|
|
|
|
|
|
|
||
|
|
||
|
|||
Soilborne Crop Pathogens Under Direct Seeding: NematodesRichard
Smiley, Professor of Plant Pathology, Oregon State University, Nematodes are roundworms that occur worldwide in all environments. Most species are beneficial to agriculture in that they contribute to decomposition of organic matter and are important members in the food chain. About 15 percent of the 15,000 nematode species currently identified are plant parasites. Plant-parasitic species cause an estimated annual crop loss valued at $8 billion in the U.S. and $78 billion worldwide. Most of the plant parasites are less than one millimeter long (0.04-inch) and live in soil. Root disorders caused by parasitic nematodes are difficult to diagnose and often go unnoticed until stunted plants are observed, or until yields fail to attain levels expected. This paper addresses two parasitic groups (Figure 1); cereal cyst nematode (Heterodera avenae) and root lesion nematode (Pratylenchus species). Additional detail can be found in Smiley et al., 1994, and in Smiley 2000 and 2001.
CEREAL CYST NEMATODE (CCN) Heterodera avenae was first reported in the USA during 1974, in Washington County, Oregon. This nematode has now been identified in many grain-producing areas of the Pacific Northwest, including Union, Morrow and Umatilla counties in Oregon, Caribou, Fremont, Jefferson, Madison and Teton counties in Idaho, and Whitman County in Washington. A survey in Union County during 1987 indicated that two thirds of randomly sampled fields were infested. Application of Temik (aldicarb) in two fields improved yields of winter and spring wheat up to 29%, but was ecologically and economically unacceptable. CCN is spread when contaminated soil moves on or in vehicles, equipment, plants, shoes, animals, dust, water, or other means. For instance, we collected CCN cysts from tare soil in potato storage buildings in Union County, and then also from soil dropping from a truck used to haul seed potatoes to planting equipment in a production field in Morrow County. The truck discharged H. avenae 100 miles from where the seed had been grown. Seed potatoes from infested fields are transported even longer distances to fields in Washington and Idaho. Turfgrass sod produced on infested fields in Union County has been transported to new lawns being installed in at least four states; ID, OR, UT, and WA. A dryland wheat field in Umatilla County became infested with H. avenae when contaminated soil dislodged from a seed drill used previously in Union County. CCN will continue to be disseminated throughout the Pacific Northwest and to other geographic regions as agricultural equipment, automobiles, animals and plants (seed potatoes, sugar beets, mint rootstock, ornamentals, and others) with adhering soil are transported from infested soils. In the Pacific Northwest, host crops of H. avenae are produced on 70 million acres and are valued at $1.2 billion annually. Wheat is the most important host. Other hosts include barley, grass seed crops, corn and oats. Many of these crops are also hosts for pathogenic fungi that cause Rhizoctonia root rot (Rhizoctonia solani and R. oryzae), Pythium root rot (Pythium species), Fusarium crown rot (Fusarium pseudograminearum and F. culmorum), common root rot (Bipolaris sorokiniana), and take-all (Gaeumannomyces graminis var. tritici). Disease complexes resulting from H. avenae and soilborne fungi are well known. For instance, individual effects of H. avenae and R. solani on wheat are less damaging than when both pathogens are present. In Australia, wheat yield has been increased by a factor of six by fumigating soil infested with H. avenae, R. solani, and G. graminis var. tritici. Rotations to non-host
crops are particularly useful for reducing damage caused by the cereal
cyst nematode in other countries. Rotations are also effective for minimizing
damage to wheat by root-infecting fungi. Effects of rotations on combined
damage from multiple pathogens including CCN had not been studied in the
Pacific Northwest. The plant pathology program at OSU-Pendleton conducted
research to examine growth, damage and yield of winter wheat produced
annually and in crop rotations in a field infested by H. avenae and fungal
root pathogens. Plants were collected each year to evaluate growth, development, and disease incidence and severity. Root diseases present during one or more years included common root rot, take-all, Pythium root rot, Rhizoctonia root rot, and damage by CCN. Data for each parameter and sampling date were analyzed by analysis of variance. Correlations and stepwise backward multiple regressions were performed to explore relationships among parameters.
