Crop disease can be seen as a major pest that has plagued farmers for centuries and how to deal with this crisis without causing serious environmental concerns can be quite a concern to many individuals working in agriculture. Crop diseases are considered to be the nightmare of every farmer due to how its effects can often lead to famine or an attack on food security. In the global market 20-40 percent of all crops are lost due to crop disease each year. Ways of dealing with famine improved in the 17th century where the feudal system began to break down. Also during this same time period, more prosperous farmers began to enclose their own land and improve their yields to sell the surplus crops for a profit. The Irish famine was the worst to occur in Europe in the 19th century and was caused by a lack of understanding on how to deal with various involving the causative agent of late blight, which is caused by the water mold Phytophthora infestans.

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The topic of crop disease is a common issue among farmers due to the nature of which on how it can cause yields to decrease easily. The normal functioning of the physiological processes are disrupted and deviated when a crop is suspected to a disease causing potential economic risk to farmers.  Many of these farmers do not want to sell crops that are unhealthy or about to die because selling a bad crop is the same as selling no crop. Some diseases are so common that eliminating them can cause tons of resources. Aster yellows is a chronic, systemic plant disease caused by a bacterium-like organism called a phytoplasma. Ten of the most common plant diseases are blight, canker, gall, leaf curl, leaf spot, powdery mildew, root rot, wilt, stunting, and chlorosis.
Blight is the most common of the bunch due to how easily it can be recognized by the sudden death of all plant tissues including leaves, stems, and flowers. Leaf gall is a known swelling that causes galls to form on roots, stems, and branches and are known to be caused by root knot nematodes and insects. These diseases hurt farmers and businesses and the impact is often a severe issue. Depending on the crop and the disease, yields lost can range from a small number such as 33 percent to most of all of the crop.
Pathogens such as fungi and plant viruses that infect plants are known for specializing in infecting people due to people not likely to catch a disease from working with diseased plants in your garden. Plant viruses are considered to be the second greatest contributor to yield loss while fungi is the number one cause of crop disease that creates around 85% of the crop diseases. Depending on the crop and the disease the amount of damages to the yields can vary. There are non-infectious disease agents known as abiotic diseases and infectious disease agents known as biotic diseases which both usually occur depending on certain factors such as pathogens, environmental conditions, and variety of crops planted.
Annual crop losses due to crop diseases are estimated worldwide at $60 billion a year. Farmers are known for spending billions of dollars on disease management, often without adequate technical support, resulting in poor disease control, pollution, and harmful results. In addition, plant disease if it spreads can devastate natural ecosystems, compounding environmental problems caused by habitat loss and poor land management. If a farmer missed a disease and the produce got into a packing shed or market, it would do nothing to the customer unless the package is full of mold or rotten produce.  Crops such as barley and wheat are used quite often in many studies involving crop disease. Farmers use probiotics to help plants be cured. According to the Fungicide trials over 2 years (2008 and 2009) in barley showed an average yield response of 9 % to the most effective fungicide treatment, D. teresan Ramularia, which showed that collo-cygni, an endophyte microorganism, being the main pathogens found in the trials (Abrahamsen et al.2011). Powdery mildews are considered of lower importance in barley due to wide employment of bred or genetically engineered for Mildew Locus O genes or known as mlo-resistance genes, a set of genes that are encoded for plant-specific proteins structurally related to metazoan G-protein that provide crops immunity to powdery mildew fungi. On the other hand when studying barley, common root rot and stripe rust are far more common due to being less resistant to said diseases.
Many methods are used to fight diseases such as blight. Crop rotation is one of the many popular methods. Planting resistant varieties, managing optimal planting, harvesting times, planting healthy, quality material, disinfestation of farming equipment, and managing plant nutrients according to crop needs are other great methods used to stop a huge loss due to crop disease. Good gardening and farming practices are a must for preventing crop diseases. Taking care of plant debris, dying or unhealthy stems and branches, and weeds is a known method to keep crops sanitized. Better air circulation is used to keep fungi from growing and cloching the crops with a hoop system covered in plastic can be used to prevent blight. Fertilizer can be applied on the plants to make the plants have a better immune system to fight off the diseases easier.
