Field To Yield: Crops & Comments

Geoff Reeves

Agronomy topics curated by Geoff Reeves

  1. 6d ago

    Molybdenum

    Nobody soil tests for molybdenum, and in the Southeast you don't need to. Your pH number is doing that job. We dig into how Mo behaves in our soils, when soybeans actually respond, and whether there's anything to the idea that Mo can protect wheat falling number. pH is your Mo test — Molybdenum works backwards from most micronutrients. Acid soil locks it onto iron and aluminum oxides, and lime releases it. No Southeast lab offers a calibrated Mo soil test.Clay vs. sand — Piedmont red clays hold a Mo reserve that liming frees up. Coastal Plain sands have less to release, and pushing pH above about 6.2 there invites manganese deficiency.Why soybeans care — Nodule bacteria need Mo to fix nitrogen, so a Mo-short soybean looks N-deficient with poor nodulation.When seed treatment pays — On fields limed to target pH, expect no response. On acid, un-limed ground below about 5.8, a low-cost Mo seed treatment is cheap insurance, though it's no substitute for lime.The falling number question — Mo helps the plant make ABA, the hormone behind seed dormancy, and Mo-starved wheat sprouts more easily in lab studies. But no study has ever measured Mo's effect on falling number, and none has tested soft red winter wheat.What actually protects falling number — Variety choice and prompt harvest. Don't spend money on foliar Mo for wheat quality.

    Molybdenum

  2. Sep 29

    Nematodes

    They're the yield robbers you can't see, and the only way to know what's in your fields is to go looking before the ground gets cold. This episode breaks down what's feeding on Carolina row crops, how to sample for it this fall, and what to do about it before you buy a single bag of seed for next year. Fall is the window — Populations peak near harvest and crash over winter as they retreat to eggs the lab can't count. Sample late August through November; a winter sample will lie to you.How to pull a good sample — 20-plus cores, 6 to 8 inches deep, in the old row where the roots were. Keep each soil type separate, keep the bag cool like a jug of milk, and get it shipped inside two days.Where to send it — NCDA&CS in Raleigh for NC growers, or through your county agent to Clemson's Blackville lab in SC, where the Corn, Soybean, and Cotton Boards are covering the cost again this year.Know which one you've got — Southern root-knot, peanut root-knot, Columbia lance, reniform, sting, and soybean cyst all behave differently, and the standard assay won't tell root-knot species apart. Soil texture is your biggest clue.Sand tells the story — Sting won't do much without 80 percent sand and Columbia lance wants the same coarse ground, while reniform leans toward the finer stuff. Piedmont clay data is thin, and we say so.Guava root-knot is the one to watch — It's regulated in NC, it beats the root-knot resistance built into cotton, and confirming it takes a molecular test, not a look under the scope.Resistance and rotation before chemistry — Cotton's Rk genes, soybean's Rhg1 and Rhg4, and peanut resistance bred in from wild Arachis usually outperform anything you can buy in a jug, and they cost nothing per acre.Why PI 88788 is wearing out — Almost every SCN-resistant soybean on the market traces to one source, and populations are learning their way around it. Rotating to Peking-type resistance matters.Rotation works until it doesn't — Cotton and peanut break each other clean, and corn or small grains starve out cyst nematode. But sting, lesion, and stubby-root eat nearly everything, so no rotation saves you there.Where wheat fits — Small grains break cyst and peanut root-knot but host southern root-knot and sting, so wheat into double-crop beans can carry a population straight through the year.Modes of action, plainly — Fluopyram shuts down mitochondrial complex II, abamectin locks open chloride channels, aldicarb and oxamyl hit acetylcholinesterase. Different tools, different jobs.When nematicides don't pay — Trials across the Southeast show fumigation often loses to cheaper in-furrow and seed treatments, and on corn and beans the margin frequently won't carry the cost at all.What it's actually costing you — Root-knot was the number one yield-reducing cotton disease nationally in 2023, ahead of reniform and seedling disease. This isn't a sideline problem.The honest gaps — Piedmont threshold data, independent validation on biological nematicides, and published per-acre cost figures are all thinner than anybody would like.

