Marestail (Conyza canadensis) is one of the most difficult weeds to manage in no-till soybean. While classified as a winter annual, the plant has significant emergence in both late summer/early fall and in the spring. This extended emergence period greatly complicates management since the success of postemergence products is closely tied to plant size. Attempting to control populations at the time of planting often results in control failures as fall-emerged plants are too large for acceptable control.
Integrated Crop Management News
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Corn harvest is fast approaching. This year’s corn maturity is about 5-10 days behind normal. With field dry down occurring in late September and October this year, there is the potential for a later harvest of corn at a higher moisture content. The rule of thumb has been that corn dries at a rate of 0.5 to 1.0% per day in September, 0.25 to 0.5% per day in October, and almost no drying occurring in November. Of course, these rules of thumb can change with favorable or unfavorable weather conditions.
Soybean are nearing maturity across Iowa with minimal delay due to cool temperatures compared to 2016. However, soybean sensitivity to day length speeds up crop development towards physiological maturity. During senescence carbohydrates are converted into oils. Soybean seed moisture changes very little, remaining near 60 percent during the de-greening period. As the pods turn to mature color at the beginning of maturity stage (R7), seed dry matter accumulation is complete and seed moisture rapidly decreases.
The dry conditions in some areas of Iowa in 2017 have raised several soil fertility questions. In some cases, there has been relatively normal crop production and no need for management changes. In other situations with severely damaged crops, there is potential for adjustments for the 2018 corn crop.
With some farmers gaining interest in using cover crops, there are questions about possible pests that may develop when introducing new plants on the farm. Consider these insect-related issues when planting crops in the fall. Hessian fly (Photo 1) is a potentially destructive pest in winter wheat; however, cultural control can minimize the potential damage and economic loss.
Although generally good, corn and soybean crops are quite variable across Iowa as harvest season approaches. Spotty rainfall, in many cases too little but in a few cases too much, along with sandy or clay soil spots, and temperature extremes or storms have resulted in varying ear, and bean pod and stalk sizes, both among nearby fields and in some cases within fields or even individual rows. Such variations put a premium on combine adjustment this fall.
Drought conditions during most of the growing season in Iowa can have a profound impact on soil heath, just as when we have extreme wet conditions. The effect of drought can be noticed very clearly on crop performance when the lack of water availability is severe. This water stress can affect soil chemical, physical, and biological activities that are essential for plant and soil health.
It’s that time of year when corn yield estimations increase. The USDA NASS objective yield survey came out on August 17. This report indicates the third highest yield on record (behind 2016 and 2015) at 188 bushels per acre. Moderate to severe drought conditions are undoubtedly the cause for the reduced yields in Iowa this year. It should be expected that there will be large variation in yield within fields but also from one field to the next depending on hybrid selection, date of planting, and field uniformity.
Dry conditions this summer in some parts of Iowa will result in low and variable crop yield. Low or variable crop growth and yield significantly affect phosphorus (P) and potassium (K) uptake and removal with harvest. If dry conditions continue into the fall soil sampling season soil-test P, K, and pH results also may be affected complicating test interpretations.