Any factor that increases the likelihood of flooding will improve conditions for the infection of the phytophthora organism. Varietal resistance, tolerance, and seed treatment are all valuable tools to minimize losses due to Phytophthora.
Stalk rots are the most important and common diseases of corn. Gibberella and anthracnose stalk rot are fungus diseases that can cause premature ripening, chaffy ears and lodging.
The general term "fungicide" is often used to describe chemicals that combat fungi.
Leaf blight diseases are most effectively controlled by selecting hybrids with disease resistance. Rotation away from corn and burial of corn residue may also be helpful.
Powdery mildew and leaf rust are two of many wheat diseases. Stewart's wilt is a corn disease and sclerotinia affects soybeans and alfalfa crops.
Good agronomic practices like proper seeding rates, seeding dates, balance fertility, crop rotation, weed control, insect control and seedbed preparation all help control diseases.
Both take-all and Cephalosporium stripe are favored by wheat year after year in the same field. Rotating away from wheat two or more years helps reduce fungal carryover.
Burying crop residues helps lessen the chance of fungal diseases by enhancing decomposition of plant material and death of the disease-causing fungi.
Oat diseases that have caused problems in recent years include loose smut, covered smut, crown rust and barley yellow dwarf virus. Sclerotinia is a fungal disease of soybeans and alfalfa.
There are no varieties of wheat resistant to head scab. This disease is usually more severe when wheat follows corn because the fungi causing scab and Gibberella stalk rot are the same.
Although there are many diseases attacking the soybean plant, Phytophthora damping-off and root rot is the most destructive disease in Ohio.
Anything that prolongs the time from when the seed is placed in the ground, to the time the plant no longer needs to draw from food stores in the seed itself, increases the possibility of disease infestation. Poor seed placement, cold temperatures, excessively wet or dry soil conditions and a host of other factors can contribute to the problem.
The major corn diseases can be grouped into four categories: leaf blights, stalk rots, ear rots and virus diseases.
Gibberella causes head scab in wheat, stalk and ear rot in corn and seedling diseases in both crops.
Sclerotinia stem rot, or white mold, can be recognized as a white mold beginning soon after flowering that causes a girdling lesion on the stem. Although some varieties show smaller yield losses under disease conditions, there is no resistance to the white mold. Since deep plowing is needed to bury sclerotia, a two-year no-till rotation away from soybeans would not provide effective control.
Most measures prescribed for control of field crop diseases are non-chemical, simply because fungicides and other disease control chemicals are expensive. Use of resistant varieties and hybrids, crop rotation and good agronomic practices all help control diseases.
The corn virus diseases, maize dwarf mosaic and maize chlorotic dwarf, are potentially destructive in fields infested with johnsongrass. Aphids and leafhoppers pick up the virus by feeding on johnsongrass and subsequently may transmit the virus to nearby corn plants. Planting resistant or tolerant hybrids helps control the disease.
Although several leaf diseases are common every year, they seldom destroy enough tissue to reduce yield. All varieties show susceptibility and continuous cropping may increase the problem. No chemical controls are recommended.
Use of resistant varieties is important for control of powdery mildew, leaf rust and Septoria diseases. Supplying optimum nutrition to produce healthy plants will help reduce the harmful affects of foliage diseases. However, excessive use of nitrogen fertilizer will favor the development of powdery mildew and Septoria diseases.
Field crop diseases occur when pathogens attack susceptible plants, during environmental conditions that favor infection and growth of the pathogen within the plants.
Phomopsis seed decay results from fungal infection of pods and seeds when plants mature during wet weather. Prevalence of wet weather during seed dry-down will enhance the disease development. Moldy seeds have poor germination and will probably die before emergence.
Plant stress due to lack of moisture, leaf disease, insect injury and nutrient deficiency tends to increase the incidence of stalk rot. Continuous corn tends to contribute to stress and stalk borers permit stalk rot fungi to enter the plant. A soil test value of 300 lbs. K/A is excellent for corn production.
A recommended management practice for control of disease in corn, soybeans and wheat is to plant only high quality treated seed with a high germination percentage.
All leaf blight diseases cause loss of green leaf tissue and may cause shriveled and lighter test weight grain. When leaf damage is severe, plants may be predisposed to stalk rot diseases. Yield loss is usually related to the time when the upper leaves of the plant become infected. Severe yield loss occurs when the upper leaves (the ear leaf and those above the ear) become infected at or soon after tasseling. If disease does not occur on these leaves until six to eight weeks after tasseling, yield loss will be minimal.
The key to successful disease control is correct identification of disease problems. This can be done quickly by using publications with color I.D. photographs and/or advice from competent sources. Fungicides may provide effective or economical control of some diseases, but proper identification is essential for both short- and long-term disease prevention and control.
Although Rhizoctonia root rot can be identified under almost any weather condition, widespread outbreaks would be more prevalent when weather conditions are dry in the spring and wet later in the season.
Cool, wet weather from mid-April through flowering is favorable for the development of powdery mildew and Septoria tritici leaf blotch while Stagonospora nodorum blotch and leaf rust are favored by warmer, wet weather. Stagonospora nodorum glume blotch and head scab are likely to appear if wet weather persists through early June.
Because rapid germination and seedling growth reduces the probability of seedborne diseases, placement of seed in warm soil with optimum seed to soil contact is a critical non-chemical practice. Judicious use of a seed treatment fungicide may also help minimize seed and seedling diseases.
Integrated Pest Management, while having many definitions, involves the use of economically and environmentally sound practices. IPM helps crop producers identify all pests, determine the need for control methods, and choose the appropriate combination of control methods for the situation (General IPM definition derived from several publications.)
The cornerstone of successful disease control is correct identification of disease problems. Producers facing specific problems can fine-tune their disease control strategies to those few diseases encountered each year. Those with little experience identifying diseases should seek help from competent sources. Several publications are available that provide color photos of the major diseases and complete descriptions of factors affecting their development. These can be obtained from an Ohio State University Extension office in each county. Disease samples can be submitted to the Plant and Pest Diagnostic Clinic at The Ohio State University for diagnosis.
All of the above. Best management practices for Sudden Death Syndrome include reducing soybean cyst nematode problems, crop rotation, improving soil drainage and planting of earlier maturing varieties.
Soybean Cyst Nematode populations can increase if winter annual weeds are not controlled properly. Management of soybean cyst nematode also includes use of crop rotation and resistant varieties, as well as preventing the introduction of the SCN pest.