Bean harvest was rolling this week. Hearing non-irrigated beans in the area ranging from 40-60 bu/ac and irrigated beans going 70-90+. Regarding solar radiation and some wondering about smoke impact on drydown, I ran data from 9/1/20 though 9/26/20 for Harvard and York weather stations. Then looked at long term average for this same September time-frame from 1996-2020. Both stations showed slightly higher solar radiation in 2020 compared to the long-term average for September (York: 379 and 372 langleys respectively) (Harvard: 383 and 376 langleys respectively). And, it was higher yet for 2020 when I queried Sept. 10-26 for same time periods. So, unsure solar radiation was the factor impacting drydown for this part of the State?
Small Grains and Weed Control: Been watching weed control particularly in soybean fields. For future columns/winter programs, I’d like to hear from you. What weed control approaches have worked in your soybean and corn fields? I’m curious about all systems and all types of weed control options. Please share at email@example.com or give me a call at the Extension Office. Thanks!
In the past, I’ve shared weed control begins at harvest by not combining patches of weeds or endrows full of weeds. I realize that’s difficult to do, and for many fields, we’re past this point. From a system’s perspective, another option to aid weed control is to plant a small grain such as wheat, rye or triticale this fall. We had a whole edition of CropWatch devoted to wheat production here: https://cropwatch.unl.edu/2020/september-4-2020. 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 but produces the latest into late May/early June. All keep the ground covered from light interception penetrating the soil surface which allows weed seeds to germinate. While I’ve observed this in farmers’ fields, there’s also recent research from K-State that supports the impact of a small grain in rotation for weed control.
One study 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 or with residual herbicides of flumioxazin + pyroxasulfone (Fierce). Ten weeks post-termination, palmer amaranth biomass was 98% less in winter wheat and 91% less in spring oat compared to no cover crop.
Another study in Manhattan from 2015-2016 compared fall-seeded rye; a residual tank-mix of glyphosate, dicamba, chlorimuron-ethyl, tribenuron-methyl, and AMS; and no fall application. Four spring treatments included no spring application or three herbicide tank mixes: glyphosate, dicamba, and AMS alone or with flumioxazin + pyroxasulfone (Fierce) as early preplant, or as split applied with 2/3 preplant and 1/3 at soybean planting. They found the fall rye completely suppressed marestail while fall herbicide suppressed biomass by 93% and density by 86% compared to no fall application. They also found rye to reduce total weed biomass (including palmer amaranth) by 97% or more across all spring applications. In both studies, soybean yields were best with the combination of cover crop + herbicides or the combination of fall + spring herbicides compared to no cover and no herbicides.
The way I think about this for conventional systems is that the use of a small grain in the system reduces the pressure on the chemicals for having to provide all the control. It also buys some time for chemical control, perhaps even removing one application (based on these studies, small grain delayed at least a month till 50% palmer germination). Economically, while there’s the expense of seeding and purchasing the small grain seed, what are the other economics to consider? What could the small grain provide by reducing an additional chemical application, adding a forage crop after harvest, selling seed (if there’s a market), selling straw (depending on location for moisture savings & ability to get a cover back in for weed control), etc.? Just some considerations this fall looking at weed control by adding a small grain.
Crop Update: So grateful for this past week’s weather in aiding harvest progress! Also grateful to all the growers who worked with me in on-farm research this year and for all the studies harvested this past week!
One of the more frequent questions/comments I’ve received the past few weeks is regarding yields. It sounds like irrigated yields for corn and even soybean are around 5-15% lower than what farmers hoped for in this part of the State. Most aren’t necessarily ‘bad’ yields, just not what was desired. Irrigated corn is mostly going 225-245 bu/ac with high-yielding genetics and everything else aligned correctly going 250-265 bu/ac. And, as more fields are harvested, there may be some better yields due to the long grain fill period. There’s irrigated fields of soybeans that did 50-60 bu/ac. What is positive is non-irrigated yields for both corn and soybeans with non-irrigated beans sometimes out-yielding the irrigated ones.
The impacts of the difficult cold, wet planting season could be seen season-long in fields
with uneven plant emergence and eventually variable ear height and kernels/ear. That plant to plant variability can add up to yield impacts more than one realizes. There’s also field variability due to ponding/flooding in fields, hail/wind damage, and additional challenges during harvest with wind and moisture leading to lodging and/or ear loss and some soybean shatter.
The high humidity and leaf wetness along with cool, wet weather allowed for more disease in both corn and soybean. Perhaps one reason why non-irrigated corn and soybean are yielding well was due to reduced disease pressure from reduced plant population and increased air flow. I know of a handful of irrigated soybean fields in 2019 planted on seed corn acres where, to the line, the soybean on seed corn had more sudden death syndrome (SDS) pressure and less yield than the soybean on soybean corners of fields. I had never before seen this so striking.
My hypotheses: 1-Test for soybean cyst nematode in the seed corn acres vs. corners. Anything that will move soil will move SCN, including equipment. 2-Fusarium virguliforme (pathogen that causes SDS), reproduces best on corn kernels followed by corn residue, followed by soybean seeds and residue. Even if the seed corn acres had a cover crop and were grazed, cattle don’t easily pick up loose kernels lost to the 2018 hail storm or harvest loss. 3-SCN in the field + great conditions for SDS in 2019 allowed for synergistic effect of more SDS and yield loss.
Cloudy weather also played a role in photosynthesis and ultimately yield. Dr. Roger Elmore and colleagues shared the following research on shading and yield impacts. “Many researchers have investigated the effects of lower solar radiation on corn using shade cloth of different densities. These can effectively block solar radiation by 10% to 90% or more (e.g., Schmidt and Colville 1967, and Reed et al. 1988). Invariably they found that shading the crop two to three weeks after silking (R1) reduced yields more than shading before R1. Most also find that hybrids differ in their responses to shading.” (This can help explain the tip back due to kernel abortion some of you asked me about after pollination). “Very few researchers used shade cloth during the grain-fill period, which would be similar to the reduced solar radiation period central Nebraska experienced the third week of August.
Early et al., 1967, shaded plants around the “reproductive phase” for 21 days as well as during the “vegetative stage” for 54 days and the “maturation phases” for 63 days. Shading during reproductive stages reduced plant yields the most, but 30% shading during the maturation stages ― what we consider the seed set and grain-fill periods (R2-R6) ― not only reduced yield per plant 25% to 30% but also reduced kernels per plant and the amount of protein per plant. Researchers in a new study shaded plants from silking to maturity (R1-R6) (Yang et al., 2019). Shading reduced yields more with higher plant populations than with lower populations.” (This may also help explain why non-irrigated fields with lower plant populations may have good yields in spite of cloudy conditions in 2019).