Bright yellow patches (hot spots) in pea fields signal the presence of these microscopic worms that parasitize roots of pea, Pisum sativum; faba bean, Vicia faba; and vetches Vicia spp. Even green areas of infected fields may harbor low levels of nematodes, cysts, and infected roots. Color photos show damage and disease cycle. Detection methods and prevention by site selection and crop rotation are discussed. 8 pages

Inglis, Debbie

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 EB1872 The existence of the pea cyst nematode (PCN) was confirmed in westernWashington green pea fields in the summer of 1993. Like cyst nematodes on othercrops, PCN can survive for long periods of time without a host. It causes severedamage when infested soils are planted to a susceptible crop. Control can bedifficult, and eradication is unlikely. Preventive approaches that help limitestablishment in pea fields and minimize build up of soil populations are critical toPCN management.  Pea cyst nematode (Heterodera goettingiana) is a microscopic worm that parasitizesroots of pea (Pisum sativum), faba bean (Vicia faba), and certain vetches (Viciaspp.). Field symptoms occur as patches of stunted, bright yellow plants (Figure 1).These patches, at first small and circular, later may extend throughout large areas ofthe field. Depending on soil type, expansion of the patches may take years becausenematodes move slowly in soil. However, when farm equipment shifts nematodes toother parts of a field, new patches often appear and spread quickly.Infected plants may have small pointed leaves that begin to turn bright yellow atflowering. Yellowing progresses rapidly from the base to the top of the plant. Theroot systems of affected plants develop poorly. Few nitrogen-fixing nodules orsecondary roots form. Remaining infected roots branch perpendicularly from the taproot. Lemon-shaped cysts (leathery bodies of the adult females up to 0.5 mm indiameter) develop in the roots. Cysts are white when young but turn brown with age.The cysts usually slough off the roots after plants have flowered. Cysts areespecially difficult to find when roots are decayed by root rot fungi. Figure 1. Bright yellow,diseased plants in patches inpea field.   PCN overwinters in soil as eggs encased in brown cysts. When temperature andmoisture conditions are favorable in the spring, juvenile nematodes hatch from theeggs. Host root exudates can induce hatching of H. goettingiana eggs inside thecysts. Once juvenile nematodes penetrate roots, they feed on root cells and molt(Figure 2). Eventually, adult females (Figure 3) with 150+ eggs each, develop intonew cysts (Figure 4). In western Washington, only one cycle of egg hatching, rootinvasion, and cyst development is thought to occur per growing season. Mature cysts(Figure 5) can survive in soil for 10 or more years and are spread primarily byinfested soil adhering to equipment and plant materials, or by water movement. Figure 2. Juvenilenematodes feeding on pearoot.          Figure 3. Swollen male andfemale nematodes in pearoot.          Figure 4. Numerous whitecysts on pea root.          Figure 5. Mature nematodecyst with eggs andemerging juveniles.     Information from England and Italy indicates that egg production generally occurs at50°F to 55°F when soil moisture is adequate. Above 57°F, females develop intocysts, but egg production usually ceases. If cysts form, they are small and containfew eggs. Egg hatch and root invasion is suppressed above 77°F soil temperatureeven in irrigated crops. Temperature also affects invasion of pea roots by PCN inwestern Washington. In greenhouse studies more PCN juveniles penetrated pea rootsat 50°F than at 64°F or 79°F. When peas were planted at 2-week intervals from lateApril to early June in a field near Mount Vernon, total nematodes per gram of roottissue was significantly higher in the first and second plantings compared with thethird and fourth plantings. Conversely, yield (as vine and pod weight per stem) atpea maturity was significantly lower for the first two plantings compared with thelast two plantings.PCN can cause considerable reduction in crop yield. Heavily infested land mayproduce no crop and require long rotations before peas can be grown again. In someareas of the world, yield losses of 20% and 50% can result from 3 and 8 eggs pergram of soil for pea, 5 and 15 eggs per gram of soil for broad bean, and 20 and 78eggs per gram of soil for vetch, respectively (Table 1). Complete crop failure hasbeen reported at 32 eggs per gram of soil for pea. Similar losses were obtained forgreen pea cultivars (Spring and Sundance) in western Washington when dry seedyield averaged 18% less at 5 eggs per gram of soil and 87% less at 25 eggs per gramof soil compared with plants grown in PCN-free soil.In the absence of host plants, PCN cysts can persist in soil for several years. Apopulation decline of 50% the first 3 years and 50% each year thereafter wasobserved in both the Netherlands and England. These countries now practice longrotations (5 to 6 years and up to 15 years, respectively) in some areas. A moremarked population decline occurred in field experiments in southern Italy (wheresoil temperatures are higher than in northern Europe) in both fallow plots and plotscultivated with wheat or oats. There the population declined by 68% in the 1st yearand 85% after 4 