Columbia Root-knot Nematode Control in Potato EM 8740 • November 1999 Using Crop Rotations and Cover Crops $1.50 R. Ingham, R. Dick, and R. Sattell he Columbia root-knot nematode Dependence on fumigant nematicides can be (Meloidogyne chitwoodi) attacks potatoes reduced or eliminated if M. chitwoodi popula- T and causes injury to tubers in the Columbia tions are depressed sufficientlyDATE. by rotating Basin of Oregon and Washington as well as other potatoes with nonhost crops. Nematode popula- areas of the Pacific Northwest. Infected potato tions can be reduced further when cover crops tubers become rough and bumpy on the surface. with a nematicidalOF action are included in the Inside the potato, adult female nematodes rotation. produce brown spots that discolor further during frying. Control with The FDA does not allow nematodes in pro- OUT cessed potato products. If 5–15 percent of the nematicides tubers in a field are culled (i.e., rejected) because Nematicides kill nematodes directly if the of infection, the entire field may be rejected. IS nematodes are exposed to the agent long enough. Depending on the price for potatoes in a given However, when M. chitwoodi populations are year, the resulting loss can total $250,000 or high, application of nematicides may not reduce more for a 120-acre (49-ha) irrigated circle. nematode levels sufficiently to prevent economic M. chitwoodi can complete many generations damage. 1,3-dichloropropene (Telone II), applied during the Columbia Basin’s long, warm information:at rates recommended by its label, provides the growing season if host plants (plants in which best control of any single nematicide, but occa- M. chitwoodi can reproduce) are present. Even sionally infections still are present after its use. In when sampling finds no juveniles per 250 g dry some cases, more than one nematicide is used for soil at planting time, there may be sufficient adequate disease and nematode suppression, nematodes present to cause economic damage at e.g., 1,3-dichloropropene plus metham sodium harvest. Nematode density may be so low that (Vapam). Note that a separate label for the sampling misses them, or theycurrent may be present in PUBLICATION combined use of 1,3-dichloropropene and the soil below the sampling depth. (M. chitwoodi metham sodium permits lower application rates has been found as deep as 6 feet below the soil of each than are required if either is used alone. surface.) Traditionally,most M. chitwoodi is controlled with THISchemical nematicides, many of which risk Fumigants versus nonfumigants suspension for use on potatoes due to health and Fumigants such as 1,3-dichloropropene and environmentalFor concerns. It is essential to develop metham sodium are injected into the soil to a and refine alternative strategies for controlling depth of 18 inches. Metham sodium also can be Columbia root-knot nematode now, so that applied through chemigation. Both are phyto- productive http://extension.oregonstate.edu/catalogand profitable potato acreage will not toxic (they kill plants), so they must be applied be lost if nematicide use is prohibited. before planting. Russ Ingham, associate professor of botany and plant pathology; Richard Dick, professor of soil science; and Robert Sattell, former faculty research assistant in crop and soil science; Oregon State University. 1 Nonfumigants such as ethoprop (Mocap) and but not all plants are an adequate food source oxamyl (Vydate) are broadcast over the soil (host) for M. chitwoodi. Thus, rotating potato surface and mixed into the soil with tillage, or are production with fallow periods or nonhost cash applied with irrigation water. Nonfumigants are and cover crops can reduce populations. Some not phytotoxic and can be applied before or after cover crop residues also produce nematicidal planting if permitted by the label. compounds as they decompose that kill All nematicides are expensive to buy and apply. M. chitwoodi. Some weeds are good hosts for Fumigants generally are more effective than M. chitwoodi and must be controlled to minimize nonfumigants but also cost considerably more. nematode reproduction. Nonfumigant costs are approximately $120–220 Research at Oregon State University and per acre, and fumigant costs vary from $250–480 Washington State University has documented per acre. that selected crop rotations decrease M. chitwoodi populations to levels resultingDATE. in less than Potential suspensions 5 percent culls (Ingham, 1994). Use of nonhost All registered nonfumigant nematicides cash and cover crops in potato rotations may are carbamates or organophosphates, and reduce root-knot OFnematode populations enough 1,3-dichloropropene is a B2 carcinogen. All that the less expensive nonfumigant nematicides carbamates, organophosphates, and B2 carcino- are effective. gens are at the top of the suspension “hit list” developed to implement the Food Quality ReproductiveOUT indices Protection