Understanding the difference between bacteria, fungus and virus will help with the diagnosis
Plant diseases can be difficult to diagnose. So often, they display the same symptoms as plants that are perfectly healthy, except for stresses imposed upon them by our poor cultural practices. When a plant is diseased, it is because of a bacteria, fungus, or virus. A better understanding of each will help you diagnose and treat the problem if possible.
Bacteria
Not all bacteria are bad for plants and soil. In fact, most are beneficial, and there are millions! However, there are approximately 200 types of bacteria that cause diseases in plants. They are most active in warm and humid environments, so this is when you’ll see the most evidence of their presence.
There are several symptoms of bacterial infection. One is leaf spot. In this case, the bacteria that attacks the plants, produces a toxic chemical that kills the surrounding plant cells. The plant then reacts defensively by killing off the surrounding plant cells, thereby isolating the infected cells. In some cases, these dead cell areas drop out, creating what looks like “shot holes” in the leaves.
Bacteria can clog the plants ability to deliver water and nutrients to the rest of the plant. Eventually the plant begins to wilt or droop. This process can occur rapidly, and within one day, you can see a dramatic decline in your plants.
Other symptoms cause the plant tissue decline, such as in cankers and soft rot, which are sunken areas produced by dead plant tissue. In other cases, abnormal growth is the symptom, referred to as galls. Plants respond to these bacterial invasions by producing a rapid abundance of new cells. This is often evident is unusually large, misshapen growths somewhere on the plant or root.
Bacteria can spread in several ways, including insects, splashing water, other diseased plants, or tools. They enter plants through tiny openings either through damage, or cuts, but also through natural opens in the plant itself.
Once plants are affected, they can be difficult to control. Remove infected plants or parts immediately from the garden. Do not add these parts to your compost pile. Instead, destroy them. Once present, controls options are limited. Copper based sprays provide some help, but are not a cure. Bacteria are best controlled as a preventative measure, treating plants before damage is even present. Additionally, good cultural practices are always helpful. This includes sanitation of equipment, and removal of all plant debris.
Fungi
Like bacteria, many more fungi are actually good for the garden. But, unlike bacteria, there are thousands of fungi that are harmful to plants. For this reason, you are likely to encounter fungal problems most often. Because fungi are present in the soil and above ground symptoms of fungal attack can appear above and below ground. These include rotting or dead roots, or large swelling on roots below ground. At the soil level, new seedling stems can rot and flop over. Above the soil line, plants can display leaf spots, mildews (white or gray powdery patches on foliage), rusts, and wilts.
Fungal spores are very small and light, and can travel great distances through the air to infect other plants or trees. They are also spread by water, animals and insects, and people.
The best way to prevent fungi from attacking your plants is to buy disease resistant varieties whenever possible. Other ways include minimizing the amount of water contacting foliage. Water at the soil level and early in the day. This allows foliage to dry out quickly, should it become wet. It’s also helpful to provide good air circulation through proper spacing between plants, and pruning.
To control fungal outbreaks, as with bacteria, remove all infected plant parts, or plants. You may also choose to apply a fungicide. There are many products available for treatment, organically (copper, sulfur, and baking soda are common) or synthetically. These treatments are best at preventing the germination of new fungal spores, so applications before outbreaks occur will provide the most effective control.
Viruses
Even viruses on occasion can be beneficial, but for the most part, they are bad news in the garden. They can persist for many years, before they appear as a problem, and when they do, they often show up in one of a few primary ways. First, plant foliage may appear yellow, or they may appear as mosaic patches of yellow, light green, or white. Next, the plant may appear stunted. In addition, the plants are often misshapen or malformed. Specifically, the leaves may be rolled, or swollen or puckered, or they may be abnormally narrow.
Unlike bacteria and fungi, viruses are not spread by water or wind. Instead, they must physically enter the plant. One of the most common vectors of viruses are insects. Insects feed on infected plants and transmit the viruses to healthy plants when they feed again. Other ways include plant propagation, contact by humans, and infected seed.
Unfortunately, once infected, there are no chemical treatments for eliminating a virus. Once detected, you should remove all suspected plants. Although this can seem like drastic measures, it is the most effective way to reduce continued spread. It is difficult to prevent viruses from affecting your plants. Your best efforts will be to look for virus-resistant cultivars, provide physical barriers, such as floating row covers, or to actively eliminate vectoring pests from entering your garden.
About Joe Lamp'l
Joe Lamp'l is the Host and Executive Producer of the award winning PBS television series Growing A Greener World. Off camera, Joe dedicates his time to promoting sustainability through his popular books, blog, podcast series, and nationally syndicated newspaper columns. Follow Joe on Twitter
Is it true that cinnamon is a natural fungicide? If so, will sprinkling cinnamon on my roses, apple trees and lawn help deter and prevent the spread of fungal diseases?
