Friday, May 30, 2014

Is it an Armyworm or a "Look-a-Like"?

Missouri recently cautioned growers to watch for armyworms in it's Southern region, and Illinois has reported some armyworm in wheat as well.   It is therefore, time to conduct a little armyworm review:

The True Armyworm, Pseudaletia unipunctata, can actually be a pest in corn, pasture, and wheat.  Female armyworm moths do not overwinter in Illinois, Indiana, Iowa, Missouri, or Wisconsin (the Burrus/Hughes sales footprint).  Instead, moths migrate back into our area each growing season from the Southern United States.  Moths arrive in the Midwest and then deposit numerous eggs in small clumps on the lower portion of grasses.  The eggs hatch around early-mid May, and the resulting larvae tend to feed at night or during overcast days.  When not feeding on the plant, larvae hide in leaf sheaths and beneath crop debris.  When found on the soil surface, they are usually curled up.  The larvae tend to prefer grasses, but at high enough populations they will feed on broadleaf plants.  A generation of true armyworm larvae tends to appear in May/June, and in July/August (The Handbook of Corn Insects notes a possible third generation in some areas). 

Picture of a True Armyworm.

 True armyworm larvae have three pair of true legs near the head, and five pair of false legs (prolegs) toward the tail.  Each false leg has a dark diagonal smudge-like marking (an especially useful feature often used to identify the pest).

Correct identification is important because some look-a-like insects may be found in the field.  If those look-a-likes are assumed to be true armyworms, the grower might overestimate the population – assume an economic threshold has been hit – and spend dollars on insecticide that is not needed.  

A recent example of look-a-like found in Missouri was the white-lined sphinx moth caterpillar.
White lined sphinx caterpillar.
The armyworm scouting message is the same as it is for many pests – scout and scout frequently (at least weekly).  If one fails to do so, they just might miss the opportunity to catch armyworms, while they are still a minor issue. Six armyworms per foot of row is the type of population requiring an insecticide in wheat.  Two to three larvae per square foot likely require control in grass pasture.  In corn, damage to twenty-five percent of plants and/or some plant death is considered significant. Corn near grassy areas, corn near small grains, or corn planted into a cover crop tends to be slightly more at risk than corn elsewhere.

Sunday, May 25, 2014

Corn Nematodes: The Good, Bad, and the Ugly (True or False)

