ISSUE 9   July 10, 2008

SUNFLOWER RESPONDING TO IRRIGATION

In North Dakota sunflower is commonly grown as a dryland crop. University research and farmer experience has shown that sunflower will respond positively to irrigation with yield increases over dryland yields common on droughty soils and in dry years. Sunflower can be grown on a wide range of soils and under different climatic conditions. Low sunflower yields may be caused by any of the following or their interaction: incorrect plant population, poor soil fertility, excess moisture, drought conditions, insufficient weed control, diseases, insect damage, bird depredation, plant lodging, late planting and harvesting losses. It is important to manage all the factors listed and if possible, supply irrigation water to the crop if needed.


Figure 1. Average yields of 26 sunflower hybrids
during the dry growing season and average yield
of 31 hybrids in a season with above average rainfall.

Figure 1 indicates that there was a very large yield response to irrigation during a dry growing season, however during the season with above average rain the yields between irrigated and dryland sunflower were similar. White mold in the irrigated sunflower reduced the yield potential during the wetter year. Under irrigation some lodging was observed especially in the taller varieties. Sunflower plants were leaning because the heavy heads pulled the plants over as the roots were not able to anchor the plant in the wet soil. Some neck breakage occurred in the irrigated trials but few heads were completely lost. The recommended plant population for irrigated sunflower in our region is 24,000 to 28,000 plants per acre planted in 30 inch rows.

Water utilization by sunflower depends on the sunflower hybrid, date of planting, timing of irrigation, soil types, soil fertility and plant populations. Optimum utilization of water occurs if N, P and K levels are sufficient for high yields.

Water deficiency between flowering and maturity negatively impacts yield more than at other times in the development of the plant. Irrigation management becomes much more critical from early flowering until maturity. Irrigation should maintain soil moisture at 80% of field capacity at flowering stages and at 70% of field capacity at other times. The exact timing and number of irrigations depend on rainfall distribution and stored soil moisture. Typical of all high value irrigated crops, monitoring of the crop and top level management practices are vital in order to obtain high economic returns.

Resources:

A site-specific irrigation scheduler can be accessed on the NDAWN Web site http://ndawn.ndsu.nodak.edu/  To use the irrigation scheduler, you need to log in to the NDAWN Web site and create a user name and password.

Information about irrigation can be found at the following NDSU web site: http://www.ag.ndsu.nodak.edu/abeng/irrigation.htm#irrigationwatermanagement

Crop water use tables can be created for different crops and locations: http://ndawn.ndsu.nodak.edu/crop-water-use-table-form.html  

Soil, Water and Plant Characteristics Important to Irrigation: http://www.ag.ndsu.edu/pubs/ageng/irrigate/eb66w.htm  

Hans Kandel
Extension Agronomist - Broadleaf Crops
hans.kandel@ndsu.edu

 

USING GLYPHOSATE AND OTHER HERBICIDES PRE-HARVEST IN SMALL-GRAINS

With winter wheat in the middle of grain-filling and other small grains not that far behind, it is now time to think about harvesting. If green weeds in the crop will hinder the harvesting process there are several herbicides labeled for pre-harvest weed control (refer to the 2008 Weed Control Guide and the labels of approved products for additional details). Weed control with pre-harvest herbicides, however, is generally disappointing as weeds at this time are tall, nearing maturity and slow growing. Furthermore, green weeds can take a week or more to dry down even with an effective treatment.

Glyphosate, in addition to controlling weeds, is labeled for use in aiding the dry down of the crop itself (as opposed to controlling and drying down weeds in the crop). Glyphosate is a systemic herbicide and takes from 7 to 10 days to effectively kill the growing parts of the crop, consequently an increased rate in dry down is not immediately visible. Traditionally, fields that had excessive green material were swathed. Swathing enables faster dry down than pre-harvest glyphosate if significant levels of green material are present in the crop. A standing crop that has been treated with glyphosate, however, will dry faster than a swathed field after a rain.

When using glyphosate pre-harvest observe the following guidelines:

  • Apply glyphosate only after the crop has reached physiological maturity. For most varieties this occurs at a grain moisture content of about 30%. At this moisture content the grain is in the hard dough stage; if you run your thumb nail across the kernel, the indentation will remain. Applying glyphosate before physiological maturity can reduce yield, test weight and seed germination.
  • Because germination can be affected when applied too early, glyphosate should not be used in fields that will be used for seed or on barley intended for malt.
  • Pre-harvest applications of glyphosate must be made at least 7 days before harvest.
  • As with all agricultural chemicals, read and follow the label when using herbicides pre-harvest in small grains.

    Joel Ransom
    NDSU Extension Agronomist - Cereal Crops
    joel.ransom@ndsu.edu


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