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,  “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 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

Asian Citrus Psyllid Quarantine Established in San Luis Obispo County

Breaking News: NEW ACP Discovery


Victoria Hornbaker, APHIS Citrus Program Manager, announced TODAY the first confirmed Asian citrus psyllid find in San Luis Obispo County as reported in a San Luis Obispo County Ag Commissioner’s press release.


Hornbaker also announced a Science Advisory Panel Report Stakeholder meeting will be held on April 16, 2014 at 9 am at CDFA headquarters, 1220 N Street, Room 220, Sacramento, CA 95814. To participate via conference call, please call 866-692-3158 and use participant code 87947483.

The meeting agenda follows this article.

Martin Settevendemie, Agricultural Commissioner/Sealer, County of San Luis Obispo announced detection of an adult Asian Citrus Psyllid in an insect trap on March 26th in a residential landscape near Arroyo Grande. The discovery prompted a high-density trapping delimitation survey of the immediate and adjacent area – about a nine square mile area – and no other ACPs were found.

A quarantine restricting the movement of citrus nursery stock and citrus fruit within a five-mile radius around the detection site has already been established by the California Department of Food and Agriculture to prevent the spread of this serious plant pest. “We are working with growers to get everyone in compliance with the regulation. This will help them understand what the requirements are to move any product outside of the quarantine area,” said Settevendemie.San Luis Obispo County Ag Commissioner Logo

CDFA announced that they will be conducting spray eradication treatments approximately 800 meters around the detection to eradicate this pest.

The first detection of the Asian Citrus Psyllid in California occurred in San Diego County in 2008. Since then, it has been found throughout southern California.

“This insect pest is of serious concern to California’s commercial citrus because it is responsible for spreading Huanglongbing, also called citrus greening disease, a plant disease that is fatal to all types of citrus trees. This includes citrus trees in countless landscapes across the county as well as local commercial citrus orchards valued at over $13 million in 2013,” according to Settevendemie.

Over the past ten years nearly 50% of the commercial citrus groves in Florida have been killed by this disease. The University of Florida estimates the disease has tallied more than 6,600 lost jobs, $1.3 billion in lost revenue to growers and $3.6 billion in lost economic activity for the state. The disease does not affect human health.

A single orange tree infected with Huanglongbing was found in a Los Angeles County backyard in 2012. To date no additional detections of the disease in California have occurred.

Staff from the San Luis Obispo County Agricultural Commissioner’s office and officials from the California Department of Food and Agriculture continue to search for this pest by monitoring hundreds of insect traps placed in urban neighborhoods and commercial orchards throughout the county.

“It is difficult to close off all potential pest pathways into the county. An engaged community of all county residents is critical in successfully excluding pests such as Asian Citrus Psyllid,” said Settevendemie.

Community members can do the following to protect backyard citrus trees and the local citrus industry:

        Buy Local! Purchase citrus trees from reputable local sources selling plants that have been routinely inspected by the Agricultural Commissioner’s staff.
        Do not transport citrus plants or plant parts into the county from quarantine areas. Call 805- 781-5910 for information about quarantine areas.
        Check residential landscaping often for signs of unusual symptoms or strange insects. Contact the local University of California Cooperative Extension’s Master Gardener Program at 805-781-5939 for help in identification of unusual plant symptoms or pests.
        If asked, allow the Agricultural Commissioner’s staff to place an insect trap in your yard and cooperate with officials if it becomes necessary to exclude or eliminate Asian Citrus Psyllid from San Luis Obispo County.

For more information about the Asian Citrus Psyllid visit the California Department of Food and Agriculture website or the San Luis Obispo County Agricultural Commissioner/Sealer’s website.



AGENDA FOR: ACP/HLB Ad Hoc Science Advisory Panel Report

Stakeholder Review/Conference Call

April 16, 2014, 9:00 a.m.


Call-in number: 866-692-3158

Passcode: 87947483

– This meeting is open to the General Public –



1. Call to order, introductions – Jason Leathers

2. Review of Science Advisory Panel Questions and Answers

3. Review of Science Advisory Panel Report

a. Rapid Detection of HLB Infected Trees and/or Psyllids

b. Longitudinal Study being Conducted at the UC Davis Containment Facility

c. Potential for Movement of CLas Infected ACP with Fruit Movement

d. Recommendations Regarding Areawide ACP Treatment Program

e. Recommendations Affecting Quarantine Area

f. Recommendations Affecting Citrus Nurseries

4. Additional Questions/Review Items