Winter wheat in all rotations was more healthy and productive than wheat produced annually. Root damage ratings from CCN were high in annual wheat (treatments 1 and 2), and were intermediate in the wheat/fallow, wheat/pea, and wheat/barley/fallow rotations (treatments 3, 5, and 6). Damage ratings were lowest in treatments where hosts had not been present for two or more years. Incidence or severity of CCN damage did not differ among tillage treatments for annual wheat. Grass weeds in alfalfa led to an increase in CCN damage to the following wheat crop, with 13 and 65 percent damaged plants from weed-free and weedy alfalfa, respectively. Alfalfa with grass weeds perpetuated the potential for damage, whereas weed-free alfalfa allowed production of a healthier wheat crop. Barley and Kentucky bluegrass did not increase the amount of damage caused by CCN, and may, therefore, be poor hosts for the CCN biotype (race) present in the study area. Studies of CCN genetics are needed to clarify this observation. Many interactions were evident among root diseases and CCN. Rotations did not have a significant effect on incidence or severity of Rhizoctonia root rot or take-all. CCN damage and Rhizoctonia root rot were negatively correlated during early spring but were not correlated during late spring. A strong positive correlation between Rhizoctonia root rot and Pythium root rot occurred. Pythium root rot was most frequent and damaging in wheat/pea rotations (treatments 6 and 7) or wheat following two years of fallow (treatment 4), and least frequent and damaging following bluegrass or annual wheat in tilled soil. Pythium root rot was negatively correlated with CCN. Common root rot occurred on 10 to 20 percent of the plants in all treatments except annual no-till wheat and both treatments containing alfalfa. Take-all became more prevalent in annual no-till wheat and in wheat following weedy alfalfa than in wheat following host-free rotations. There was no consistent effect of tillage for annual winter wheat, although the yield decline with re-cropping occurred one year earlier with tillage than with no tillage. Damage from CCN was lower with no-till than with tillage but the opposite was true for Pythium and Rhizoctonia root rots during 1991, and take-all and Pythium root rot during 1992. A trading of damage caused by various pathogens in a root disease complex caused yields to be comparable in the tilled and untilled annual wheat. The complexity of interactions in soils infested with multiple pathogens or parasites suggests that it will be difficult to develop predictive guidelines for specific crop rotations unless disease history is known.
Figure 2. Relationship of winter wheat yield to post-harvest numbers of H. avenae during 1990. Multiple regression analysis indicated that the strongest determinant of yield was combined damage from CCN and take-all, with CCN having the dominant effect (Fig. 2). Sources of resistance are known for CCN but not take-all. Rotating crops and introducing genetic resistance to CCN will most effectively control wheat affected by both of these pathogens. In conclusion, cereal cyst nematode can cause significant damage to continuous annual wheat, and to wheat following fallow or broadleaf crops contaminated by grass weeds or volunteer cereals. Winter wheat yields were highest when wheat was rotated with any other crop or fallow. This was particularly evident for wheat following fallow, peas, mustard or bluegrass. Crop rotation was the most critical factor affecting health and productivity of the wheat crop. The type of rotation was not as important as the use of any rotation crop or summer fallow. The cereal cyst nematode is generally recognized for causing more severe damage to spring wheat than winter wheat, but spring wheat was not evaluated in this study. ROOT-LESION NEMATODES (RLN) Root lesion nematodes are well known for damaging high-value irrigated crops (potato, mint, alfalfa, etc.) in the Pacific Northwest. While RLN are typically present in very low (non-damaging) numbers in winter wheat-summer fallow rotations, they have the potential to become numerous and damaging when dryland fields are cropped annually. Symptoms of root damage are likely to be confused with symptoms of nutrient deficiency, drought, or fungal root diseases. Lesions created by RLN also provide opportunities for heavier infection by fungal pathogens. Increasing evidence exists that RLN are causing damage in at least some cereal crops in the Pacific Northwest. For example, high numbers of P. neglectus and/or P. thornei have been detected in unthrifty stands of annual no-till hard red spring wheat in Walla Walla County, winter wheat exhibiting poor spring green-up and uneven plant height in Umatilla County, unthrifty wheat following canola in Union