May 23: Corn is looking good for the most part with few major concerns yet. Some have commented on the yellow-looking corn. This is most likely due to cool, wet soils rather than any nutrient issues. There may be field-specific issues such as saturated soils, compaction, and some herbicides that can cause this yellowing too. Also had a call on cutworms in seed corn but not widespread calls on this yet. Extension Educators have set up light traps for tracking cutworm moths and you can find that information here: http://go.unl.edu/rhhe. Cutworms will cause the most damage the first 7 days after corn emergence so scouting is important. The York County Corn Grower Plot was planted on April 24th with the corn currently at 2 leaf stage. Special thanks to Ron, Ray, and Brad Makovicka for hosting and the work put into this plot each year!
May 1: It never ceases to amaze me how quickly planting occurs each year! Corn planted the week of April 10th has emerged and for those fields that received hail from last week’s storms, I’m hoping we don’t see disease issues later on. Also of note, some have asked me about the CropWatch soil temperatures as they are higher than what some of you have been measuring in your fields before planting. The CropWatch soil temps at http://cropwatch.unl.edu/cropwatchsoiltemperature are averages of 24 hours under bare soil which may be different than the residue conditions in your fields and is an average of the entire day vs. one point in time. This may help explain some of the differences.
Many stands of alfalfa are lush green with over a foot of growth at this point. I looked at some alfalfa in Clay County that got dinged by cold temperatures in areas of the field and stopped growing. At this time I’m also finding quite a few aphids and a few alfalfa weevils. A disease common this time of year called spring black stem can be observed in nearly all alfalfa fields right now in the lower canopies. This disease consists of small black lesions on the leaves which eventually cause the leaves to turn yellow and drop. Normally this disappears with later cuttings as humidity and rainfall are typically high during the first cutting and can be managed with cutting the alfalfa. One option to consider according to Dr. Bruce Anderson, our Extension Forage Specialist, is to consider cutting alfalfa before bloom. He shares that weather can cause long delays and alfalfa doesn’t bloom very aggressively during spring. Bruce felt there were advantages to cutting alfalfa when it is 15-20” tall before bloom during first cutting including: weather compared to later spring, spread out alfalfa harvest if you consider cutting one field earlier, reduction in insect and disease problems by early harvest, and high feed value. It also potentially allows the second cutting to be ready before the summer heat which can lower forage quality. Disadvantages include lower yield from cutting early which could be made up in later harvest, regrowth may be slower if cut early, and the need to allow for longer recovery after first or second cutting to maintain long-term stands. So, harvesting before bloom may be something you wish to test in one of your fields this year and consider how this works for you, especially if you did have some frost damage or are having insect/disease issues in your alfalfa right now.
On May 6, quite a storm was unleashed in south central Nebraska. Soybeans that had been planted two to three days before the storm seem to have emerged fine, while those planted May 5-6 tend to have uneven emergence and crusting. This is occurring regardless of tillage type, residue cover, etc. Many farmers have been running pivots to help the soybeans break through the ½- to 2-inch crust, often applying an inch of water before they see stand improvements.
The primary question for growers has been “Should I replant?”
UNL on-farm research has shown less than 1.4-2.0 bu/ac yield difference between planting 90,000 and 180,000 seeds/acre. (See report.) In our research, 90% of the planted stand was achieved at both seeding rates in irrigated 30-inch rows in no-till and ridge-till fields.
Consider what was found in 2006 in one dryland field in Nuckolls County where populations of 100,000, 130,000, and 160,000 seeds/acre were planted. This field was at the cotyledon stage when it was hailed. Some plant stands dropped to 67,000. Yield was 4 bu/ac less than in the 160,000 seed/acre planting that had a final stand of nearly 98,000. The average yield in the field was 40 bu/ac. While this is only one field and one year of research, it is an example of how soybean plants can compensate for reduced populations by branching and how August rains in dryland can still allow reasonable yields to be produced.
UNL research conducted by Dr. Jim Specht, UNL Soybean Physiologist, also has shown that for every day planting is delayed after May 1, there is the potential to lose 1/4 to 5/8 bushel per day. As we near the end of May and early June and consider that late planting yield penalty and the dry soil conditions (particularly in dryland fields), along with the seeding rate results from this UNL on-farm research, we are recommending that growers leave stands in many fields. Based on our on-farm research, leaving dryland stands of at least 65,000 plants/acre and irrigated stands of 90,000 plants/acre is likely a better choice than replanting.
We realize that there are some larger gaps in various rows in the field, and while we don’t like to see that, the gaps are disappearing as plants continue to grow and branch out. Keep in mind that a gap in one plant row will be compensated by plants in the adjacent flanking rows. They will form extra branches to take advantage of the sunlight, thus single-row gaps may not be as yield-reducing as you might think — especially in 15-inch row spacings.
We’re also seeing how resilient soybeans are. Some soybeans have been in the ground for two weeks and in many cases, are fairly healthy below the crust. Soybean seedlings emerge by pulling (not pushing) their cotyledons upward. The seedlings rely on the cotyledons as a reserve source of carbohydrate, protein, and lipid to support early seedling development until leaflets open for photosynthesis. When a seedling tries to pull its cotyledons through a crack in the crust, the crack may be too small and the cotyledons may be stripped off.
The plumule, which is the seedling stem tip and its undeveloped leaves above the cotyledonary node, may remain, but without the cotyledons to serve as a carbon and nitrogen source, development of new seedlings with small leaflets will be slow. These plants may not become competitive with surrounding plants in terms of pod and seed production. Therefore, when counting seedlings to determine plant stand after a soil crusting event, count only the seedlings that have at least one cotyledon. You can count seedlings missing cotyledons if they have large unifoliolate leaves that will soon unroll such as the picture on this page.
Recommendation: When deciding whether to replant your field, consider UNL research findings that showed a minimal yield difference between stands of 90,000 and 180,000 seeds/acre. We recommend leaving irrigated soybean plant stands of 90,000 or more and dryland plant stands of 65,000 or more. Uniformity of plant stands is also important, but “patch” planting may be used to deal with local areas of low plant stands.
For more information on reduced soybean planting rates, see the April 20, 2012 CropWatch story, Drop Soybean Seeding Rate and Save $10-$18 per Acre.