Water Requirement vs Water Supplied (a different perspective)
R. Scott Tubbs & Wesley M. Porter, UGA
When considering monthly rainfall averages, looks can be deceiving. For example, let’s look at the
rainfall received during the current 2022 growing season at Midville, GA according to the University of
Georgia Weather Network (georgiaweather.net). In Table 1, the section labeled A shows the cumulative
rainfall based on the standard monthly total. However, if we were to shift the calendar by 3 days
earlier, we have results as shown in the section labeled B. The distribution of rainfall appears
considerably different when represented this way, even though the season total is the same. Here, the
majority of the month of June is much drier (and not shown is the fact that over half of that amount
came in a single event – 1.07 inches on June 14). July appears drier, while August is much wetter. Yet if
we shift the calendar the opposite direction by merely 1 day later as in section C, the results look
substantially different once again. In this case, the majority of the months of June, July, and August
appear much more evenly distributed. Hence, in scenario B, August appears to have nearly 4.5 inches
(over 3x) more rain than June. Although scenario C shows August to have only around 1 additional inch
of rain than most of June. Here, June doesn’t look like it suffered much, especially given the stage of the
crop with much lower water demands early in the season.
Oh, the difference a few days can make! The point of this exercise is that it is important to assess how
the rainfall distribution is occurring in smaller increments rather than larger chunks when trying to meet
the crop’s overall needs and supplementing with irrigation. It is very important to note, crop water
requirements are about timing and distribution of water, not just total amount.
Table 1. Precipitation accumulation at Midville, GA in 2022. Monthly averages represented in three
different ways.
Breaking it down to a weekly distribution, we can get a better understanding of how the crop’s overall
water demand is being met or missed. For the example below, I am using actual rainfall data from the
Tifton, GA weather station and comparing it to the peanut crop’s weekly water demand in two different
planting scenarios. The water demand curves represented below (dashed blue line in the Figures) are
based on the UGA checkbook method, which was developed on historical average rainfall conditions and
a planting date of May 1.
Figure 1 represents a peanut field planted during the last week of April. The historical average rainfall
(dotted red line) does a fairly nice job of matching the crop’s weekly water demand (dashed blue line).
It is typically drier early in the season when we need to get equipment in the field to get seed in the
ground, and also later in the season when we need to start digging. It is typically wetter during the
period of peak fruiting and pod fill. The 2022 actual rainfall data (solid yellow line) is demonstrating
similar patterns to the overall crop need and historical averages, despite a few peaks and valleys. There
is an overall deficit of 2.66 inches of water if subtracting total rainfall received vs. total water needed at
this stage. However, that does not mean that this crop is only behind by 2.66 inches of irrigation water
in order to meet the crop demand. Since excess rainfall in one week is typically not available in weeks
where there are other deficits, we have to consider irrigation totals on a weekly basis in order to meet
the crop’s demand for that specific week. When taking that into consideration, a total of 7.69 inches of
irrigation would be needed to bring each week with a deficit up to the total crop’s need.
If we shift this same concept to a peanut crop that was planted late in the planting window (i.e. the first
week of June), then the crop’s water needs do not match the historical average rainfall as closely. The
crop’s peak water demand comes at a time when rainfall is typically becoming more scarce.
Fortunately, the current rainfall received up until this point in the 2022 season is meeting the crop’s
needs. There is actually a 7.07 inch surplus of water in total. However, this again does not necessarily
distribute to when the crop needs it. In total, the supplemental irrigation needed at this point in the
season has been 2.33 inches, although that has all come within the last two weeks as water demand
(dashed blue line) is increasing while rainfall received (solid yellow line) has been less than that line on
the curve. Hence, the late planted crop should be in good position to produce an excellent yielding
crop, based on rainfall up until now. However, with the most critical water demand coming over the
course of the next 4-5 weeks, rainfall will need to continue to be above the historical averages if
maximum potential production is going to be maintained. Continued consistent rainfall over the next
month could position the late planted crop to be better than the early planted crop. However, a dry
spell over the next month could spell disaster for the late planted crop while the early planted crop has
essentially already maximized production and just trying to maintain what is already on the vines.