Cinnamon is not a generally recognized fungicide for organic disease control.
Joe, I just happened to find your article through a Google search. I am so upset. I’ve spent probably thousands of dollars over the years in plants, garden soil, etc. My phlox, which used to be 3 ft tall & gorgeous started turning brown & dropping leaves & then slowly other plants started turning brown & losing leaves too. Now my hydrangeas have yellowing leaves with brown spots. My coneflowers died off mid-summer & now look black. Help! I’m just sick. I can’t afford to buy all new plants. Is this fungus? I haven’t seen any mites or bugs. What should I do to save my plants? THANK you for any help you can offer.
Joan,
We empathize with your garden challenges. It’s hard to diagnose your problems without seeing the plants.
I suggest you take photos and or samples to your local extension service and they should be able to make
the best recommendations for how to solve your problems.
Hey Jos,
If my crab apple has markings of a fungal disease do I need to remove the affected leaves and then spray anti fungal? Sadly it is most of the leaves on the tree.
I apologize if you answered something similar above.
Steve,
You have the right idea. Once the leaves are infected, it could be scab (which may be treated with fungicides) but spraying is a preventative so you would spray new growth before it shows signs of being infected. Unfortunately, if the variety you have is susceptible to this fungus
you will have to spray every year. My suggestion is to consider planting a selection that is resistant to scab, fireblight and other problems crabapples suffer from. The Morton Arboretum has a great list and article about this. I hope it helps, and you won’t have to spray.
Here is the link. Best of luck. http://www.mortonarb.org/trees-plants/tree-plant-descriptions/crabapple-cultivars
Plant a mustard as a cover crop, and till it in before it goes to seed. Wait 2 to 3 weeks before planting anything there. Mustard will help fumigate the soil. You will have to add good beneficial before planting.
okay here’s my question I have four cucumber plants that were growing well got about six cucumbers from them and then all of a sudden they started to wilt badly. looked up online and it appears I have bacterial wilt is t there anyway I can prepare my garden for next year besides moving all of the dirt which is very costly and expensive
Try planting them in a different location–a separate bed for example. That could make all the difference to avoid exposure to the bacteria in the soil that is affecting the plants.
Joe, I have some plants in a flower bed about 10 feet from our salt water pool. Last, we began noticing that some of the shrubs were beginning to loose leaves and the branches were bare. A crepe myrtle tree is also showing signs of disease on the trunk dropping what feels like water drops from the leaves. My question is this: if we dig up all of those plants, do we need to treat the ground around them before planting new plants?
My guess is that it’s the environment of the nearby salt water that is causing this. The evaporation or the mist around the pool could be enough of a residual effect to adversely impact your plants. Treating soil would not help. I think it’s starting as an above ground issue.
Hello Joe. I live in a track home . i have placed raised beds in area with full sun. I dont have room to rotate my crops much without placing taller plants south of lower growing plants. I had thripe, kill off potato plants in 1 area. powdery mildew and either bacterial wilt or fusarium kill my cucumbers in another area. and black spot and blight. there isn’t an area that hasn’t had some disease and in some areas many types of disease. i tried to by some resistant varieties, plastic mulch to control splash and inches of leaves as mulch in another. i am nervous that if this year turns out the same as last year, ill have to do something drastic to correct my soil or not have a garden for a few years. do you have any suggestions? is there a cover crop or treatment that i can do to my soil to correct the levels of good and bad bacteria and fungus, short of digging it up and refilling the beds with new soil?
I have a very large old-forestTulip Poplar in my yard that suddenly died over the winter. I do not know the reason, but I am noticing clusters of tiny mushrooms along its roots. They begin as little white round balls and then develop into tiny mushrooms. I have never seen this before. I am an experienced gardener and am really stumped with this. Do you have any suggestions?
Hello Sir,
Few days ago I cultivate the American Saffron in my farm . after growing of plants some plants are dried and dead .when I diagnosis other plants the symptoms are_
small pore holes present on the leaf. some insect are found which absorbed the water or something their food from leaf of the plant.some spider net_ network also present surrounding the plant.
so please give some advice which of treatments should be do? as well as above symptoms which type of possible diseases they show whether it is bacterial / fungal / viral??
Hi Yogesh. It’s so hard to diagnose a problem remotely and without pictures. But just from what you say and mention “holes” and “spider net” my first guess is spider mites. Do you see black sooty mold residue on the undersides of the leaves?
If so, that’s more reason to suspect spider mites. Do you have an extension service or farm agent that can help you diagnose the problem with a site visit or you can take some damaged plants to him? Other options include digital diagnostics where you can email pictures of the details and a university extension service or agricultural department can help you. good luck!
HI Joe!
I bought three healthy PNW wax myrtle bushes. Planted two, put layers of organic fertilizer with it.
I did water from the top as they are behind a fence. I started noticing some gold leaves, but am super busy, and just thought it was the fall turning of a few leaves. Then upon closer inspection it is some kind of bacteria or fungus! Spotted leaves turning yellow and a little red. : (
I took off the infected leaves, and am spraying with a fungicide.
Should I prune they way back? Even if we are headed into Fall and Winter (Oct. 11)
I dearly want to save them – they are crucial to a hedging barrier I’m trying to establish.
Thanks for any advice!!
~Ardis
Hi Ardis. Could be insect damage causing the discoloration. Have you inspected the leaves, especially the underside for microscopic insects. Another sign is black sooty mold which is the frass of spider mites. If you detect such signs, spray with insecticidal soap on the undersides of the leaves. You have to come in contact with the pests to control them using this eco-friendly but effective product. I don’t think it’s disease but I’m just giving my best guess.
Having said all that, are they getting “enough water”??? Newly planted shrubs and trees really need deep, thorough watering for extended time. Here in Atlanta, I”m still watering by hand, deeply to shrubs and trees I planted 13 months ago! Otherwise,they turn yellow and die. Finding the time to water them thoroughly so the roots get soaked but then have time to dry out again and repeat the process for many months is necessary in the absence of good rain in order for them to fully establish to where they are no longer dependent on your to water. And overhead watering just won’t get the roots the amount of water they really need. So take a hard look at that.
Lastly, the red color in the leaves might be a seasonal response or a nutrient deficiency. Have you had your soil tested?
Bottom line: either not enough water, spider mites, and unrelated factor is nutrient deficiency.
I think I have a fungus in my yard, but I’m not sure. We have only lived at our house for 9 months and earlier this summer starting noticing our grass dying off at opposite ends of the front yard. For the past 2 months we noticed something coming up from the ground. It looks like blobs of foam, but are not soft. They are hard, but can be broken in half by hand, showing all the layers (like a sectional picture of the layers of the earth). It also smells pretty bad. After digging in the lawn today, I found that 6-12 inches below the surface are a bunch of roots that are crumbly. There is no tree nearby, but I take it there used to be. Are the smelly hard blobs a fungus? If so, is it safe and how do I get rid of it? Thanks!
Yes, it sounds like you are seeing the nature in action of fungal decomposition of tree roots and organic matter below the surface, directly related to old tree roots. It’s very common to see above ground activity as you’ve described. There’s nothing you need to do and no harm or risk to you or otherwise. Let nature take its course and allow this to continue to decompose. Your lawn will not be harmed in the process.
hello, what is the chemical/fungicide suitable for virus related deseases on large trees , like nut meg. propiconazole and tebuconazole will do good??
If you really mean virus Tony, there is no chemical that you can use to treat that. If it’s a bacteria or fungus, that is treatable. However, before you treat anything, I suggest you get the proper diagnosis. You can send in a leaf sample to your county extension service. Or some offer distance diagnostics where they will work off of a digital image. To find the county extension service near you, use this link: http://nifa.usda.gov/partners-and-extension-map?state=GA&type=Extension
Hello. I am in school and I am doing a project on What happens to the way plants grow if there are no microorganisms in the soil, and I wanted to use this website for a citation. But i have a question on what happens if there are no microorganism in the soil? does it grow slower or will the plant not grow?
It depends on what you’re feeding the plants with McKenzie. In soil that isn’t contaminated with synthetic fertilizers, the microorganisms are a key part of the nutrition plants need to thrive. However, plants can still grow and thrive in soil or soil-less mixes that have no microorganisms IF they get their nutrition through supplemental means, such as synthetic fertilizers.
Think about hydroponic or aeroponic systems. These are plants that are growing, producing and thriving in growing conditions without any soil and only fed by artificial fertilizers. So that’s the only way they can survive. In an organic growing environment in soil, without synthetic fertilizers, the micronutrients/ organisms are necessary for survival. Good luck and keep me posted on your findings!
Great article on fungus! I grow baby’s tears ground cover, also known as soleirolia soleirolii in miniature gardens. But, I also have a white cloudy fungus that I can’t get rid of! I’ve tried Agri Fos and Serenade but the fungus keeps coming back. I also tried a baking soda, dish soap and oil only to bruise them. The fungus really took hold after my husband told me that Green King’s Fertilizer and Super Thrive vitamins are best rather than Osmocote for miniature gardens. The dwarf trees, shrubs and vines are ok; the real fungus is with the baby’s tears. I have stopped using King’s Fertilizer used in the bonsai community and went back to Osmocote. Is there anything in Super Thrive that can cause active fungal growth? Do you have any suggestions or ideas? Everyone I have talked to are trying to help but no one has the answer. I don’t think this is normal as I’ve backed up the watering schedules too.
