Published at: 15 April 2024

"The disease transmitted by Dalbulus maidis caused significant physiological damage and yield reduction. Therefore, specialists from INTA provide recommendations for utilizing the cereal as a forage resource and minimizing losses."

The main corn-producing area of the country has been affected by a complex of diseases transmitted by a single vector insect, the corn leafhopper (Dalbulus maidis), whose main impact on plant physiology is to hinder the arrival of nutrients and assimilates to the ears and affect grain filling. Many late-planted corns showed early infections that dramatically altered plant morphology, their ears, and led to almost total grain yield losses. In the face of this situation, the final destination of these batches is uncertain. Therefore, a team of specialists from INTA provides recommendations to assess the possibilities of ensiling, silaging, or harvesting based on the green material, plant and grain volume that can be obtained, and cost-benefit.

Due to the high percentage of affected batches and the wide range of severity levels and impact on ear formation and grain quality, Facundo Ferraguti, coordinator of INTA's National Corn Network, refers to the most frequent inquiries related to the convenience of utilizing corn as a forage resource (from a batch that at first glance, its grain yield will not be satisfactory).

Damage by spiroplasma (Spiroplasma kunkelii) varies greatly depending on the corn genotype and the phenological stage at which the plant is infected. Early infections, up to the fully expanded four leaves stage, cause the most damage to the crop. Infections between the four leaves (V4) and tasseling cause intermediate damage, and minor infections occur at advanced stages, from tasseling onwards, with plants growing shorter and reducing their grain yield (less filling of ear tips).

"The main symptoms of the pathogen complex transmitted by the leafhopper are the shortening of internodes (stunting), reduced ear size, and anomalies such as exaggerated prolificacy and multi-ear (bouquet ears). This creates heterogeneity in plant height and ear insertion," Ferraguti explained.

Another characteristic of "affected ears is that the kernels typically have a corky consistency, causing them to bend and break easily into small pieces, making threshing operations difficult and overloading the separation section with foreign material," Ferraguti explained.

In this regard, Ferraguti stressed the importance of "evaluating the destination of the grain (silage or grain harvest), carrying out timely harvesting to avoid prolonged field drying with consequent loss of quality and safety; paying special attention to combine regulations to avoid yield losses and prevent commercial quality from deteriorating." And he emphasized the need to control volunteer corn after harvest to reduce hosts.

According to Marcelo Druetta and Ignacio Luna, both specialists in crop management at the Quimilí Agricultural Experimental Station, Santiago del Estero, INTA, regarding the scenarios that can be projected for the next season, they agree that different variables should be analyzed, bearing in mind that the situation may be modified based on the characteristics of each productive region.

The high incidence and severity values of the disease observed this year in non-endemic areas had not been previously recorded. In this sense, if a benign winter is combined with few frosts allowing greater vector survival and the availability of corn at staggered planting dates, especially in affected areas, the problem is likely to remain significant.

Considerations for Harvesting

Fernando Scaramuzza, coordinator of INTA's Precision Agriculture and Agricultural Mechanization Project, pointed out that, in the presence of an affected batch, it is recommended to characterize and quantify the type of damage to evaluate the need to configure the combine harvester to perform differential work. "Mainly, work should be done on adjusting the header to minimize losses caused by shelling and unevenness of ears, but also by plant overturning and different sizes among them, with the positive aspect that we are working with flat-profile headers."

Initially, Scaramuzza explained, work should be done on the cover plates or ear thrashers, trying to identify the variability of ear sizes present in the batch and the diameter of the stalk. Therefore, the other point to adjust is the corn ear threshing area. "It is the place where the ear should detach from the plant on the cover plate to avoid excessive material entering the threshing system, forcing it with the result of increased tail losses."

Regarding the speed of the rolls and the forward speed of the combine harvester, Scaramuzza explained that "a balance must be achieved in both speeds, and for this, most corn headers have a variable gearbox that allows adjusting this aspect. We must ensure that the rolls go at the lowest possible speed and as parallel to the ground as possible, aiming for the plant to travel the length of the roll, lowering the plant to ensure that a low biomass volume enters the threshing system."

On the other hand, Diego Villarroel, a precision agriculture specialist at INTA Manfredi, Córdoba, indicated that the characteristics and regulations of a cross threshing system (conventional) recommend that the corn threshing cylinder must have threshing bars with thick grooves (corn bars) and with the inter-bar spaces lined with ear compression plates. "This lining allows for better treatment of variable-sized ears, reducing losses of ear chunks with grains due to tailing," he noted.

Regarding the regulation of the opening or closing between the cylinder and the concave at the beginning and end, it will depend on the crop moisture, for which the diameter of the largest ear of an average batch to be harvested must be measured. "The regulation must be adjusted to the cylinder revolutions to achieve quality threshing with the least percentage of foreign material and reducing losses to a minimum. It will be important in this season to work with the return, as many grains will be attached to ear chunks seeking a new opportunity to detach from them," Scaramuzza explained.

Furthermore, in the case of axial threshing systems, Villarroel reminded that the grain quality achieved is higher due to a larger threshing surface with a smoother and progressive operation. For corn, it will suffice to place the corn threshing bars and concave (concave) to then regulate revolutions and clearance, depending on the axial threshing system, which can be centrifugal or frictional.

Regarding the forward speed, Mauricio Santa Juliana, a harvesting specialist at INTA Manfredi, stated that in the affected areas or sectors of the batch, harvesting should be done at a maximum speed of between 3 and 4.5 kilometers per hour. "It is important to remember that in those headers that do not have a head speed variation system and without automatic adjustment of ear plates from the cabin, it will be the operator who must adjust the clearance between the plates (another reason to work at low speeds in complicated sectors) and adapt the head speed to the advance speed (factory set to work at 7 or 8 kilometers per hour)."

Regarding threshing, Santa Juliana pointed out that "it is important to line the stone trap to prevent the material entering from the feeder from getting stuck and overturned and to enter the threshing cylinder in an orderly manner." He added: "Regarding the concaves, use the factory originals for corn, with round bars of 19 millimeters in good condition and not cemented, otherwise the clearance between the cylinder and the concave tends to be closer, pressing and grinding more material for good threshing (it is also not recommended to use cemented or filled bars in the cylinder)."

"Given that the material affected by Spiroplasma produces uneven grain sizes and low weight, it is necessary to consider the revolutions per minute of the fan to avoid exceeding and increasing losses through tailing," Santa Juliana indicated.

Finally, Scaramuzza and Villarroel emphasized the need to identify crop yield through the yield map. "Through this registration of georeferenced data, we can quantify damage by environment and plan better volunteer corn control (one of the key factors in vector survival) in a targeted manner during fallow periods and before starting the next crop's planting, as a key control tool for the next season."

With the support of
Fondo Coreano de Alianza para el Conocimiento en Tecnología e Innovación (KPK)