It should also be noted that the checkbook curves shown above are a general guide to demonstrate how
water demand increases, peaks, then decreases over the season. However, many other factors are
involved in more accurately determining the localized needs of a given field, including soil type/texture,
organic matter content, porosity/drainage, and other soil health characteristics. Advanced scheduling
techniques have been developed in recent years to assist in meeting the crop’s irrigation requirements.
There are smartphone apps, web-based schedulers, soil moisture sensors, etc. that are more precise in
targeting actual irrigation requirements. These can be very useful in meeting the crop’s water demands
to reach (and maintain) maximum yield potential.
End of Season Irrigation for Peanuts
David Hall, Jason Mallard, and Wesley Porter, UGA
The only thing that is consistent from year to year is that each season is different and variable. While
last year had high amounts of rainfall, this year has been very hot and dry from May through the end of
June. Since the end of June, we have been getting sporadic rainfall across parts of the state. Thus, you
need to monitor what your current soil moisture condition is and make appropriate decisions moving
forward. Additionally, keep an eye on the long term forecast and the tropics. Up to this point, we have
been getting the sporadic rainfall, but we have been lucky that there have not been any significant
tropical events. That can change in a blink of an eye as we focus on the tropics closely this time of year.
An ill-timed and slow-moving storm from the gulf can be devasting.
Luckily, we have had some reprieve from the hot and dry weather that we saw early in the spring.
Unfortunately, some of the rainfall and high humidity is causing disease issues. Dr. Kemerait has been
sounding the horn weekly that the conditions are conducive for costly diseases. With peanut water
needs winding down towards the homestretch, the last thing a producer would want to do is schedule
irrigation without boots on the ground or moisture sensors relaying real time data, therefore risking
increased disease outbreaks or soil drying out. During peak water demand and dry weather, it is fairly
simple to schedule irrigation events. This time of the season water demand begins to fall off quickly and
most have been receiving ample rainfall. Do not let your guard down if we enter a dry period with dry
hot west winds. (We prefer those conditions after digging!) Sandy soils can dry out fast and we are
looking at what appears to be a great crop. Remember, heavy downpours that exceed the soil water
holding capacities basically become run off. We have received much of that this year.
The month of September is when the majority of our peanuts are dug and most of them are now well
past the peak water demand and need less than an inch of water per week. Now is a good time to start
thinking about irrigation termination for earlier planted peanuts planted in mid-April to early May.
Unlike corn and cotton, we do not have a physiological irrigation termination trigger for peanuts. Once
you reach 140 DAP or 2500 GDD’s (sometimes these can separate due to extreme temperatures),
digging should be considered based on maturity board checks. They can help indicate if you will be
digging early, on time or later than expected. This tool can help you tremendously in irrigation
scheduling. Hopefully, digging and harvest time will bring favorable weather. In the meantime, if in
doubt about moisture these last few weeks, walk your fields, review moisture data, watch the weather
closely and consult your UGA Extension County Agent if you would like a second opinion.
One of the biggest concerns with digging peanuts is that too much moisture can cause excessive soil on
the shell, especially in heavier soils and too little moisture can making digging difficult. Keep in mind the
timing of harvest, your soil type and how much available moisture is actually in the soil if irrigation is
needed to aid in the digging of peanuts. In clay type soils you are much more apt to apply too much
water and end up having to park the digger for a day, totally defeating the purpose of irrigating to
prepare the soil for proper digging when you are ready.
Please refer to Figure 1 below for irrigation requirements, and when to start thinking about terminating
irrigation.
Weather and Climate Outlook for September 2022 and Beyond
Pam Knox, UGA
Most of the Southeast experienced conditions in August that were wetter and warmer than usual,
although as usual there were variations across the region. Some areas are still feeling the impacts of too
much rain, while others have experienced dry conditions that have reduced yields in their crops. The
humid conditions and lack of sunshine in the areas that have experienced a lot of rain are feeling the
impacts in the form of abundant fungal diseases and a difficult time for farmers to get into their fields.
September so far looks like it will be a continuation of warm and wet conditions, although there will be
some more seasonal periods and some areas. There will be some periods of dry weather scattered amid
the rainy days, so you will need to watch the weather forecasts carefully to find those windows of
opportunity to work in the fields.
