Determination of yield loss caused by Soybean Cyst Nematode (<i>Heterodera glycines</i>), SCN, on SCN-resistant and SCN-susceptible soybeans using the adjacent strip comparison (2000).

Determination of yield loss caused by Soybean Cyst Nematode (Heterodera glycines), SCN, on SCN-resistant and SCN-susceptible soybeans using the adjacent strip comparison (2000).

Principal Investigator:

R. Mac Riedel, Plant Pathology Dept.
J. Bruce Eisley, Research Associate, Entomology Dept.

Cooperators:

Ohio State University Extension

Jim R. Jasinski, Extension Agent 2, Southwest District Office
Greg Meyer, Ext. Agent, Warren County
Curtis E. Young, Extension Agent 2, Northwest District Office

Thanks to Tom Doerge, Troy Putnam, and Sandy Thomas from Pioneer Hi-Bred International, Inc. for their support of this project.

Introduction

SCN is present in 53 of 88 Ohio counties. These counties produce over 90% of the soybeans harvested in this state. Yield reductions in individual infested fields have ranged from near total loss to a few percent. Attempts to link pre-plant soil populations of SCN to levels of yield loss in small plots have lead to formulation of a series of action levels for Ohio farmers, but the correlation of small plot work to whole field experience is not good. In part this is caused by problems with pre-plant estimations of SCN populations in large fields but also to the discrepancies between yield measured in small plots with yields measured with grower field equipment and the effect of soil type on nematode biology. The use of GPS techniques to correlate nematode populations with harvester yields should give much better estimations of SCN effects on yield.

Objectives of this work are the following:

A. Improve estimations of soybean yield loss based on pre-plant nematode counts in light and heavy soil;
B. Determine the effectiveness of genetic resistance as a management technique for; SCN; and
C. Demonstrate to growers the use of resistance for management of SCN.

Methods and Materials

Plots were located in a 21 A field of sandy loam soil (Ottakee and Spinks soils) in Wood Co. (near Bowling Green) and 22 A field of silt loam soil (Blanchester and Clermont soils) in Clermont Co. (near Blanchester). Fields were divided into plots 180 X 180 ft (approximately 0.75 A) using GPS techniques. These coordinates were used to correlate harvester yields with SCN populations in the plots.

Each plot at both sites were sampled in the Spring to determine pre-plant counts. The Wood Co. site was sampled again after harvest (See Figure). The Clermont Co. site was not sampled in the fall because of wet soil conditions. One in. X 8 in. cores were taken on a 30 ft X 30 ft grid (approximately 30 cores per plot). The Wood Co. site had spring, 2000, counts ranging from undetectable to less than 2000 eggs/200 cc soil in most plots (See Figure). About 4 plots had populations between 2000 and 8000 eggs/200 cc. The Clermont Co. field had very high spring counts in most plots. Most of the plots in Blanchester Silt Loam had counts above 10,000 eggs/200 cc soil (See Figure). Most of the plots in the Clermont silt loam had populations between 8000 and 10,000 eggs/200 cc. One plot in the northwest corner of the field had populations between 200 and 2000 eggs; SCN-susceptible varieties 92B61 (Wood Co.) 93B82 (Clermont Co.) resistant varieties 92B91 (Wood Co.) and 93B66 (Clermont Co.) were planted in adjacent strips using techniques outlined in On-farm testing using the adjacent strip comparison method by Doerge and Gardner.

Results and discussion

In Wood Co. in 1999 there was excellent correlation between Spring counts of SCN and soybean yield. In heavily infested areas in 1999 on this light soil resistant varieties out yielded susceptible varieties by 10 to 15 bu/A (See Figure). The research site in Wood Co. in 2000 was selected because SCN populations were generally on the low side. As in 1999, when populations were above about 2000 eggs/200 cc soil the resistant variety out-yielded the susceptible variety by up to 10 bu/A (See Figure). At lower populations in this soil resistant and susceptible varieties yielded similarly. In the heavily infested, heavier textured soil in Clermont Co. resistant beans out yielded susceptible by an over all average of about 9 bu/A (See Figure). In individual plots of heavily infested Blanchester Silt Loam, resistant bean yields were close to 20 bu/A better than susceptible beans. This advantage was particularly note worthy since the growing conditions in Clermont Co. were good in 2000, and it is generally thought that SCN will be most destructive when additional environmental stresses are imposed on the crop.

The economic importance of SCN was demonstrated in 2000 in these research plots. The importance of genetic resistance in management of SCN mediated yield reduction was likewise well illustrated at both sites in 2000. Comparisons of results from the Wood Co. site for 1999 and 2000 indicate that the present recommended levels for planting susceptible soybean varieties (< 2000 eggs/200 cc soil) is probably close to correct for Ohio conditions. It is clear that resistant beans will give excellent yields at population levels significantly above present recommendations (<5000 eggs/200 cc soil). While economically it makes sense to use genetic resistance in soils with higher populations, it may be a poor idea in terms of managing the development of SCN populations capable of reproducing on and damaging resistant beans.

At this time, a majority of our growers subscribe to the idea that SCN is not an important pathogen in heavy soils. Results from the Clermont Co. site will educate Ohio growers to the potential for SCN to damage beans grown in such soils.

As a further observation, the Clermont County Producer who has a GPS yield monitor on his harvester, has noted significant yield differences in this field over several soybean crops. High SCN populations closely follow these yield differences. It seems to us that once SCN is present on a farm, GPS yield monitors may enable growers to keep track of SCN population changes with minimal use of soil samples after the initial mapping.

Summary

SCN can significantly reduce the yield of susceptible soybeans in light or heavy textured soils when populations over about 2000 eggs/200 cc soil exist. Genetic resistance is an excellent, cost effective means of managing SCN damage.

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