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Continue To Scout Emerged Corn, Soybeans

Continue To Scout Emerged Corn, Soybeans

Keep an eye on young corn stands for signs of insects, weed issues and other problems. Likewise for emerged soybeans. If you're still planting or replanting beans at this late date, stick with a full season variety.

It's the second week of June and corn is up and growing. But you should still continue to scout emerged corn stands, says Brian Lang, an Iowa State University Extension field agronomist at Decorah in northeast Iowa. Check your corn stands for:

1)  Population, seed depth and plant spacing.  Did you get what you intended with your planter settings?

2)  Early-season weed issues.  Pre-emerge herbicide program working?  Weed escapes?  Know the weeds of importance for your post-emergence program.

3)  Insects.  Above ground insects to look for are black cutworm, armyworm, common stalk borer, corn Flea Beetle. For below ground insects, watch for these signs: If you find gaps, missing plants or wilted plants, look for grubs, wireworms, and seed corn maggot. Hop vine borer is an above ground pest, but bores up into the stem from below ground.  So scout for hop vine borer, too.

Handy insect scouting calendar can help organize your scouting

Here is a corn insect scouting calendar to help organize scouting activities:

Be sure to scout emerged beans also. Look for good emergence, problems with soil crusting, damage from hail, etc. A final stand of a uniform 100,000 plants per acre should maximize yields, and it seldom pays to replant stands of 70,000 to 75,000 plants per acre, because of the cost of replanting and yield penalty for the delayed planting.  

It takes about 5 plants per foot of row in 36" to 38" rows, 4 plants per foot in 30" rows,  3 plants per foot in 20" rows and 2 plants per foot in 15" rows to equal about 70,000 to 75,000 plants per acre.  For drilled beans it is easier to use a hoop to take stand counts. It takes 10 plants per hoop with a 33" diameter hoop, and 12 plants per hoop with a 36" diameter hoop to equal about 70,000 to 75,000 plants per acre. The following 2008 article by a former ISU Extension agronomist provides additional information on soybean plant populations.

Still planting/replanting beans, stay with a full season variety. Stay with "normal" adapted maturity soybeans for your area of Iowa until about mid-June, says Lang.  For soybean planting that is delayed into June, if feasible, it is suggested to use narrower rows (such as 15 or 20-inch vs. 30-inch) since late planted soybeans don't develop as robust and cover the rows as well as earlier planted soybeans.

ISU seeking samples of soybean plants that show "damping off." Lang doesn't anticipate soybean stand problems with Damping-Off (see reference on this seedling disease at: ).  However, if you spot this problem, please call your ISU extension crop specialist ASAP, as ISU Extension would like to collect plant samples with Damping-Off symptoms.

Keep an eye out for insects, and scout and manage accordingly

Watch for armyworm especially if it's corn following winter rye or in a spring herbicide killed CRP field. Armyworms tend to feed on leaf edges first. Heavy infestations on young corn (V7 growth stage or less) can consume the entire plant.  On older plants, they often do not consume the midrib of the leaf. 

Many larvae may feed on the same corn plant. As long as they do not consume the main growing point, corn can recover. Treatment: Many insecticides are labeled for control, and Armyworm is easily killed with insecticides. Armyworms larger than 1.5 inches long are basically done feeding and will soon be pupating.  Additional information and photos are at:

Black cutworm on corn not bad this year. "I've had only one report of feeding damage, and that was in Delaware County," says Lang. Some corn in southern Iowa has been treated for Black Cutworm this spring. You should continue to scout for this pest until corn reaches V5 stage of growth. Information on scouting and thresholds is at:

Corn flea beetle is infesting some fields. This is an infrequent (also rare) pest for Iowa other than there is more importance of it in seed corn fields.  An ISU article discusses flea beetles in central Iowa, including recommendations.

Thresholds for insecticide application are: 1)  For field corn, prior to corn growth stage V5, 50% of plants with severe feeding injury and 5 or more beetles per plant. 2)  For seed corn, on susceptible inbreds, treat when you see10% of the plants with severe feeding injury and 2 or more beetles per plant.

Corn rootworm hatch looks to be normal. University of Illinois specialists are anticipating a fairly normal hatch period for corn rootworm larvae.  For northeast Iowa, that means hatch basically starts the week of June 6.

Did you forget to provide rootworm protection at planting? If you forgot to use a soil insecticide or insecticide seed treatment (i.e. Poncho 1250) and/or didn't plant a Bt rootworm traited seed where you thought you did, what do you do for an over the top rescue treatment for corn rootworm protection?  With the EPA removing Furadan 4L as an option for corn after planting for rootworm treatment, the only product left is Lorsban Advanced.  For post-emergence, use directed spray of Lorsban to the base of the plant and ahead of the cultivator. It is also labeled with chemigation. Here is the label:

Hop vine borer – treat at spike stage. There are a few fields in northeast Iowa with a known history of Hop Vine Borer problems, says Lang. This insect tends to stay in the same areas of a field year after year.  If you have identified this as a pest in a field, or more likely in part of a field, ISU's recommendation is to apply a pyrethroid insecticide at initial corn emergence (spike stage).  You can find a photo of Hop Vine Borer and many other insects in the Iowa State Entomology Image Gallery, at:

Identification of below ground insects. Here are links to photos of common "below ground" insects to aid in trouble-shooting corn and soybean plant emergence problems.

Grape Colaspis

Seed Corn Maggot  a possible concern following spring manure or spring green-manure plow-down.

True White Grubs

Manure Grubs  sometimes following spring manure applications, large populations can cause damage.


Potato leafhopper is an insect that threatens alfalfa and usually migrates into Iowa starting late May. Start scouting for this pest after 1st crop of hay is harvested and continue through August. Scouting tips and photos are available in this 1999 article:   When calculating the economic threshold, count both the adult and nymph.  Close-up photos of an adult and nymph are at:   Use a sweep net for scouting. ISU recommends a 15-inch diameter sweep net.  These can be purchased from many sources including:  Ben Meadows ( $39.20 for #300478 aluminum handle)

Slugs in soybeans have been seen, but feeding is only mild. Lang has seen some very mild slug feeding on soybeans. See attached photos. "I only mention this to help with crop scouting identification, not that any treatments are needed," he says. "On rare occasions slugs can be a problem. This is seen more often in eastern states like Ohio, and they have a publication that deals with this pest." It is available at:

Soybean aphid? If you follow Lang's soybean aphid scouting in past years, you know he finds his first aphids in soybeans in the first week of June. This 2011 season is no exception. "By Decorah we have a trial planted on May 6. It is currently at V1 stage of soybean growth," he says. " As of today I have 2.5% plants infested with aphids (1 out of 40 plants with just 1 aphid per plant) for an average of 0.025 aphids per plant. This is normal at this time, and as usual we will monitor soybean aphids weekly and report our findings."

For corn foliar diseases, farmers are coming up on first applications of fungicides on corn, or perhaps not. The University of Illinois posted 2010 data compiled from multiple states (Illinois, Indiana, Iowa, Ohio, Wisconsin, Minnesota, Kansas) and indicated that a greater yield response was observed when fungicides were applied at R1 compared to V6, with the largest response being when V6 applications were followed by R1 applications. Cost effectiveness of V6 applications are still inconsistent, but with the high market price for corn we will likely see increased activity on this in 2011. For the summary of the data go to:

Herbicides on emerged corn. Here is a summary check list on maximum stage of corn development for post emergence herbicides.

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