Module 1 -- Non-parasitic Disorders

Most plant pathologists concentrate on those problems caused by parasitic organisms (primarily microorganisms). However, it is important to recognize non-parasitic disorders of plants so that these can be differentiated from plant diseases when Master Gardeners are confronted with clientele problems.

These non-parasitic disorders include:

• nutrient imbalances
• temperature extremes
• toxic chemicals
• mechanical injury
• water imbalances
• air pollution
• genetic defects

Most of the examples used throughout this tutorial will come from our 23 years experience with diseases of commercial vegetables in Florida. This is our primary area of responsibility. Therefore, naturally, our collection of photographs reflects this activity in the execution of our daily tasks. However, the principles of plant disease diagnosis are applicable to all situations, be they a 500-acre commercial tomato field in southern Florida or an annual flowerbed in Pensacola.

Each figure below is associated with a question. See if you can select the correct answer.

Fig. 1. What caused this widespread damage to this snap bean field in Homestead (hint: the damage appeared rapidly on January 13 of the winter vegetable season)?

a.) Spray drift from an adjoining orchard
b.) A lightening strike
c.) A rare genetic disorder
d.) Frost

Fig. 2. What is the common name of this problem on the tomato fruit? (Hint: The damage is always on the outside of the canopy.)

a.) Phosphorous deficiency
b.) Sunscald
c.) Weather fleck
d.) Scab

Fig. 3. What is the cause of darker green flecks or spots on this immature tomato fruit? (Hint: it is on all fruit surfaces.)

a.) Sunscald
b.) Unusually dry weather
c.) A genetic disorder
d.) Fertilizer burn

Fig. 4. What is this problem on ficus?

a.) Potassium deficiency
b.) Excess water
c.) Frost injury
d.) Mechanical injury from leaves rubbing in the wind.

Fig. 5. In what plant organ did this problem originate?

a.) Leaves
b.) Fruit
c.) Roots

Fig. 6. Examine this picture. These potato plants showed this brown flecking on leaves almost overnight. The entire field is uniformly affected. The location of the field is in Homestead, Florida in southeast Miami-Dade County. It occurred in early November.

Select the most probable cause for this problem.

a.) Frost injury
b.) Air pollution
c.) Metribuzin herbicide injury
d.) Excess of boron

After answering the above questions, go on to: Module 2 -- Parasitic Diseases and the Plant Pathogens that Cause Them