University of Florida

Plant Pathology Guidelines for Master Gardeners

Contact: Dr. Richard Raid

Oh No! A Quiz

Now it is time to see how much you have learned.

In the following pictures, you need to describe the symptom and determine if this is:

  • Bacterial
  • Fungal
  • Viral
  • Abiotic or Non-Pathogen-Induced Problem

Remember that control measures are routinely available for many diseases and once a problem has been pigeon-holed into one of these four categories listed above, similar control measures exist for many problems in that category.


Figure 77

Host - snap bean.

Figure 77
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Figure 78

Host - cucumber.

Figure 78
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Figure 79

Host - tomato.

Figure 79
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Figure 80

Host - mango.

Figure 80
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Figure 81

Host - tomato.

Figure 81
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Figure 82

This strawberry plant is in the middle of a patch that shows a definite damage gradient from East to West (most severe damage at eastern end, no damage at western end). What caused it?

Figure 82
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Figure 83

Host - snap bean.

Figure 83
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Figure 84

Bean pods.

Figure 84
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Figure 85

Host - tomato.

Figure 85
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Figures 86 & 87

Host - tomato.

Figure 86

A cut stem from one of the above plants placed in water.

Figure 87
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Figure 88

What happened to these tomato plants?

Figure 88
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Figure 89

What may have caused this problem on avocado fruit?

Figure 89
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Figure 90

What is the peculiar symptom seen at the base of this potted sunflower?

Figure 90
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Figure 91

What is the symptom evident on the mango flower cluster on the right? What is the cause?

Figure 91
See Answer »


Figure 92

This is the last quiz question!

Note the more or less circular to oval area of dead plants in the middle of a tomato field. This problem appeared literally almost overnight around October 1st in southern Florida. The area is not low. All the other plants are perfectly healthy. All cultural practices are the same as those normally used.

Figure 92
See Answer »


Hopefully, this Web tutorial has sharpened your plant disease diagnostic skills and made you more aware of the role of plant diseases in the framework of plant health.

Figure 93


Answers

Figure 77

Symptom: Stem rot. Fungus (see sign of fungus growing in stems). This is white mold of snap beans.

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Figure 78

Symptom: leaf spot (or possibly leaf blight). Bacterium (note watersoaking of underside of leaf). This is angular leaf spot of cucumber.

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Figure 79

Symptom: stunting, off color, mottling. Virus. This is tomato mottle virus affecting stake tomato.

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Figure 80

Symptom: leaf spot. Fungus. Leaf spots appear fairly dry. Fungus may be the best answer simply on the basis of the 85% rule. Since the leaf is from a mango tree, this is, not surprisingly, mango anthracnose.

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Figure 81

Symptom: wilt; when the lower stem is cut across horizontally and the cut end immersed in water, no cloudy streaming is seen. Fungus. This is Fusarium crown rot of tomato.

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Figure 82

This is herbicide injury. Herbicide applied in a walkway just east of the strawberry patch drifted in the prevailing easterly wind over the patch, creating the gradient in severity of the damage.

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Figure 83

The symptom seen here is a leaf spot. It is bacterial. Although it doesn't look particularly watersoaked or greasy, the clumped nature of the spots suggest bacterial origin. This is because bacteria are primarily dispersed in splashing rain so that a group of bacterial cells all land with a water drop in approximately the same area. This is bacterial blight of snap bean.

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Figure 84

The symptom, evident if you look closely, is a fruit spot. There are tiny, slightly raised black pimples on these bean pods (fruit). This is fungal. The disease is Alternaria spot of snap bean.

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Figure 85

The symptoms are mottling, stunting, and misshapen leaves of tomato. The problem is definitely viral. The disease is tomato yellows, an aphid transmitted virus.

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Figures 86 & 87

The symptoms here are primarily wilting with some necrosis (browning) of the tomato foliage. Fig. 87 shows the famous bacterial streaming, so the problem is, of course, bacterial. The disease is bacterial wilt of tomato.

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Figure 88

Don't ignore the obvious! Someone ran over these poor tomatoes. We refer to this facetiously as "tire blight".

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Figure 89

The symptom is probably best described as a fruit blight. But the name of the disease is more descriptive - avocado scab. It is fungal. This conclusion may best be reached by the process of the elimination. It is certainly not typical of either a bacterial or viral infection and remember that about 85 percent of all plant diseases are caused by fungi.

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Figure 90

This is a gall or tumor. It happens to be a bacterial gall. The disease is crown gall of sunflower.

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Figure 91

Using the strictly correct botanical nomenclature, the symptom is panicle blight (the flower cluster is a panicle). Flower blight would be fine. The disease is fungal. Because it is on mango, the disease is - you guessed it - anthracnose.

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Figure 92

The problem is a lightning strike! This is actually what happened in this commercial tomato field. The stems of the plants near the center of the strike are hollow due to the extreme heat of the electricity.

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