Issue 10, June 28, 2013
What Does Plant Disease Sanitation Really Mean?
A plant pathologist’s goal is to properly identify and manage plant disease to reduce the economic and aesthetic damage to plants. Unfortunately, many still think that our goal is to control plant disease by spraying fungicides. We focus on an integrated disease management approach, which includes exclusion, eradication, protection, and resistance. But, what do all of these really big words mean? When it comes to managing plant disease, utilizing prevention and suppression of plant pathogens is recommended. Some ways to suppress a plant disease are rotation, resistant varieties, sanitation, leaving land idle, or weed control. Sanitation is one of the many ways to achieve “eradication”, when practicing integrated disease management and is defined as the elimination of plant disease pathogens. How do you think that plant pathogens survive from year to year? They survive on plant debris and infected plant parts after each growing season. Here are some recommended sanitation practices:
Plant pathogens are less likely to survive if organic matter is quickly decomposed. In addition, tillage can help eliminate plant roots that linger after harvest in the soil and can harbor plant pathogens.
In some cases, weeds can be a source of plant pathogens and it is suggested that weeds be controlled. If you believe weeds are diseased, they should be buried, burned, or removed, and not composted. In other cases, numerous weeds can increase humidity, which could make conditions more favorable for plant disease.
Some insects may need to be controlled because they could be vectors of plant pathogens and transmit plant pathogens such as viruses or bacteria to plants. Plant disease vectors include aphids, leaf hoppers, and cucumber beetles.
This year, the U of I Plant Clinic will be recommending more pruning of trees, thanks to the development of fungal cankers after drought stress and the increase of the bacterial disease, fire blight. If you notice branches are dead or have sunken, dark cankers, with foliage that is yellow, brown, wilted or absent, you may need to prune. If you fear further plant pathogen spread during the growing season, pruning should be done in dry weather. Ideally, pruning usually should be done in late winter or early spring, when trees are dormant. The key is to prune PROPERLY! Pruning cuts should be made in healthy bark and wood, several inches below the diseased or dead area. Pruning tools should be sharp and used in a manner that promotes a smooth cut to help with wound closure. Remember, when pruning an entire branch, wood should be removed before it meets the collar. The branch collar should not be removed.
For additional information on pruning, please refer to the following fact sheet: http://www.ag.ndsu.edu/pubs/plantsci/trees/h1036.pdf
Does covering wounds on trees help? We do not recommend that you cover a wound, because recent research indicates that this practice is of no value and might even accelerate wood decay.
Removing dead plant material
In most cases, plant parts should be removed as soon as you notice they are diseased or dead during the growing season. Raking leaves, removing dead fruit, or digging up entire plants (including roots) are all examples of sanitation. The dead plant material could contain bacterial, fungal, or even viral pathogens. The next question is always what do we do with this diseased plant material? The diseased plant material should be buried, burned, or properly disposed away from your healthy plants! It is not recommended that you pile this material near the garden. There are conflicting opinions, when it comes to composting diseased plants. Ultimately, death of plant pathogens will depend on the effectiveness of your composting system. Generally, composting of diseased plants is not recommended because the composting heat may not entirely (100%) kill all of the disease organisms. As you use and spread compost, you could also be spreading plant pathogens. Most plant pathogens are host specific; therefore, using compost consisting of leaves, grass clippings, or shrubs in the vegetable garden can be done, because these plant pathogens most likely will not affect the garden plants. However, some research institutions recommend destroying diseased leaves and needles.
Avoid movement or destroy soil pathogens
Don’t forget that plant pathogens can be present in the soil; therefore be sure not to move contaminated soil to other areas. Remember to disinfect or destroy boots, stakes, cages, pots, saucers or anything else that has come into contact with the soil. Soil within pots should not be reused from year to year. It is recommended that dead plants and soil in pots be placed in the trash. Root rot pathogens such as Pythium, Phytophthora, and Rhizoctonia as well as wilting plant pathogens such as Verticillium can all affect a wide array of plants, so proper disease identification is needed and replanting with the same host plant is not recommended. I am often asked if there is a way to remove plant pathogens from the soil. Fumigation can be costly, but is used in commercial situations. Soil removal can be attempted; however, it is difficult to completely remove plant pathogens from the soil. If replanting, in an infested area, we often recommend a cultivar with some resistance or a non-susceptible host plant. We also encourage good cultural practices (proper planting, proper site, watering/not overwatering, pruning, or fertilization), to keep the plant in good health to avoid future plant disease infection.
Disinfect machinery, tools, pots, equipment, and even HANDS
It is very important that you disinfect machinery or tools after use to prevent plant pathogen spread to other plants. Disinfecting can be done with steam, hot water under pressure, or a 10% (1 part bleach to 9 parts water) or 10% soak for 30 minutes). Some research institutions even recommend soap and water or rubbing alcohol for disinfection. No matter the disinfecting method, whatever you are cleaning should be allowed to dry. Remember that bleach can discolor metal or clothing. Corrosion of cutting tools due to disinfection via bleach is also a common complaint. One tip might be to rinse with water and treat the cutting tool with a light spray of cooking oil after it has come into contact with a bleach solution. I have recently come across some new research compiled into a fact sheet that discusses other alternative options for the disinfection of cutting tools and can be found at the following link: http://puyallup.wsu.edu/~linda%20chalker-scott/horticultural%20myths_files/Myths/Pruning%20tools.pdf