All nematodes are bad False
Nematodes are tiny, microscopic round worms lurking in the soil. Not all of the nematodes in the soil are bad, as some nematodes help to recycle nutrients. The nematodes that we are concerned with are those that are pathogenic to plants.Plant pathogenic nematodes feed on plant parts and need plants in order to survive or they will perish.
Most corn nematodes feed on rootsTrue
Most plant parasitic nematodes that attack corn will feed on roots with their stylet (piercing mouth part that can be compared to a hypodermic needle). There are two types of root feeding nematodes: ectoparasites feed from the outside of the root, and endoparasites feed from the inside of the root. Endoparasitic corn nematodes, such as lesion nematode, are considered more damaging, because they are reported to cause greater economic losses. This is because they spend most of their time inside the root, which can cause issues to occur with the structure and function of the root.
Corn nematodes can cause a yield loss, without obvious symptoms – 
Corn nematodes can feed on roots for 28 days or up to a year, depending on the species. The damage caused by corn nematodes will depend on their populations. If corn nematode numbers are extremely high, they can obviously injure or kill plants, especially seedlings, but this is a rare occurrence. However, corn nematodes at lower populations can cause yield loss without any sign of damage. Different states have different ranges of population numbers, which correlate with different corn nematode species, in which they consider thresholds for nematode damage or yield loss to occur. Corn nematode damage can go easily unnoticed most of the time. In addition, corn nematode injury can cause plants to be stressed, which in turn, can cause corn to be more susceptible to other problems such as disease. Therefore, corn nematode injury can be easily confused or misdiagnosed with other issues.
Corn nematodes are mostly a problem in sandy soils False
The larger nematodes (needle, sting, stubby root, and root knot nematode) can be found in soils with > 70% sand; however other nematodes (dagger, lance, lesion, ring, stunt, spiral) can be found on all soil types. For example, the U of I Extension (2009-2010) nematode survey revealed that corn nematodes (especially lesion) were found in about half of the cornfields in Illinois with densities at or above the threshold for moderate to severe risk of injury (yield loss).  
All corn fields have an equal risk of nematode attack False
Fields with a corn on corn rotation, minimum or no tillage, or no nematicide option can be more at risk for corn nematode attack because rotation, soil disturbance, or protection can help to reduce corn nematode populations.
You can test your field for corn nematodes True
Corn nematodes should be diagnosed before the V6 growth stage of corn.
Soil (not overly wet) and root zone should be sampled randomly throughout the field. Different labs recommend different amounts of soil cores (12 to 25) and
soil depths (6 to 12 inches) from the root zone (this is because you want to get a sample of roots to test for endoparasitic nematodes such as lesion nematode. ) It is a good idea to keep track of where you have sampled, so that you can go back and monitor nematode populations. Do not try to break up the soil cores or drop the soil samples, because this could kill corn nematodes before they reach the lab, which could cause you to have inaccurate lab results. If you think that you have corn nematode “hotspots” in the field, you may want to sample from that area as well as a “healthy” area, so that you can compare results. If you are still in doubt, it may be best to call the lab before you send a sample, so that you can provide the lab with an adequate sample. For example, some labs do not recommend that you sample after the R3 corn growth stage.

There are management options for corn nematodes True
Depending on the corn nematode species, rotation of crops, tillage, and controlling grassy weeds may help to keep nematode populations in check or below damaging thresholds. Rotation to crops such as alfalfa, cotton, rice, soybeans, or sorghum may be a good control of needle, sting, and some lesion nematode species that have narrow host ranges.There are limited choices of soil applied nematicides. One common example of a soil applied nematicide is Counter insecticide, which has been known to reduce nematode populations in season. However, this occurs early in the season, and there could be a nematode resurgence later in the season. Corn nematicide seed treatments include Avicta ® and VOTiVO™. Again, each of these will have to be used each year and only provide early season control. Nematode numbers could again resurge in mid or late season. Avicta’s active ingredient is abamectin, which is a natural fermentation product of Streptomyces avermitiles, which can inhibit the nematode’s nervous system. This nematicide seed treatment is not systemic or taken up by the roots and can be considered mobile or eventually lost within the soil profile. VOTiVO’s active ingredient is Bacillus firmis and does not kill nematodes. It acts as a repellant or physical/chemical barrier and is also not
systemic or taken up by the roots. It can grow on the root surface, but only provides early season protection. Again, nematode testing should be done to evaluate whether corn nematode populations are being kept in check by these management options. 
Many of the Catalyst™Brand Products that were planted in 2014, had Cruiser® 500 (the 2x rate normally applied) plus Avicta®, specifically all 7893 3111 as well as 4685 3111 lots that begin with 113 or 114. The new Burrus, Hughes, and PowerPlus® products had Poncho® 500 VOTiVO™on them in 2014, and many of the current products were also shipped with Poncho® 500 VOTiVO™ too. Check the lot number/treatment code to be sure.

Thursday, May 22, 2014

Estimating Hail Injury to Soybeans

Hail injury can vary among fields, so each soybean field will need to be evaluated separately.  Most soybeans now are early in their development, so the first step will be to determine growth stage, leaf loss, growing point, and axillary buds.  If there is more than one leaf cotyledon or leaf tissue present, there is hope, because soybeans will be able to regrow. However, keep in mind, that if one or both of the cotyledons are lost, early in the growth of the soybean, the growth rate will be reduced.  Leaf loss means that the cotyledon leaves are absent or brown in color.