    Nematodes

  3. Sep 22

    Soil Testing, Part 3: Phosphorus

    We've covered pH and potassium. Now the nutrient that behaves like nothing in a Corn Belt textbook. On our Piedmont clays, phosphorus is hard to build, slow to move, and — on thousands of acres with a litter history — already piled up higher than any crop can use. Geoff and Glenn dig into why that happens, what your soil report is actually telling you, and where the money is. Why P sticks — Aluminum and iron oxides grab phosphate and slowly bury it, which is why a heavy application on a low-testing field doesn't all stay available.The lime connection — Getting pH into the low 6s makes your existing phosphorus work harder. Part 1 pays a dividend here.Index isn't ppm — NCDA&CS reports a P-Index, not parts per million. Compare it to a Midwest bulletin and you'll reach the wrong conclusion.Where the line actually is — The state recommends zero P above a P-Index of 50, and the real critical level on Piedmont ground is closer to 10. Most fields in North Carolina are well past both.The litter math — Poultry litter runs about 1:1 nitrogen to phosphate. Corn wants closer to 1.7:1, grass 3 or 4 to 1. Fertilize for nitrogen and you over-apply phosphorus every single year.Starter fertilizer, honestly — NC State tested corn and cotton across all three regions on very high P soil and found no response. Keep the rig, change what's in it.When the soil quits holding — Those binding sites are finite. Fill them up and phosphorus starts leaving in runoff. That's the chemistry behind PLAT and P-based application limits.Drawdown reality — Crop removal will bring a loaded field down, but plan on a decade or more, not a season.The actual answer — Move the litter to your low-testing fields and buy nitrogen for the high ones. Nobody needs to quit using litter.

    Soil Testing, Part 3: Phosphorus

  4. Sep 15

    Soil Testing, Part 2: Potassium

    Potassium is the nutrient where Midwest thinking gets Southeast farmers in trouble. Our soils don't bank K the way theirs do, and the numbers on your report don't mean what a lot of folks think they mean. We work through the soil chemistry, the plant physiology, and the arithmetic behind reading an NCDA&CS report for potassium. Our soils don't hold a K reserve — Midwest 2:1 clays trap and slowly release potassium between the layers. Piedmont kaolinite doesn't. There's no savings account here, which means the crop is living on what's on the exchange complex right now. Yes, potassium leaches in the Southeast — Low CEC means few places to hold a K ion. Add sand and rainfall and applied K moves. Calcium and magnesium from lime actively push K off the exchange, which is why fall-banking K on a Coastal Plain sand is a losing proposition. How to read the K index — and why base saturation misleads you — The K-I is a rescaled ppm number with no CEC in the equation. We run the conversions on air. And we work the math that matters: 3% K saturation on a CEC 3 sand is about 75 lb K₂O total, while 3% on a CEC 12 clay is 300 lb. Same percentage, four times the potassium. Chase the index, not the ratio. Some soils physically can't hold a season's worth — We calculate maximum K holding capacity by CEC class and compare it against what corn, cotton, soybeans, and wheat actually pull. On the lightest ground, splitting isn't a refinement — it's the only way the K stays there. Cotton is the problem child — Roughly 70% of cotton's K comes in by first bloom, on a small root system, right when bolls take over as the sink. That's why you see late-season deficiency on the upper leaves and Stemphylium on fields that soil-tested fine. We cover UGA's foliar K work and where it actually pays. Crop-by-crop rates, removal, and litter credits — NC's actual K₂O equations by index, removal figures for grain versus silage and grain versus baled straw, and why poultry litter K credits nearly pound-for-pound while litter N doesn't.

    Soil Testing, Part 2: Potassium

  5. Sep 8

    Soil Testing, Part 1: pH

    Every fertility decision you make sits on top of soil pH. Get it wrong and you’re paying for phosphorus the soil won’t release, nitrogen the crop can’t use efficiently, and soybean nodules that never form. In the first episode of our soil testing series, we get into why Piedmont soils fight us on acidity, how often you really need to pull samples, and what your NCDA&CS report is actually telling you. Why we test in the Southeast — Piedmont Ultisols are old, weathered, kaolinitic, and low-CEC. Bases leach out, nitrogen fertilizer drives pH down, and there’s not much buffering to hold the line. NC State data show 37% of row-crop samples come back below pH 5.8 — and about 9% are already over-limed.How often to pull samples — Once every three years works on stable Piedmont clay. We talk through when that’s not enough: sandy low-CEC ground, cotton, heavy nitrogen programs, and after a big lime application.What pH actually is — The difference between active acidity (what the meter reads) and reserve acidity sitting on the exchange sites. That gap is the whole reason a pH number alone can’t tell you a lime rate.Aluminum is the real yield thief — Below about pH 5.5, aluminum goes into solution and attacks the root tip directly, shutting down cell elongation. You get short, stubby, brittle roots that can’t chase water. Manganese toxicity rides along with it.What we shoot for — pH 6.0 on mineral soils, 6.2 for cotton, and why chasing 7.0 costs you manganese, zinc, and boron.Buffer pH — and why North Carolina doesn’t report one — Most states run a buffer (Adams-Evans, Mehlich, Sikora) to estimate reserve acidity. NC skips that step and calculates lime straight from exchangeable acidity, or “Ac,” on your report. We walk the actual equation. This also means NC’s CEC number isn’t comparable to a private lab’s.Tennessee dolomite vs. South Carolina calcitic — The geology behind each, why dolomite reacts slower, and how to decide. Short version: let your magnesium index make the call, not a Ca:Mg ratio.Buying lime on the tag, not the sticker — Calcium carbonate equivalent and fineness combine into effective neutralizing value. We run the arithmetic so you can compare two quotes on delivered tons of actual neutralizing power.Gypsum is not lime — It’s calcium sulfate. It won’t move your pH. We cover what it’s actually good for, including subsoil aluminum.

