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.

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