NDSU Extension Service - Ramsey County

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June 18, 2012 Agriculture Column

Howdy!!!  The weather has certainly changed with many more showers than what we started the spring with.  The more humid conditions and of course wetter conditions has mad conditions more favorable for disease pressure in our cereal grains (in particular).  I have included information about soybean aphid and fungicide timing in cereal grains.

Soybean Aphids

Soybean aphids have been reported in extremely low numbers from a few locations in eastern North Dakota. The first report was from southwestern Barnes Co. on 31 May. This is the earliest soybean aphid occurrence that we’ve ever had in North Dakota. Soybean aphids were found by a crop consultant on 6 June in southern Grand Forks Co., and on 7 June I found a few soybean aphids in our trials near Mapleton in east-central Cass Co.

In addition to soybean aphids, several beneficial insects were observed. Green lacewing adults were present and laying eggs. Lady beetle adults and pupae were present, as were a few minute pirate bugs and one big-eyed bug. All of these beneficial species are voracious aphid predators. It is important to know that beneficial insects are also present in soybean right now and are controlling what few soybean aphids are out there. Each year we receive questions about tank-mixing an insecticide with glyphosate or other herbicide applications, particularly the last glyphosate application which usually goes on at about the R1 soybean growth stage. We DO NOT recommend this practice. Broad-spectrum insecticides will kill beneficial insects that are naturally keeping aphid populations in check. Aphids that reinvade such a field have the potential for extremely rapid population growth as there are no natural enemies to control them. Conserve beneficial insects – don’t spray until and unless you reach the economic threshold (ET). The ET for soybean aphids is 250 aphids per plant in 80% of the field.

best stage for applying fungicides for Scab Control in Wheat and Barley

For most regions of the state, conditions this year have been too dry for the development of Fusarium Head Blight (FHB or Scab) on wheat and barley. Most winter wheat is already beyond the most sensitive stage for FHB development. Spring wheat and barley, however, are now approaching this critical stage and the Fusarium Head Blight Risk Assessment map currently indicates some risk for FHB development in a few areas of northern North Dakota. As wetter and cooler weather moves into the state, it may be necessary to apply fungicides to protect wheat and barley crops that have not yet flowered. The effectiveness of fungicides to control FHB is partially dependent on the growth stage of the crop at the time of application.

Timing in wheat – The optimum time to apply recommended fungicides for FHB control in wheat (winter, spring and durum) is at early flowering. Applying fungicide at this stage helps to protect vulnerable florets from Fusarium damage during fertilization and early grain-filling.  The period between head emergence and flowering is usually about three days. Since not all spikes emerge at the same time, I recommend applying fungicides when most of the main stem and first tiller spikes have reached early flowering. Furthermore, experience has shown that it is better to apply fungicide too early rather than too late.

Timing in barley – Flowering in barley begins just before the spike emerges from the boot, so barley florets are not overly susceptible to scab infection. Scab infections do not generally impact yield in barley.  The scab fungus, however, is able to infect the glumes of barley and produce DON which impacts its market value, particularly if it is being sold for malt. The malting and brewing industry is sensitive to very low levels of DON. The optimum stage for applying fungicides to protect the glumes of barley from FHB infection is when the spike is fully emerged from the boot.  With barley the appearance of the first spikelet from the boot is a good indication that the best stage for spraying is only a few days away.  Joel Ransom Extension Agronomist for Cereal Crops

 

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