There’s times after I write this column on Sunday nights that I could turn around and write another one after Monday hits! Last week was one of those weeks, so here’s considerations for this week. Also, reminder to remove ET gages and irrigation scheduling equipment from fields before harvest.
Woolly Bear Caterpillars have been around since fair time at lower levels in landscapes and fields. However, they are showing up fairly heavy in later season soybeans right now, so it’s wise to be scouting for them. They’re doing a lot of leaf defoliation, yet also watch the pods for clipping or feeding on them. The economic threshold for defoliation is 20% in reproductive stages. I have been seeing them dying in fields from beneficial fungi as well, so look for dead/dying caterpillars and consider this as well. Decisions to treat are very field dependent. Organic options include various Bt products which impact caterpillars but don’t hurt other beneficial insects. Be aware of pre-harvest intervals (PHI) listed on the label (also pages 338-344 of 2021 Weed/Disease/Insect Guide); most products list 18+ days.
(Photo captions below): 3 woolly bears on this plant (left), lots of defoliation (top, right), and what dead woolly bears due to beneficial fungal pathogens look like (notice the duller color-they start almost looking a gray/white with age and don’t move).
Fall Armyworms: My phone went crazy again last week about them. Feel badly for all who had to reseed new alfalfa seedings, reseed cover crops, reseed small grains, and for all reseeding lawns. Their feeding happens so quickly. Even those who cut older stands of alfalfa were finding the armyworms weren’t killed after cutting. I was most commonly asked if cover crops or small grains should even be planted/replanted until the fall armyworms disappeared. Yes, they should as these small grains and covers obtain better establishment and growth the sooner they’re planted. The fall armyworms will eventually move south; however, entomologists don’t know the exact trigger for that. With the moths still flying, we may continue seeing larval feeding for a few weeks. What I told people who called or texted was to plant (being prepared with a product in mind should you need it), scout once the new seedlings start coming and be ready to apply a product if necessary. I listed a number of products in last week’s column, including organic options for consideration. Not every field nor lawn is impacted; it’s all dependent upon where the moths lay their eggs. A field or lawn that was impacted once may not be impacted again.
Harvest: Beans have dried down fast in spite of some green stems and leaves attached. Hearing moistures ranging from 10-14% on 2.0-2.5 maturity beans with yields depending on rain and disease. Even the corn is drier than what it appears inside some of these fields as I’m taking on-farm research notes. With harvest most likely ramping up this week, please be safe! It’s really dry which makes for dangerous road conditions and greater fire potential.
Harvesting soybeans as close to 13% is a goal for which to aim, in spite of the challenge. It’s perhaps a combination of art and luck depending on environmental conditions. Consider beginning harvest at 14% moisture making combine adjustments and operating at slower speeds as necessary. While there’s a dock of around 2.5% for the first 2 points delivering wet beans, delivering soybeans much below 13% moisture reduces profits because there’s fewer bushels to sell (load weight divided by 60 lbs/bu assuming 13% moisture). Selling soybeans at 8% moisture, you’re losing about 5.43% yield; at 9% moisture, it’s 4.4%; at 10% moisture, 3.3%; at 11% moisture, 2.25%; and at 12% moisture, it’s 1.14% yield loss. That doesn’t take into account additional risk for shatter losses during harvest. Only 4-5 beans on the ground can add up to a bushel/acre loss due to shatter. The following are profit examples:
Example 1. If the grower was to sell beans at 13.8% moisture, he/she would be docked 2.5% of the selling price of $12.30/bu, reducing the actual price to $11.99 per bushel. Total income per acre would be: 75 bu/ac yield x $11.99/bu = $899.25 per acre gross
Example 2. If the soybeans were harvested at 9% moisture, there would be 3.3 fewer bushels per acre to sell (4.4% of 75 bu/ac yield due to water loss): 75 bu/ac – 3.3 bu/ac =71.7 bu/ac yield x $12.30 = $881.91 per acre gross. In this example it’s better to take a dockage for selling beans at 13.8% moisture than sell them at 9%. The difference is a positive gain of $17.34 per acre or around $2341 on a 135 acre field.
Example 3. If the soybeans were harvested at 12% moisture, there would be 0.86 fewer bushels per acre to sell (1.14% of 75 bu/ac due to water loss): 75 bu/ac – 0.86 = 74.14 bu/ac yield X $12.30 = $911.92 per acre gross. If you can’t hit 13%, it’s still pretty profitable to sell them for 12% moisture compared to the other examples. Here’s wishing you a safe and profitable harvest!
