So Much Depends Upon a Strong Green Bough: The Vital Importance of Plant Health

Dr. Tim Widmer is the ARS National Program Leader for Plant Health in the Crop Production and Protection Program area. He works on issues including the National Plant Diseases Recovery System, as well as antimicrobial resistance, soil health, and Ag-Biosecurity. More detailed information about recent work he has led can be found in "Impact of the United States Department of Agriculture, Agricultural Research Service on Plant Pathology: 2015–2020".

Welcome Dr. Widmer to Under the Microscope.

UM: Why should people be concerned about plant health?

TW: It can directly affect the availability and prices that they pay in the grocery store, and the plants they grow in their own gardens.

UM: How is plant health related to our daily lives, especially food security?

TW: Everyone needs food, including animals, and that comes from plants. If plants become diseased or are eaten by insects, then the amount of available food can decrease. Depending upon the severity, this may lead to food shortages and higher consumer prices. Any reduction in food due to declining plant health will have an ever-larger impact as the world's population increases and we need to produce more food on equal or less available farmland.

UM: What plant diseases are of greatest concern to growers right now? Which plants are affected?

Symptoms of the severe strain of wheat stem rust (Ug99) on wheat. (Photo courtesy of the ARS Cereal Disease Laboratory)

TW: There are two things to look at here. One is diseases that directly impact food security, in staple crops such as wheat, corn, soy, potatoes, and fruits and vegetables. There are numerous diseases of each of these crops. Viral diseases are of increasing concern because they are usually transmitted by insects or by seed, and movement of plant material around the world can quickly spread them to new areas. The other issue is how diseases impact the bioeconomy of nonfood crops, like ornamental and landscape plants. A good example is sudden oak death, which kills some oaks, but is not lethal for ornamental plants, and so can often go undetected. To reduce its spread, many regulatory policies were put in place to restrict movement of certain ornamental plants, costing the industry millions of dollars.

UM: What are the biggest issues of concern for our main crops, like corn, wheat and soy?

TW: There are several issues. Plant diseases such as wheat blast and a severe strain of wheat stem rust called Ug99 are of concern for wheat production, tar spot for corn production, and soybean rust for soy production. In addition, herbicide-resistant weeds are becoming more prevalent. Insect pests are also always a concern, including wheat stem sawfly and soybean aphid. 

UM: What factors have historically protected our food supply from widespread plant diseases? Are the risks different now, and if so, why?

TW: In general, synthetic fungicides and antibiotics have been the main option in the past 30 years. However, there is an increasing trend to reevaluate these chemicals due to environmental, health, and safety concerns and the increase in resistance by pathogens.

In addition, breeding for host resistance to specific pathogens has been a very important sustainable management option. The downside is that it takes time to develop and produce enough plant material. We also must understand the plant genetics well, as pathogens can overcome the genetic resistance mechanisms over time. With changing climate patterns, there is also increased risk that pathogens will appear in new regions, and that changing conditions will increase the aggressiveness of the pathogens.

Symptoms of wheat blast disease on wheat. (Photo courtesy of Gary Peterson, USDA-ARS)

UM: Where do new plant diseases come from, and how do they spread?

TW: They usually come from locations where a pathogen has co-evolved with a native host. Often, it's not even considered a pathogen, as the host is not killed, and both co-exist. However, pathogens can infect more than one host and if moved to a new area, or if a new host is introduced to that area, the pathogen may be more aggressive toward the new host, killing it. Plant pathogens mainly spread by humans (global trade, travel, etc.), infected seeds and plant material being moved around, insects, and weather events (rain, wind, hurricanes).

UM: How has climate change affected plant health, and how will it affect it in the future?

TW: First, temperature, drought, or flooding can stress a plant so it is increasingly susceptible to a pathogen that it might resist if it were healthy. We may see pathogens, insects, and weeds appear in regions previously unreported. With increasing temperatures, insects and pathogens may appear in regions where they had never been observed before because of lower winter or nighttime temperatures.

Soybean leaves infected with soybean rust. (Photo by Christine Stone, USDA/ARS, D521-1)

UM: What steps are we taking now to protect U.S. crops from various plant diseases, both known and emerging?

TW: The first is to be aware early, so that we can understand the potential impact and where diseases most likely will establish and spread. Then, we can research resistant varieties, develop diagnostic tools so that the pathogen can be correctly identified, and the proper management strategy can be employed if it is discovered, and understand where the pathogen is most likely to enter the U.S. The best measure is to prevent diseases from entering the U.S. It is important to work with international partners. More information can be found on the National Plant Disease Recovery System website.

UM: Is there anything we should be doing differently in our agricultural practices to help protect against plant diseases?

TW: Overall, I think we are doing a very good job, which is why a constant food supply can be taken for granted. However, we can improve by developing international collaborations to help monitor potential new and emerging pathogens before they enter the U.S. and look at innovative technologies to improve sustainable management practices, including technologies that may not have been considered for use in agriculture. 

UM: How do you translate your findings from research into practices that farmers can use?

This is extremely important. At ARS, the research results are communicated directly to growers through presentations at grower meetings and trade journals and demonstrated at field days where the grower can see firsthand comparisons between different management strategies.

A tree in California killed by sudden oak death. (Photo courtesy of Tim Widmer)

UM: Are there natural remedies or recommendations for backyard growers to protect their plants from pests and diseases?

TW: There are several recommendations. The first is to find a reliable source of plants that are pest- and pathogen-free. Some may spray the plants with a fungicide that will mask symptoms, but the pathogen is still present and will show up later. Second, sanitation practices help reduce further spread should a plant become infected. They include removing any diseased material and disposing of it properly, clearing fallen leaves and debris, and pruning small branches for adequate airflow within the tree canopy. Finally, make sure the plant has proper nutrients to make it strong, as weaker plants may be more susceptible to pathogens and insects.

UM: What do you want growers and the public to take away from International Plant Health Awareness Day?

TW: I would love it if people understood that plants can get sick too, and that it is not an accident that there is an adequate food supply here. It's often taken for granted, because we have such abundance. However, if not taken care of properly, the food supply could be in danger if a devastating pathogen of a major staple crop enters the U.S., and we are not properly prepared. We saw a glimpse of this indirectly with the pandemic, when the supply chain was disrupted. Imagine if the supply itself (a.k.a. plants for food) were severely reduced. Historically, we have seen this before, as in the case of the Irish Potato Famine.