The soybean growing point is located between the 2 cotyledon leaves (when the soybean first emerges - VE or VC growth stage).  If the growing point becomes injured, the axillary buds will come out of dormancy and develop near the stem, above the leaf petioles (where the leaf meets the stem).  If the plant gets cut or snapped off below the cotyledons, the plant will die.

The growing point will next produce 2 unifoliate leaves (V2 growth stage), above the cotyledons, and these unifoliate leaves also posses auxillary buds above their leaf petiole, where it meets the stem.  Again, these axillary buds are dormant, until an injury occurs to the growing point, and then, these axillary buds become activated to produce soybean growth.

This picture provided by Hans Kandel, NDSU, is a great visual to help in field evaluation and more on soybean growth and development can be found at:
Next, take stand counts (1/1000th of an acre) throughout the field (not just one area of the field) to get an idea of the injury.  Do not count soybeans that are missing leaf tissue, have brown leaf tissue, or are cut below the cotyledons.  The hula hoop method can be used, or you can measure off 17.5 feet within 30 inch rows, and count each uninjured plant to get an average plant population.  If you have 15 inch rows, you can still measure off 17.5 feet, but be sure to count plants on each side for the average plant population.

Remember that soybeans can tolerate low populations and may only have a small amount of yield loss, with a wide amount of plant loss. Populations of 100,000 have the potential to produce maximum yields and populations around 80,000 could potentially produce 90 percent of the maximum yields.  However, the maximum yield potential may be reduced if there are gaps or gaping holes within your field.  You quickly start to lose your maximum yield potential as the plant population average across the field is below 50,000.

Wednesday, May 21, 2014

Tom Burrus explains Kinze® Multi Hybrid Planter Techonology at its Best

Brian Six, Account Manager for Burrus, has been the lead operator of the Kinze® prototype Multi Hybrid 4900 electric drive planter utilized by Burrus.  Brian Six said, "While I was operating the planter, Raven Industries called to say ‘Please stop the planter so we can update the monitor programing’, - I could see that Raven technicians, located in South Dakota, were working on my tractor monitor, while I was located in fields of Illinois, Missouri, or Wisconsin."

Sometimes plans would change, and another Burrus field would need a new prescription.  Jerad Ropp, the Burrus Precision Planting Consultant, would write a prescription, then  e-mail the prescription to Brian Six's tractor, and then Brian was able to download the prescription onto a thumb drive, stick it into the monitor, and be ready to plant without leaving the cab. “This is quite a revolution from how we operated just 10 years ago” says Tom Burrus, President of Burrus Hybrids.  “The planter has been on 22 farms for corn testing, and now, we are utilizing the Kinze® prototype Multi Hybrid 4900 electric drive planter for Burrus soybean research.”  For additional information, you can read:  Update From Tom Burrus - Kinze® 4900 Electric Drive Prototype Multi Hybrid Planter Soybean Research 

Brian Six, Burrus Account Manager as well as the operator of the Kinze® prototype Multi Hybrid 4900 electric drive planter

Sunday, May 18, 2014

Thoughts on Early Season Soybean Damping Off from a Diagnostic View

Yes, soybeans can be vulnerable to pythium and Phytophthora roots rots (and even Rhizoctonia root rot).  Pythium and Phytophthora spp. belong to the group of fungal-like organisms called the oomycetes, which are also known as water molds.  Moisture has to be present for zoospores (spores) to infect roots. Most pythium species can infect corn and soybeans (as well as other crops), but as research continues, they are finding that some pythium species may prefer to infect corn; whereas other pythium species may be more likely to infect soybeans.  Hystorically, pythium species are more likely infect early because they favor cooler temperatures (50 to 60 F); however, further research has shown that some pythium species may infect at warmer temperatures.  Phytophthora spp.prefer temperatures of 77 to 86 F and have a very, wide host range.  Phytophtora root rot can attack/kill soybeans at all growth stages.