Fall Armyworms: Received numerous reports of fall armyworm damage this past week from Kansas-Nebraska state line north to York. Damage was occurring in new alfalfa seedings in addition to established alfalfa, a new triticale seeding, and several lawns. With moths still being observed, we may see fall armyworms around for a few weeks yet, so it would be wise to be watching any alfalfa, wheat, rye, triticale and lawns for them. There’s no good way of knowing where they’ll appear; it’s all based on where the moth chooses to lay her eggs. Several reports of one field affected while the field next to it is fine. Same with lawns. Egg masses are fuzzy white masses that can include up to 200 caterpillars and the eggs can hatch in 2-5 days. Newly hatched larvae will be thin and often black/gray in color. I have some pictures from my colleague Jody Green at jenreesources.com.
In town, if you find the egg masses on lawn furniture, siding, or garden features, simply wipe them up with paper towel and discard in the garbage. They’re far easier to control when the larvae are ¾ inch or less. When they get larger than this, insecticides aren’t as effective, and usually, by that time, so much damage has occurred that the area will need reseeded. Products with active ingredients such as bifenthrin or permethrin are effective and are options for both farmers for fields and also homeowners with lawns. Sevin is also an option for both. Kentucky bluegrass lawns may be able to recover from rhizomes regrowing in the spring. However, fescue and ryegrass will need intervention this fall for reseeding. An organic insecticide option is Dipel which will take a little longer to work, but is still effective on smaller larvae. For lawn situations, it’s important to water the insecticide product in the ground to get the granules off the leaf blades and into the soil.
(Photo caption: Fall armyworm moth, egg mass, and larvae. Photos via Jody Green and UNL Entomology).
Large grubs on concrete: Had several reports last week of large white grubs on concrete stairs, sidewalks, and driveways. They are really large, up to 1.5 inches. What’s interesting about them is they crawl on their backs! These are grub larvae of the green June beetle which is a large beetle that often sounds like it’s ‘buzzing’ during June and July. The adult beetle can cause damage to ripening fruits such as stone fruits and berries. However, the grub larvae are not a major turf pest, unlike other grub species. They feed on thatch layers and organic matter, but don’t really attack lawn roots. They make holes in the soil, so rain and irrigation will drive them out onto concrete.
Small Grains and Weed Control: Last week I mentioned considerations for wheat planting. Even if small grains aren’t taken for seed, they do a tremendous job for weed and erosion control, provide an option for grazing, and uptake excess moisture and nutrients (helpful in seed corn field situations). Small grains, particularly oats and rye, have been proven to help with reducing soybean pathogens such as fungi and nematodes causing SDS and SCN. I’ve been watching a couple side-by-side soybean fields in which one was planted green into rye and the other didn’t have rye. Even the farmer commented on it to me this week how the quarter without rye has senesced earlier and has problems with anthracnose and Diaporthe complex (including pod and stem blight) while the other is essentially disease free.
Wheat provides an option for both grazing and grain. Rye provides the best option for earliest green-up/growth in the spring and longest seeding time as it can be seeded into December. Triticale provides the most biomass, including for haying and small grain silage, but produces the latest into late May/early June. It’s too late to plant oats for the fall, but they are an option for the spring. All keep the ground covered from light interception penetrating the soil surface which allows weed seeds to germinate.
Researchers from K-State looked at marestail (horseweed) and palmer amaranth control from 2014-2015 in no-till soybeans at six locations in eastern Kansas. They also found the majority of marestail emerged in the fall (research from UNL showed up to 95% does). They compared five cover crop treatments including: no cover; fall-sown winter wheat; spring-sown oat; pea; and mixture of oat and pea. Cover crops were terminated in May with glyphosate and 2,4-D alone compared to a control of no herbicide use. Ten weeks post-termination, palmer amaranth biomass was 98% less in winter wheat and 91% less in spring oat compared to no cover crop and no herbicide control. The same cover crops were also compared to a no cover crop treatment where all received a May herbicide application of 2,4-D and glyphosate with residual herbicides of flumioxazin + pyroxasulfone (Fierce). With the addition of residual, there was no difference in palmer amaranth biomass in the no cover crop with residual herbicide and all the cover crop species where a residual herbicide was added. I share the Research Figure on my blog site which is incredibly visual and have shared it in pesticide trainings as well. To me, it so visually shares how well residual herbicides can work, which we’re aware of. However, what strikes me the most is how much work that residual had to do on its own to achieve the same control as a cover crop + residual herbicide. Adding the cover crop reduced the load of the herbicide alone and is another tool in the toolbox. It also shows how effective cover crops for weed control can be for organic systems if there’s a solid way for terminating them. I realize cover crops don’t fit every field or every situation. Just some considerations as we especially think of situations where planting a small grain this fall could be used for weed and erosion control and/or grazing.
