Reducing Wheat Diseases

Winter and early spring has been warmer than normal. The lawns are green and so is the wheat. Is this due to adequate nitrogen? More likely it’s adequate iron and magnesium. In warm springs, iron is more plant available to make chlorophyll and magnesium is the central element for chlorophyll. If your wheat is yellow, even after spring nitrogen applications, it may be due to a lack of iron, especially on fields with poor soil structure. Soil tests may show high iron, but its in the wrong form. Golf courses often use iron to green up grass. 

Looking ahead, what changes in fertility might enhance wheat disease resistance or simply enhance wheat growth and yield. Often, when scouting wheat, white leaves may be seen which is a sign of nickel deficiency. Nickel (Ni2+) activates the urease enzyme that allows plants to use external and internal urea as a nitrogen source. Nickel (2+) is one of the least toxic metals and stimulates microbial growth. 

Adequate nickel improves wheat growth and yield. Adequate copper (Cu2+) causes the greatest reduction of disease. Mild Cu2+ deficiency causes 5-20% yield reduction, mild Cu2+ deficiency 20-50% yield reduction and severe Cu2+ deficiency causes 50-100% yield reduction in all cereal crops! High soil organic matter or muck soils typically are the lowest in Cu2+. Copper increases plant resistance to diseases rather than a direct effect on any one disease. Copper deficiency results in less lignin production because Cu2+ is needed to activate the enzyme that makes lignin. Copper also increases starch in pollen and wheat heads. 

Copper deficiency is associated with limp stems and leaves, deformed heads, and poor overall wheat growth. Wheat diseases directly associated with a lack of Cu2+ include Cephalosprium (gramineu) stripe and leaf diseases like Cephalosprium stripe and wheat rust (Puccinia striformis). Unfortunately, Latin names have to be used to identify many diseases because there are many types of rusts, leaf diseases, root rots, and other diseases. 

In relationship to plant available calcium (Ca2+) in plant tissue, plants need adequate Boron (B) soil test levels (1-2 ppm) to get Ca2+ into plant tissues. Boron B maintains Ca2+ in cell wall, enhance vascular tissues, and is known to decrease many pathogenic microbes that cause root roots like Rhizoctonia, Pythium, and powdery mildew. 

A given form of nitrogen (NO3- or NH4+) may decrease one disease while increasing another disease. Nitrogen is used to make amino acids, protein, and enzymes, so a balanced N fertilizer program is important for good plant health. Nitrates (NO3-) promote growth and the Auxin hormone. Ammonium (NH4+) promotes yield and the cytokinin hormone. Split applications of nitrogen help reduce many diseases. Always add sulfur (S) to nitrogen to enhance nitrogen efficiency. Microbes and plants need a 10:1 ratio of nitrogen to sulfur for ideal growth and yield. Low S is associated with Rhizoctonia, stem rusts, and powdery mildew. 

Excess ammonia (NH4+) is associated with wheat diseases like Rhizoctonia, powdery mildew, stem rusts, and wheat stripe rusts. A lack of ammonium is associated with root rot (Fusarium), tan spot, and nodorum blotch (stagnospora). Too much nitrate (NO3-) increases Fusarium root rot. 

A lack of phosphorus (P) and a lack of potassium is associated with many wheat diseases. Excess P may increase viral diseases because P is critical to their reproduction. Adequate P increases tillering, is a component of strong cell walls, enhances energy transfer and is backbone to DNA/RNA. Pythium and Fusarium are enhanced when P levels are low. 

Adequate potassium (K) increases nitrogen content and strengthens cell walls to help increase plants resistance to diseases. Potassium (K) is a nutrient that is used by plants to balance electrical charges. It is often absorbed by plants and then excreted back into the soil to get other essential nutrients. In some cases, either too much or too little K causes disease while adequate K promotes good plant health. Stem rusts, stripe rusts, leaf rust, glume blotch and leaf blotch (Septoria spp) are all enhanced when P and K levels are deficient. 

Zinc (Zn), Manganese (Mn), and Chlorine or chloride (Cl) are other important nutrients which enhance disease when they are lacking. When a soil has adequate chlorine, it enhances the plant uptake of manganese. Zinc activates key plant enzymes and increases disease resistance. Adequate Mn is needed to keep healthy plants growing. A lack of Zn increases root rots (Fusarium, Rhizoctonia). A lack of Mn and Cl increases Rhizoctonia, stem rusts, leaf rusts, and Cephalosporium stripe. Molybdenum deactivates viruses by denaturing their protein coats and decreases Phytophthora spp. and nematodes. Most plant diseases are greatly reduced or eliminated when plants have adequate plant nutrients.