Crop Update: This past week’s top question was about yellow looking and/or buggy whipped corn and weed control. Much of what we’re seeing can be attributed to cool, wet conditions this spring. Yellow striping on leaves is often due to sulfur deficiency but could be combined with other nutrient deficiencies depending on conditions. Purdue University has a nice guide with pics if you’d like to check it out: https://www.agry.purdue.edu/ext/soilfertility/news/Striped_Corn.pdf.
Most of what I looked at or received questions about was yellow and/or buggy whipped corn due to herbicide injury. This isn’t uncommon for pre-plant residual herbicides to impact corn more in years where we have wet conditions, cooler temps, and plants that are slower to emerge/grow. Yes, some of these products are considered ‘safe’ for corn, and they shouldn’t kill it. It’s just we’re experiencing a strange year with cool, wet conditions and the corn is metabolizing the chemical but not growing fast enough, thus the injury. Situations which may be extra sensitive are ones in which corn was planted too wet with slots not closing or if corn was planted too shallow. Soil applied grass herbicides and those with pre-mixes containing atrazine may be experiencing more of the buggy whipping or yellowing from Group 15 growth inhibitor herbicides. Yellow/purple leaves and sometimes ‘bottlebrush’ looking roots can be exhibited from Group 2 ALS-inhibitor herbicides. Herbicides in Group 27 with ‘bleacher’ chemistry are re-activated with rain events and we’re seeing some yellow/white corn and milo due to that. Dr. Kevin Bradley, University of Missouri, wrote an article that shares photos and trade names if you’re interested in checking that out: https://ipm.missouri.edu/IPCM/2009/4/Cool-Wet-Soils-Can-result-in-More-Corn-Injury-from-Preemergence-Residual-Herbicides/. I realize it’s frustrating, but overall these are good products and it’s the weather conditions causing the problems. Each day of sunshine and warmer temps are helping corn to grow out of the symptoms and look greener/healthier in most cases.
The other concern is the rain has moved herbicides down into the soil and we’re beginning to see weed flushes of waterhemp and palmer on the soil surface. Chris Proctor, Extension Educator, addressed this in CropWatch and Nebraska Farmer as we think of post-emergence control right now in both corn and soybean. There are additional trade names with similar chemistries mentioned and this isn’t an endorsement of specific products. “There are a number of effective herbicide options in corn such as Acuron, Laudis, or Diflexx Duo. In soybean, herbicide options are much more limited. When coupled with traited seed, Liberty, or Xtendimax can be effective at controlling these weeds postemergence, and in a Roundup Ready system Warrant Ultra or Flexstar GT are good options. It’s not too early to plan how to improve weed control in fields with a history of difficult-to-control weeds. A good preemergence herbicide program, use of narrow row-spacing, and even cover crops, when used as part of an integrated management plan, can improve control of herbicide-resistant weeds.”
Thistle Caterpillars: Painted lady butterflies migrate north from the southern U.S. and
Mexico each spring. The butterflies have been around for a little over a month and thistle caterpillars have been found feeding in soybean the past few weeks. Last week, I was seeing higher populations in early planted soybeans in Clay and Nuckolls counties. Larvae can feed from 2-6 weeks depending on weather. Treatment thresholds for vegetative stages are 30% defoliation. Each field needs to be assessed regarding percent defoliation and larval stage. Some fields I checked had larvae that were pupating or already emerged as adults. Other fields had larval stages that will still feed 2-5 weeks, depending on weather. Much information we read says they stay on field borders, which I’ve seen to be true later in the growing season. But right now, I’m finding situations where they’re fairly consistently infested throughout the field. Some may consider adding an insecticide to your post-herbicide application. If you have dicamba-tolerant soybeans, be sure to check the product’s website regarding approved tank-mix partners.
Irrigation Scheduling Workshops for wet years will be held Wednesday June 19th, 12 noon, at The Leadership Center, 211 Q St (E Hwy 34) in Aurora and Tuesday June 25th, 12 noon, at the Chances R Restaurant, 124 West Fifth Street, York. The program will start with lunch at 12:00 pm, followed by the speakers and wrap up around 1:30 pm. The Upper Big Blue NRD will provide the lunch. RSVP is not required but appreciated for a meal count. Call the Hamilton County Extension office at 402-694-6174 or email Steve Melvin at firstname.lastname@example.org. Dan Leininger with the Upper Big Blue NRD will speak on installing sensors and Steve Melvin will speak on deciding when and how much water to apply using watermark sensor readings.
It’s nice seeing cattle being turned out into corn stalks! One point that I haven’t mentioned recently is that we all need to be checking the herbicide label for any grazing restrictions of crop residues.
So check the labels from in-season applied herbicides to row crops and fall-applied herbicides to crop residue for any potential grazing restrictions…and any restrictions on grazing cover crops planted into crop residues following application of those chemicals to a row crop. If the label doesn’t specify any restrictions, then it should be ok. If you want to be on the safe side, a rule of thumb many chemical reps use is to use the pre-harvest interval for the amount of time to wait before grazing stalks.
Some labels will say that residue should not be grazed or baled and fed to livestock. Sometimes studies were actually conducted to know there is a safety concern. In other cases, the chemical company may not choose to conduct all the studies the Environmental Protection Agency (EPA) required for labeling due to high costs. If that’s the case, the EPA requires the strongest restrictive language be placed on the label.
Regardless, if it says there’s a grazing restriction on the label, the label needs to be followed as it is a legal document and the law. Your cattle may/may not be affected by grazing stalks or cover crops where a chemical with a grazing restriction is on the label, but there may be other concerns such as problems with the chemical affecting the calf or being retained in the cow’s milk.
For quick references, the 2015 UNL Guide for Weed Management shows Forage, Feed, Grazing Restrictions for Row Crop Herbicides on pages 174-177. A new weed guide will be released January 2016. These pages just provide a reference; it’s truly best to read and follow the label.