Later in fall, I expect to see drier conditions appear. This is not unusual in October, since this is the driest
month of the year for many parts of the region, but it could be drier than usual as La Niña remains
strong and continues to affect our weather over the fall and winter. Generally La Niña has the strongest
signal in southern Georgia and Alabama and into Florida, with more northern areas less predictable
because the strength of the La Niña is more important in how it affects those regions.
The big question mark in all of this is the tropics. After a very quiet July and August (the quietest since
1941!), we are seeing some life in the tropics as we enter the peak of the Atlantic tropical season. The
storms that are expected to form early in September are all predicted to turn north before they get
close to the East Coast so won’t provide much impact to us. However, there is still more than half the
season to go, and some years, like 1961, had quite a few storms in the second half compared to the first
half, so don’t write off the season just yet. The eventual path and strength of the storms will determine
what impacts we are likely to see, and of course we don’t know where any storms that develop will go at
this point. The best I can say is to keep watching the forecasts to make sure you know what is coming in
time to make preparations well ahead of any rain or landfall that might occur.
Peanut Digger-Shaker-Inverter Setup and Operational Considerations
Simer Virk and Scott Monfort
With peanut harvest approaching, growers will start digging peanuts soon across most of the
state. Along with considering when is the right time to dig peanuts, proper setup and operation
of peanut digger-shaker-inverter is also important to minimize harvest losses and to ensure
optimal equipment performance and efficiency during harvest. Below are few considerations
for growers to keep in mind when digging peanuts to prevent any mechanically induced yield
losses due to improper digger setup and/or operation:
• Using an RTK Guidance system/Auto-Steer on the tractor while digging peanut helps in
maintaining the digger path directly over the row center or over the planting path and
results in approximately 10% reduction in yield losses compared to when digging peanuts
with a tractor without an auto-steer system.
• Before beginning harvest and making any adjustments specific to the harvest conditions,
inspect the digger carefully for any broken, bent or missing parts as well as the sharpness of
the blades. Dull blades fail to cut the tap root resulting in dragging roots or dislodging pods
from the plant.
• Make sure that tire pressure in the tractor tires as well as the rear gauge wheels on the
digger is adequate and same in both tires. Also check if both tires are the same size.
• Adjust the digging angle (and therefore depth) by adjusting the length of the top link on the
digger. Digger blades should be set at a slight forward pitch and at the depth where they cut
the tap root just below the pod zone. Both an excessively shallower and deeper depth of
the digger blade can result in significant digging losses.
• Blade angle/depth is also dependent on soil type and texture. Any considerable change in
soil type within or among the fields will also require a change in blade angle/depth
adjustments as clay soils usually need a more aggressive angle whereas sandy soils require a
less aggressive blade angle.
• Digging speed should be optimized based on the prevalent in-field conditions at harvest.
Generally, the optimal ground speed for digging peanuts is between 2.5 and 3.5 mph.
Speeds above 3.5 mph can result in an increase in digging losses and therefore should be
avoided.
• Set the rattler conveyor speed to match or just slightly above the forward travel speed of
the tractor while digging peanuts. Conveyor speeds slower or too fast than the tractor
speed can both result in increased pod losses.
• The conveyor depth should also be adjusted where it picks up vines with its teeth just
clearing the soil. Additionally, if needed, adjust the knocker wheels up or down to regulate
the amount of shaking where is enough to remove the soil from the vines.
Remember, properly dug and inverted peanut plants will form a uniform, fluffy, well-aerated
windrow with very few pods touching the soil so make sure to keep a close watch on the digger
operation in the field and adjust settings accordingly as and when needed.
Points to Consider for Late-Season Disease Control in Peanuts
Bob Kemerait, UGA
Late-season disease recommendations for a peanut crop are often confusing. Reasons for this
include A) digging/harvest dates are not “set in stone”, B) the incidence of one disease versus
another affects choice of fungicides, C) disease can be cryptic, as in the case of underground
white mold, D) there are a number of fungicide options that can be deployed, and E)
approaching rains can make it necessary to quickly change management plans. While there
may not be a single “best” recommendation, some solutions are better than others. These
solutions have three things in common: a) timeliness, b) use of the right products (emphasis
that there is often more than one “right” product), and c) use of the right products at the right
rates. Late-season management decisions are more important now than they ever have been
as much of Georgia’s peanut crop remains in the ground for nearly 150 days. Our historic
“spray every 14 days for a total of 7 sprays” may not go the distance anymore.