County, unthrifty winter wheat following green peas in Umatilla County, grass seed experiencing production problems in Umatilla County, and wheat cropped annually for 20 years in Nez Perce County. Nematologists at WSU-Prosser reported in 1986 and 1992 that RLN reduced growth of winter wheat in greenhouse tests. P. thornei and P. neglectus now are recognized for an ability to cause severe damage to wheat and other crops in non-irrigated regions of Colorado, Utah, Australia, Canada, Israel and Mexico. A better understanding of cropping systems in which RLN become numerous, and relationships between nematode numbers and suppression of potential grain yield, are important as growers face increasing economic and ecological pressures to increase cropping intensity and reduce tillage between crops. A survey of parasitic nematodes in 10 eastern Oregon and Washington counties was conducted, with emphasis on fields cropped annually. Ten to 20 soil cores (1-inch diameter x 4-inch depth) were collected directly in crop drill rows and mixed in a single bag. Equal numbers of plants were collected from the same sites. Samples were sent to the OSU Nematode Diagnostic Laboratory for nematode extraction and identification. Results are reported as nematodes per kilogram of soil (e.g., xx/kg soil), or nematodes per gram of fresh root tissue (e.g., xx/g root); 1 kg = 2.2 pounds, 1 g = 0.04 ounce. Soil and plant samples were collected shortly before or after harvest during 1999. RLN numbers were assessed for four Oregon (Moro, Echo, Pendleton, Pilot Rock) and one Washington (Ralston) location. Four experiments at the OSU Research Center at Moro were sampled. Crops included canola, lupin, and annual no-till spring wheat planted for the third and fourth consecutive years. No-till spring wheat produced annually for seven years was sampled near Echo. Fourteen experiments at the OSU Columbia Basin Agricultural Research Center near Pendleton were selected at random to represent a broad range of crops and cropping systems. Samples were also collected from two on-farm experiments where farm-size equipment and best management practices were used. Seven such rotations were sampled from Dr. Dan Ball's research trial near Pilot Rock, including continuous no-till spring wheat, spring barley/fallow/winter wheat with conventional or chemical fallow, fallow/canola/winter wheat with chemical fallow, and winter wheat/fallow with fallow prepared by moldboard plow, chisel, or herbicides. Winter wheat was planted into all plots during the sixth year, from which samples were collected for this survey. Five treatments were sampled from Dr. Frank Young's research trial near Ralston, including continuous spring wheat and rotations of spring wheat/spring barley, spring wheat/summer fallow, and winter wheat/summer fallow. During 1999, RLN were detected in all samples except those from Ralston. Populations of P. neglectus in two fields of annual no-till spring wheat at Moro (1,090 and 2,570/kg soil) were much higher than in nearby canola (140/kg) and lupin (20/kg) crops planted into summer fallows following winter wheat. Both P. neglectus and P. thornei were detected at Pendleton. Numbers were highest in annual spring (3,970/kg) and winter (1,610/kg) wheat, and in recrop canola (910/kg). Populations were lowest (less than 50/kg soil) in rotations of winter wheat following summer fallow, spring barley following canola, and no-till spring wheat following winter wheat. A mixture of P. neglectus and P. thornei was also present at Pilot Rock. Numbers in the winter wheat treatments were highest in the 3-year rotation that included canola (303/kg soil; 4,369/g wheat root) and lowest (7 to 25/kg soil; 127 to 305/g wheat root) in the 3-year rotation that included barley and summer fallow. Intermediate numbers (167/kg soil; 1,059/g root) occurred in annual spring wheat. Nematode numbers were generally lowest in rotations where winter wheat was produced once in three years rather than every other year or annually. Wheat yield at Pilot Rock was inversely correlated with RLN populations in roots (Fig. 3) and soil but it is not clear whether yields responded more to numbers of RLN or to available soil moisture, which was not measured. It is of interest, however, that similar yield trends occurred in these treatments during earlier years when drought was not a factor. Samples were collected in 2000 during spring, summer and autumn at 109 sites in seven Oregon counties (Gilliam, Morrow, Sherman, Umatilla, Union, Wallowa, Wasco) and three Washington counties (Adams, Lincoln, Walla Walla). Sites included 49 commercial fields, 26 research plots in commercial fields, and 34 experiments at research stations near Lind, Moro, and Pendleton. Data collected for each sample included site location indicators (altitude, latitude, longitude, nearest town, property owner or operator), tillage (direct drill or cultivated), recent crop history, numbers and species of parasitic nematodes, numbers of saprophytic nematodes, and symptoms of fungal root and crown diseases. Population dynamics through the season were also examined by collecting an additional 39 samples at sequential dates from some sites. During 2000, RLN were identified in 94 percent (139 of 148) of samples collected. Numbers ranged from zero to 2,449/g root, and from zero to 35,960/kg soil. The dominant species of RLN were P. neglectus and P. thornei. Other parasitic genera were also detected during the survey. Pin nematodes (Paratylenchus species) were present in 15 samples and had populations as high as 7,670/kg soil under dryland conditions and 20,210/kg soil under irrigation. Stunt nematodes (Tylenchorhynchus species) were present in 57 samples and had populations up to 2,430/kg soil under dryland conditions. Cereal cyst nematode (H. avenae) was identified in two of three Union County samples subjected to a special extraction treatment based on existing knowledge
Figure 3. Wheat yield and numbers of Pratylenchus neglectus in wheat roots following the 1999 harvest in a crop rotation and weed management study near Pilot Rock, OR; y = yield in bushels/acre, x = logarithmic transformation for numbers of P. neglectus/g root, r2 = correlation coefficient, p = degree of statistical confidence. that cyst nematodes were present in that region. Nonparasitic (beneficial) nematodes were present in all soils and numbers ranged from 330 to 21,890/kg soil, with no relationship between nematode numbers and tillage, cropping history, or irrigation. Although high numbers of RLN occurred in roots and soils of some annually cropped fields in low-rainfall, non-irrigated regions of Oregon and Washington, it is not yet possible to provide a meaningful interpretation of these observations. High numbers do not necessarily equate to high potential for damage because damage depends on complex interactions among the species and numbers of nematodes in or on roots, the crop species and variety, crop growth stage, crop rotation and tillage management, activity of fungal pathogens, and soil temperature, moisture and texture. Estimates of yield damage under field conditions are needed to interpret the population dynamics reported in this paper. In the absence of that information, reference values of 300 RLN/g root and 1,000 RLN/kg soil are being used for comparisons with reports from other regions. Economic damage to field crops has been reported at or above those numbers in several other regions or countries. It is anticipated that threshold values for dryland crops will be lower than for irrigated crops because the potential exists for water and nematode stress to become additive when crops deplete soil water reserves before maturity. Crops in about 40
percent of the fields sampled during 2000 had more than 300 RLN/g root
(Table 2). RLN numbers were influenced by crop rotation but not by tillage.
Winter wheat rotated with summer fallow always had less than 100 RLN/g
root. High numbers (more than 300/g root) occurred in 44 percent of the
situations in which crops were produced more than two of every four years.
In annual crop systems, RLN numbers in cereal roots and root-zone soils
were slightly higher when the cereal followed a broadleaf crop rather
than another cereal. This compares favorably with control of P. thornei
and increased wheat yield with crop rotation in Mexico, Isreal and Colorado. RLN numbers were
generally lower in roots of barley than wheat, although exceptions did
occur. Thirteen barley samples were collected, and three had RLN in excess
of 300/g root and ten had numbers below that level. About half the 102
wheat root samples had RLN in excess of 300/g. Australian scientists investigated
a situation in which wheat yields were consistently low on certain fields.
Wheat plants over entire fields were stunted, had reduced tillering, and
sometimes had yellowing of the lower leaves. Grain yields were commonly
half that expected in the region. All affected fields had clay soils and
had been cultivated for a minimum of 10 years. Application of the nematicide
Temik reduced P. thornei numbers from 400/kg soil to zero and increased
yield of nematode-susceptible wheat by up to 51 percent and nematode-resistant
barley by 10 percent. For comparison to the Australian study, the population
of P. thornei in wheat at Pendleton was up to 10 times higher (4,000/kg