Both pythium and Phytophthora root rot pathogens can cause cause a brown rot to occur on soybean roots or hypocotyls.  In my opinion, it is very, difficult to make the distinction between pythium and Phytophthora root rot within the field, when soybeans are infected at early growth stages.  This is when your state's Plant Clinic may come in handy as they have "many diagnostic tricks up their sleeve", such as examining oospores (spores) within roots via a microscope (pythium), examining lemon shaped sporangia growing on roots or hypocotyls (Phytophthora), or use a form of Enzyme-Linked Immunosorbent Assay (ELISA) , a technique used to detect antibodies or infectious agents in a sample (Phytophthora).

It looks like a root rot or damping off on soybean.  Have these plants been infected by pythium or Phytophthora spp.? - Pictures taken at the U of I Plant Clinic

Lemon shaped sporangia (fruiting structures that contain spores) of Phytophthora - Picture taken at the U of I Plant Clinic
Oospore (spore) of Pythium found embedded within roots - Picture taken at the U of I Plant Clinic
If you have soybean damping off or root rot early in the season in your field, why should you care if it is infected by pythium or Phytophthora?  The answer is management.

Both pythium and Phytophthora spp. are more likely to infect plants that lack vigor or that are planted in a poor location. Further investigation of plant stress may lead to clues why infection may have occurred. Since both of these pathogens require moisture for infection, it makes sense that flooding, lower lying areas of the field as well as clay soils that have a higher water holding capacity may be more at risk for pythium and Phytophthora infection.  Therefore, improving or the addition of tile drainage could offer some aid in some situations.  

Fungicide seed treatments can offer control early in the season, but keep in mind that not all of them specifically protect or are registered to be used against the oomycete fungi like pythium and Phytophthora.  The reason I say "early season control" is because these fungicide seed treatments do not last forever.  These seed treatments are located on the seed and may not offer protection to the soybean's roots or hypocotyls. There is always the chance of resistance to fungicide seed treatments, but has not yet been documented in "our neck of the woods."

There is no resistance available within plants for pythium; however there is resistance available within soybean for use again Phytophora.     
1.) root resistance (several genes) - This is expressed in the root, almost a complete resistance, qualitatively inherited and harder to breed

2.) partial resistance (several genes) - This is expressed in the roots after the cotyledons and true leaves are exposed and is said to reduce colonization of the roots as well as slow the expansion of lesions, qualitatively inherited and harder to breed

3.) R- gene resistance (single gene) - "R-gene mediated resistance has been described for 14 Rps genes and most have been mapped on the soybean genome. Commercially, only six genes, Rps1a, Rps1b, Rps1c, Rps1k, Rps3a and Rps6, have been deployed and one more, Rps8, is in commercial development."  They are expressed in the seed early in germination (effective early and throughout the growing season), and are measured in lab/greenhouse assays by inoculating hypocotyls of young seedlings to see if there is a hypersensitive response.  R-gene resistance is the most common, because it is the easiest to breed.  .Not all Phytophthora races will be controlled by R-gene resistance.

R-gene and partial resistance are most commonly used today in soybeans.

What can you do?
1.) If you have a soybean root rot problem, determine if it is pythium or Phytophthora by contacting your agronomist or utilizing a Plant Clinic, so you can properly manage the problem.

2.) Keep track of what fungicide seed treatments that are on your seed.  Are they the right seed treatments for use against oomycetes (water molds)? Are they they same type of fungicide seed treatments that you are using on corn?   Could you be setting up a situation for resistance to occur?

For additional information on seed treatments, you can go to: 
What is on your seed?
Specific Activity of Soybean Seed Fungicides

3.) If you have a Phytophthora problem, what type of resistance are you utilizing? At Burrus, you can find this information in the Production Selection Guide .  If you have questions, you can contact an agronomist.  Do you have a race of Phytophthora that is not controlled by single gene resistance?

For more information on Phytophtora root rot in soybeans, you can refer to the following: