PROGRESS REPORT TO THE OREGON PROCESSED VEGETABLE COMISSION, December 20, PRINCIPAL INVESTIGATOR: Alex Stone, Dept.

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1 108 PROGRESS REPORT TO THE OREGON PROCESSED VEGETABLE COMISSION, December 20, 2002 TITLE: Impact of cover crops and organic amendments on root rot of corn. PRINCIPAL INVESTIGATOR: Alex Stone, Dept. of Horticulture TELEPHONE: (541) GRADUATE STUDENT: Heather Darby (541) PROJECT FUNDING: $15,916 SUMMARY OF WORK: 1. Soils of high disease severity. Container trial: Soil amended with composted dairy manure suppressed root rot after two amendment cycles. Dairy manure did not suppress root rot. Sudangrass reduced severity of root rot by 20% in 1 out of 2 field soils tested. No other cover crops suppressed root rot in either soil. Almost all cover crop species increased corn root biomass in one out of two soils. Annual ryegrass, oats and sudangrass reduced root biomass in one of two soils after one amendment, but annual ryegrass increased root biomass after the second amendment. All the casual agents of root rot of corn (Pythium arrhenomanes, Phoma spp., and Drechslera spp.) were isolated from the roots of all annual ryegrass and cereal rye plants examined. These pathogens were isolated from oats and sudangrass once. 2. Soil of low disease severity. Field trial: Soils amended with manure and compost suppressed root rot by up to 81 %. Suppressiveness was strongly related to microbial activity. 3. Field scale cover crop trials: A field scale cover crop trial was established in late summer and fall of 2002 on the OSU vegetable research farm. A demonstration cover crop trial was established at Kenagy Family Farm (Peter Kenagy) in Albany. INTRODUCTION In general, additions of organic matter amendments (organic wastes and plant residues) to field soils have been shown to suppress a variety of soil-borne diseases. Organic matter mediated suppression has been associated with enhanced competition between soil microorganisms for carbon and other nutrients (e.g. iron and nitrogen), antibiotic production, direct parasitism of the pathogen, and induced resistance in the host plant. An increase in the soil's microbial activity is often associated with suppression of the disease of investigation. In most instances multiple years of amendment allow for more predictable improvements in yield, quality, and disease suppression. Cover crops are a common form of organic amendment and can play many roles in a cropping system. Cover crops have been traditionally used to cycle nutrients, protect soil from water and wind erosion, and suppress weeds. Less research has been conducted on their effects on plant diseases. Cover

2 109 crops have been shown to reduce, enhance, or have no effect on plant diseases. A cover crop can act as a host for a soilborne pathogen, resulting in an increase in pathogen populations and disease incidence in subsequent agronomic host crops. On the other hand, cover crops can increase the populations of beneficial organisms. Plants have the ability to change the composition of the soil microbial community through selection of the microbes associated with their plant tissues roots, leaves and stems. Some crops, such as mustard family plants and sudangrass, can actually destroy pathogen propagules immediately after incorporation. These plants contain compounds which break down during soil incorporation into chemicals that have detrimental effects on the survival of fungal mycelia and resting structures such as sclerotia and chlamydospores. Experiments were conducted in 2001 and 2002 to determine the effect of cover crops and manures on root rot of corn. A container study (utilizing a soil with a history of the disease) and a field study (in a field with no history of root rot of corn) were initiated to determine the impacts of organic amendments and cover crops on corn root rot. Field trials established in 2002 will investigate the impact of cover crop species on corn root rot, biomass, and yield. MATERIALS AND METHODS 1. Soils of high disease severity. Container trial: The objectives of the study were to determine the effect of green manuring with cover crops and amending soils with manures (and the frequency of these treatments) on the severity of root rot of corn and bean. In 2001 and 2002, container studies were conducted to evaluate the impact of cover crops on root rot of corn. Soil was collected from two different fields that have had a history of severe root rot symptoms. The soil was sampled in April of 2001 and March of 2002, screened, and placed into 16 L plastic containers. The experimental design was a randomized complete block. Containers were arranged in shade houses outdoors at the OSU vegetable farm. Treatments were initiated in May. At this time, cover crops were seeded at recommended field rates and organic wastes were incorporated into the soil. Containers were watered as needed. 2001: The experiment was a 14 x 2 factorial treatment design (42 treatments) replicated 4 times, and included 14 treatments (cover crops, organic wastes, and fallow control) and 2 amendment dates. The treatments included 11 cover crop species (five cereals annual ryegrass, oats, cereal rye, triticale, and sudangrass; two legumes common vetch and crimson clover; two mustards yellow mustard and rape; Phacelia, and oilseed flax), raw (15 dry tons/a) and composted (25 dry tons/a) dairy manure, and an unamended control. The soil was sampled from Country Heritage Farm in Dayton. 2002: Only those treatments that generated significantly more or less disease than the control in the first experiment were grown in the second year of the experiment. The treatments were annual ryegrass, oats, cereal rye, sudangrass, raw and composted dairy manure, and an unamended control. The soil was sampled from Jim Belden's farm in Stayton. Cover Crop Amendment Cover crops from all containers were harvested 2 months after planting. At harvest time, shoots were cut at the soil surface with pruning shears. Approximately 10 % of the total shoots were subsampled and weighed. The remaining shoots were weighed and cut into approximately 2.5 cm pieces. The top 15 cm of soil from the container was than placed into a 40 L plastic tub, and the roots were hand-harvested. Roots were visually assessed for severity of root rot. Symptomatic root pieces

