Improved Nutrition Decreases Pests
New University of Florida research shows that healthy plants with high levels of nutrients resist plant pests. As farmers get ready for spring planting, applying fertilizer enhances plant growth, yield, and reduces pests. Dr. Arnold Schumann outlines benefits certain nutrients give to plants to fight various fungus, bacteria, and viral diseases. In general, nutrient and pathogen relationships are quite complex. Pathogens (disease organisms) alter the plant’s ability to take up nutrients, how they transport them, how they are used etc. Often, pathogens damage the roots, stems, and leaves so that the plant cannot produce a crop. Sometimes pathogens tie up nutrients or damage the vascular system for moving nutrients around in the plant. Secondary infections often occur and sick plants attract insects that also damage the plant. Keeping plants healthy includes creating nutrient-rich food which is also beneficial for livestock and human health.
Most people think of nutrients as plant food needed to get better growth and higher yields. Good mineral nutrition also affects plant resistance or susceptibility to pathogens and pests. Disease resistance is genetically controlled but is influenced by environmental factors. Mineral nutrition is an environmental factor that can be controlled in agriculture to reduce pathogens and pest infestations.
How do mineral nutrients affect disease resistance in plants? Good mineral nutrition can affect two primary disease resistance mechanisms. First, thicker cell walls create mechanical barriers to pathogens. Second, good mineral nutrition creates natural compounds (flavonoids, antioxidants) which protect against pathogen invasion. Higher mineral nutrient density not only protects the plants from disease, high nutrient density also protects the animals and humans that eat the nutrient-dense food from disease. Animals instinctively know when food is nutrient-rich. Actually, so do humans! The flavonoids (improved flavor) of nutrient-rich food tell you the food is nutrient-rich!
The Florida researchers use an orange as an example to show nutrient balance. Generally, in good oranges, the nitrogen (N), phosphorus (P), and potassium (K) make up 81% of the nutrients in an orange. The P is the lowest and the K is the highest. On secondary nutrients, Calcium (Ca), Magnesium (Mg), and Sulfur (S) make up 18.7% of the nutrient content. Good levels of Ca are associated with sweetness and high sugar content. However, adequate Mg is needed to make chlorophyll and sugars while S is needed to form proteins. The remaining 0.3% is the micro-nutrients (iron, manganese, zinc, copper, chloride, boron, molybdenum). Micro-nutrients are needed in small amounts but activate many beneficial biological processes. All these nutrients need to be in balance in order to grow well, produce high yields, and to resist pathogens and pests.
For good fungal resistance, balanced mineral nutrient levels are important. Good K levels strengthen cell walls so they do not leak. Fungal spores often thrive on leaky roots and leaves. Potassium enhances cellulose to make cell walls thicker. A lack of Ca and boron causes a buildup of sugars in the stem and leaves which insects can sense, causing insect infestations and feeding. Adequate plant Ca and boron activate many natural disease resistance mechanisms. When insects attack a plant, they open up wounds for disease pathogens to enter. Too much N or too little N increases fungal infection. N is needed to make proteins, but too much can tie up some micro-nutrients, and too little means plants have lower protein production. Too much N also ties up silicon needed for strong cell walls. Adequate levels of copper are needed to fight fungus. Copper acts like a natural fungicide to reduce fungus populations. Soil-applied Mn also greatly reduces fungal diseases.
On bacterial diseases, some of the same mechanisms apply. A lack of K, Ca, and boron causes similar pathogen problems like the fungal diseases. In addition, a lack of N enhances most bacterial diseases, but some bacterial diseases thrive on high or excess N in the plant. On viral diseases, adequate zinc is needed to unzipper the viral DNA so viral reproduction is decreased.
Disease relationships to K content are most consistent. Research articles (534) found that adequate K reduced bacterial and fungal diseases 70% and insects and mites 60% of the time. Adequate K plant tissue levels generally always result in increased resistance to pathogens and pests. Potassium deficiencies created by overapplication of dolomite or magnesium lower this resistance. In dry years, K levels are often low in the plant. Adding 1.5 gallons of citric acid in a 2” x 2” band increases K soil levels for plant uptake. In general, any nutritional deficiency hinders plant metabolism and results in a weakened plant, which lowers disease resistance.