Root-Knot Nematodes

Root-knot nematodes, Meloidogyne spp., are some of the most damaging plant pathogens. Several of the most common species of root-knot nematodes have been confirmed to reproduce and cause damage on sunflower, including M. arenaria, M. hapla, M. incognita, M. javanica, and M. hispanica. Meloidogyne spp. occur worldwide but are especially common in temperate, subtropical, and tropical regions. Countries where Meloidogyne spp. have been confirmed to affect sunflower include the United States and the African nations of Egypt, Mozambique, South Africa, and Zambia. Root-knot nematodes tend to cause the most damage to plants grown in sandy soils. Among these species, M. javanica has been shown to reproduce to the highest population density on sunflower

Diseases Caused by Parasitic Nematodes

Some plant-parasitic nematodes occur in every [sunflower] production field. Nematode populations likely include multiple species, although not all species cause notable disease. Symptoms depend on the species, the population density, and the crop\u27s interaction with environmental factors. Several nematode species are known to cause disease in sunflower, although little research has focused on their impact or management in the crop. The highest population densities of plant-parasitic nematodes often occur in isolated areas that are randomly distributed in fields, as do the most severe plant symptoms. Symptoms are not necessarily diagnostic for nematodes, and the problem may be misdiagnosed. The most common aboveground symptoms caused by nematodes include chlorosis (yellowing), stunting, and wilting during the day (with the plant recovering during evening hours). These symptoms may occur in isolated areas of fields associated with higher nematode population densities. Symptoms on roots are often overlooked but can be useful in making diagnoses, because they may implicate nematode damage as a potential cause and they vary by nematode species. Root symptoms caused by nematodes include lesions, misshaped roots (with stubby tips, enlarged galls, or unusual branching), and necrotic (dead) roots. Any of these symptoms can mimic those caused by other biotic or abiotic stresses and should not be strictly relied on when making a diagnosis. Submitting soil and root samples to a laboratory for nematode analysis is necessary for an accurate diagnosis

Northern Corn Leaf Blight

Northern corn leaf blight (NCLB) is a disease of corn caused by a fungus, Exserohilum turcicum (sexual stage Setosphaeria turcica). Its development is favored by cool to moderate temperatures and high relative humidity. Historically, NCLB has been more common and severe in states in the eastern Corn Belt, but its incidence has increased in Nebraska and the western Corn Belt in recent years. The disease is distributed throughout most of the corn-growing areas of the United States. The disease also occurs sporadically throughout other humid corn-producing areas of the world. In Nebraska, the disease has been most serious in the extreme eastern counties but is becoming increasingly common in central Nebraska during years when weather conditions are favorable for disease development. Yield loss caused by this disease can be extensive, up to 30–50 percent in susceptible hybrids when the disease develops early in the season, prior to tasseling. However, when disease severity is minor or its development is delayed until well after silking, yield impacts are usually minimal

Root-Lesion Nematodes

Root-lesion nematodes, Pratylenchus spp., are among the most commonly encountered plant-parasitic nematodes, with one or more species occurring in almost every field. Their small size (0.4-0.7 mm long) relative to most other plant-parasitic nematodes enables them to survive in almost any soil texture. Their wide host range and distribution make them one of the most damaging nematodes worldwide, ranging from cool temperate to tropical environments. At least eight species of root-lesion nematodes have been associated with sunflower

Grain Storage Management to Minimize Mold and Mycotoxins

As most dryland corn producers are aware, the dry and hot growing season in 2012 resulted in reduced corn yields with moderately lower test weights. Along with the reduced test weights are concerns about potential mycotoxin contamination in the drought-stressed grain. The only way to know for sure if there are mycotoxins in your grain and which specific mycotoxins are present is to collect representative grain samples and have them tested by a certified laboratory. Many species of fungi can cause ear rot diseases and molding of grain. Most of these fungi become associated with the grain in the field but may continue to grow and reproduce if grain is stored under favorable conditions of moisture and temperature in the bin. Harvested corn is NOT necessarily safer in the bin than in the field with regard to maintaining grain quality. If there was a problem with ear rot diseases in the corn in the field, there will likely be grain mold problems in the bin. Even under the best storage conditions, grain mold fungi are likely to continue to grow in the bin, where some can also produce mycotoxins. Under these conditions, it is important to cool and dry harvested corn as quickly as possible – preferably within 48 hours of harvest. It is NOT recommended to store infected grain, particularly for extended periods of time. In addition, grain that is damaged during or after harvest, such as during handling or storage by insects or other mechanical means, is much more prone to fungal infection by grain molds. Ear rot diseases and grain molds can lead to substantial reductions in grain quality that can ultimately cost producers who may be penalized at elevators or by loss of feed quality

Efficacy Evaluation of Foliar Fungicide Products on Diseases of Field Corn in Nebraska, 2012

