Managing Soybean Cyst Nematode with the Soil Test and Crop Rotation

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1 Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Volume No.1, Issue Number 15, September 16, 2009 Managing Soybean Cyst Nematode with the Soil Test and Crop Rotation By Dale Cowan CCA-ON Senior Agronomist AGRIS Co-operative & Wanstead Farmers Co-operative Soybean Cyst Nematode (SCN) populations are increasing in some fields and I think it is safe to assume that some level of SCN exist in most soybean fields. This microscopic round worm causes significant damage to susceptible soybean varieties by feeding on the roots and drawing nutrients from the plant as well as causing entry points for introduction of root diseases such as Sudden Death Syndrome. The direct and indirect impact on yield is significant. We will cover the following aspects of managing this pest. When to Sample What are the Symptoms Interpretation of Soil sample Results for SCN Management of the SCN population When to sample Now is a good time to test soybean fields for SCN. Soil sample in a similar, random manner as you would for a regular nutrient test. However insert the soil probe at angle through the soybean root mass. When sampling suspected areas, pull some of the sample cores from the edge of the trouble spot not just the center. Sampling in the middle of bad spot will not likely result in representative values as the root mass is diminished and the food source will be insufficient to support high populations. The greater and more significant activity will be on the advancing outer edge where the root mass is sufficient to support higher populations. Collect a separate sample for the nematode test. Do not dry the soil sample; take it directly to the local AGRIS/Wanstead branch for shipment to the laboratory.

2 What are the Symptoms The first thing that will be noticed is lower yields. This may take a few years to be realized as weather can dictate planting dates, and management interactions can cause a host of other reasons for fluctuating yields from year to year. The SCN has no direct symptoms that are easily identifiable which is why it is hard to accept that they may be present in your fields. However the SCN does contribute to a host of symptoms indirectly; most notably stunted areas of soybean growth, uneven or wavy growth patterns across the landscape, (which may exhibit a nitrogen, potash or manganese deficiency), root rots and increased disease pressure. The picture below is characteristic of SCN presence in soybean field. Oval or circular patches are evident. Bottom picture shows signs of potassium deficiency induced by heavy SCN infection Digging up plants and examining roots will reveal tiny white to lemon yellow cyst on the soybean root. They are much smaller than root nodules and often times are very clean as soil does not stick to them. The cyst is actually the female nematode with her head buried in the root to feed on plant nutrients and the distended body protruding from the root, which is loaded with eggs. Which later detach and form the cyst. Each cyst can contain upwards of 250 eggs. Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Page 2

3 Upon soybean senescence the cyst will detach. It may rupture and release the eggs. Some may hatch and perish others my lay dormant waiting for a soybean plant root or other host crop, the cyst may stay intact for several years and release the eggs at a later date. The picture below of a magnified root shows the female nematode. The white part will become the cyst. Eggs hatch into juvenile nematodes that only move short distances until they encounter a soybean root. It is only the female that stays and propagates on the root. There are 16 different races of SCN identified. Interpretation of Soil Sample results for SCN The soil lab will return a report stating the number of eggs in 100 grams of soil. The following chart provides the information necessary for interpretation of the result into a knowledge-based management decision. We have seen some reports come back in the 5000 to 18,000 egg count range, definitely a high risk environment. (5000 eggs per 100 grams of soil is equivalent to 45,454,545,000 eggs per acre or 227,000 eggs per soybean plant at 200,000 plants per acre).mind bender isn t it? If your results fall into the eggs per 100 grams of soil, that is a low risk situation with minimal potential for yield loss when using a susceptible variety. If your count falls into the 2000 egg range that would be considered a high risk environment for a susceptible variety resulting in up to 50% yield loss. The recommendation is for 6 years of a non host crop to lower the population. Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Page 3

4 14-1. Potential Risk of Yield Loss for Various SCN Population Levels SCN population (eggs per 100 gm of soil) Risk Rating Potential Yield Loss Rotation (coarse, sandy soils) 0-1,000 (fine-textured silt or clay) 1,000 (coarse, sandy soils) 2,000 (fine-textured silt or clay) 10,000 (all soil types) Low risk 0%-20% 4 year Low risk 0%-20% 4 year High risk 20%-50% 6 year High risk 20%-50% 6 year Resistant variety may be damaged 50%-100% Source: Welacky, Anderson and Tenuta. Agriculture and Agri-Food Canada and OMAFRA, nonhost Management of the SCN Population Management involves 4 basic steps 1) Sampling to know the size of your SCN populations 2) An effective crop rotation with non host crops 3) Sanitation - Transport of SCN 4) SCN resistant varieties. SCN Population Size The size of the population will determine the strategy for control. A low population and a 1 year rotation with a non host crop may be sufficient to keep the population in check. One year with a non host crop may lower the population by 55%. An egg count in soybeans at 700 may get cut down to 380 eggs in one year with a non host crop. A population of 5000 cut by 55% still leaves 2750 eggs, a very high risk situation. Knowing where you are starting from is important. Not all SCN survive every year so there will be a fluctuation year over year in population counts. However they can build rapidly in a soybean crop. To go through the life cycle from egg to egg takes 28 days with a soil temperature at 75 F or 24C. Therefore many generations are possible in a single season. Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Page 4

