SW MN IPM STUFF 2017 Issue 15

8/22/2017

This newsletter is also available in a print-friendly pdf format: SW MN IPM STUFF 2017-15

This newsletter and the advice herein are free. You usually get what you pay for.

Crop weather

Rainfall, air and soil temperatures, degree-days, soil moistures, and other current and historical weather data for the University of Minnesota Southwest Research and Outreach Center (SWROC), a little spot about two miles west of Lamberton, MN, can be found at http://swroc.cfans.umn.edu/weather.

Hail and wind damage to reproductive stage corn and soybeans can lead to poor seed fill and diseased seeds. Saturated soils can cause yield reductions if they persist. Unfortunately, there has been too much of these uncooperative weather events over the past week.

Bacterial leaf streak of corn sample request reminder

Bacterial Leaf Streak

Bacteria Leaf Streat - Waseca, County

If you observe this disease you can help us try to understand the distribution and factors influencing the disease in Minnesota. Dean Malvick's lab will confirm the presence of bacterial streak at no charge. At this point the reports have all been from south central Minnesota. It is important to understand where this disease occurs in Minnesota and how it compares to isolates from other states. U of M Plant Disease Clinic sample submission instructions and forms can downloaded and used to submit samples.

Submit suspected bacterial leaf streak samples to:
Dean Malvick
495 Borlaug Hall
1991 Upper Buford Circle
St. Paul, MN 55108
dmalvick@umn.edu
(612) 625-5282

Including the following information on the form will be helpful in understanding the range of symptom expression and epidemiology of this disease. Hybrid information will be helpful in understanding if there is a genetic component to infection. The location information will be used to help generate maps but field specific information will not be published.

  • Location
  • County & GPS Coordinates
  • Disease information
  • Hybrid(s) affected (if known)
  • Describe incidence (% of plants with symptoms/field wide or localized)
  • Describe severity of symptoms (percent of corn leaf area affected/individual leaves or most of the plant)
  • Any weather events that may have infected disease (hail, high wind, flooding)

Soybean

Top Dieback
Pod and Stem Blight

Things got a bit too wet in some areas and one of the results was a sudden appearance of yellow soybeans. There are several factors leading to yellowing on the upper plant. IDC prone soils have caused issues this year on some varieties. Waterlogged soils and oxygen-starved roots can reduce nutrient uptake issues for other nutrients as well. Do the symptoms match deficiency of iron, nitrogen, sulfur, or potassium?

In addition to low soil fertility levels, yellowing and Potassium deficiency-like symptoms of the upper leaves can be associated withsoybean cyst nematode (SCN), clover root mealybug or soybean aphid. Diaporthae/Phomopsis fungi can cause yellowing and death of upper leaf margins. Pod and stem blight can cause the death of upper vegetative growth as well as cause symptoms on pods and seed. This disease can also be associated with SCN infestations.

Multiple factors can be involved. Do not rule out SCN as a possible cause when yellow beans appear.

Soybean aphid watch 2017

Soybean aphids are still present and reaching economic threshold levels in new areas. Yes, it is late in the season and many are reluctant to add another crop input expense. However, if your soybeans have not yet reached full seed (less than the R6 stage) and have 1000s of aphids/plant, I would not advise waiting for entomopathogenic fungi or other bio-controls to catch up.

We recommend using the 250 aphid/plant threshold through the R5 stage. While less common, significant and economic yield losses from very large, late developing, soybean aphid populations can still occur during R6. Giving up on an increasing aphid population during R5 can lead to unpleasant surprises in R6. Pre-harvest intervals (PHI) are now an increasingly important factor in insecticide decisions.

Happy trails,

Bruce