Pests and Diseases Cause Worldwide Damage to Crops

Pests and Pathogens Place Global Burden on Major Food Crops

By Pam Kan-Rice, UC Agriculture & Natural Resources

Scientists survey crop health experts in 67 countries and find large crop losses caused by pests and diseases

Farmers know they lose crops to pests and plant diseases, but scientists have found that on a global scale, pathogens and pests are reducing crop yields for five major food crops by 10 percent to 40 percent, according to a report by a UC Agriculture and Natural Resources scientist and other members of the International Society for Plant Pathology. Wheat, rice, maize, soybean, and potato yields are reduced by pathogens and animal pests, including insects, scientists found in a global survey of crop health experts.

At a global scale, pathogens and pests are causing wheat losses of 10 percent to 28 percent, rice losses of 25 percent to 41 percent, maize losses of 20 percent to 41 percent, potato losses of 8 percent to 21 percent, and soybean losses of 11 percent to 32 percent, according to the study, published in the journal Nature, Ecology & Evolution.

Viruses and viroids, bacteria, fungi and oomycetes, nematodes, arthropods, molluscs, vertebrates, and parasitic plants are among the factors working against farmers.

Food loss

“We are losing a significant amount of food on a global scale to pests and diseases at a time when we must increase food production to feed a growing population,” said co-author Neil McRoberts, co-leader of UC ANR’s Sustainable Food Systems Strategic Initiative and Agricultural Experiment Station researcher and professor in the Department of Plant Pathology at UC Davis.

While plant diseases and pests are widely considered an important cause of crop losses, and sometimes a threat to the food supply, precise figures on these crop losses are difficult to produce.

“One reason is because pathogens and pests have co-evolved with crops over millennia in the human-made agricultural systems,” write the authors on the study’s website, globalcrophealth.org.  “As a result, their effects in agriculture are very hard to disentangle from the complex web of interactions within cropping systems. Also, the sheer number and diversity of plant diseases and pests makes quantification of losses on an individual pathogen or pest basis, for each of the many cultivated crops, a daunting task.”

“We conducted a global survey of crop protection experts on the impacts of pests and plant diseases on the yields of five of the world’s most important carbohydrate staple crops and are reporting the results,” McRoberts said. “This is a major achievement and a real step forward in being able to accurately assess the impact of pests and plant diseases on crop production.”

The researchers surveyed several thousand crop health experts on five major food crops – wheat, rice, maize, soybean, and potato – in 67 countries.

“We chose these five crops since together they provide about 50 percent of the global human calorie intake,” the authors wrote on the website.

The 67 countries grow 84 percent of the global production of wheat, rice, maize, soybean and potato.

Top pests and diseases

The study identified 137 individual pathogens and pests that attack the crops, with very large variation in the amount of crop loss they caused.

For wheat, leaf rust, Fusarium head blight/scab, tritici blotch, stripe rust, spot blotch, tan spot, aphids, and powdery mildew caused losses higher than 1 percent globally.

In rice, sheath blight, stem borers, blast, brown spot, bacterial blight, leaf folder, and brown plant hopper did the most damage.

In maize, Fusarium and Gibberella stalk rots, fall armyworm, northern leaf blight, Fusarium and Gibberella ear rots, anthracnose stalk rot and southern rust caused the most loss globally.

In potatoes, late blight, brown rot, early blight, and cyst nematode did the most harm.

In soybeans, cyst nematode, white mold, soybean rust, Cercospora leaf blight, brown spot, charcoal rot, and root knot nematodes caused global losses higher than 1 percent.

Food-security “hotspots”

The study estimates the losses to individual plant diseases and pests for these crops globally, as well as in several global food-security “hotspots.” These hotspots are critical sources in the global food system: Northwest Europe, the plains of the U.S. Midwest and Southern Canada, Southern Brazil and Argentina, the Indo-Gangetic Plains of South Asia, the plains of China, Southeast Asia, and sub-Saharan Africa.

“Our results highlight differences in impacts among crop pathogens and pests and among food security hotspots,” McRoberts said. “But we also show that the highest losses appear associated with food-deficit regions with fast-growing populations, and frequently with emerging or re-emerging pests and diseases.”

“For chronic pathogens and pests, we need to redouble our efforts to deliver more efficient and sustainable management tools, such as resistant varieties,” McRoberts said. “For emerging or re-emerging pathogens and pests, urgent action is needed to contain them and generate longer term solutions.”

The website globalcrophealth.org features maps showing how many people responded to the survey across different regions of the world.

In addition to McRoberts, the research team included lead author Serge Savary, chair of the ISPP Committee on Crop Loss; epidemiologists Paul Esker at Pennsylvania State University and Sarah Pethybridge at Cornell University; Laetitia Willocquet at the French National Institute for Agricultural Research in Toulouse, France; and Andy Nelson at the University of Twente in The Netherlands. 

