A few weeks ago we mentioned reports of armyworms in forages and the need for growers to check their stands for signs of insect feeding. Over the past week or so, this concern has grown considerable, and problems are occurring in rangelands, forages, cover crops including rye, and wheat fields. Not only is Ohio experiencing problems, but numerous Midwest states are reporting similar instances of large numbers of armyworms feeding in fields, especially in newer plantings. An excellent article on the problem is available at the Kentucky Pest News site that was written by our colleague, Doug Johnson, that discusses the problem and answers various questions (http://www.ca.uky.edu/agcollege/plantpathology/extension/kpn/current.html). Until we get a few hard freezes, expect much of this feeding to continue. Make special note of whether armyworm feeding is killing off pasture or forages, or any newly sown planting. Those plants might still be alive and continue to grow.
Soybean rust is making a late breaking appearance in many of the southern states, both those that border the Mississippi river as well as Georgia and South Carolina (http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi?host=All%20Legumes/Kudzu&pest=soybean_rust&language_sel=1 ). Some of these developments were the result of Hurricane Isac back in early September and some were there before this storm. I have started to receive some samples of leaves - just to see if the spores could make it to Ohio on the back of a hurricane. This information is important to have for the year when a hurricane might hit in July, with the same level of rust in the south - it helps develop the models that can help us with management in the future. As of today - no soybean rust was found on these leaves collected from fields in Brown, Highland, Wood, Hardin, Hancock and Union counties. If any fields survive the freeze this week, we may try again next week.
From these samples there were lots of leaf spots including: bacterial leaf blight, downy mildew, Septoria, Cercospora leaf blight, frog eye leaf spot, and Phyllosticto leaf spot. There was also some evidence of soybean virus diseases including soybean necrotic vein virus and bean pod mottle virus. Interesting there were aphids on the leaves collected in southern Ohio. There were also assorted other ‘fauna’: thrips, mites, and bean leaf beetles to name a few.
The goal of 4R Nutrient Stewardship strategies, are to maximize economic productivity and limit offsite nutrient losses that cost both the grower pocketbook and society. The 4 R’s include:
· ‘right’ rate to meet crop needs and minimize offsite movement
· ‘right’ source selected for location and timing of application
· ‘right’ time based on source and crop needs
· ‘right’ placement so the nutrients are available to the crop and stay on site
The 4 Rights are interconnected and work with each other in the overall agronomic production system. As we enter the fall, here are a few reminders of 4R principals to apply:
1. To determine the right rate of phosphorus, potassium and lime, collect a representative soil test. The investment in a representative soil testing program is well worth the expense. A new factsheet, Soil Sampling to Develop Nutrient Recommendations AGF513-12 (https://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins/Soil_Sampling_to_Develop_Nutrient_Recommendations_AGF-513-12.pdf), highlights the steps to obtaining a reliable, representative soil sample as the basis for developing a fertilizer recommendation. The key is to properly divide up the field landscape, take representative sample cores and select a laboratory to do the analysis. The Tri-State Fertilizer Recommendation for Corn, Soybean, Wheat and Alfalfa E-2567 provides recommendation information based off soil test results. The tri-state guide and other supplemental information provided is at https://agcrops.osu.edu/specialists/fertility/fertility-fact-sheets-and-bulletins
2. Once a rate is determined, attention needs to be given to source, placement and timing of the nutrient. In Ohio, both phosphorous and nitrogen are nutrients that can have offsite consequences to water quality which we want avoid. We also want to keep them in place from an economic standpoint for the crop we want to grow. No sense sending dollars down the ditch.
Whether phosphorus is from a commercial fertilizer or organic source such as manure, broadcast surface applications have the greatest risk of offsite movement. In fall 2011, high phosphorous levels in tributary water samples seemed to coincide with periods where broadcast fertilizer applications occurred followed by rainfall events. Shallow incorporation tends to reduce phosphorous losses has been shown during rainfall simulator studies. However, caution is warranted to tillage practices that increase soil exposure and erosion losses. Alternatives such as row starter fertilizer or strip tillage should be considered in erosion loss situations.
Fall nitrogen management:
Ohio State University does not recommend fall applied anhydrous ammonia as a preferred method of nitrogen application. Years of field research shows fall applied anhydrous ammonia can be susceptible to loss and can result in significant corn yield decreases of as much as 30%, but generally 10-15%. Our shallow, poorly drained soils with systematic subsurface drainage, cause fall anhydrous ammonia applications to be riskier for us than our neighbors to the west. Late winter and early spring warm weather periods lead to conditions where ammonium is converted to nitrate via nitrification. Nitrogen in the form of nitrate can be lost by leaching (under cool, excessively wet conditions) or by denitification (under warm, excessively wet conditions).
If work load management makes fall anhydrous ammonia application necessary, keep the following in mind. First and foremost, soil temperatures should be below 50 degrees F. Nitrifying bacteria are active until soil temperatures reach 32 degrees but activity significantly decreases at 50 degrees or less. Remember, our goal should be to keep nitrogen in the ammonium form in the soil as long as possible because it is not as susceptible to loss as nitrate. If anhydrous ammonia is to be applied in the fall, it is a good idea to use a nitrification inhibitor. The inhibitor will slow the conversion of ammonia to nitrate. Realize that the inhibitor does not provide inhibition indefinitely, so the combination of nitrification inhibitor and cooler soil temperatures is necessary.
A good discussion of fall nitrogen application is provided in a recent article of University of Illinois’s the Bulletin, which can be found at http://bulletin.ipm.illinois.edu/article.php?id=1725
- Glen Arnold (Nutrient Management Field Specialist),
- Debbie Brown (Shelby),
- Sam Custer (Darke),
- Amanda Douridas (Champaign),
- Rich Minyo (Corn & Wheat Performance Trials),
- Les Ober (Geauga),
- Pierce Paul (Plant Pathology),
- Steve Prochaska (Agronomy Field Specialist),
- Adam Shepard (Fayette),
- Alan Sundermeier (Wood),
- Harold Watters, CPAg/CCA (Agronomy Field Specialist),
- Eric Richer (Fulton)