Plant Diseases

by Stephanie Suesan Smith on November 22, 2010

We have all had plants die on us.  Sometimes the cause is obvious — a big chunk chewed out of the plant, or so many bugs they kill the plant.  Other times, the cause is not so obvious.  Then it is often a disease that killed the plant.

I am not foolish enough to try to cover every disease that attacks a plant.  I will, however, try to discuss the types of organisms that infect plants and how to identify them.  It is much easier to combat a disease if you know the general organism you are dealing with.  You have these choices:

  • Viruses
  • Bacteria
  • Fungi
  • Nematodes

See, even guessing, you have a one in four chance of being right.  Things are looking up all ready.

Viruses are the same sorts of things that give humans colds and the flu.  You can spread them by using tools on one plant then using the same tools on another plant without sterilizing them.  The same goes for your gardening gloves.  Be aware  of this is you have a sick plant — use different gloves and sterilize your tools before moving on.

Bacteria are spread most often by splashing water.  For example, when you turn on the hose and let it run full stream to water a flower bed, the rushing water splashes dirt on the plants.  That dirt contains bacteria that can infect the plant.

Fungi like damp, mild weather.  The spores are spread on the wind or in the water.  Equipment can also spread it.  Powdery mildew is an example of fungi.

Nematodes are small, wormlike things that feed on the roots of a plant.  Root knot nematode is the most common of these in the home garden.

The best way to combat all of these problems is to water appropriately, fertilize appropriately, and plant varieties of plants that are immune to the diseases common in your area, if possible.  A healthy plant is much more likely to fight off a problem, just as a healthy person can fight off a cold.  It is also important to rotate your crops so that you do not plant vegetables from the same family in the same spot for at least 24 months.  That keeps bacteria or viruses in the soil from having a ready food supply of their favorite vegetable.

If you can, train vegetables up on a trellis, even ones such as cucumbers and other crops that are not usually caged.  This means air can circulate better and the fruit does not contact the ground.  Clean fruit is not only healthier, it is nicer to deal with at harvest time.

Nematodes are hard to deal with.  It is best to plant resistant varieties of plants.  If you can’t, rotate in resistant plants every other year to help keep the nematode numbers down.

There are a few fungicides and things to treat sick plants.  Mostly, you treat them by yanking them and throwing them in the trash before they infect their neighbors.  Keeping your plants healthy is the best defense against disease.

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{ 6 comments… read them below or add one }

Heather November 23, 2010 at 12:52 am

This is a very common problem in my garden. Hope these tips will find a solution out there.
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Reply November 23, 2010 at 3:18 pm

I’ve faced nematodes …and they need a real “delicate treatment”…thanks for advice


Ben from Green Powder June 28, 2011 at 10:08 pm

I have a weeping willow planted in the back that I planted a few years ago. A woodpecker is after it, of all things. It’s a pretty young tree and I don’t know what to do to discourage the woodpecker from poking holes all over it. I can’t even understand why it would go after such a young tree. It’s just odd. Have any good woodpecker discouraging methods? 🙂
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Stephanie Suesan Smith June 29, 2011 at 5:56 am

The tree is sick, or the woodpecker would not be bothering it. Woodpeckers drill holes to extract grubs, which are themselves a secondary problem. You need to consult with your county Extension agent or an arborist to find out what the primary problem is.


Ben from Green Powder June 29, 2011 at 9:49 am

That’s good to know, thank you. I really don’t want the willow to die. It’s the main attraction in the middle of a grass lawn. It’s such a beautiful tree and it’s been struggling the whole of its life. In the first few years, deer would eat its tender bark, now grubs seed to have taken up residence and a woodpecker. I’ll definitely look into some anti grub products.
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Stephanie Suesan Smith June 30, 2011 at 6:46 am

The grubs are also a secondary infection. You need to have a tree specialist look at this tree before you spend any more money on it. Treating the grubs is difficult without knowing why they are there in the first place.


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