3 110 were surface disinfested and plated onto water agar for pathogen recovery and identification. Only the casual agents of root rot of corn were identified. Subsamples of both roots and shoots were oven dried at 60 C, and reweighed to determine moisture of the incorporated plant parts. The cut up pieces of shoots and roots were mixed into the top 15 cm of the soil, and the soil was placed back into the container. The cover crops were allowed to decompose for 6 wks. After decomposing for 6 wks, one half of the containers were reseeded with cover crops or re-amended with organic wastes. The remaining containers were used to evaluate the effect of a one-time soil amendment on suppression of root rot of corn and bean. Corn Bioassays Soils were placed in 550 ml plastic tubes and placed on the greenhouse bench. Corn seeds, cv Golden Jubilee, were surface disinfested in 10% bleach for 5 min and rinsed in distilled water before planting into the plastic tubes. Plants were watered as needed and fertilized weekly with water soluble at the recommended rate. Corn plants were harvested at 5 wks, plant height recorded, rootballs washed and evaluated for severity of root rot, and shoots and roots oven dried at 60 C and weighed. Disease was evaluated by visually assessing the percentage of the radicle with lesions. Disease rating was based on a 0 to 4 scale where a score of 0 meant no lesions and a score of 4 meant 100 % of the radicle had lesions. Soil of low disease severity. Field trial: The objectives of the study were to determine the effect of raw and composted manure amendments on root rot of corn and bean. Plots were established at the Oregon State University Vegetable Research Farm in Corvallis on a Chehalis silt loam during The previous crop was snap bean (Phaseolus vulgaris). Plot size was 20 x 30 ft. The experimental design was a randomized complete block with 5 treatments replicated 8 times. The 5 treatments comprised of two rates of raw dairy manure (7.5 and 15 dry t/a) and composted dairy manure (12.5 and 25 dry t/a), and an unamended control. Amendments were applied in the spring of each year and incorporated into the soil with a rotovator. Plots were planted to sweet corn cv, "Golden Jubilee" in 2001 and to snap bean cv, "Oregon 91G" 910" in Bulk soil was collected from plots prior to planting to simultaneously conduct corn bioassays in a greenhouse environment. Soil microbial activity (rate of hydrolysis of fluorescein diacetate/fda) was measured 4 wks after planting. Infield In-field and Greenhouse Corn Bioassays Treatment soils were placed in 550 ml plastic tubes. Corn seeds, cv "Golden Jubilee", were surface disinfested in 10% bleach for 5 min. and rinsed in distilled water before planting. At 5 wks corn plants were harvested and evaluated for root rot severity. Statistical analysis Treatments were compared with analysis of variance and treatment means separation were obtained using a LSD test when significant F-tests (P <0.05) were observed. Regression analysis was used to identify significant relationships (P < 0.05) between disease and microbial activity. Field scale cover crop trials: Two cover crop trials were established in 2002: Experiment station field trial: Two trials were established. Trial A was planted to cover crops in 2002 and will be planted to corn in Trial B will be planted to cover crops in both 2002 and 2003 and planted to corn in Cover crops were sown in 20' x 20' plots replicated four times in a randomized complete block design. Soils were collected at planting from all plots in a block and composited. Cone

