken to protect their crop as best they
can as they limp towards harvest.


The decision for “best” practices is based upon
1) projected time until harvest,
2) how much disease is in the field, and
3) overall yield potential of the crop.


If there is not much time left until harvest (less than three weeks until digging), or if there is too
much disease in the field, or if the yield potential is low because of other reasons, then there
may not be any reason to spend more money on fungicides. However, in other situations
growers can be justified in making a final fungicide application; the trick becomes what
fungicide, or combination of fungicides, to apply. Perhaps the biggest change in disease
management for peanuts over the course of my career has been that in the past peanuts were
often dug 125-135 days after planting while we now wait 150 days (or more) before digging.
This delay in harvest means that growers may need to consider an additional, final fungicide
application to protect yield.
Below are some typical situations that peanut growers may find themselves in and suggestions
for control.


1. Grower is four or more weeks away from harvest and currently has excellent disease
control.
a. Suggestion: I recommend that the grower apply at least one more fungicide at
least for leaf spot control. It wouldn’t hurt to use a mix of a protectant fungicide
(chlorothalonil) + a curative with attention to the PHI (e.g. Alto has a 30 day PHI,
Domark and Topsin have a 14 day PHI)
b. Suggestion: Given the low cost of tebuconazole, the grower may consider
applying a tank-mix of tebuconazole (7.2 fl oz) + chlorothalonil (1.0 pt/A) for
added insurance of white mold and leaf spot.
c. Notes on sulfur (specific formulations), Aproach Prima (picoxystrobin +
cyproconazole), and Absolute MAXX (trifloxystrobin + tebuconazole)
i. SPECIFIC formulations of sulfur can be used with products like
tebuconazole, azoxystrobin, Headline, and Aproach Prima to improve leaf
spot control. I prefer that growers use such early-to-mid-season and not
late in the season.
ii. If used late in the season, Absolute MAXX (14-day PHI) and Aproach
Prima (30-day PHI) must be mixed with chlorothalonil. They are
appropriate late-season where leaf spot is not well-established in the
field.


2. Grower is four or more weeks away from harvest and has disease problems in the field.
a. If the problem is with leaf spot: Grower should insure that any fungicide applied
has systemic/curative activity. If a grower wants to use chlorothalonil, then I
strongly suggest that they mix a product like Provysol (mefentrifluconazole),
thiophanate methyl (Topsin M), cyproconazole (Alto), tetraconazole (Domark)
with the chlorothalonil. Alto has a 30-day PHI; the other fungicides have a 14-
day PHI. Growers are NOT encouraged to use Priaxor or Miravis late in the
season, especially where leaf spot is a problem.
b. Provost Silver is also performs well as compared to other fungicides for lateseason leaf spot management.
c. If the problem is white mold: Grower should continue with fungicide applications
for management of white mold and leaf spot. If they have completed their
regular white mold program and are within 40 days of anticipated harvest, then
they should extend the program, perhaps with a tebuconazole/chlorothalonil
mix, Provost Silver, or Fontelis. Each of these fungicides has a 14-day preharvest interval.
d. If the problem is underground white mold: Underground white mold is difficult
to control. Applying a white mold fungicide ahead of irrigation or rain, or
applying at night, can help to increase management of this disease.
3. Grower is three or less weeks away from projected harvest and does not currently have
a disease issue. Good news! This grower should be good-to-go for the remainder of the
season and no more fungicides are required.
4. Grower is three or less weeks away from harvest and has a problem with disease.
a. If leaf spot (or rust) is a problem and 2-3 weeks away from harvest, a last leaf
spot fungicide application may be beneficial. If leaf spot is too severe
(defoliation more than 20%), then a last application will not help. See above for
suggested applications.
b. If white mold is a problem and harvest is 3 weeks away, then it is likely beneficial
to apply a final white mold fungicide, as above. If harvest is 2 weeks or less
away, then it is unlikely that a fungicide will be of any benefit.
c. NOTE: If harvest is likely to be delayed by threat from a hurricane or tropical
storm, then the grower may reconsider recommendations for end-of-season
fungicide applications.


Growers, in general, are encouraged to wait until appropriate harvest maturity to dig their
peanut crop. However severe disease in a field may mean that growers should dig ahead of a
projected digging date to minimize harvest losses.
There are no “hard and fast” recommendations for conditions when digging early is advised,
however here are some suggestions for when the grower is within two weeks of harvest.
1. Tomato spotted wilt, even when severe, is generally not a reason to dig early.
2. Significant defoliation from leaf spot diseases, 50% and beyond is reasons to consider
digging early to minimize harvest losses.
3. Active white mold in a field that affects greater than 40% of the crop could make digging
early necessary.
Again, there are not hard and fast, but guidelines for timing “best” harvest.