Tuesday, August 26, 2014

Soybeans - Aphids, White Mold, and Weeds

August 26, 2014 - Much needed rain was received across the area this past week.  Crop conditions in SE MN are quite variable, from very good to so-so.  Here is what we are seeing. 1) Soybean aphids - Populations have continued to increase in SOME fields, thus still a problem that needs to be dealt with.  However, not all field have required treatment.  As we scouted across the area, populations remained low in some fields, where others exploded and needed to be sprayed.  Scouting should continue until soybeans reach R6.5 (seeds fill the pods and pods and leaves begin to turn yellow).   2) White Mold - This disease, unfortunately, is showing up in soybean fields that received more seasonal rain, have lush foliage, and were wet in June.  When you combine this with our cooler than normal summer, white mold becomes a problem.  3) Weed Escapes - Soybean fields that seemed clean early, don't look as clean any more.  Waterhemp, common lambsquarters and giant ragweed has been popping through the canopy in quite a few fields.  There's nothing that can be done now, BUT you can map those areas, confirm which weeds are out there (hard to tell at 60 mph) and start planning your weed control program for next year.   Lisa M. Behnken
White Mold girdling the stem in Soybean - 8/26/14

Leaf symptoms of white mold in soybean- 8/26/14

Wednesday, August 13, 2014

Soybean Aphid Update - August 11 & 12, 2014

Here are the results from the speed scouting fields around Olmsted County. We have been  scouting these fields over the past 3 weeks. The Speed Scouting Process - collect 30 plants throughout the field.  Count aphids on 11 plants, noting (+) if over 40 aphids/plant and (-) if less than 40 aphids/plant.  If  6 or less plants have over 40 aphids/plant, stop and then re-sample field in 7-10 days.  If you reach 7-10 plants with over 40 aphids/plant, continue counting aphids on 5 more plants, repeating the steps based on the number of plants with over 40 aphids/plant until you have counted all 30 plants.  The results will be a) Do Not Treat - re-sample in 7 -10 days, b) Re-sample field in 3-4 days or c) Confirm TREAT Decision by re-sampling in 3-4 days, then apply insecticide when confirmed.  

We will also make general observations in the field as we scout, population increasing, population exploding, presence of beneficial insects etc. As you can see, the population is increasing, and 3 Fields moved into the Confirm and Treat category. We will continue to scout these fields.  Lisa

Results August 11 & 12, 2014 in Olmsted County

Field 1 = 0 of 11 plants with over 40 aphids/plant = Re-sample in 7-10 days

Field 2 = 6 of 11 plants with over 40 aphids/plant = Re-sample in 7-10 days

Field 3 = 4 of 11 plants with over 40 aphids/plant = Re-sample in 7-10 days

Field 4 = 23 plants with over 40 aphids/plant = Stop Sampling, re-sample in 3-4 days

Field 5 = 27 plants with over 40 aphids/plant (population exploding) = Confirm TREAT in 3-4 days and then apply insecticide

Field 6 = 25 plants with over 40 aphids/plant = Re-sample in 3-4 days

Field 7 = 30 plants with over 40 aphids/plant, population exploding (since last week) = Confirm and TREAT
Field 8 = 30 plants with over 40 aphids/plant, population increasing, not exploding = Re-sample in 3-4 days and Confirm TREAT Decision

Field 9 = 4 plants with over 40 aphids/plant = Re-sample in 7-10 days

Field 10 = 8 plants with 40 or more aphids/plant = Re-sample in 7-10 days

Monday, August 11, 2014

Monday, August 11 Update

Monday, August 11, 2014   Scouting fields around the area today and observed several things. 1. We need rain. 2. Soybean aphid numbers are on the rise. Some fields reaching treatable levels. I will post the speed scouting results tomorrow. 3. Spider mites are present in fields. 4. Japanese beetles are present in some fields. 
Japanese beetle feeding in research plots near Rochester, MN. The treatment threshold in soybean is based on percent leaf defoliation.  Treatment should be considered at 20% leaf defoliation from bloom to pod fill. 


Friday, August 8, 2014

Keep Scouting for soybean aphids

Update on Soybean Aphid numbers around Rochester - Keep Scouting

August 8, 2014
Lisa M. Behnken

We have been scouting several soybean fields in the area for aphids over the past three weeks.  The soybean aphid numbers have been very low, most plants have very few aphids per plant, with only one or two plants at over 40 aphids/plant (counted as a positive plant using the Speed Scouting method).  This is well below the economic threshold of 250 aphids per plant, 80% of plants with aphids and population increasing. 

The only "hot spot" we have is in our plot area at Rochester.  This location is the first place we found soybean aphids this year (always is) and the population has been increasing.  These are droughty soils, and there is plenty of buckthorn nearby to provide a source of aphids for early colonization.  Having said this, the population has not reached the economic threshold yet.  We will continue to scout these fields for a few more weeks, targeting Monday and Tuesday and will keep you posted.

We use the speed scouting method to collect and evaluate the aphid population.  We collect 30 plants randomly (as recommended) across the field and evaluate them in the lab so we can do additional counting if necessary.  This method is still an approved and effective method of scouting for soybean aphids. Worksheets are available at:                     http://goo.gl/UC9vus.

See updated information about soybean aphids from UM Extension Entomologist, Bob Koch and IPM Specialist, Bruce Potter at        http://www.extension.umn.edu/agriculture/soybean/pest/docs/soybean-aphid-scouting.pdf

Note: If seed treatments that included insecticides were used in your fields, aphid populations will be "reduced" for awhile. Our field research has shown about a 2-week delay in aphid population establishment when seed treatments with insecticides were used at planting.  So, keep scouting. 
Soybean aphids found in our Rochester plots.  This is the only location (of those we are scouting) with aphid numbers approaching, but NOT at, the economic threshold level.