Growers often request advice on adjusting digging dates based upon disease in the field.
Generally, it is best to wait until harvest maturity is reached in order to assure maximum grade,
rather than digging the peanuts early. For example, though tomato spotted wilt may be severe
in a field in 2022, I generally recommend waiting until harvest maturity to dig the peanuts,
unless other diseases, like white mold, are “piggy-backing” on top of the plants already affected
by the tomato spotted wilt. However, where defoliation from leaf spot is severe, as it is in
some field now, then it may be critical to digging earlier than planned in order to protect yield.
Georgia-06G can withstand defoliation of 50-60% IF digging is NOT delayed past maturity. Any
unexpected delays in digging will result in yield losses. Where white mold is severe, for
example greater than 50% incidence, the grower should consider digging early. Significant
defoliation from leaf spot diseases and severe outbreaks of white mold can increase digging
losses by weakening peg-strength.
NOTE: A critical consideration for choice of fungicides late in the season is that pre-harvest
intervals (PHI) vary among fungicides. For example, Alto has a 30-day PHI, and Elatus and
Convoy have 40-day PHI, compared to 14-day PHI for other fungicides such as Provost Silver
and Fontelis. Growers must always check the label to make sure on all of these.
Below are some typical situations that peanut growers may find themselves in and
suggestions for control:
Grower is 4 or more weeks away from harvest and currently has excellent disease control.
• Suggestion – I recommend the grower apply at least one more fungicide for leaf spot
control with an inexpensive white mold material mixed with it, for good measure. It is
generally helpful to use a mix of a protectant leaf spot fungicide (like chlorothalonil)
mixed a leaf spot fungicide with some curative activity (e.g., Alto, Domark, Topsin) for
best protection.
• Suggestion – Given the low cost of tebuconazole, the grower may consider applying a
tank-mix of tebuconazole + chlorothalonil for added insurance of white mold and leaf
spot.
o NOTE 1: If white mold is not an issue, then the grower may stick with a leaf spot
spray only.
o Note 2: If grower has planted Georgia-06G or Georgia-12Y and the plants are
leaf spot-free at 4 weeks prior to the anticipated digging date, an additional
fungicide application for leaf spot may not be needed if grower is willing to
watch/scout the field for other disease, for example peanut rust, and put a
fungicide out if harvest is unexpectedly delayed, as with the approach of a
hurricane.
Grower is 4 or more weeks away from harvest and has disease problems in the field.
• 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 they would mix
a product like thiophanate methyl (Topsin M) or cyproconazole (Alto), with the
chlorothalonil. Others may consider applying Priaxor, if they have not already applied
Priaxor twice earlier in the season. Provost Silver from Bayer Crop Science has become
a “go to” product for helping to protect peanuts from leaf spot diseases late in the
season. Provost Silver is NOT a “silver bullet” but it has performed very well. A tank-mix
of Provysol + tebuconazole may also be appropriate.
• If the problem is white mold – Grower should continue with fungicide applications for
management of white mold. If they have completed their regular white mold program,
then they should extend the program, perhaps with a Fontelis, Provost Silver, or
tebuconazole/chlorothalonil mix. If the grower is unhappy with the level of control from
their fungicide program, then we can offer alternative fungicides to apply. Where white
mold AND leaf spot are late-season problem, then adding a little extra to the Fontelis for
additional leaf spot control may be beneficial.
• 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.
Grower is no more than 3 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. SEE NOTE BELOW ABOUT HURRICANES.
Grower is 3 or fewer weeks away from harvest and has a problem with disease.
• If leaf spot 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 (more than 25% defoliation
already occurs), then a last application will not help. Tank mixing chlorothalonil with a
systemic fungicide, like thiophanate methyl, Domark, or other appropriate systemic
fungicide, could be beneficial.
• If white mold is a problem and harvest is 3 weeks away, then it is likely beneficial to
apply a final white mold fungicide. If harvest is 2 weeks or less away, then it is unlikely
that a fungicide will be of any benefit.
o 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.
Finishing “strong” in the 4th quarter of the 2022 peanut season is important. Finishing “strong”
means timely applications, ahead of rains or storms if necessary, using the right fungicide
combination at the right rate. Your yield depends on it.