Congratulations to all the 4-H youth who competed at the Nebraska State Fair this past weekend! The talent of our youth never ceases to amaze me. It’s also so encouraging to see life skills being developed such as public speaking, plant and insect identification, and the responsibility and care for animals.
Also so grateful to receive rain last night! And, that should finish up irrigation, or get it pretty close, for many that didn’t have late-planted crops. It’s really important to know your crop growth stage and to finish well. There’s some fields that are obviously over-irrigated with water standing after this last rain. On the flip side, it’s important to monitor soil moisture and crop growth stages to not stop too soon in spite of the long irrigation season and how tired farmers are. Several questions last week on ‘how’ to finish with irrigations and when physiological maturity occurs in soybeans.
Last irrigation: if you’ve been triggering irrigation during the growing season based on the recommended 35% depletion (average of 90 kpa on watermark sensors), you would have around 1.28” of moisture available in the top 4 feet for the plant in silt loam soils. A consideration for a step-wise approach I’ve used is this: Corn at ½ milk line needs around 13 days or 2.25” to finish the crop to maturity-so subtracting that from 1.28 would be 0.97”. As we consider allowing the soil moisture profile to deplete to 50-60% for recharge over the winter, a person could delay to 40-45% depletion (around 130 kpa average on watermarks) before triggering irrigation the first 7 days and then allow for 50% depletion (around 150 kpa average on watermarks) that last 7 days to finish irrigation for corn.
Soybeans range from full seed (R6 end of seed enlargement) which needs 18 days or 3.5” of water; R6.5 (leaves yellowing/pod membranes still clinging to seed) which needs 10 days or 1.9” yet; or physiological maturity in which the pod membrane has separated from the seed and no more water is needed. The NebGuide, “Predicting the Last Irrigation of the Season”, speaks to yellowing leaves as the beginning of physiological maturity. But the question I kept getting last week was “how yellow is considered yellowing leaves?”. Perhaps a better indicator for today’s varieties would be to also look at the pods. Until the pods reach R7, physiological maturity, the plant is still utilizing water. At R7, at least 50% of the field plants will have one mature pod anywhere on the main stem. A mature pod is considered when the pod membrane no longer clings tightly to seeds in that pod (this is like black layer on corn where the nutrient/water supply is cut off from the kernel forming the black layer). So essentially, if you pull off a pod on the main stem, carefully open it up and look at the membrane surrounding the seed. If it’s still clinging tightly to it, it’s not quite mature. If you see separation of the membrane and seed, it’s considered mature and will no longer use water. There can be a range of pod stages on a plant, but between yellowing leaves and pod color changes, one can get a pretty good idea when R7 has occurred and no additional water is needed for the plants. The timing of the ending R stages in soybean is determined by planting date and varietal maturity group, though the date of R7 can be hastened if water stress and high temperatures prevail in August — something we are seeing this year.
Soybean stems typically turn brown shortly after R7 begins, though the stem can remain green longer due to a number of reasons, including fungicide use. The final soybean stage is R8, which occurs when 95% of pods have attained maturity and have a variety-dependent color of brown or tan. Seed moisture in a soybean pod dries down from 70% at R7 to about 13% at R8. This has shown to be around 12 days based on research, but can be faster or slower depending on solar radiation, humidity, temperature, wind speed and soil surface moisture.
So, for scheduling last irrigation in beans: if we use the same example of having 1.28” of available water at 35% depletion in silt loam soils in top four feet, soybeans would need 2.22” with 18 days to finish at R6 or 0.62” with 10 days to finish at R6.5. Using the stepwise approach, one could again allow the soil moisture to dry down to 40-45% the first week and 50-60% the second week. This also allows room to catch rain like we finally experienced last night.
Fall armyworms have been on the increase in alfalfa and pastures recently, so please be scouting as they can decimate a field quickly in the late larval stages. The threshold is 3 or more per square foot and they’re easier to control if the larvae are ¾ inch long or less. When they’re larger than this, they’re more difficult to control and choosing to harvest the alfalfa may be a better control method. Insecticide options include products with active ingredients including the pyrethroids, Alpha-cypermethrin (Fastac CS), Beta-cyfluthrin (Baythroid XL), cyfluthrin (Tombstone), Gamma-cyhalothrin (Proaxis, Declare), Lambda-cyhalothrin (numerous products), permethrin and Zeta-cypermethrin (Mustang Max), organophosphates, chloropyrifos (numerous products), and carbamates, carbaryl (Sevin) and methomyl (Lannate).