Mississippi County

Mississippi County Agronomy News

Wheat Harvest (PDF file)

As wheat harvest begins, one suggestion to ensure harvest efficiency is to check your machine frequently.  Things can change within the same field as well as from field to field.  A few simple ground counts will give some indication to combine performance.  In general, it takes 20 kernels of wheat per square foot to equal a bushel per acre when spread evenly across the field.  Remember counting behind the combine is total harvest losses (preharvest, header/threshing, and separating).  To pinpoint where adjustments need to be made a guide from Kansas State University suggests taking an average of three counts in three locations, in front (preharvest), under (header/threshing) and behind (separator) the combine. 

Header Loss (bu/A) = Preharvest count-Header count/20.  Because the 20 kernel number is based on an even distribution and separator spreaders generally concentrate grain in a smaller area than the header, the guide indicates that in order for kernel counts behind the separator to equal separator losses, kernel numbers per square foot will vary based on spreader type.  A bat type spreader  is 65,  straw chopper is 50, and chaff spreader is 25.  Therefore, Separator Loss = Separator count-Header count/65 or 50 or 25. 

On average under good harvesting conditions, machine harvest losses should be less than 5% of crop yield.   The guide also has a step by step diagnostic flow chart that could be beneficial.  The guide is available on the web at  http://www.oznet.ksu.edu/library/ageng2/MF2026.pdf or stop by the Extension Center for a copy. 

First and Second Generation Corn Borers

Monitor conventional corn fields for first and second generation Southwestern (SWCB) and European corn borers (ECB).  Check 10 plants in 10 spots in the field.  Look for small egg masses on upper leaves and whorls.  Southwestern corn borers are typically the dominant borer in Southeast Missouri.  SWCB eggs appear as a flat membrane on the leaf.  They develop in parallel rows of reddish-orange lines prior to hatching.  SWCB larvae are white with black spots and a brown head.  Larvae will feed on the plant for 11 to 14 days then begin to tunnel. 

First generation eggs are usually found on upper leaves.  Shot holes on larger leaves indicate larvae feeding and could indicate that larvae have already began to tunnel.   Check deep into the whorl to see if larvae are still present.  Once larvae enter the stalk, insecticide applications are no longer feasible.  Second generation which begins in late June—early July are usually found a node above or below the ear.  This generation is consider most damaging.    The most effective timing is at larvae hatching.  Economic threshold for SWCB is when 25% of the plants have egg mass or small larvae.

ECB eggs resemble fish scales are and usually found on the under side of top leaves near the midrib.  ECB larvae are tan with rows of light brown spots and black heads.  Economic thresholds for ECB are when 50% of the plants are infested.

Bean Leaf Beetles and Stink Bugs in Soybeans

With soybean emergence, monitor fields for bean leaf beetles.  Bean leaf beetle feeding is identifiable by the small round holes between major leaf veins.  The beetle’s coloration or markings may vary, but they all possess a black triangle at the base of their forewings.  Typically there are two generations in Missouri.  Economic thresholds vary according to growth stage.  During seedling stage, treatment is warranted when 5 or more bean leaf beetles and one damaged plant per foot of row is found.  Past seedling up to bloom 10 or more beetles per foot of row AND more than 30% defoliation is present.  Bloom to seed maturity 10 or more beetles per foot of row AND 20% defoliation OR 15 beetles per foot of row AND at least 10% pod damage.  Also, take into consideration the beneficial insect complex when making a decision.

Stink bugs are attracted to plants once they start to bloom.  Peak populations typically occur from August through September.  Both green and several species of brown stink bugs may feed on soybeans, and proper identification is important because control recommendations differ depending on which species is most common in the field.  Stink bugs feed primarily on pods and seeds.  Feeding punctures are identifiable by the presence of small brown or black spots.  This feeding damage reduces both seed quality (discolored, deformed) and quantity (aborted or shriveled seeds).  Before applying an insecticide take note of the percentage of parasitized eggs (darker than normal) and other stink bug predators present in the field.  Also determine the distribution of the stink bug infestations.  Are the stink bugs clumped along the border of the field or across the entire field?  Insecticide treatments are recommended once infestations reach two or more stink bugs (large nymphs and adults) per 3-row feet. 

Nematodes

Nematodes have been addressed in past issues of this newsletter and other extension publication.  However, nematodes need to be mentioned every once in a while because they will appear in crops that you least expect and some years injury is more pronounced due to environmental conditions.  This season we had an excellent March for planting corn.  Early planted corn followed by cool/cold weather with some moisture increases the potential for plant stress.  When a plant is stressed it is growing slow and is more susceptible to secondary problems such as seedling disease, herbicide injury and/or nematodes.

Recently I was informed of a corn field which tested positive for Stubby Root Nematode, not to be confused with Root Knot Nematode (RKN).  Corn is the most susceptible of our agronomic crops grown in SEMO to stubby root nematode.  However, like RKN, stubby will feed on vegetable crops and soybeans.   Stubby root nematode feeds at the growing points of roots causing short thickened roots, thus the name stubby root.  Unfortunately, stubby root has a wide host range so rotation is out and at this time there are no resistant corn varieties.  There are three options, two of which are not real practical options:  fallow, non-host crop of rye or tobacco, and the other option is nematicides at planting.  When using nematicides always check the label for herbicide interactions, which can cause injury.

Before making a insecticide decision you need to obtain a nematode sample to know where you stand.  To determine what nematodes are present in your field have a complete parasitic nematode test done.  If you have noticed in some fields that your soybean yields are decreasing, despite good management efforts, it could by time for a HG (Race) Test.  Check out our county agriculture website for details or stop by the extension office for more information.

WEBSITES OF INTEREST

Mississippi County Web:  http://outreach.missouri.edu/mississippi

UOE Farm Management: http://outreach.missouri.edu/seregion/fmmkt.htm

MO Dept. Conservation: http://www.conservation.state.mo.us/landown/wild/quail/

Southeast Ag Extension:  http://outreach.missouri.edu/seregion/ag/index.shtml

Delta Center Weed Control Page:   http://www.psu.missouri.edu/deltaweeds/

Ag Electronic Bulletin Board (AgEbb): http://agebb.missouri.edu

Crop Performance: http://agebb.missouri.edu/cropperf/vartest

MO Irrigation: http://agebb.missouri.edu/irrigate/  

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		University of Missouri Extension Mississippi County mississippico@missouri.edu Updated 05/24/04