4 111 tube bioassays were conducted on each composite sample to determine whether the soils in the plot were naturally infested with root rot. There is a moderate level of disease potential in Trial A and a low level of disease potential in Trial B. Cover crops were chosen based on their demonstrated ability to suppress pathogens and/or enhance plant growth, or their widespread use in the Willamette Valley. Four combinations of species are included in the trial. Sudangrass "Piper" was planted on August 10, 2002, and the fifteen others were planted on Sept. 20, The treatments are: Foenugreek, Phacelia, Saia Oats, Common Vetch, Crimson Clover, Meadowfoarn, Meadowfoam, Berseem Clover, Sudangrass "Piper", Biomaster Pea, Sorghumsudangrass hybrid, Rape (Canola), Mustard Mix ("Caliente"), and the mixtures Oats/Common Vetch, PhaceliaNetch/Crimson Clover, Common Vetch/Biomaster Pea, and Saia Oats/Biomaster Pea. In the spring of 2003, aboveground cover crop biomass measurements will be taken. Cover crops will then be incorporated and allowed to decompose for at least three weeks. Corn will be sown, and samples will be evaluated at the six leaf stage for root rot. Soils will be sampled and greenhouse cone tube bioassays will be conducted to assess root rot severity. The remaining corn will be grown to maturity and ear weight and quality, number of ears, biomass, leaves fired, and disease severity will be measured at harvest. On-farm demonstration trial: An on-farm demonstration trial was installed at Kenagy Family Farm (Peter Kenagy) in Albany. The trial was planted to winter cover crops: Berseem clover, foenugreek, Phacelia, oats, common vetch, winter pea "Biomaster", and mustard blend "Caliente". Cover crops were planted in 25 ft. strips the length of the field. One strip was left fallow as a control. The field was divided into three sections (across the treatment strips) to delineate three "blocks". Soil was sampled from three locations in each treatment strip (representing the three "plots"). Cone tube corn root rot bioassays were conducted on each soil sample (as described above) to determine corn root rot disease potential in each "plot". Disease severity was moderate to high across all plots. Corn will be planted in this field in 2003 and disease severity will be evaluated at the 6 leaf stage and at harvest. RESULTS 1. Soils of high disease severity. Container trial: Cover Crop Disease Assessment Symptomatic lesions were observed on the roots of annual ryegrass and cereal rye on plants from every pot and every cover crop planting cycle. Pythium arrhenomanes, Phoma spp., and Drechslera spp. were recovered from some of the lesions on these plants. Pathogens were isolated from oats and sudangrass roots from only one pot (out of four) from one (out of six) planting cycles. Effect of Cover Cropping and Amendment on Corn Biomass Results from 2001 and 2002 were analyzed separately because the soil was collected from two different fields. In field soil one, the highest corn biomass production occurred following cover cropping with legumes (Table 1). This can most likely be attributed to the carryover effect of N from leguminous crops (although there may be other mechanisms involved as well). Soils amended twice with compost generated significantly higher corn biomass than all other treatments with the exception of the legumes. Two cycles of green manuring with sudangrass had an adverse effect on corn growth (Table 2). There are two possible reasons that this occurred: 1) the high amounts of hydrocyanic acid produced by decomposing sudangrass may have stunted corn growth, or 2) the microorganisms sequestered N from the corn plant to aid in the decomposition of sudangrass. Sudangrass has been shown to decompose slowly especially under nitrogen-limiting conditions. In field soil two, only the compost treatment generated significantly higher biomass than the unamended control.

5 112 Table 1. Sweet corn biomass after one or two amendment cycles (field soil one). Treatment One Two 9 9 CEREALS annual ryegrass *t cereal rye * oats * triticale * sudangrass LEGUMES common vetch 5.12* 4.93* crimson clover 4.75* 475* 5.04* MUSTARDS yellow mustard * rapeseed OTHERS Phacelia * oilseed flax 5.13* 3.55* ORGANIC WASTES manure * compost * CONTROL Fallow t Treatments followed by a **are significantly different from the control (P <0.10). Table 2. Sweet corn biomass after one or two amendment cycles ( field soil two). Treatment One Two 9 9 CEREALS annual ryegrass cereal rye oats sudangrass ORGANIC WASTES manure compost 6.011' 6.01*t 4.28* CONTROL Fallow t Treatments followed by * are significantly different from the control (P <0.10).

6 113 Effect of Cover Cropping and Amendment on Severity of Corn Root Rot Severity of root rot of corn varied little among treatments (Figs. 1 and 2). In field soil one, corn planted in soil after two compost amendments had 12 % less root rot than corn grown in the fallow control (Fig. 1). The compost treatment had as much as 50 % less disease than the control after one or two amendments in field soil two (Fig. 2). Manure amendments did not have a significant effect on root rot severity compared to the fallow control. Sudangrass had significantly less root rot compared to the control in soil one but no difference was seen in soil two cee c,40 % e5 e (" Co. e % go' e Soil amendment Fig 1. Impact of one or two amendment cycles on root rot severity of corn in field soil one. t Within an amendment, treatments followed by * are significantly different from the control (P <0.10).

