Nematodes in Corn and Soybeans – More Questions about Annual Ryegrass’ Ability to Control the Pests

I frequently get calls and letters about annual ryegrass. Here’s one, from a CISCO Seed agronomist that exemplifies some of the difficulty in farming today…how to get the best, most accurate information to folks in a timely fashion.

Dave Robison wrote:

I was at a meeting earlier in northern Indiana this week and a producer brought me a report showing that he had quite a population of Lesion Nematodes in his corn field.  The count indicated that there were enough lesion nematodes to cause problems (he is seeing pretty severe problems in spots in his corn field).  The crop consultant believes that possibly the Annual Ryegrass cover crop he planted into may have caused (or helped cause) his Lesion and Lance nematode issue.

Here’s my response:

Dave,

I am not an “expert” on lesion nematodes but consulted with Mike Plumer and did some research on the subject.    Lesion nematode populations seem to be increasing across the Corn Belt. This may be due to growers using Bt corn or a pyrethroid insecticide instead of an organophosphate and carbamate insecticide?  I know from my work with soybean cyst nematode that very few farmers have tested their fields.  One question would be if this grower ever had this field tested in the past for lesion nematode?

Recent University Of Illinois study http://corn.osu.edu/newsletters/2011/2011-04/nematodes-in-corn 550 fields were surveyed and nematodes were found in every field, at populations ranging from 100 to 4000+ nematodes per 100 cc of soil. Most of these were plant parasitic nematodes, belonging to more than nine different genera, of which the “tylenchides”, nematodes with small styles and pointy tails, were the most frequent. These were found in 99% of the fields. However it is unclear what these organisms are doing in corn fields, since members of this group include plant parasites as well as parasites of fungi and algae.  The lesion nematodes (Pratylenchus) were the second most prevalent nematode in Illinois cornfields survey by Dr. Niblack and her team. These were found in 84% of the fields. These were also found at population level considered above moderate risk thresholds in more than 50% of the fields in which they were present.

Southern Michigan survey  - June 2010 survey included 366 samples. Of those, 83% contained lesion nematodes in the soil or corn roots and 39% contained dagger nematodes, which are in the moderate-risk category. Only 2.5% had no nematodes. –  http://www.agweb.com/article/whip_corn_nematodes/

Background info – http://web.aces.uiuc.edu/vista/pdf_pubs/1103.PDF
sampling  video K State – www.youtube.com/watch?v=8iBAqRFUrrA

Some research indicates that annual ryegrass may suppress soybean cyst nematode. Univ of Guelpf suggests that wheat and perennial ryegrass will decrease nematode populations.

Dave – I don’t think we have near enough information to make any type of conclusion (especially with all the challenges this year – late planting, too wet, too dry, possible compaction, etc ). Literature seems to indicate that corn on corn and no-till may stimulate higher nematode populations. Nematode counts from one field without more background information and replicated trials doesn’t provide much information.  Maybe a sampling program in Indiana needs to be initiated.

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