    Soil Testing, Part 1: pH

  6. Sep 1

    Pyroxasulfone

    Post resistance has taken most of the traditional cleanup options off the table in Southeastern ryegrass. That makes pyroxasulfone the best soil-applied tool we have for stopping ryegrass before it ever establishes. Geoff Reeves walks through the chemistry behind its staying power and lays out a two-pass overlapping residual program built to draw down the seedbank and keep this chemistry working. In this episode: Killing it in the crack. Pyroxasulfone shuts down very-long-chain fatty acid (VLCFA) elongases in germinating seedlings before the shoot ever reaches daylight — which is exactly why it does nothing to ryegrass that's already up.Low rate, tight binding. It runs at roughly one-eighth the rate of the older chloroacetamides. High enzyme-binding affinity, low water solubility, and moderate soil binding are what stretch the residual window.Two passes, overlapped. A fall application — late October into November — with a burndown partner like glufosinate, followed by an overlapping pass around February to catch the spring flush.No water, no herbicide. You need 0.5 to 0.75 inches of rain to activate it. Sitting dry on the surface, it lets ryegrass through even though the product is right there.Where resistance actually comes from. Target-site resistance is rare here. The real risk is the declining low-dose tail at the end of the residual window, which selects for metabolic, GST-based resistance. Full label rates and zero tolerance for seed-set on escapes are what keep the seedbank shrinking.Rotation and cover crops. Fitting winter peas, crimson clover, or cereal rye into the program for added ryegrass suppression — without boxing yourself in on the next cash crop or blowing through seasonal rate limits.

    Pyroxasulfone

  7. Aug 25

    Soybean Desiccation

    Soybean Desiccation Late-season desiccation is one of the few tools that lets you pick your harvest date instead of letting the weather pick it for you. In the Southeast, that's the whole argument — a September storm can undo a season's work in a night. But the same application that buys you a week can cost you real yield if it goes out too early. This episode is about reading the crop and getting the timing right. Buying days ahead of the storm. A harvest aid applied at the right stage can pull harvest forward 5 to 10 days, and up to 15 days in the Deep South. In hurricane season, those days are the point.R7 is the line. Timing is the entire decision. Land-grant trial work shows up to 68.5% yield loss from an application at R5.5, versus no measurable loss at physiological maturity (R7). Green pods are still filling seed, and you can't shortcut that.Fast versus thorough. Sodium chlorate dries down quickly on a 0-day preharvest interval. Saflufenacil runs a 3-day PHI. Paraquat gives the most complete burn but carries a 15-day PHI. Your combine schedule decides which trade-off you can live with.What a desiccant won't fix. These products manage green weed biomass and leaf tissue. They don't cure green stem, they don't pull moisture out of the seed, and they won't stop pod shattering.

    Soybean Desiccation

  8. Aug 18

    Stink Bugs

    Stink bugs cost Southeast soybean growers real money every year — but not all stink bugs are created equal. This episode breaks down the full complex hitting Piedmont and Southeast beans and gets into the science behind why some are so much harder to kill. How they actually damage a pod — the enzyme cocktail they inject that shrivels seed, drags out maturity, and can trigger green stemWhat your sweep net counts are really telling you — thresholds by species, and why grain and seed beans aren't scouted the same wayWhy brown stink bug shrugs off a pyrethroid that drops its green cousins dead — the biochemistry behind itWhy redbanded stink bug might be the toughest bug in the field — lower threshold, deeper feeding, and a knack for reinfesting after a spray If you scout beans in July and August, this one's for you.

    Stink Bugs
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Agronomy topics curated by Geoff Reeves

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