soil) in annual spring wheat. Repetitive samplings from May to October revealed that RLN numbers in cereal roots were lowest during May and generally built up to their highest level as plants reached maturity. The summer of 2000 was very dry but autumn rains began on September 3 and were frequent into the winter. Volunteer cereal and grass weed seed germinated in September and seedlings became established before the sampling date in October. Numbers of RLN in volunteer cereal seedlings and downy brome during October were comparable to numbers of RLN in planted spring and winter cereal crops during May. Many growers allow volunteer to survive through the winter. If a spring crop is to be planted the volunteer and weeds are killed several weeks before the new crop is planted. If a winter wheat crop is to be planted, the field is usually cultivated, fertilized, and maintained weed free by multiple rod weedings during the summer. In each case, however, the presence of volunteer surviving through the winter greatly reduces the effective interval of the sanitizing break from one harvest to the next planting. The phenomenon named the "green bridge" has been emphasized for reducing damage by fungal pathogens but is equally applicable to nematodes, insects and virus diseases. For instance, with Rhizoctonia root rot of spring barley, productivity in the Pacific Northwest can be increased as much as 50 percent by killing volunteer and weeds during the early winter rather than waiting until early spring. Lesion nematodes have wide host ranges. P. neglectus infects all cereals as well as rotational crops such as grain legumes, pasture legumes, and oilseeds (Table 3). However, nematode multiplication differs greatly in roots of various crop species and among varieties within each species. Resistant varieties reduce nematode multiplication even though nematodes successfully invade their root system. Tolerant varieties allow multiplication and can carry high numbers of nematodes, but plants remain thrifty and yield well. Growth and yield are strongly reduced when roots of susceptible, intolerant varieties are invaded by nematodes. Knowledge of these relationships have important implications for crop rotation strategies, as production of each crop and variety will result in varying populations of nematode available to attack subsequent crops. High numbers of RLN were found in many of the broadleaf crops sampled. Some broadleaf crops currently recommended to "break the disease cycle" in wheat seemed more favorable than cereal crops for RLN multiplication (Table 4). For instance, RLN numbers in spring wheat roots were higher when the wheat was planted after mustard, canola or lentil than after spring wheat. The number of RLN exceeded 300/g root in each of these annual no-till crops. When an annual no-till field was planted successively to spring barley (2 years), mustard, and then winter wheat,
and then divided into various broadleaf crops during 2000, the reference level of 300 RLN/g was equaled or exceeded in roots of lentil, chickpea and narrow-leaf lupin. Numbers of RLN in this cropping system were much lower in roots of flax and safflower than lentil, chickpea (garbanzo bean) and lupin. Observations of high RLN numbers in other commercial fields were also made for several broadleaf crops and for cereals following either broadleaf crops or grass seed crops. Canola is considered a good to moderate host for P. neglectus and a poor host for P. thornei in Australia. Barley and lentil are considered intermediate hosts and chickpea and wheat varieties are highly variable. For instance, wheat varieties in Australia have up to 20-fold differences in numbers of RLN/g of root tissue, indicating very large differences in genetic potential to restrict RLN multiplication in roots. Australian nematologists consider rye, triticale, safflower, lupin and pea as poor hosts that may help reduce P. neglectus numbers in soil for the next crop (Table 3). It is unclear whether crop reactions will be the same in the Pacific Northwest, where crop genetics and production systems differ from those in Australia. We observed that RLN reached high numbers in two lupin varieties imported from Australia (Table 4). Since this crop is considered a poor host for RLN multiplication in Australia (Table 3), further research is needed to determine if lupin is truly a favorable host in the Pacific Northwest. During 1999 and 2000 there was an apparent absence of RLN in many fields in Adams and Lincoln counties of Washington. However, it was clear that the nematodes were present but below the easily detectable population levels because other fields in the same area, or on the same farm, had high numbers that apparently occurred in response to management systems on those fields. For instance, RLN were generally not detectable in nonirrigated fields near Tygh Valley and Lind, but reached high numbers in adjacent or nearby irrigated fields (Table 5). RLN numbers near Harrington were highly variable depending on sequences of annual crops growing in nonirrigated fields.
