Invaded harvest: losses caused by late weed infestation in corn crops

In Brazil it is observedand rapid growth in corn cultivation, especially that planted in the off-season. This growth occurs both in cultivated area and in productivity. In the 2011/2012 harvest year, Brazilian corn production counting the first and second harvests reached 72,9 million tons, with a national average productivity of 4,48 t/ha in the first harvest. Data from CONAB/2012 reveal that in the Central-West region there was a significant increase in cultivated area, around 40,25% in relation to the previous harvest, reaching an average productivity of 7,67 t/ha. of this cereal is mainly due to the increase in demand for consumption and the diversity of products used in animal and human supplementation.

Corn cultivation involves several processes that lead to success in the final profitability of the crop. Among these processes, harvesting stands out as one of the most important in culture. During harvesting, losses occur mainly due to misuse and inadequate adjustment of the machine, as well as other factors, such as: environmental conditions, inadequate soil preparation, incorrect sowing time, plant spacing and density, unadapted cultivars , weed infestation, grain moisture content, age and condition of the machine and lack of operator training.

In Brazil, it is estimated that grain losses due to weed interference are around 20 to 30%. In these crops, these plants can increase the water content of the grains, reducing their commercial value, and consequently influencing the increase in the loss rate at the time of harvest. Its presence in crops requires the adoption of detailed control practices, reducing the yield of the harvesting operation, increasing the cost of production and, consequently, reducing agricultural efficiency.

The viola string (Ipomoeasp.) is an annual, herbaceous, climbing plant, with stems with dense hairiness, germinates, emerges and grows, reaching up to 3 meters in length. This plant does not cause losses in production if it affects the crop after the critical period of competition, but its high population can make the harvesting operation unfeasible, causing bushing, dragging and tipping of the crop, and subsequently wear of the components of the cutting platform. , in addition to affecting the final yield of the crop, causing losses to the producer.

In mechanized harvesting, losses are common and are acceptable up to a limit of 0,8 sc/ha. The final profitability of the activity is directly associated with the maximum reduction of these losses. A recent study on this problem, carried out in the southeast region of the State of Goiás, quantified the losses caused by the viola string infestation. The results showed that the problem is of great relevance to the producer as it leads to a drastic drop in crop productivity.

The study carried out monitored the harvest of a high-tech hybrid, intended for the production of medium-cycle grains, with sowing density varying from 60 to 65 thousand plants per hectare. Planting was carried out in the first half of November 2011, using the direct planting system, with a seeder-fertilizer adjusted to distribute 2,9 seeds per linear meter, with a spacing of 0,45 m between rows. 400 kg/ha of formula 08-20-18 (N-P-K) were applied to the sowing furrow, and top dressing with 200 kg/ha of urea, carried out in the V3 and V4 development phases. The harvester used was a rotorAxial machine, with a 13-row platform and 0,45m spacing. The adopted working speed was 4 km/h.

Samples were collected consisting of five replications for treatments with and without the presence of viola strings, each repetition with a distance of 50 meters between them. Each block was represented by repetition, carried out in different areas in the field, representing the total cultivated area of ​​60 ha. The quantification of grain losses in ears was carried out by placing on the ground, immediately after the harvester passed, a wooden frame and string with a total area corresponding to 30m², where only the ears within the limits of the frame were collected, and then threshed and weighed. To quantify the losses of loose grains, a 2m² frame was placed after the harvester had passed, where the grains that had fallen to the ground were collected and weighed, with the humidity corrected to 13%. The total loss was quantified by summing the losses of grains in ears with the losses of loose grains in the soil.

The losses occurred in the area with viola string were higher than those found in the area free from the weed. This increase is related to the fact that it causes bushing in the components of the cutting platform and the tipping of plants, thus making it difficult to collect these ears.

The total losses found in the area without viola string infestation were 2,4sc/ha, and for the area with infestation it was 20,3 sc/ha (Graph 1), that is, viola string showed an increase in losses of almost ten times more than areas without infestation.

Figure 1: Relationship of loose grain losses, grain losses in ears, and total losses in sc/ha in the mechanized harvesting of summer corn due to infestation of viola string in cultivation areas, located in the municipality of Ipameri (GO).

The losses in loose grains quantified in the area with viola string infestation were 0,24 sc/ha, and 0,44 for the area with viola string infestation, that is, almost twice as much as in the area no infestation.

The average losses found in this work presented rates of around 11,94%, of which 97,79% are located on the cutting platform and 2,21% on the internal mechanisms. The high rate of losses on the cutting platform may be due to the dragging and tipping of the crop, caused by the weed that has a habit of wrapping itself around the crop. A second factor would be the incompatibility of the number of cutting platform lines with the number of seeding machine-fertilizer lines, thus favoring this increase in the occurrence of grain losses in ears. In order to reduce this problem, it is necessary to employ specific management practices for weeds that interfere with mechanized harvesting, aiming to optimize the harvest, preventing its proliferation, and reducing the seed bank of these plants in the soil, enabling the production of corn in subsequent harvests. These practices can be used through the targeted application of herbicides between the rows on a complementary basis, with the main objective of improving harvest conditions, helping to control so-called late weeds. These herbicides are applied between the rows of corn, so that the spray jet only reaches the lower leaves and does not reach the upper leaves of the corn. These plants must be at a minimum height of 40 to 50 cm.

Viola string drastically increases losses in mechanized corn harvesting. It is recommended to manage these plants in order to avoid further damage to both the crop yield and the reduction of wear and tear on the harvester.