By Greg LaBarge, CCA, Ohio State University Extension
Scouting fields to monitor crops throughout the growing season help you make more informed management decisions and stay on top of issues as they develop. In addition, regular scouting can help identify future changes needed to maximize production. Every year seems to present us with new and, in some cases, unexpected pest problems. Therefore, I would suggest that scouting has increased importance, attributed in part to changing weather patterns and pest adaptations.
Weather shifts give us new pests or an increased window of opportunity for a known pest. For example, the 2021 growing started with widespread alfalfa weevil in Northwest Ohio and ended with fall armyworm over most of the state. Over a 35-year career, there are two, maybe three years, where alfalfa weevil was a treatable problem, and it was a first with fall armyworm. Then, we added the corn disease tar spot to our list of concerns between those two insect issues. Each year, we are presented with a learning opportunity about insect and disease pests, which partially relate to changing weather patterns.
Pests are also adapting to our practices. An example here is weeds are adapting to the herbicides we rely on for weed control. Of course, we are all familiar with herbicide resistance, but today herbicide resistance has an expanded meaning.
We have talked about “site of action (SOA)” resistance for years. Herbicides kill plants by disrupting a plant process that forms an essential product for plant growth. With SOA resistance, the plant modifies that essential process disrupted by the herbicide, and the herbicide is no longer effective. Our strategy with SOA resistance is to rotate herbicides or use multiple herbicide modes of action when we spray.
Weed scientists have identified another form of resistance in recent years called “metabolic resistance.” In the simplest terms, metabolic resistance can be thought of as the plant breaking down the herbicide molecule into harmless by-products. The consequence of metabolic resistance is that weeds may quickly develop resistance to multiple modes of action. An example weed for metabolic resistance is waterhemp.
Extension specialist Mark Loux has identified Ohio waterhemp populations with resistance to seven herbicide groups: 2, 4, 5, 9, 14, 15, and 27. Across the Midwest, a single waterhemp population might have resistance to six herbicide groups. Our strategy when metabolic resistance exists is to shift from managing herbicide modes of action to reducing weed exposure to herbicides using non-chemical methods and killing escapes to prevent seed development. I can hear Dr. Loux’s voice echoing in my head, “No pigweed left behind, Go Rogue! Stop the seed.” A few hours walking a field to eliminate waterhemp will have potential long-term benefits to your weed control program.
Have a farm plan to periodically scout fields and take action to identify abnormal crop growth. OSU Extension offers several scouting resources to assist you. One is the Field Guide for Corn, Soybean, Wheat, and Alfalfa, available in print and PDF from our publications office (http://estore.osu-extension.org/). The guide has color pictures to help identify plant symptoms, insect, and diseases. In addition, our Crop Observation and Recommendation Newsletter is a weekly summary of observations across the state. Finally, your local Extension educator is another resource for identifying field issues. If it is something our educators have not seen before, they can quickly reach out to a specialist at OSU.
Nutrient deficiency symptoms
When you are out scouting fields, you may find discolored plants. Discolored plants can be from disease, insect, or nutrient deficiency. If we do not see evidence of insect or disease, we start to think about nutrients. Foliar symptoms of nutrient deficiencies often look similar at first glance. Still, we can identify the nutrient by closely observing the discolored pattern on the leaf and where affected leaves are located on the plant. We can combine plant symptoms with a tissue test result, and possibly a soil test, to confirm the deficient nutrient.
Table 1 lists nutrients and symptoms of that nutrient when deficient in corn, soybean, and wheat. Two words, “chlorosis” or “chlorotic,” frequently appear in the table. Both terms describe when leaves start yellowing and progress to tissue death (brown) over time.
Once you identify a nutrient deficiency, take time to determine the cause. A fertilizer application will not necessarily correct the problem you are seeing. Nutrient deficiencies can occur under different soil and temperature combination that impact root growth, limiting nutrient uptake. For example, sidewall compaction, general field compaction, root diseases, or where soils are flooded, dry, or cold can lead to foliar nutrient deficiency symptoms even though adequate nutrients are available. Therefore, we can save money on an unneeded fertilizer application by identifying these conditions where symptoms disappear once roots recover.