Field topography also influenced numbers of RLN. In a field near Pendleton (Table 5), RLN were much more numerous in winter wheat roots in a shallow drainage (10-30 feet wide) than in areas of the field immediately outside the drainage. The elevation of the drainage was only a few feet lower than the rest of the field, and the very gentle slope through the depression did not affect tillage and planting operations. Samples were collected both inside and 100-feet outside the drainage because wheat in the drainage was chlorotic and growing more slowly during the spring. The overall appearance of wheat in the drainage resembled a sulfur deficiency or damage by Pythium root rot. Wheat outside the drainage was dark green, vigorous, and looked "normal." Wheat and barley collected during May and June (2000) were evaluated for symptoms of root diseases caused by fungal pathogens. Symptoms of Rhizoctonia root rot were observed on about 80 percent of the 104 samples, and take-all was observed on about 50 percent. Strawbreaker foot rot affected 18 percent of the plants. Multiple diseases were detected on some of these plants. Results of the current survey indicate that RLN are present throughout the region and can multiply rapidly in response to irrigation and certain cropping systems. Shifting from a winter wheat/summer fallow rotation to annual cropping can lead to dramatic increases in numbers of parasitic RLN. It also appears that barley might be less favorable than wheat for multiplication of RLN, and that some broadleaf crops are favored hosts. Some fields previously tilled conventionally and planted to winter wheat are now being planted annually with no-till spring crops. More specific information on damage potential and crop sequence or variety effects is urgently required as growers move steadily away from the winter wheat/summer fallow rotation. While tillage intensity seemed to have no influence on numbers of RLN in our region, high populations of RLN occurred in roots of some broadleaf crops that are being evaluated to diversify crops in the annual cropping systems. Moreover, diseases such as Rhizoctonia root rot and take-all were not eliminated in wheat that followed summer fallow or crops of mustard, canola, lentil, safflower, alfalfa and pea. These observations are important because nematodes and fungal root pathogens often interact to cause damage more severe than either of the individual agents. Interactions of fungal pathogens and nematode parasites have not been studied in nonirrigated crops in eastern Oregon or Washington. In conclusion, root lesion nematodes are present in many non-irrigated fields in the inland Pacific Northwest. While it is currently impossible to establish direct associations between nematode numbers and yield constraints for broad-acre field crops, there is an accumulating body of circumstantial evidence that lesion nematodes are imposing a negative impact on crop yields in at least some dryland cropping systems in this region. More emphasis is needed for surveys of parasitic nematodes and crop damage estimates in dryland fields. If yield constraints are demonstrated, it would be possible to introduce genetic resistance into new cereal varieties and to design crop rotations with this constraint in mind. It also would be possible to equip commercial laboratories with modern molecular diagnostic systems that can offer reduced sample processing time and reduced skill in nematode taxonomy, compared to the time and expertise currently required for workers in nematode diagnostic labs. DIAGNOSTIC SYSTEMS FOR THE FUTURE Modern diagnostic systems are being developed to detect and quantify to amount of inoculum for soilborne plant pathogens in soil and plant tissue. These systems are based on the extraction of pathogen DNA directly from soil or plants. Scientists at the South Australian Research and Development Institute (SARDI), Adelaide, Australia developed tests for root pathogens of small grain cereals into a commercially available testing system. These tests are proprietary with SARDI and have now been licensed to C-Qentec Diagnostics, a subsidary of Aventis CropScience. Farmers in Australia are currently able to obtain a report on the amount of inoculum of soilborne pathogens for about $A4 per acre. The results for the fungal pathogens are expressed as picograms (pg) of DNA of the pathogen per gram of soil. For parasitic nematodes, the results are expressed as numbers of nematodes (or eggs) per gram of soil. Tests currently available include Fusarium pseudograminearum and F. culmorum (Fusarium crown rot), Gaeumannomyces graminis var. tritici (take-all), Rhizoctonia solani AG-8 (Rhizoctonia root rot), Heterodera avenae (cereal cyst nematode), and Pratylenchus species (lesion nematodes). A similar set of diagnostic systems has been under development at Pendleton since 1998, including tests for Pythium (9 species), Fusarium (5 species), Gaeumannomyces graminis (3 varieties), and Rhizoctonia (2 species). These tests have been particularly valuable for rapidly and precisely identifying the pathogens, identifying components of disease complexes that are very difficult to evaluate using traditional methods, and providing improved insights into processes of disease development and the spread of pathogens in plants and soil. Technical challenges still limit our ability to use these tests for certain plant and/or soil systems, and to use the data as a basis for predicting potential disease outbreaks. Nevertheless, they have proven very useful and there is a definite need to also develop molecular diagnostic protocols for detecting nematodes in irrigated and nonirrigated field crops in the Pacific Northwest. ACKNOWLEDGEMENTS The Oregon Wheat
Commission, USDA-CSRS-Pacific Northwest STEEP Research Program, and a
Cooperative Research Agreement with the USDA-ARS (Pullman) funded this
research, which was performed as a component of Oregon Agricultural Experiment
Station Project 268. Appreciation is given for assistance by technical
staff at the Columbia Basin Agricultural Research Center, USDA-ARS (Pendleton),
OSU and WSU Extension Service faculty in each county, OSU Nematode Diagnostic
Laboratory, Dr. Russ Ingham (OSU Nematologist), and growers and researchers
who gave open access to their commercial fields and experiments. Cereal Cyst Nematode:
Root Lesion Nematode:
|
||||
 Contact
us: Hans Kok, (208)885-5971
|
Accessibility | Copyright
| Policies | WebStats | STEEP Acknowledgement |
||||