UC Agriculture and Natural Resources researchers and educators draw on local expertise to conduct agricultural, environmental, economic, youth development and nutrition research that helps California thrive. Learn more at ucanr.edu.

Boost Biomes Working on Disease Resistance

Researching the New Frontier

By Jessica Theisman, Associate Editor

California Ag Today recently spoke with Robert McBride of Boost Biomes. McBride explained his vision for the company.

“It’s the new frontier; It has not been researched that much,” he said.

He told us that the company is working on getting the correct microbes into the soil to enhance plants’ productivity.

“I would say the key thing that we think about in terms of getting the right microbes into the soil is that microbes are kind of like a plant’s second genome,” McBride said.

Genomes have the ability to impact the plant’s phenotype, along with the way the plants grow in different temperatures and soil salinity levels.

“They can change the flavor of the fruits and it is all controlled by the microbes in the rhizosphere,” McBride explained.

Boost Biomes is interested in controlling pest resistance. The microbiome shifts to a state that is protective.

“What we would like to do is take soils that are not protective and encourage that shift to happen more quickly,” McBride said.

Boost Biomes takes advantage of the natural microbes in the soil and rhizosphere that protect the plants.

“We are trying to identify the right network to put into the soil to get into the rhizosphere to make the plants resistant against diseases,” McBride explained.

Brexit Affects U.S. Agricultural Trade

Joel Nelsen’s Commentary on Washington D.C. Meetings, Brexit and U.S. Agricultural Trade

By Lauren Dutra, Associate Editor

Joel Nelsen, president of California Citrus Mutual based in Exeter, Calif., spoke about his advocacy for growers and the impact Brexit has on U.S. agricultural trade as he arrived at the Fresno Yosemite International Airport from Washington, D.C. last week. Brexit is an abbreviation of “British exit,” which refers to the June 23, 2016 referendum by British voters to exit the European Union (EU), according to Investopedia.

Nelsen explained, “There were two missions I was on while I was in Washington. One had to do with a proposal to allow lemon imports from Argentina. We’re definitely opposed to it because of pests and diseases, and a lack of transparency in that country over the last one to two decades.”

“We have a comment period,” Nelsen continued, “but we have asked for an extension on that comment period because of the scope of the rule and the economic impact, and we haven’t heard a word on that,” he said. “We met with our colleagues and friends in Washington, D.C.  Senator Feinstein, Senator Boxer and a couple of House Office Committees have agreed to make a phone call to the Secretary of Agriculture and get a determination on that,” he said.

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The second purpose of Nelson’s trip was to discuss trade and the impact on the U.S. economy due to the recent Brexit, as Nelsen is chairman of the Fresh Fruit and Vegetable Agricultural Technical Advisory Committee (ATAC), a national trade committee that offers information and advice about agricultural products and trade issues to the USDA Secretary of Agriculture and the U.S. Trade Representative. “People from across the country came, and we talked about trade subjects, such as the Trans-Pacific Partnership (TPP) agreement and Britain’s separating itself from the EU,” said Nelsen. “It’s obvious that this upset everybody; Ambassador Michael Froman, United States Trade Representative (USTR) who advises the president on international trade and investment issues, said, “I know what I don’t know, and I don’t know a lot right now.”

Nelson explained, “We think [Brexit] will slow down the fresh fruit and vegetable sector, as well as the passage of the Transatlantic Trade and Investment Partnership (T-TIP). According to the USDA Foreign Agricultural Service, since the U.S. market share of agricultural products and food imported by the EU—the world’s largest importer in the category—is shrinking despite continued growth of the EU market, T-TIP negotiations offer a major opportunity to address unjustified tariff and non-tariff trade barriers to U.S. exports.

“Quite frankly,” Nelsen summarized, “we’re less than excited about [T-TIP] because it didn’t address the inherent problem that we have from competition: fresh fruit and vegetable producers in the EU get a direct subsidy and growers in the United States do not.”

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Some additional members of the ATAC for Trade in Fruits and Vegetables include:

  • Julie Adams, Almond Board of California
  • James R. Cranney, Jr., California Citrus Quality Council
  • Robert Guenther, United Fresh Produce Association
  • Richard Hudgins,
    California Canning Peach Association
  • Randy Hudson, National Pecan Growers Council
  • Marcy L. Martin, California Fresh Fruit Association
  • Matthew McInerney, Western Growers
  • Ken Melban, California Avocado Commission
  • Mike Montna, California Tomato Growers Association
  • Jim A. Zion,
    Meridian Growers, LLC