A foliar fungicide efficacy trial was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory near Clay Center, NE. DeKalb corn hybrid DKC 64-83, rating of “good” (6 out of 9) for gray leaf spot (GLS), “very good” (4 out of 9) for common rust (CR), and “good” (5 out of 9) for southern rust (SR), was planted on 26 Apr in 30-in. rows at a target population of 30,600 plants/A. The trial area was disked with soybean as the previous year’s crop. Five foliar fungicide treatments and a nontreated control were replicated six times in a randomized complete block design. . . . The AUDPC calculations indicated that the fungicide treatments containing Headline 2.09 EC, in general, reduced GLS, CR, SR severity compared to other treatments. 500-count kernel weights ranged from 6.52 oz for the non-treated control to 6.63 oz for Headline 2.09 EC, 9 fl /oz A. There were no significant differences among treatments for 500-count kernel weights. Grain moisture at harvest ranged from 14.9% to 15.1%. Regalia Maxx, 8 fl oz/A, was the lowest yielding treatment at 271.3 bu/A while the nontreated control, Headline 2.09 EC, 6 fl oz/A, and Headline EC 2.09 EC, 6 fl oz + Regalia Maxx, 4 fl oz were the highest yielding treatments at 276.2 bu/A. There were no significant differences in yield among all treatments

Corn Disease Update

The growing conditions during 2013 contributed to several disease problems in corn. Cold and wet conditions early led to development of seedling diseases. The hail-damaged corn in many areas of the state during the season led to ear rot diseases that were exacerbated by cooler conditions and increased grain moisture. Diseases have been a problem throughout the season and could extend beyond harvest into storage of some corn

Efficacy Evaluation of Foliar Fungicide Products on Diseases of Field Corn in Nebraska, 2012

A foliar fungicide efficacy trial was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory near Clay Center, NE. DeKalb corn hybrid DKC 64-83, rating of “good” (6 out of 9) for gray leaf spot (GLS), “very good” (4 out of 9) for common rust (CR), and “good” (5 out of 9) for southern rust (SR), was planted on 26 Apr in 30-in. rows at a target population of 30,600 plants/A. The trial area was disked with soybean as the previous year’s crop. Five foliar fungicide treatments and a nontreated control were replicated six times in a randomized complete block design. . . . The AUDPC calculations indicated that the fungicide treatments containing Headline 2.09 EC, in general, reduced GLS, CR, SR severity compared to other treatments. 500-count kernel weights ranged from 6.52 oz for the non-treated control to 6.63 oz for Headline 2.09 EC, 9 fl /oz A. There were no significant differences among treatments for 500-count kernel weights. Grain moisture at harvest ranged from 14.9% to 15.1%. Regalia Maxx, 8 fl oz/A, was the lowest yielding treatment at 271.3 bu/A while the nontreated control, Headline 2.09 EC, 6 fl oz/A, and Headline EC 2.09 EC, 6 fl oz + Regalia Maxx, 4 fl oz were the highest yielding treatments at 276.2 bu/A. There were no significant differences in yield among all treatments

What’s New in Plant Pathology

Extension Plant Pathology Team Update Plant and Pest Diagnostic Clinic Update Disease Management Products Table 1. Foliar Fungicide Label Updates Table 2. New Product

Four Common \u3ci\u3eSetaria\u3c/i\u3e Species Are Alternative Hosts for \u3ci\u3eClavibacter michiganensis\u3c/i\u3e subsp. \u3ci\u3enebraskensis\u3c/i\u3e, Causal Agent of Goss\u27s Bacterial Wilt and Blight of Corn

Goss’s bacterial wilt and blight, caused by Clavibacter michiganensis subsp. nebraskensis (Cmn), has reemerged as an important disease of Zea mays (corn) in the U.S. Midwest. Results from a 2011 multistate survey indicated that Setaria spp. (foxtail) were often present in corn fields with a history of Cmn. The objective of this research was to determine if Setaria spp. that are common in the Midwest are susceptible to infection by Cmn. In the greenhouse, seedlings of four Setaria spp., including S. viridis (green foxtail), S. faberi (giant foxtail), S. verticillata (bristly foxtail), and S. pumila (yellow foxtail), and Zea mays (Golden Cross Bantam sweet corn, GCB) were inoculated with a suspension of 1.0 × 107 bacteria cells. The trial was arranged in a randomized complete block design and repeated once. Percent of symptomatic leaf area was visually estimated eight days after inoculation. S. faberi exhibited the highest levels of disease among the four Setaria spp., with disease incidence similar to what was observed on Z. mays. S. viridis was the next most susceptible. Symptoms were also observed on S. viridis, S. verticillata, and were lowest for S. pumila. Bacterial streaming was confirmed microscopically and Cmn was reisolated from the four Setaria species. Results indicate that these four Setaria spp. are susceptible to Cmn, thus serving as potential sources of inoculum