Ramsey County Ag Column

By Bill Hodous

May 18, 2009

Howdy!!!!

Well it is time to get rolling with the Ag Alert again.  This year will be a bit different as I will send out the ag alert to elevators and one mall.  This is not to eliminate anyone but hopefully make the ag alert more accessible to everyone.  I know what you’re thinking, how is that going to make the ag alert more user friendly to everyone, well I am going to publish the ag alert in the Edmore Herald and Devils Lake Journal.  This will reduce the cost to anyone asking for this information.  I will however have it available, through the use of email, if you are interested.  You will need to contact our office with that information at 701-662-7027.  A few of you have already done so.  NDawn readings as of this morning were bare soil at 51 degrees and turf soil at 42 degrees.  The highly saturated soils will keep the temperatures lower than normal.  It does however look like we will be in the field full force this week!!!!!  Hurrah, Hurrah.

ROW-CROP STARTER PLACEMENT

     A 2 inch to the side and 2 inch down from the seed placement (2 by 2; or 2 X 2) in no way inhibits seed germination as does a seed-placed application. The maximum limits on fertilizer applied at planting recommended in our row-crop fertility circulars refers to seed-placed application and not any application (except for anhydrous ammonia) with at least 2 inches separation between the seed and the fertilizer. For a 2 X 2 application, any rate of N plus any other nutrient to at least the limit of our recommendation charts is acceptable if using liquid or dry non-anhydrous ammonia products.

For corn, we suggest that when rates of N exceed 50 lb/a in the 2 X 2 band, a separate small P application be made with the seed for a "starter" effect. Since sunflowers and dry beans exhibit no "starter" P response, this extra application is not necessary for those crops.

ARE SEED-APPLIED INSECTICIDES NECESSARY FOR CONTROL OF SOYBEAN APHID?

     Many area soybean producers are wondering if the adoption of an insecticide seed treatment will offer control of soybean aphid and whether this associated input cost is economically justifiable when a foliar insecticide application may also be needed. Extension Entomologists have been evaluating this issue. In 2008, NDSU Extension Entomology evaluated the following treatments at

Johnson, MN for control of soybean aphid in a large strip trial: 

1.   Untreated check

2.   Insecticide seed treatment alone (Cruiser MAXX at 3 fl oz/cwt)

3.   Foliar insecticide alone (Warrior II  wt 1.28 fl oz/acre)applied at the economic threshold (ET) of 250 aphids/plant in 80% of the field

4.   Combination of seed treatment plus foliar application at ET.

Soybean aphids reached ET during the first week of August, and Warrior II insecticide was applied on 7 Aug by a commercial applicator. Soybean was at R3 to R4 growth stage.

     In 2008, aphid invasion occurred in late July and the population built up very rapidly. For pre-spray aphid counts on August 7, there were no significant differences in aphid densities among treatments

Treatment means indicated that aphid populations were at or just above ET. For aphid densities at seven days after application (14 Aug) and at 14 days after application (20 Aug), foliar sprayed treatments had significantly lower densities than the seed treatment alone or the untreated check. Treatment means on these dates indicated that aphids were well above ET for the untreated check and for the seed treatment alone, while mean aphid counts on the foliar treatment and seed treatment plus foliar were considerably below ET. For yield, the foliar treatment and the seed treatment plus foliar had significantly higher yields than the untreated check and the seed treatment alone. There was no significant difference in yield between the untreated check and seed treatment alone, or between the foliar spray treatment and the seed treatment plus foliar spray (Figure 2). These data indicate that there was no advantage in using an insecticide seed treatment to control soybean aphids when aphids invade the soybean field late in the season. 

     In 2008, Dr. Ian MacRae of the University of Minnesota evaluated foliar insecticides, foliar insecticides + fungicides, foliar fungicides, insecticide seed treatments, and insecticide seed treatments + foliar insecticide + foliar fungicide combinations for control of soybean aphid in Lamberton, Minnesota. Treatments included:

     1.   Untreated check

     2.   Cruiser MAXX seed treatment

     3.   Warrior II applied at V3

     4.   Headline applied at R3

     5.   Warrior II applied at R3

     6.   Warrior II & Headline applied at R3

     7.   Cruiser MAXX & Headline applied at AP (at plant) & R3

     8.   Cruiser MAXX, Warrior II & Headline applied at AP & R3

     9.   Cruiser MAXX & Warrior II applied at AP & R3

     10.  IPM (ET) Threshold

The R3 treatments were applied 29 July and the ET treatment was applied on 2 Aug. Warrior II was applied at the rate of 1.6 fl oz/acre and Headline was applied at the rate of 6 fl oz/acre. Treatments that kept soybean aphid population below ET and provided the highest yield included all of the foliar-applied insecticides at R3 (Treatments 5, 6, 8 and 9) and at ET (Treatment 10). Dr. MacRae looked at the economics of an intensive management approach costing $30-35/acre (insecticide seed treatment at $10-12/acre, foliar fungicide at $14/acre, and foliar insecticide at $10/acre) versus an

IPM approach (treating at ET) costing $16/acre (scouting costs at $6/acre, foliar insecticide at $10/acre). The difference between the intensive and IPM treatments was at least $15/acre. If the average soybean producer in northwestern MN produces 550 acres of soybean, each producer would save approximately $8,250 if using the IPM approach over the intensive management approach!

     These data indicate that a well-timed foliar insecticide applied at ET was the best pest management strategy to optimize control of soybean aphid and prevent unnecessary repeated insecticide  applications. The foliar insecticide applied at ET generally had higher yield and was the most economical treatment. Seed treatments may have some early-season control of aphid infestation only when infestation occurs early in the season (June). However, peak soybean aphid infestations typically occur later in the year (late July or early August) in North

Dakota and northwestern Minnesota.  Remember, insecticide seed treatments are effective in controlling other early season pests of soybeans, such as wireworms, seed corn maggots and overwintering bean leaf beetles.

Janet Knodel, Extension Entomologist              

524 4th Ave #5, 2nd Floor Ramsey County Courthouse
Devils Lake  ND  58301
701-662-7027
email - NDSU.Ramsey.Extension@ndsu.edu