Looking ahead over the next week to 10 days, the forecast is for warmer temperatures and high humidity. This will create very favorable conditions for white mold and leaf spot on peanut- your growers must get after it in the fields. We will likely see more areolate mildew and target spot on cotton. Got areolate mildew? I think the cotton crop needs to be protected until within 4 weeks of planned defoliation. Now is also perfect for spread of soybean rust.
For more information about managing foliar diseases in cotton from Dr. Bob please go HERE
How to Fertilize Drowned Out Cotton (Glen Harris): Obviously, it has been a wet growing season in
South Georgia. It reminds me of 2013 when it rained every day in June. Up until then I really didn’t think
you could drown a South Georgia sand. But when all the pore space in even our sandy soils gets filled with
water we reach saturation or ‘waterlogging”. This may cause the cotton plant to shut down or not function
properly to the point where it doesn’t take nutrients up from the soil very well if at all. Since nitrogen is the
fertilizer nutrient needed in largest amounts by plant, the nitrogen deficiency symptoms or “yellowing” of
the leaves shows through the most.
Some areas of the cotton belt in Georgia have received more rain than others. Also, It appears that early
planted (May) cotton is looking better than late planted (June) cotton. I’ve heard a lot of people say “ I
leached out or lost all my fertilizer”. I’ve also heard growers say it’s been so wet I have not been able to
sidedress my cotton”. “Should I replace some N and K on the ground? Should I switch to foliar? What
should I do?
Normally we (UGA) would recommend applying ¼ to 1/3 of your total N rate and all of your K to the soil
at planting, followed by sidedressing N between first square and first bloom. Normally…we (UGA) would
recommend switching over to foliar feeding N and K after the 3rd week of bloom, or in other words no more
N or K soil applied after this point. But this is not a normal year (is there such a thing anymore?).
So let’s look at a few common scenarios: 1) May planted cotton and you were able to get your sidedress
nitrogen applied. Cotton has been blooming for at least 3 weeks, now you’ve had a bunch of rain and the
crop looks yellow. Should you apply more N and K to the soil (if it gets dry enough to get a fertilizer truck
or buggy in the field)? Probably not. For three reasons. One, the N and K may not be all leached out. Only
the nitrate form of N is leachable and K is not as mobile as N. Two, the waterlogging is hopefully temporary
and as soon as the soil dries out some the plant can take up N and K again. And three, since the cotton has
been blooming for at least three weeks, the roots are not as efficient at taking up nutrients, plus they may
have been damaged or compromised by the wet weather (and maybe some nematodes too). Basically, even
if you apply more N and K to the soil the plant will have a difficult time taking them up. So the
recommendation is? Foliar feed with N and K.
Scenario number 2: June planted cotton just starting to bloom and has not been sidressed with N. Looks N
and K deficient. Since the cotton has just started blooming there is still time to soil apply N. The
recommendation would be to apply 30-50 lb N/a to the soil. I would not soil apply K at this late point. And
even after soil applying N, be prepared to foliar feed with N and K after the third week of bloom.
Scenario 3: June planted cotton that has been blooming for 3 weeks and no sidedress N applied. This is a
tricky one. Again, normally we would switch to foliar feeding at this point. However, it would be difficult
to apply enough nitrogen foliar. Therefore, I would still apply 30-50 lb N/a to soil on this cotton. As in
scenario number 2, time is an issue, with only 4-6 weeks of potential boll setting time left you don’t want
to go with too high of rate in either of these situations.
So a few things to keep in mind:
1) Not all of your soil applied N and K may have leached out
2) Switch to foliar N and K after 3rd week of bloom (unless no sidedress N has been applied)
3) Petiole and tissue sampling are a good way to confirm if you are N or K deficient.
Custer’s Last Stand or Using Wipers or Mowers For Late-Season Weed Control in Peanut Fields (Prostko)
At some point, peanut growers must realize that it is futile to continue spraying herbicides over the top of their crop. Either the weeds are too big and/or pre-harvest intervals cannot be followed. In that case, there are 2 last resort weed control options for troublesome fields. These include the use of either a non-selective applicator (i.e. wiper/wick bar) or a flail mower. Flail mowers (vertical blades) are preferred over rotary mowers (horizontal blades) because they uniformly distribute debris rather than dump it on one side of the mower (which can cause major digging problems). The main goal with these weed control methods is to increase fungicide deposition and/or improve harvestability. At this time of year, it is really way too late to recover any weed competition related yield losses. Here are a few things to consider for both options.
1) A 33% or 50% solution of paraquat (depending upon formulation) is legal to apply in a non-selective applicator for the control of Palmer amaranth. Check out page 223 in the 2021 UGA Pest Control Handbook for more specifics (tractor speed and weed heights are very important). This treatment will also work well on Florida beggarweed and sicklepod. No other herbicides are labeled for this type of application so don’t bother asking me about Liberty or dicamba (FYI, they don’t work well in these applicators either!!!). I have tested several types of applicators over the years and prefer any of the ones pictured below. You can also check out the following slide set for more information about the research I have conducted on non-selective applicators (https://www.gaweed.com/slides/prostko-swss-2011/index.html).
2) I have used a flail mower to clean up my weedy test plots for many years. I usually set the mower to remove about 2″-3″ of the peanut crop in addition to topping any weeds that are there. Generally, 1 pass with the flail mower is OK but 2 passes are better (opposite directions). Check out these pictures from earlier today.
Other Things going on…
Below is a picture of “Tar spot” caused by a fungal pathogen Phyllacora maydis. This is the first time Dr. Bob has seen it in Georgia. Please note the rough, black specks on the leaf surface.
Northern corn leaf spot (Bipolaris zeicola) which produces numerous, small-to-medium sized red/brown spots, sometimes with appearance of concentric rings. Typically, corn is most severely affected by northern corn leaf spot early in the season and then grows out of it. There has not been a lot of research in reference to fungicides for management of northern corn leaf spot, but as it is closely related to northern and southern corn leaf blights. If a grower does spray, applications as early as V6-V8 would be appropriate.
Below is an example of Anthracnose caused by Colletotrichum graminicola. Anthracnose can be severe after extended periods of cloudy, humid and wet weather, especially when these conditions occur during early grain-filling periods. Most common and economical control for anthracnose is the use of resistant cultivars. A 2-year rotation with plant species other than sorghum will help to minimize the amount of inoculum in the field. Clean cultivation, elimination of probable weed hosts (e.g. Johnsongrass) and enhancement of the conditions that hasten decomposition of host residue also help to control the disease. There are a couple of fungicides that can be used in grain sorghum against anthracnose including pyraclostrobin (Headline) and/or azoxystrobin (Quadris). Always see label for proper fungicide use, restrictions and additional information.
If you have questions please contact your local county Extension agent.
Jeremy Kichler is the County Extension Coordinator representing the University of Georgia Cooperative Extension in Colquitt County. His email is jkichler@uga.edu .