Hi BB. Thanks for the good words here. I’m sorry I can’t be any help here. I’ve never used Super Thrive but I do know one gardening friend who I really admire that loves it. But that is the extent of my experience.
We have a an elm or oak tree with a greenish mold or fungas around the tree and going up the tree now, some spots have like a cluster of flowered looking spores or fungi. It has always blossomed with leaves, this year there is no leaves and limbs are brittle. I did notice a couple of new sprouts trying to leaf though, wondering if there is still hope. So saddened by this. Is my tree dead or is there a treatment to help it live. Tree is over 50 yrs or so old
Hi Jule. I can’t say what the state of your tree is without inspecting it. However, it does sound as though your 50 year old tree is def. in decline. It happens. And this is a common time to notice lichen and other non-harmful growth attached to trees. So what you see growing is likely not the problem, just a sign that your tree is likely weakening. I would have it inspected by a Certified Arborist –not a guy with a chainsaw. There’s a big difference!
my red green an yellow pepper plants had spots on them an i treated them with a spray that i got from someone that work at a nursy,an he told me that it would not get read of them but keep them under control.just have to treat every 7 r 8 days but he said they sould be ok since i cought it early.im a landscaper an been doing landscaping for 25 years so what i did to my plants that leaves that had the spots on them is i cut all the leaves off of the plants an hoping to just start over like the plant will have a fresh start an just keep treating them every week an make sure that its getting plenty of food ect…. do uthink that they will be ok,r bny me cutting the leaves off is not going to do anything to them?
You can remove those leaves as long as you keep plenty on the plant to photosynthesize. The idea of removing the diseased leaves is to help prevent the disease from spreading. But don’t do so when it’s wet and try not to touch other leaves in the process. Otherwise, you’ll be helping to spread the disease yourself.
After getting a tissue sample, if it is bacterial leaf blight. They make biologicals that will help. These are pathogen specific. Google agriphage.
I have removed a apricot tree that had wood rot down the center of the trunk. I would like to plant another tree in the same area, can I? Is there a product I can used to kill the bacteria to prepare the soil?
Thank you!!
Don’t worry about it Beverly. Most soil bacteria is good and you don’t want to sterilize your soil. Just find the replacement tree you want and plant it where you want, even in the same place. The wood rot on your apricot tree could have been caused by so many things, and most likely not bacteria in the soil.
How can a fungus grow resistance against fungicide?
Can someone tell me the basic differences between plant viruses and fungal viruses?
which micro organism causes more damage to the plant?
I have currently either bacterial or fungal leaf spot affecting two of my jalapeno plants. They are in pots so i immediately separated them from the rest. After a week of cooler weather the plants continued to grow leaves unaffected. I wanted to see if the plant could build its own immunity towards the disease on it’s own. I am not sure if it has yet since the lower leaves still show infection. However it has peppers that though small are showing stress lines as if ripe. Are these safe to consume?
Totally safe to consume Andrew. The stress lines are likely unrelated to any disease issues and I suspect are a factor of environmental conditions only, not disease related.
Hi. Thank you for the share.
This is a nice and simpel article concerning plant disease.
I think for those who are not really and deeply related to plant disease subject, it will be very useful to understand a little bit about the concept of “triangle disease”….
I have a climbing rose bush that drops all its leaves every summer. Can it be saved and how?
Thanks for the info.
Hi Anna. There are many possibilities on what is going on. But by the fact that you say your rose drops it’s leaves “every” summer, that tells me that it recovers each year too. Is it getting enough sun? Too much water? Is it flowering? Roses are very forgiving with severe pruning. Perhaps establishing a new flush of growth on new wood by cutting back in late winter or early spring my rejuvenate your plant. A balanced fertilizer in spring and mid summer should help as well. Just not too much.
IS THIS THE REASON WE GET THOSE “MUSHROOM” TYPE PLANTS (FUNGI) IN ARE LAWN?? WE HAVE BIG OLD ROOTS FROM A TREE THAT USED TO BE IN OUR FRONT LAWN. WE ALSO GET SOME IN OUR BACK LAWN. HOW CAN WE GET RID OF THIS FUNGI COMPLETELY??
Yes. The mushrooms are there because of the organic matter in your soil. They are particularly common in lawns were tree roots are decaying beneath. The mushrooms in your lawn are doing no harm and a good sign that your soil has important organic matter beneath (at least in those areas). The only thing I would suggest if you don’t want to see them is to kick them over in the lawn. Otherwise, they will come and go soon enough.
this is very good information about bacteria, fungi and viruses but the question i asked was how does bacteria, fungi and viruses grow and that was not answered in this text. hopefully you will improve this and then this text will be perfect.