Act. Cash crops, cover crops, and weeds can be Nematicides have experienced sudden suspen- rated with a reproductive index (R value) that sions by the EPA in the past. For example, the ISindicates the reproductive efficiency of fumigant 1,3-dichloropropene was suspended in M. chitwoodi on a particular plant. R values are California with little notice in 1990. The same obtained by counting nematodes in soil samples year, the manufacturer of the nonfumigant taken before planting and after harvest (or aldicarb (Temik) voluntarily withdrew its use incorporation). The calculation is: nationwide following the detection of higher thaninformation:R value = final population ÷ initial population expected residues in potatoes. The host status of a crop is defined as follows: If effective fumigants are suspended, potato R > 1.0 = Good host; nematode levels will stay the acreage will be drastically reduced unless alterna- same or increase. tive cultural control strategies are implemented. R 0.1–1.0 = Poor host; nematode levels will decrease to 10–99 percent of initial levels. Oregon State University research has shown that R < 0.1 = Nonhost; nematode levels will decrease nonfumigants alone do not provide adequate to less than 10 percent of initial levels. control in most conventionalcurrent rotation systems, PUBLICATION Note that R values may vary considerably and even they are at risk of suspension. among cultivars of the same crop. In other words, some cultivars of a particular crop may be non- Breakingmost the cycle hosts, while others are hosts. The R value also THISIf M. chitwoodi population levels are high or may vary with the particular race of M. chitwoodi; are deep in the soil, enough nematodes to cause for example, alfalfa is a host of race 2 but a damageFor may remain even after nematicide nonhost of race 1. Proper cultivar selection is applications. Thus, control of M. chitwoodi often essential when using crop rotation to suppress involves a combination of methods. nematode populations. Growers should always It’s possiblehttp://extension.oregonstate.edu/catalog to reduce M. chitwoodi popula- find out the R value for the variety they plan to tions over time by depriving them of a suitable plant with respect to the race of M. chitwoodi environment in which to reproduce. Plant- present in their fields. parasitic nematodes must have plants to feed on, 2 Although absolute R values usually vary from Rotation crop host status year to year and field to field, the R values of Many crops currently favored for rotation with tested crops are relatively constant when com- potato, such as wheat, field corn, cereal corn, and pared to each other under the same conditions. alfalfa, increase Columbia root-knot nematode For that reason, a relative R value often is populations greatly. (Alfalfa increases only reported. The relative R value makes it easier to populations of M. chitwoodi race 2.) compare the results of one test with another. It is Nonhost summer crops include supersweet calculated as: corn (certain cultivars), pepper, lima bean, turnip, (R value crop) cowpea, muskmelon, watermelon, and squash Relative R value = crop (Ingham, 1990). The diversity of choices (R value reference crop) The reference crop usually is a specific field increases each year as more varieties are tested. corn cultivar. Table 1 lists several crop varieties and their respective R values. DATE. Table 1.—Reproductive efficiency (R values) of Meloidogyne chitwoodi race 1 on selected rotation crop cultivars. Means followed by the same letter are not significantly different (p=0.05).OF1 Common name Cultivar name R=Pf/Pi Potato Russet Burbank 68.00 a Cereal corn Pioneer x816W OUT 58.53 a Cereal corn Pioneer 3737 28.24 ab Cereal corn Pioneer 3283W 22.66 ab Field corn Pioneer 3732 IS 12.38 abc Sudangrass P877F 9.53 abc Cereal corn Pioneer x8516 6.68 abc Sudangrass P855F 6.64 abc Popcorn Robust 30-72 4.90 abc Popcorn Robust 47-31 3.84 abc Popcorn Robust 20-60information:3.58 abc Popcorn Robust 30-71 3.57 abc Popcorn Robust 10-84 3.27 abc Popcorn Purdue 410 2.98 abc Sudangrass Pipper 1.52 bcd Sudangrass Sordun 79 0.89 bcde Popcorn currentRobust 30-77 0.77 bcde Sudangrass PUBLICATIONTrudex 9 0.57 cde Wheat Stephens 0.48 cde Rapeseed Ceres 0.094 def Rapeseed Westar 0.069 def Turnip most Forage Star 0.068 def THISSudangrass Trudex 8 0.043 ef Wheat Hard Red 906R 0.036 ef Rapeseed Cascade 0.034 ef PepperFor California Wonder 0.0081 fg Muskmelon Tokyo King 0.0013 gh Squash http://extension.oregonstate.edu/catalogButternut 0.00075 gh Cowpea California Blackeye 0.00024 h Muskmelon Superstar Hybrid 0.00006 h Lima bean Henderson Bush 0.00006 h 1Oregon Potato Commission, 1989–1990. 3 Cover crop host status effective at killing M. chitwoodi than those used Cover crop host status also varies among crops for animal or human consumption because they and among varieties of a particular crop. Cover contain higher levels of glucosinolate.