7 114 III Amendment 1 0 Amendment 2 6_<)" 6_<1.%.G1 qt.* o Soil amendment Fig 2. Impact of one or two amendment cycles on root rot of corn in field soil two. t Within an amendment, treatments followed by * are significantly different from the control (P < <0.10). 4e, %. b'c' v". <*f.00,,f>t zgo cd,4.44 'V 4 e ff 4z,,t? cd Soil amendment Fig 3. Impact of one or two amendment cycles on corn root biomass in field soil one. t Within an amendment, treatments followed by * are significantly different from the control (P <0.10).

8 115 Effect of Cover Cropping and Amendment on Corn Root Biomass: In soil one, many cover crop species (annual ryegrass, cereal rye, oats, triticale, common vetch, and yellow mustard) increased corn root biomass after the first amendment cycle (Fig. 3). Compost also increased root biomass, but manure and the other cover crop species had no effect on corn root biomass (Fig. 3). After the second cycle, all treatments but cereal rye, rapeseed, sudangrass, and Phacelia increased root biomass (Fig. 3). In soil two, annual ryegrass, oats and sudangrass reduced corn root biomass after cycle one, while all other treatments had no effect (Fig. 4). The annual ryegrass and the compost and manure treatments increased corn root biomass after cycle two (Fig. 4) Soil amendment Fig 4. Impact of one or two amendment cycles on corn root biomass in field soil two. t Within an amendment, treatments followed by * are significantly different from the control (P <0.10). 2. Soil of low disease severity. Field trial: In 2001, HMS, LMSC, and HMSC had significantly lower (P <0.05) levels of root rot than the unamended control soil (Fig. 5). Compared to the control, disease was suppressed as little as 21 % in the HMS and as much as 84 % when soils were amended with HMSC. After the second year of amendment, corn grown in all treatments had from 46 % to 71 % less root rot than the unamended control. As soil microbial activity increased, the severity of root rot of corn decreased (Fig. 6).

9 116 LMS HMS LMSC HMSC Soil amendment Fig. 5. The impact of raw and composted manure amendments on severity of root rot of corn in a field trial. t f Within an amendment, treatments followed by * are significantly different from the control (P <0.10) Microbial activity (ug hydrolyzed FDA min-1 g-1 dry wt) Fig. 6. The relationship between microbial activity and severity of root rot. DISCUSSION: Raw and composted manure amendments show potential for suppression of root rot of corn. These materials increase microbial activity, which is strongly related to disease suppression. While the application of manures and composts is not practiced by most corn growers at this time, these results indicate that increasing microbial activity in field soils (and this could be achieved through other means, e.g. high biomass cover cropping) may be one strategy for reducing disease severity.

10 117 The choice of cover crop species can influence the severity of root rot of corn, although in our work the results varied from soil to soil and species to species. The cover crop work was conducted in containers, and this may not be a very effective means of understanding the impact of cover cropping on the severity of root rot of corn. The cover crops do not grow as they would in field soils, and don't generate equivalent quantities of biomass, which may be the most significant impact of cover crops on soilborne diseases (as it supports microbial activity). For this reason, all future work will all be conducted in field trials. Annual ryegrass and cereal rye may be hosts to the pathogens implicated in the corn root rot complex. Isolation of organisms from these plants (on a consistent basis) supports the theory that some cover crops may be hosts to the pathogens that cause root rot of corn. However, the container work also indicates that cover cropping with annual ryegrass can also increase corn root biomass. The impact of a specific cover crop on corn growth and disease severity, and ultimately yield, will be the result of many interacting factors. These may include its biomass (and its effects on overall microbial activity), its specific impacts on soil microbial ecology, its effects on corn nutrient status, as well as whether or not it has potential as an alternate host to pathogens. Two cycles of treatments of an infested field soil with sudangrass significantly reduced the severity of corn root rot; however, cover cropping with sudangrass also reduced corn biomass. On the other hand, cover cropping with legumes had no effect on corn root rot but significantly increased corn biomass production. Mixing species that can generate suppression with those that generate growthpromotion may prove valuable. Effects of sudangrass in field soils (and after winter decomposition) may be different than the effects observed in this container trial. Negative effects of sudangrass on corn biomass may be due to N immobilization and therefore could be managed through fertilization. It is important to keep in mind that the utilization of each cover crop species (and the maximization of its benefits) within the context of each farm and cropping system may require fine-tuning.