years.Seventeen legumes common to the Pacific Northwest were evaluated as potentialhosts to pea cyst nematode in the greenhouse and field. Nearly all tested plants (bothprocessing and dry pea, faba bean, chickpea, lentil, hairy vetch, lima bean, snapbean, alfalfa, red clover, yellow clover, black medic, Alsike clover, lupine and sweetpea) had some detectable level of root invasion. However, cyst development duringthe growing season only occurred on peas and faba bean. These hosts also supportedhigh numbers (150 +) of eggs per cyst. Faba bean yielded more cysts per plant andin turn, more eggs per plant than peas, due to its greater root mass. Although vetchserves as a host of pea cyst nematode in other areas, hairy vetch was not a good hostin this study. xTable 1. Effects of pea cyst nematode population densities (eggs per gram) onthree hosts.*Host Plant ToleranceLimit20% YieldLoss 50% YieldLossPea 0.5 3 8Broad bean 0.8 5 15Vetch 2 20 78* from Greco, N., H. Ferris, and A. Brandonisio. 1991. Effect of Heterodera goettingiana on the yield of green pea, broad bean and vetch. Revue Nematol:14(4):619-24.      ENUMERATION.Consider the relationship between PCN soil population density and injury to pea toprevent PCN buildup to levels causing severe crop loss. Once high populations ofPCN occur, eliminating PCN from soil is very difficult because of long soilpersistence. Removing pea from the rotation becomes the only economic solution.Recover PCN cysts and estimate cyst numbers per 100 grams of field soil. Thencalculate numbers of eggs per gram of soil (see Table 2). This calculation requiresknowing the average number of eggs per cyst. In our studies, the number of eggs percyst usually has averaged around 170. Randomly sample several areas in a field toinsure fair estimation of population levels; repeat field sampling each time youconsider planting a pea crop. Depth of sampling is also important. In studies nearMount Vernon, we have detected cysts not only in the plow layer but also in thesubplow layer, from 10 to 18 inches deep (Figure 6).  Figure 6. Number of cysts (per 100 gramsof soil recovered from a pea cyst nematodeinfested field site at different soil depths.  xTable 2. A simple technique of drying, floating, collecting and counting driedcysts from PCN-infested field soil, and then calculating number of eggs pergram of soil.    Supplies Needed:25- and 80-mesh screens, 8 inch diameter*20 X hand lens*3/4 x 1/2-inch glass petri dish*plastic squirt bottle, 4-qt bucket, turkey baster (orvacuum pump), soil screensugar solution (1 lb table sugar-bring volume to 1 qt.with water)*Can be purchased through vendors of scientific products such as VWR Scientific Procedure:1. Collect soil from surface 4 to 6 inches deep wheredamage in field by PCN is suspected.2. Screen soil through 1/2-inch sieve to break up all clumps.3. Completely air dry the soil.4. Measure 100 g dry soil (about 2.5 fl oz or about 5 Tbsp).5. Place a 4-qt bucket on top of the two mesh screens (25stacked on top of the 80).6. Place dried soil in bucket; fill quickly with water toviolently agitate the solution.7. Stir well after filling.8. Let stand for 30 seconds.9. Slowly add more water until debris on top washes overedge into screens below.10. Stir again.11. Slowly add more water until debris washes over theedge again.12. Carefully empty water from bucket onto screens untilsoil begins to appear.13. Gently spray water through 25-mesh screen to washsmallest particles of debris onto 80-mesh screen.14. Remove the 25-mesh screen.15. Wash remaining debris on 80-mesh screen to one placenear the rim.16. Line the edge of a petri dish with a 3/4-inch wide stripof paper towel.17. Use squirt bottle with sugar solution to wash debrisfrom 80-mesh screen into paper-lined petri dish.18. In center of dish swirl sugar solution with glass rod;cysts will adhere to paper towel.19. From the center of the dish, carefully suction off sugarsolution with turkey baster or vacuum apparatus.20. Gently peel off paper and place on flat surface; usehand lens to find cysts (brown and lemon-shaped, about 0.5mm in diameter).   step 11  step13 steps 17  step 19 step 20    Calculation:Assuming 10 cysts are obtained per 100 grams of soil andan average of 170 eggs per cyst (based on our studies), thiswould represent 17 eggs per gram of soil, (10 cysts/100 g x170 eggs/cyst = 17 eggs/g).Note: For the most accurate enumeration of pea cyst nematode (PCN)soil populations, numerous soil samples per field, quantification of theaverage number of eggs per cyst for each sample, and the correctidentification of cysts by trained personnel is required. When workingwith PCN, be careful to properly dispose of PCN-contaminated soilsamples and water according to Washington State Department ofAgriculture guidelines.    