5 An Effective Crop Rotation with Non Host Crops Understanding the differences between a host crop, poor host and non host helps to determine the best population management strategy. Weeds also play role in population control. A host crop such as soybeans fosters and encourages the growth and development of the SCN. A poor host crop does the same thing but not as well as host crop. A non host crop does not provide an environment that supports SCN development at all. Knowing this creates the opportunity to break the growth cycle and control the population of the SCN and reduce it to a low risk status. The following table lists the crops and weed categories in the various host capacities. Plant Good Host Poor Host Non Host Crops Soybean Canola Alfalfa Snap beans Sweet Clover Barley Dry beans Red Clover Corn Adzuki beans Alsike clover Oat Lima beans Hairy Vetch Pea Sorghum Wheat Vegetables Weeds Purple nettle Wild mustard Henbit Common chickweed Common mullen Pokeweed In some parts of our trading area wheat and soybeans have become the standard crop rotation. Often times two or more years of soybeans are grown before the wheat crop is planted. Most of this takes place in the heavier clay soils. It was originally thought that SCN preferred sandy to loamy soil however the SCN has moved into the heavier soils. Red clover may at times be under-seeded into the wheat. From the table above you can see that red clover is listed as a poor host and is less effective in controlling SCN build up. Although wheat is a good non host crop and may reduce populations by 55% the effectiveness of this rotation all depends on the initial SCN populations. The uses of SCN resistant varieties have offered the ability to maintain reasonable yields in these kinds of rotations. However it is not without risk. Sanitation SCN moves very short distances in a field. Often times affected areas are oval or circular and stretched in the direction of tillage operations. SCN can be transported great distances on soil peds stuck to machinery and deposited in other fields. Often time the pattern of SCN is traced back to the initial tillage pass immediately inside the laneway or down a dead furrow. Any mechanism that moves soil can move SCN. Surface erosion by wind and water can move SCN around the field or to neighboring fields. If you have knowledge of which of your fields are free of SCN, then work them first and move to infected fields afterward. However cleaning the machinery with pressure washer at the end of the season is vital to remove potentially contaminated soil. Admittedly this may be too late for some fields, as it is like closing the gate after the cattle are gone. Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Page 5

6 SCN Resistant Varieties Resistant soybean varieties are an effective tool for management of SCN. SCN densities usually decrease when resistant soybeans are grown because most SCN juveniles are unable to feed and develop on the roots of the resistant varieties. In any naturally infested field, a few SCN juveniles (usually less than 1 percent) will be able to reproduce on the resistant varieties. When a repeated use of a particular variety resistance is used the nematode population of resistant types increases in number. Eventually, the SCN population will be able to reproduce as well on a resistant variety as a susceptible variety. The number of SCN juveniles that can reproduce on resistant varieties declines when susceptible soybean varieties are grown again. These nematodes do not compete well for food with the other SCN juveniles in the soil that cannot feed on the resistant varieties. There are 3 sources of genetic resistance PI88788 or PI Peking and PI Hartwig. The varieties available in Ontario have PI88788 resistance. So far no notable resistance has developed to cause concern. (Greg Tylka, extension plant nematologist. Revised January 1994). Rotating between host and non host crops but also using a SCN resistant variety is important. In a high risk field the following sequence may be advantageous to managing SCN and maintaining crop yields and soil quality. Please note that some fields have been encounter with egg counts greater than 10,000. After 3 or more years of no soybeans, resistant varieties have been affected when planted to soybeans again. Always test your soil for SCN. Know what population we are managing before we choose to plant. 1st year Wheat* 2nd year PI88788" SCN-resistant soybeans 3rd year Corn* 4th year PI88788 SCN-resistant soybeans/ another variety with PI th year Corn* Test for SCN in fall 6th year SCN-susceptible soybeans, if population is low 7th year (repeat 1st year) *Nonhosts Corn in the rotation is important, not only as a non host but for adding organic matter. With a harvest index of 50% every pound of grain you harvest produces a pound of dry matter stover. This adds to the organic matter cycle in the soil to maintain soil carbon, biodiversity and healthy soil. No other crop offers this contribution. Part of the strategy for managing SCN is to maintain and increase soil productivity. Crops grown with adequate fertility and good soil structure are better able to withstand production stresses including SCN infection. Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Page 6

7 Consequently, it is more critical for maximizing yield throughout the rotation by maintaining proper fertility and soil ph levels. A whole farm management approach to, seed selection, crop protection products, disease and fertility management becomes more important in optimizing genetic traits and creating the opportunity for greater success. To test for SCN call your local branch, our crop and customer service specialists are willing to help GROWMARK, Inc., AGRIS Co-operative Ltd., Wanstead Farmers Co-operative Ltd. The information provided in this letter is general in nature and specific information should be obtained by review of product labels and consultation with the manufacturer. Such information can be materially affected by inaccurate data or assumptions, varying circumstances, known or unknown risks and uncertainties, and many other factors which are beyond the control of GROWMARK, Inc., AGRIS Co-operative Ltd., Wanstead Farmers Co-operative Ltd. and results can vary widely. The user will not rely on any information provided herein and GROWMARK, Inc., AGRIS Co-operative Ltd. and Wanstead Farmers Ltd. will not be liable for any reliance on that information. The FS logo is a registered trademark of GROWMARK Inc. and all trademarks contained herein are the intellectual property of their respective owners. Brought to you by AGRIS Co-operative and Wanstead Farmers Co-operative Page 7