There are many organizations or programs that are known for disease control, but how these organizations want to solve disease control in a sustainable or in a profitable way is contested among different individuals. Cooperative Agricultural Pest Survey (CAPS) Program is one program that makes sure harmful plant pests and diseases are detected as soon as possible, before they have a chance to cause significant damage. Plant Pest and Disease Management and Disaster Prevention Program is a combined effort by the USDA APHIS to strengthen, prevent, detect, and mitigate invasive pests and diseases. Preventive and direct plant protection measures could limit economically unjustified pesticide treatments and limit the negative impact of pesticides or other crop protection measures on the surrounding environment. Sustainable plant protection requires a joint effort among stakeholders such as advisors, growers, experts at authorities, and researchers. Cultural and biological approaches are favored over pesticides when used to protect crops from pests and crop disease. Exploiting diversity in crops is the best option to improve food security in a changing climate due to how this method can reduce diseases by 73%. Finding advances in microbial diversity and ecology go hand in hand with creating a more sustainable means to fighting crop diseases. The development and improvement of molecular methods which are monoclonal antibodies, enzyme-linked immunosorbent assay and DNA-based technologies that make it possible to detect, identify and better understand the agents that cause plant diseases (Berlin). Research has shown that micro and macro organisms living in, on, or around the plant can take full advantage of the mutualist plant compartment in an innovative and sustainable diversity system.
 The work of the USDA’s Animal and Plant Health Inspection Service (APHIS) is one of the most common organizations that deal with ill plant fields. APHIS distributes funding to individual states to expand or enhance pest surveys, identification, and inspection under the Plant Protection Act. Farmers usually spray chemicals meant to kill germs or pests. They also may rip out and destroy sick plants. The goal is to make sure that the sick genes do not pass on to the offspring. In the past, analysis for finding said crop diseases were a lot harder to identify. Farmers would have to plant their next crop before finding out which diseases had attacked the previous crop (Hulick). According to a study done by Nutter Jr, the terms “crop injury” and “crop damage” are defined by measurable symptoms and signs caused by plant pathogens or pests as any reduction in the quantity and quality of yield that results from crop injury. These scientific terms are a part of our understanding of how disease severity relates to a yield loss. For example, barley often can have its value be cut by 2 dollars per crop when under a severe disease.
With so much extensive care done by farmers during both the growing stages and harvest to ensure infected crops do not enter market or processing, what do we do about post harvest diseases? Post harvest diseases can occur during storage, or even in the field without showing symptoms until later on. Post harvest diseases usually consist of bacterial and fungal infections and can affect large quantities of crops without proper precautions. An article from Charles Wilson titled Biological control of post-harvest diseases of fruits and vegetables: alternatives to synthetic fungicides stated “Spoilage of fruits and vegetables after harvest often causes losses as great as 25–50% of the harvested crop.” This is a loss that can occur quite easily if not taking the extra precautions needed and can also be the most frustrating because it is also the most preventable cause of disease.
At this point in agricultural advancements we are able to prevent the crop diseases in numerous ways in the form of chemicals as well as just simple farm management to ensure high productivity and a high output. This is necessary to our economy to meet the needs of our growing population. The way farmers maintain healthy crops is with the use of pesticides and herbicides, new species of disease resistant plants, and taking precautions.
Pesticides, fungicides, herbicides, and other synthetic chemicals have received a large amount of criticism over the last several years due to its harmful effects in the environment. However, synthetic chemicals like Round-Up can be argued that effective pesticides leads to an increase in production. The chemicals do not directly affect the plants ability to produce, but instead it protects the plant and keeps it healthy enough to produce. A study from the Mid-Atlantic region of America titled “Evaluation of Prophylactic Sprays on Pest Abundance, Foliar Damage and Yield in Winter Wheat” was conducted to show the effects of fungicides on a couple different plots of grain. The study began in 2009 where a plot of land was infected by disease after getting hit by large amounts of rainfall during the heading stage. “Under these conditions, fungicide applications appeared to reduce disease pressure which contributed to yield gains.” This is just one example of the numerous years and amount of data they recover that lead to the belief of fungicides and other synthetic chemicals leading to a reduction of crop diseases, created a higher yield.
Disease threshold plays a huge role for when farmers known when it is a good time to spray crops. It is usually best to apply pesticides when pest numbers or crop damage reach economically damaging levels known as thresholds. One example of a model is reported  by  Hobbelen which shows that fixed spray timings  against  Zymoseptoria  tritici, a fungi, are less effective later in leaf life.  The sprays do not deposit directly onto  the leaf surface as easily as when spraying in the leaf’s earlier life. The same data suggests that the strongest risk to a crop occurs from infections arising between the emergence of leaf 2 and the flag leaf and roughly two latent periods before these leaves would naturally start to senesce. Soil must be dry and there must be little rain when also applying pesticides. Fungicides are best sprayed early in the morning but herbicides are usually sprayed much later.
