Palmer amaranth was first identified in Iowa in 2013. Currently, we know it is established in five Iowa counties, but we suspect it is more widespread than this (Fig. 1). This past weekend we were made aware of a new infestation of Palmer amaranth in Fremont County, distant from the initial infestation in this county. In addition, a suspicious looking Amaranthus species was found in Madison County – the owner is allowing a few plants to develop seedheads in order to make a positive identification.
Integrated Crop Management News
Links to these articles are strongly encouraged. Articles may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If articles are used in any other manner, permission from the author is required.
This spring consisted of wet field conditions for many regions across Iowa during planting season. When soil moisture is at or exceeds field capacity, there is an increased potential for soil compaction, particularly at topsoil depths. Soil compaction at planting time can impact root growth and development for the rest of the growing season, and can be a serious problem for Iowa farmers. However, with proper field management, compaction can be minimized.
Most herbicide applications have ceased for the year, but it is not too late to evaluate how well the program worked and what changes might be necessary for next year. Rather than just falling back on old habits, analyze your program closely to look for improvements for future years.
Surviving weeds from this year will affect weed pressure in next year’s crops. Identifying this season’s management successes and failures will make weed management and herbicide purchase decisions easier this winter.
A few places in southeastern Iowa and surrounding states have already reported heavy twospotted spider mite populations with prolonged feeding in soybean this year. I recommend scouting corn and soybean fields for mite infestations this year because they thrive in hot and dry conditions. The U.S. Drought Monitor estimates about 70% of Iowa is abnormally dry or in severe drought as of June 28, 2016.
Interest in monitoring and applying nitrogen (N) to corn at mid- to late-vegetative growth stages has gained interest in recent years due to wet spring conditions and equipment available to move through tall corn. Also, some farmers and crop advisers have been monitoring soil nitrate-N concentrations throughout the growing season. The question that has come up is what do soil nitrate-N concentrations mean when sampled at mid- to late-vegetative growth stages?
Weather conditions over the last three weeks were far from average (Fig. 1). Across our Forecasting and Assessment of Cropping sysTemS (FACTS) locations, precipitation was 48% below average, while heat stress (defined as maximum temperature above 86oF), growth degree days (GDD), and radiation were 53%, 25%, and 19% above the long-term average. However, our northeast Iowa was the exception; it received 7 inches of rain from June 5 to June 25, while all the other sites have received less than 1 inch of rain (Fig. 1).
An easy way to check soybean fields for soybean cyst nematode (SCN) is to dig roots and look for small, white, round SCN females. The first females of the season are now visible on roots in Iowa. Checking roots for SCN females also is a good way to check if SCN-resistant soybean cultivars are being effective.
Crops are growing rapidly and questions regarding expected end-of-season yields and soil water and nitrogen (N) status in the fields become very timely. A group of faculty, researchers, farm managers, and students from Iowa State University have developed a free, publicly available online platform (http://crops.extension.iastate.edu/facts/) to provide answers to these questions.
Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. In 2016, the average hatching date will be slightly behind normal and approximately the same time as in 2014 and 2015. Development is driven by soil temperature and measured by growing degree days. Research suggests about 50 percent of egg hatch occurs between 684-767 accumulated degree days (base 52°F, soil). Most areas in Iowa have reached peak corn rootworm egg hatch or will within a few days (Fig. 1).
Soil testing is a useful and commonly used diagnostic tool for making phosphorus (P) and potassium (K) fertilization decisions. Tissue testing has been suggested for decades as another tool for these and other nutrients. However, tissue testing has not been widely implemented for P or K in Iowa or the North Central region because of inconclusive results from limited field calibration research based on crop yield response. Iowa State University (ISU) has no P or K tissue test interpretations for any crop. Therefore, research was conducted to evaluate the value of tissue testing for P and K in soybean.