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

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

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

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

Common Stalk Rot Diseases of Corn

Extension Circular 1898 (EC1898) Stalk rot diseases of corn are common, occurring in every field to some extent. Each year stalk rot diseases cause about 5 percent yield loss. Under some conditions, losses can exceed 10–20 percent, and in isolated areas losses have been as high as 100 percent. Stalk rot diseases reduce yield both directly and indirectly. Plants with prematurely rotted stalks produce lightweight, poorly filled ears because of the plant’s limited access to carbohydrates during grain fill. Infected stalks are converted from sturdy, solid rods to hollow tubes as the stalk pith pulls away from the outer rind, compromising stalk strength. Rotted, weakened stalks are prone to lodging, particularly if decay occurs below the ear. Stalk rot diseases tend to be more common in higher yielding hybrids that produce large, heavy ears. During times of stress, such as when foliar diseases cause substantial loss of leaf area, these large ears may cannibalize carbohydrates from the stalk and weaken it. Large, heavy ears also can predispose the stalk to lodging with the added weight supported above weakened lower stalk tissue. Lodging indirectly reduces yield through harvest complications and ear loss. Stalk rot diseases can be caused by many fungi and bacteria. Most of these pathogens occur commonly in the field and behave opportunistically by primarily infecting senescing, injured, or stressed plants. A single plant often may be infected by multiple stalk rot pathogens which cause other diseases of corn and other crops. Each pathogen is favored by particular environmental conditions

Corn Disease Update

Goss\u27s Bacterial Wilt and Blight ... Symptoms ... 2011 Survey results ... New alternate hosts identified ... Goss\u27s Wilt Management Strategies ... More Resources ... Literature Cited Aspergillus Ear Rot and Aflatoxin Contaminated Grain ... Table 1. FDA Action Levels for Aflatoxin in Feed and Food ... Testing for Aflatoxin ... High risk factors for aflatoxin contamination in corn ... Scouting for Aspergillus Ear Rot ... Harvest and Storage ... More Resources Stalk Rot Diseases ... Scouting for Stalk Rot Diseases ... Management ... More Resource

Landscape and Garden Plants Sample Submission to the Plant and Pest Diagnostic Clinic

Diagnoses are made easier and turnaround time is improved when the quality of plant samples is maintained. This NebGuide discusses the proper guidelines for submitting landscape and garden plants, turf, and tree samples to UNL’s Plant and Pest Diagnostic Clinic. There are several important things to consider when collecting, packaging, and sending plant or insect samples for diagnosis in a plant diagnostic laboratory. Collect an adequate amount of plant material. When feasible, the sample should include the entire plant — roots, stems, leaves, flowers, and fruits. Whole plants are needed to properly evaluate the sample. If the whole plant is not available, photos of the symptomatic plants can improve accuracy of diagnosis

Factors Affecting the Development and Severity of Goss’s Bacterial Wilt and Leaf Blight of Corn, Caused by Clavibacter michiganensis subsp. nebraskensis

Goss’s bacterial wilt and leaf blight, which is caused by Clavibacter michiganensis subsp. nebraskensis, is a disease of corn (Zea mays) that has been increasingly reported across the Midwest since its reemergence in western Nebraska, northeastern Colorado, and southeastern Wyoming during the 2006 growing season. The objective of this study was to identify environmental and agronomic factors contributing to the incidence of the disease across the Corn Belt through a multistate survey conducted during the 2011 growing season. Of the 2,400 surveys distributed throughout nine states, 486 were returned with corn leaf samples, of which 70% tested positive for C. michiganensis subsp. nebraskensisusing an enzyme-linked immunosorbent assay. The agronomic data associated with each field were analyzed using classification and regression tree and random forest analyses to identify the factors that contributed most to Goss’s bacterial wilt and leaf blight development. A χ2 test of independence was also done to determine relationships between certain variables and disease incidence. The two best predictors of Goss’s bacterial wilt and leaf blight were hybrid resistance to Goss’s bacterial wilt and leaf blight, as indicated by the seed companies’ score and a planting population density \u3e67,500 plants ha−1. Other important predictors included longitude, planting date, crop rotation, percent residue, yield history, tillage, and growth stage. Relationships between glyphosate applications, foliar fungicide applications, and corn rootworm beetle with samples testing positive for C. michiganensis subsp. nebraskensis were also detected. These data contribute to our understanding of factors that increase the risk of Goss’s bacterial wilt and leaf blight, and should enable more effective management practices to be adopted or developed

Impacts of Drought on Disease Development and Management

Drought conditions such as those that occurred in Nebraska in 2012 can impact the development of plant diseases. In general drought slows down or prevents the development of plant diseases caused by pathogens that thrive under moist conditions. However, some diseases are favored by drought. This is because when plants are stressed due to lack of moisture or excessive heat, they become more susceptible to these diseases. This article presents examples of diseases of agronomic crops favored by drought and how to manage them. Data are provided on the effect of dry or wet conditions on the profitability of applying fungicides to control foliar fungal diseases of wheat. Charcoal Rot Diseases of Field Crops Aspergillus Ear Rot and Aflatoxin Contamination Fusarium Diseases Phoma Black Stem of Sunflower Root and Crown Diseases of Wheat Management of Foliar Diseases of Wheat with Fungicides in a Dry versus a Wet Growing Seaso