Disease resistant plants are newer options in agricultural history which began taking place during the Green Revolution. The idea of scientifically breeding plants to create a stronger and more durable crop was a giant step in science. Scientists are able to pick and choose characteristics they want in a plant by breeding it with an ancestor with the help of seed banks. Seed banks are seed storage facilities where numerous seeds of the same or similar species can be stored for research or even in case of natural disasters. These seed banks are very helpful for scientist to review older species of plants to artificially breed new ones. For instance if an ancestor of the tomato plant had a very poor yield, but was very resistant bacterial and fungal diseases, that ancestor could be bred with a species that knowingly has a high yield to create a stronger plant while still maintaining a high yield that’s necessary.
There are aspects that need more research and improving. For example the constant battle between organic and non-organic farming is at an all time high right now. Consumers want healthy, organic produce, but we also know that organic farming has a greater yield-loss due to pests and diseases. Therefore improving the synthetic chemical industry and creating as safe and productive product as possible would be crucial in today’s world. Once a task is accomplished, much consumer education will be needed to ensure them it’s just as safe as organic.
Advocates for fighting disease and increasing yield come in numerous forms as there’s numerous ways to prevent a field from becoming infected. Organizations such as the National Association of Plant Breeders, or NAPB, play a large part in the research and development of creating the new species of plants. Nutrien Ag Solutions is known to be yet another company to combat the issue a farmer may encounter a reduction of yield due to disease infection. Nutrien works directly with the farmers to ensure healthy crops that lead to high production. Some of the products and services they provide are fertilizers, high performance seeds, and crop protection products. These crop protection products include herbicides, insecticides, and fungicides. These are just two examples of the leading contributors to the fight against crop disease.
As a whole, diseases affect crop productivity in numerous ways and is such a big issue in agriculture due to our rapid increase in production. Scientist and farmers worked so hard during the second agricultural revolution and Green Revolution to keep up with the demands of the American people and U.S. economy by quickly increasing our productivity and cutting down on yield losses. This fight is not over and never will be as there are diseases becoming chemically resistant, but it is important that we always stay one step ahead and are fast acting on new diseases. Everyone knows yield is a major part of our agricultural industry. We are always pushing for more and more productivity. Disease is an issue that has a direct impact on a fields yield as farmers do not want infected crops entering the food system. As stated before selling a bad crop is the same as selling no crop. The industry is heading in the right direction but I believe we can all agree that were not exactly where we want to be.
Works Cited

Berlin, Anna, et al. “Scientific Evidence for Sustainable Plant Disease Protection Strategies for the Main Arable Crops in Sweden. A Systematic Map Protocol.” Environmental Evidence, BioMed Central, 15 Dec. 2018, environmentalevidencejournal.biomedcentral.com/articles/10.1186/s13750-018-0141-3.
Chen, Guihua, et al. “Evaluation of Prophylactic Sprays on Pest Abundance, Foliar Damage and Yield in Winter Wheat.” International Journal of Pest Management, vol. 61, no. 2, Apr. 2015, pp. 161–170. EBSCOhost, doi:10.1080/09670874.2015.1028510
“Crop Protection.” Nutrien Ag Solutions, 13 Aug. 2019, www.nutrienagsolutions.com/products/crop-protection.
Fickle, Andrea. Crop Losses Due to Diseases and Theirimplications for Global Food Production Losses and Food Security. ResearchGate, Dec. 2012.
Hulick, Kathryn. “As Infections Ravage Food Crops, Scientists Fight Back.” Science News for Students, 15 Aug. 2019, www.sciencenewsforstudents.org/article/infections-ravage-food-crops-scientists-fight-back.
Nutter, Forrest W. Terms and Concepts for Yield, Crop Loss, and Disease Thresholds. Iowa State University, 2 Feb. 1993.
Sanders, Robert. “Fertilizer Destroys Plant Microbiome’s Ability to Protect against Disease.” Berkeley News, 30 July 2018, news.berkeley.edu/2018/07/26/fertilizer-destroys-plant-microbiomes-ability-to-protect-against-disease/.
“Welcome: National Association of Plant Breeders (NAPB).” Welcome | National Association of Plant Breeders (NAPB), www.plantbreeding.org/.
Wilson, Charles L., et al. “Biological Control of Post-Harvest Diseases of Fruits and Vegetables: Alternatives to Synthetic Fungicides.” Crop Protection, vol. 10, no. 3, 1991, pp. 172–177., doi:10.1016/0261-2194(91)90039-t.
Berg, F. Optimal Fungicide Application Timings for Disease Control. 5 July 2013, apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-03-13-0061-R.