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Extension > Minnesota Crop News > July 2009

Friday, July 24, 2009

New spider mite fact sheet

By Ken Ostlie and Bruce Potter

Reports of spider mite infestations continue from both soybean and corn, particularly from areas with prolonged drought.  Even if you've received rain recently, check for mite activity along field edges to determine if you've got a building problem.  You may need to factor spider mites into a soybean aphid spray decision.

The article is available on the web at: http://www.extension.umn.edu/agriculture/soybean/pest/managing-two-spotted-spider-mites-on-soybeans/.

Well so much for the relatively arthropod pest- free growing season.



Tuesday, July 14, 2009

A Comparison Of Aphid and Disease Management Practices in Soybeans

by Dr. Ian MacRae, U of MN Extension Entomologist

There has been increasing pressure to apply insecticide and tank mixed pesticides at lower thresholds based on claims of increased yield benefits. While increased commodity prices can stimulate the desire to decrease risk tolerance and increase the use of pesticides, this is not always a paying proposition.

The current treatment treatment threshold for soybean aphids (250/plant when most plants have aphids) has been adopted and is recommended by the Extension services of all of the soybean producing states in the North Central region. It is the result of many site-years of data collected from field plots mirroring commercial; production. It incorporates data from a variety of geographic locations, climate conditions, commodity prices and management costs. Most importantly, at the treatment threshold, NO economic injury is yet occurring!

Time to Scout Soybean Aphids - They've Finally Arrived in the North

by Dr. Ian MacRae, U of MN Extension Entomologist

soybean aphid.jpg
Low populations of Soybean Aphid (SBA) have been reported throughout NW MN and NE ND. Populations are still low and generally not on more than 30% of the plants. The cooler weather will slow reproduction for a few days but it is predicted to warm up by the weekend, at which time we'll start to see some more population growth and dispersal across fields. Although most fields are well below treatment levels so far, it is time to start scouting the soybean fields, getting a handle on what populations you may have and tracking progress and population growth.

2009 Soybean Cyst Nematode Survey in the Red River Valley

by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist

In 1954, the first detection of the soybean cyst nematode (SCN) occurred in North Carolina. Since that time, the nematode has become the most important disease issue of soybean in the world. Spread with soil, this microscopic roundworm continues to gain ground in Minnesota soybean-producing areas. Essentially anything that can move small particles of soil will also transport this nematode.

Final Words of Caution on Wheat Midge

by Phillip Glogoza, Extension Educator - Crops

A lot of wheat is now heading in NW Minnesota. In the northern most counties, degree day accumulations are just reaching the 1300 DD mark (see map), the point where 10% of female midge have emerged. Emergence will continue through 1600+ DD (90% female emergence).

Now is an important time to do some evening scouting and become aware of any activity in your fields. Find out now . . . Not at harvest time!

Thursday, July 9, 2009

Sunflower Rust is Widespread but Developing Slowly

by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist

Early lifecycle stage structures (pycnia) of sunflower rust were detected on volunteer sunflowers during early-June in Minnesota and North Dakota (Figure 1). These detections created concern because that meant:
  • The fungus was only two spore stages away from producing the spores responsible for epidemics (pycnia → aeciospores → urediospores);
  • it was much too early in the growing season to see rust developing; and
  • the fungus had overwintered in our agroecosystem in its sexual stage. A possible outcome of winter survival is the potential for genetic recombination by the pathogen where more virulence might occur on sunflower varieties grown here.

Understanding the Risk for a Fusarium Head Blight Epidemic in Wheat

by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist

Crop growth stages of spring wheat are rapidly approaching early flower in some locations. This is the time of year that managers must make a decision to apply a fungicide application targeted for Fusarium head blight (FHB) management.

Wednesday, July 1, 2009

Weed Control in Roundup Ready Sugarbeet

by Dr. Jeff Stachler, Sugar beet Weed Scientist
U of MN Extension / NDSU Extension

For those growers unable to apply glyphosate to Roundup Ready sugarbeet for the first time due to wet soil conditions, apply the maximum rate of glyphosate allowed. The maximum glyphosate rate for Roundup Ready sugarbeet is 1.125 pounds acid equivalent per acre (lbs ae/A). This equates to 32 fluid ounces per acre (fl oz/A) of Roundup-branded products, 48 fl oz/A of 3.0 pounds acid equivalent per gallon (lbs ae/gal) products, and 39 fl oz/A of 3.7 lbs ae/gal products. This glyphosate rate can only be applied up to the eight-leaf stage of sugarbeet. This rate should be applied to any field with weeds greater than two to three inches in height or with difficult to control species such as wild buckwheat, lambsquarters, and common and giant ragweed.

Watch for Midge as Wheat Approaches Heading Stage

by Phillip Glogoza, Extension Educator - Crops

wheat_midge_risk.jpg
There could be about 70% of the region's wheat acres at the heading stage when wheat midge are emerging, based on those acres being planted in the high risk window (Figure 1). Heading is the growth stage when wheat is attractive to female midge for egg laying, and the time the plant is most susceptible to injury from midge larval feeding. Though midge populations have been small in recent years, this will be the most wheat acres we have had that are susceptible to midge in many years.

Based on degree day accumulations, wheat midge should be emerging in the southern counties of the spring and durum wheat region (Figure 2). The oldest wheat fields have begun heading. Midge should begin emerging in the central areas over the weekend, and by the middle of next week in the northern areas.

Aphids in Small Grains - June 29, 2009

by Dr. Ian MacRae, U of MN Extension Entomologist

There have been some reports of bird cherry-oat aphids (Figure 1 and Figure 2) in small grains in NW and WC MN over the last week. The populations I've seen are at very low numbers. Add to this, the recent rainy weekend will likely have had a significant impact on those aphid populations, but it's still a good idea to scout for aphids in small grains. The most damaging aphid populations are ones that reach threshold around flag leaf stage, if populations are at or near threshold at this time, delaying treatment until heading may cost you yield.

Bacterial leaf stripe of wheat: Something to keep in mind

by Dr. Charla Hollingsworth, U of MN Extension Plant Pathologist

Bacterial leaf stripe is a disease that can usually be found on wheat in the Red River Valley (RRV) later as crop growth stages progress. The disease (caused by a Xanthomonas sp.) can develop and become severe rapidly after the crop reaches the heading growth stage. Bacterial leaf stripe (BLS) can cause significant yield losses on some varieties. Like other disease issues, development is dependent on weather conditions and the presence of susceptible plant hosts. Epidemics of BLS occurred in the RRV during 2005 and again in 2008.
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