FIELD SELECTIONMicro-plot studies near Mount Vernon indicate that once field soil levels of PCNreach 5 eggs per gram (18% potential yield loss), cropping even one time to pea canlead to a significant increase in PCN density of over 25 eggs per gram (87%potential yield loss). Planting another pea crop the following year can trigger cropfailure in the area of the field with the high egg density. When egg density in soil ishigh (25 eggs per gram) the PCN population appears to reproduce more slowly thanwhen egg density is intermediate (5 eggs per gram). However, when egg density isinitially very low or nondetectable (<0.5 eggs per gram), even one or twosubsequent pea crops can result in buildup of the PCN population to detectablelevels.One misconception concerning site selection is that PCN exists only in areas of afield where bright yellow, symptomatic pea plants exist. In fact, PCN can bedetected in green, nonsymptomatic plants well beyond the "hot spot." In one studynear Mount Vernon, nematodes were detected in a zone 75 feet beyond the center ofa hot spot (Figure 7). These pea plants remained green because the nematodepopulation was low. The next time a pea crop is planted, the size of the hot spot willprobably increase due to nematode population increases on the green plantssurrounding the hot spot. Thus, avoiding hot spots in a field during planting is notnecessarily a remedy. Hot spots represent a larger infected area than is visible andwill vary in size from year-to-year.Crop rotation is one of the best alternatives for preventing buildup of PCN tounacceptable levels because of a very limited host range. Expect the needed lengthof the rotation to increase with the severity of infestation. Generally, it takes at leasta 4- to 5-plus-year rotation out of pea or faba bean to maintain low or nondetectablelevels. If a field is infested at an economically damaging level (3 to 5+ eggs pergram of soil), an even longer break in the rotation is needed. Especially bypass fababean, because the reproductive potential of PCN on faba bean is higher than on pea.Planting dates in early spring and cool soil temperatures in northwestern Washingtonseem to enhance PCN invasion of pea roots. Delaying planting as a culturalmanagement practice can limit infection and reproduction. However, later plantingcan contribute to other pea disease problems. Monitor fields closely.Host resistance is desired in cyst nematode control. Potato and soybean breedingprograms have released cultivars resistant to the golden and soybean cystnematodes, respectively. The USDA Pisum collection was evaluated for resistanceto the pea cyst nematode in western Washington. Out of nearly 2500 types of pea(accessions) only 22 proved slightly more resistant than the susceptible controls,based on root ratings at the white cyst stage or on foliar ratings at processingmaturity. No pea cultivars with resistance to PCN were identified, and this includedearly, mid- and late-maturing types. Cultivar selection is not a control option at thistime.    Figure 7. Pea cyst nematode density(as white cysts per three plants) in afield hot spot.          A preventive management program, to limit establishment or maintain PCN soildensities at noneconomic levels is the most practical approach in PCN control at thistime. Preventive approaches include:1. Crop peas only in fields where PCN population densities are low (afew eggs per gram or less). Table 2 offers a relatively simple method torecover and estimate cysts and to calculate number of eggs in soil.2. Employ long rotations (4 to 5+ years out of pea or other susceptiblehosts such as some vetches) where egg densities are low.3. Avoid faba bean in PCN infested fields because of the nematode'shigh reproductive rate on this susceptible crop.4. Delay planting until late in the spring when soil temperatures arewarmer because cool soil temperatures of the early spring favor PCNroot infection and development.5. Power wash equipment, conveyances and footwear before leavingcontaminated fields to limit introduction into noninfested fields.    Di Vito, M. 1991. The pea cyst nematode, Heterodera goettingiana. NematologyCircular No. 188. Fla. Dept. Agric. & Consumer Serv. Division of Plant Industry. 3pp.Di Vito, M. and N. Greco. 1986. The pea cyst nematode. Pages 321-332 inLamberti, F. and C.E. Taylor, eds. Cyst nematodes. Series A: Life Sciences Vol.121. New York: Plenum Press.Greco, N., H. Ferris, and A. Brandonisio. 1991. Effect of Heterodera goettingianaon the yield of green pea, broad bean and vetch. Revue Nematol: 14(4):619-24.Kraft, J. M., R. C. Larsen, and D. A. Inglis. 1996. Pea Diseases. Pages 325-370inThe Pathology of Food and Pasture Legumes. D. Allen ed. CAB International,Wallingford, Oxon, United Kingdom.    Debra Ann Inglis, Ph.D., Washington StateUniversity Cooperative Extension plantpathologist, WSU Mount Vernon Research &Extension UnitCollege of Agriculture and Home EconomicsWSU Cooperative Extension bulletins contain material written and produced for public distribution. Youmay reprint written material, provided you do not use it to endorse a commercial product. Alternateformats of our educational materials are available upon request for persons with disabilities. Pleasecontact the Information Department, College of Agriculture and Home Economics, Washington StateUniversity for more information.Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture infurtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies areconsistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender,national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may bereported through your local Cooperative Extension office. Trade names have been used to simplifyinformation; no endorsement is intended. Published May 1998. Subject code 273. D. EB1872TOP

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Pea Cyst Nematode

Inglis, Debbie, 1953-

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