Class Seven-Plant Disease Identification and Treatment

July 11, 2014

Author: Ian Whittington

Category: General News Stories from the Garden

Something strange happened at the NFI garden the other week. Just when my peppers were finally starting to look livelier, I noticed that one of them had white marks on its leaves. And I wasn’t the only one affected. Others in the class were noticing the same thing as well.

Recently mysterious white marks started showing up on some of our pepper plants

Recently mysterious white marks started showing up on some of our pepper plants

Clearly my plant was diseased. Or at least that’s what I first thought when I noticed the marks. That may have been because plant disease was that week’s topic, so the possibility was already on my mind. But if there’s one thing I’ve learned in this class when it comes to plant ailments it’s to not make any assumptions. After all, disease isn’t the only issue that could be plaguing my plants. Sometimes what looks like a disease could be a nutrient deficiency, drought, or perhaps too much water.

So how can I figure out if one of my plants is sick? Like a detective I’d need to look at the evidence and see what it tells me about my plants’ condition. This involves:

  • Making note of conditions in the garden
    • Be aware of things like the season, temperatures, rainfall, etc.
  • Researching what diseases are common to the area and the affected plants
    • Different diseases are prevalent at different times of the year and may only affect certain plants
  • Researching insect lifestyles
    • Knowing when insects appear and reproduce can help you know when to look for diseases that they spread
  • Taking pictures, samples, and notes
    • Noting affects on the plant can help identify distinguishing signs between different diseases
My plot at class seven. I've been taking pictures to have a record of how conditions have changed through the season

My plot at class seven. Taking pictures helps me see changes.

If this process seems familiar, it’s because it’s a lot like what we did when it came to looking for pests. In fact, looking for evidence of pests goes hand in hand with disease identification. Since some insects are also harbingers of plant disease, finding evidence of one could point to the presence of another.

In a way it was kind of perfect that so many people were getting mysterious spots on their peppers around the last class. It gave us the opportunity to put our detective skills to the test and come up with a brilliant conclusion.

And just what did we come up with?

Basically, we had no idea what was wrong.

When looking at the evidence it didn’t really point to anything in particular. We knew that the plants being affected were one type of pepper: Baltimore fish peppers, to be precise. And everyone had been noticing the same oddity: white marks on the leaves. But other than that, nothing else was off. There was no other discoloration, no evidence of chewing or sucking insects, and the plants weren’t wilting. With the white marks being the only evidence of interest, nutrient deficiencies, lack of water, and insect damage didn’t seem to be the problem.

So we then considered disease. The circumstances, however, didn’t match any of the common local ones. Diseases common to the area include:

  • Late blight
    • Fungal-like disease that prefers cool, wet weather. Targets tomatoes and potatoes
  • Early blight
    • Shows up early in season affecting tomatoes and potatoes. Signs include brown spots with concentric rings and yellowing around the spot
  • Powdery mildew
    • Fungi that can thrive in dry days. Affects cucumbers, pumpkins, and squash when days are hot and dry and nights are cool.
  • Fursariam and Verticillum Wilts
    • Soil born disease. Plant appears to wilt as though dehydrated but doesn’t recover when watered.
  • Bacterial Wilt
    • Mostly infects cucumbers. Long sections of vine wilt and don’t recover. Spread by cucumber beetles.


During my last session at Common Good City Farm I found some leaves with powdery mildew. These plants were far more mature than mine

Some plants I found at Common Good City Farm with powdery mildew

After considering all this, none of us, including Joe, knew what was going on. I had showed Joe my infected plant before class started, and he pretty much told me that if my plant was diseased the only thing I’d be able to do was pull it out and throw it away. And I mean throw it away. Composting wouldn’t be an option because of the potential for spreading the disease around. So after all my time hard work my plant was possibly going to go to waste. Bummer right?

But really, in such a circumstance there’s not much else you can do. There aren’t really cures for plant disease, at least not the ones we’d be dealing with. Sure, removing infected leaves with early blight or powdery mildew could slow the spread of infection. And perhaps spraying a mixture of 1 tsp. baking powder, some dish soap, and a quart of water to non-infected leaves of a plant with powdery mildew could hinder the spread as well. But for the most part, pulling out infected plants is really the only option.

During class it seemed like Joe was heading in that direction. Except, there was still one more piece of information to consider. As it turns out, someone’s “infected” plant was producing a healthy pepper. She showed it to me when we were going around a partner’s plot to see if we could spot disease. It was puzzling, mostly because by that point I was fully committed to believing that my plant was sick and there was nothing I could do but pull it. But since it seemed the pepper plant was still doing its thing, Joe suggested we just wait it out and see what happens.

And boy am I glad we did.

In talking with Kristin, the NFI director, after class, she pointed out that the fruit of one of the Baltimore fish peppers in the NFI plots had stripes. White stripes. The plant had leaves like the affected ones, making me decide to do some research on my smartphone. And what did I find out?

Baltimore fish pepper leaves are supposed to have leaves that are white and green.

After finding a picture of a fully-grown Baltimore fish pepper plant I was ecstatic. I wouldn’t have to pull my pepper plant! But more than that, this experience taught me an important lesson. Before you start thinking something might be wrong with your plant, know how it develops in the first place. After all, if you want to have healthy plants you can’t keep trying to counteract natural progressions in their life cycles.

When trying to prune my thyme I accidentally snapped a branch off. Hopefully I didn't create openings making my plant susceptible to disease

A thyme branch I accidentally snapped off. Accidents like this could create openings for disease

Again, it all comes back to having healthy plants. I mean lets consider some keys to preventing disease in the first place.

  • Plant the right plant in the right place, at the right time
  • Do not work with plants when they are wet
  • Handle plants carefully or not at all
  • Plant in healthy soil
  • Select healthy plants
  • Do not over-fertilize
  • Rotate crops year to year, if possible
  • Plant Diversity
  • Observe


These are the pretty much the same principles we’ve been learning about the whole class. And that really isn’t surprising. Everything is tied together. Without healthy soil you can’t have healthy plants, and the best way to have both is to have conditions be as close to nature as possible. So far it seems like I’m doing all right in that respect. Now I just have to make sure my plot doesn’t get too wild for me to handle.

My pole beans at class seven

My pole beans

My cucumbers at class seven

My cucumbers

My okra at class seven

My okra

My sweet potatoes at class seven

My sweet potatoes

My peppers at week seven

My peppers

My herbs and tomatoes at week seven

My herbs and tomatoes

Some of my developing tomatoes

Some of my developing tomatoes







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