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Plant Pathology Guidelines for Master Gardeners

Contact: Dr. Richard Raid

Chemical Methods For Disease Control

As a last resort, judicious use of chemical applications may be used to mitigate plant disease losses. There are three major classes of chemical treatments:

  1. Soil Treatments
  2. Seed Treatments
  3. Foliar Sprays

Seed treatments consist of dusts or slurries applied to seed to protect primarily against damping-off caused by soil borne pathogenic in fungi.

Figure 66

In this picture the fungicide coating of the seed has been activated by the moisture in the soil and now forms a protective chemical barrier around the seed.

Figure 66: chemical seed protectants

Figure 67

Use only the recommended fungicide (not what is on sale, is left over from last season, etc.).

Figure 67: recommended fungicide

Figure 68

Use only the recommended amount.

Figure 68: use correct fungicide amount

Figure 69

Time the spray effectively. This often means starting earlier in the season than one might initially expect.

Figure 69: spray at correct time

Figure 70

Time to look more closely at those materials and approaches needed to help in your diagnostic effort and ways to seek assistance.

Figure 70: look closely at diagnostic materials

Figure 71

Try to gather as many "disease books" for reference as you can, especially those with color photographs.

Figure 71: gather books on plant diseases

Figure 72

Many county offices will have library or file copies of these valuable books and materials.

Figure 72: tomato disease book

Figure 73

An extremely useful source of diagnostic information on specific plant diseases is the collection of fact sheets and plant protection pointers put out by the plant pathology departmental of the University of Florida. Unfortunately, many of the color fact sheets are out of print. Some of these fact sheets are now available on the University of Florida, IFAS, Dept. of Plant Pathology Web site. Just click on extension publications when you get to the departmental home page.

Figure 73: gather as much disease information as possible

When a client comes in with (or even phones about) a plant health problem, it is important that you gather as much information as possible about the situation. This additional information can be critical in making the correct diagnosis. And remember to ask - clients very often will not think to offer such information unsolicited.

Things to ask include:

  • Number of plants affected
  • Pattern of development in the field or garden
  • The relative severity of the problem
  • Recent cultural practices (e.g., pesticide sprays) and localized weather conditions

Figure 74

There are times when you simply cannot figure out what the problem is. In consultation with the Master Gardener coordinator, you may decide to send a sample to one of the regional University of Florida plant disease clinics. When you do so, a form as shown will accompany the sample here:

Figure 74: form for sending in plant samples

Form to accompany sample sent to a plant disease clinic. It is important to the clinic personnel that you fill in as much information as possible. This will suggest avenues to pursue for the highest likelihood of success.

Figure 75

This picture illustrates the best way to submit plant samples.

Figure 75: best way to submit plant sample

Moisten the root ball (soil or soil mix around roots) and enclose only the root ball in a plastic bag that is secured with a rubber band or similar method. Do not enclose the foliage in the plastic bag, as it will rot by the time it gets to the clinic. Then the entire plant can be put in a paper bag.

Figure 76

Fruits can be wrapped in soft paper and place to in a cardboard box.

Figure 76: fruit in box with soft paper

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