Infection Of The Wheat With Fusarium Graminearum

The Fusarium graminearum colonizes con stalks and ear residue in the late summer and fall. Spores are then formed from the affected residues in the spring and summer after the soil has warmed and when wet environments keep the soil surface and crop residues moist for extensive periods.

Infection of the wheat with Fusarium graminearum occurs on flowering wheat heads during warm, wet periods. Favorable conditions for infection are around 60 to 85 degrees Fahrenheit with at least a 90% relative humidity. Extensive periods of high humidity are the most favorable, therefore this disease is regularly a problem when rain reoccurs over several days at or near the time of flowering. However, in some years, suitable weather conditions may occur after the flowering stage, which can produce less disease symptom development on wheat heads, but may irregularly be related with higher DON levels in the grain.

When the favorable conditions of producing the fungus are high, vulnerable wheat varieties may experience substantial yield losses of up to 50% or greater, which can be attributed to blighted or sterile florets and poor grain fill. Moderately resistant varieties often yield noticeably more than vulnerable ones in high-disease surroundings.

Vomitoxin is also a problem, reaching 2 to 10 ppm in grain taken from scabby fields. “Scabby” grain can produce major difficulties in marketing, storage, and application. Local elevators and grain terminals are known to have deduction schedules for vomitoxin contamination based on ppm DON existing in the sampled grain. And considering scab often reduces test weight, there may also be deductions for that also. They may even reject grain with DON levels above a threshold which is often set a 1 to 3 ppm, depending on the end us of the grain. Some scabby grains may be cleaned out during harvest by increasing the airflow rates while combining or by processing the grain through a clean-up step preceding delivery to an elevator.

An important thing to remember is that if the scabby wheat is needed to be stored for future delivery or utilization, the wheat must be kept dry and cool if possible to avoid increases in vomitoxin. The fungus can continue to grow on high-moisture (14% and higher) grain between 55 and 85 degrees Fahrenheit and may produce more of the vomitoxin contamination during storage. Certain livestock can withstand low levels of vomitoxin in feed while swing and other non-ruminants are very sensitive.

Currently there are no FDA “action thresholds” where DON-contaminated grain is prohibited to feed, though there are “advisory levels” which are suggested. Consistent with those “advisory levels”, beef cattle could feed on grain at around 10 ppm DON if it makes up no more than 50% of their feed ration, or 5ppm DON in finished feeds. Studies advise that dairy cattle can also endure comparable levels and that the vomitoxin is not carried into the milk. Swine can tolerate 5ppm if not more 20% of their ration and 1ppm in finished feeds, however they may refuse the feed or regurgitate it, dropping gain. Chickens, in similarity to beef cattle, the FDA advises the same threshold levels even though they tend to be more tolerant.

Symptoms of vomitoxin poisoning commonly consist of vomiting, reduced feed intake, diarrhea, and other gastric distress signs. Successful management of wheat scab entails a combined method to achieve adequate levels of suppression. Applied at the proper time, a combination of varietal resistance to scab, foliar fungicides, crop rotation, and tillage can deliver good management of this problematic fungus. Varieties with the maximum level of offered resistance to scab should be chosen for the areas susceptible to scab or when wheat is grown in rotation with corn.

Pioneer provides scab resistance rating on all its wheat varieties, using a 1 to 9 scale ( 9= excellent, 1 = poor). Wheat planed on rotting corn stalks may develop more disease during epidemics than wheat on soybean stubble. Tillage may also reduce local development by burying colonized residues, however in the more open geography, spores may travel for many miles, making tillage an impractical strategy for management scab in those particular areas.