Management of silk grass and nutsedge in sugarcane

Silk grass and nutsedge are two weeds of difficult to control in sugarcane fields. With high propagation and interfere negatively in culture, both demand a lot of attention and effort from producers to prevent and minimize losses.

A The exact origin of silk grass is not well defined, it may have appeared primarily in Africa, Eurasia, India or Malaysia. But it is a very primitive and currently considered the most widely distributed weed geographic location on the planet (KISSMANN, 1997), is second only to nutsedge. Could it be found in tropical and subtropical regions around the globe, being present in approximately 100 countries. In Brazil it is present from north to south, either as a weed or cultivated plant (in the case of forage in pastures).

A nutsedge originates from India and is the most widespread weed in the world, being found in the most diverse types of agroecosystems. It is present in all countries with tropical and subtropical climates and in many countries with temperate climates (KISSMANN, 1997).

There are reports that this plant weed was introduced into Brazil since the beginning of European colonization, in vases brought from India with other species. Your initial establishment it would have been in the regions of Rio de Janeiro, Recife and Salvador (DEUBER, R. 1992).

Features

Silk grass is also known such as Bermuda grass and has the scientific name of Bermudagrass (GURGEL, 2003). In Brazil, it is a perennial grass of herbaceous growth that reaches a maximum of 40 cm in height. When the plants are young, have a low posture and reach an erect posture only after being flowering (KISSMANN 1997).

A reproduction can be both sexual and asexual, but as its seeds are very small and short-lived, making reproduction by seeds insignificant, reproducing mainly by rhizomes and stolons (PROCÓPIO et al., 2003). The development of stolons occurs on the surface of the soil, with lengths ranging from centimeters to meters. The rhizomes are they are found underground and quite branched.

A nutsedge (Cyperus rotundus) and also known as aromatic sedge, and has similarities with silk grass, since morphological characteristics to control measures and damage caused. To the nutsedge plants are perennial, and their aerial part (known as epigeal) It has a herbaceous size up to 50 cm in height. The roots originate different tubers that remain linked in the form of a chain (KISSMANN, 1997).

Its reproduction can be either sexual as well as asexual, but reproduction by seeds is not very significant because, less than 5% are viable. Thus, the main multiplication occurs by underground tubers and bulbs. Sedge adapts to different environments edaphoclimatic, which includes locations with high temperatures. In the regions at low temperatures its development and multiplication become slow, only freezing the soil kills your tubers. They also tolerate prolonged periods of drought or flooding (KISSMANN, 1997).

Propagation

You The main means of spreading nutsedge and silkgrass occur through the use of machines and implements for soil preparation (subsoilers and harrows), planting (culm planters or MPBs) and cultural treatments (applicators of fertilizers and insecticides in the ratoon line). The implements distribute its vegetative parts (sedge tubers and silkgrass stolons) in the own plot, as well as transporting it to other plots. As they have high reproduction capacity and ease of adapting to different production environments, the infestation is quickly observed in the field, if there is no specific control be practiced.

For silk grass, each infested hectare can produce up to 40 tons of rhizomes in 0-15 cm layer of soil. A single plant can produce up to 5 meters of rhizomes in 80 days, which tend to remain dormant in the soil, providing irregular emergency flows. This characteristic contributes to persistence of the vegetative parts in the soil for long periods, and can be found up to 80 cm deep (JAKELAITIS et al., 2003).

Now, nutsedge may have its tubers found up to 40 cm deep in the soil. According to Lorenzi (1983), the intensity in the formation of chains of tubercles reaches densities of 3000 tubers in 0,4 m3 (40 cm soil x 1 m2 surface), with up to 2000 epigenous manifestations on the surface (1 m2). Jakelaitis et. al (2003) highlighted that a single tuber within a year produces a density of up to 700 new tubers, with one hectare infested can develop up to 40 tons of tubers in the 0-15 cm layer from soil.

Losses

At sugarcane culture, silk grass dominates the weed community, i.e. quickly becomes the dominant species. Provides losses in productivity which reach up to 85%, when not adequately controlled (VICTORIA FILHO & CHRISTOFFOLETI, 2004). They also reduce the number of cuts and the useful life of the sugarcane field (KISSMANN, 1997).

The damage caused by this weed is due, mainly, its high propagation capacity, which ends up “suffocating” the sugarcane, particularly in its juvenile phase, leads to tiller death and failure in the sugarcane stand they become evident (Figure 2). Normally, in a silk grass, the sugarcane practically disappears.

A single plant of silk grass can create a plant of 25 meters in diameter in just two and a half years. It is estimated that a sugarcane field with ratoon in the third cutting and with a productive potential of 80 t/ ha will produce only 45 t/ ha/ (reduction of 35 t/ha) if infested with silk grass (CANAONLINE, 2017).

Most of the losses are due to competition exerted by silk grass on natural resources (water, light, nutrients, space), but one must also consider its capacity production and release of allelochemicals in the soil, which affects and inhibits sprouting and causes growth difficulties in the crop (SILVA et al., 2005).

Silk grass has great potential to cause an increase in mineral and vegetable impurities in industry, given the volume of vegetable mass formed. It can also be a host for nematodes of the genera Meloidogyne e Pratylenchus, the most harmful to sugarcane cultivation.

Seedseed has enormous capacity of interfering in the development of cultures, so that in more than 100 countries indicate it as a “national plague” (KISSMANN, 1997). The species needs presence of sun for its establishment and tolerates very little shading. Due to this characteristic, its presence in sugarcane fields occurs in the first months after harvesting or planting the crop (maximum up to 120 days).

At the Brazil nutsedge is the best known of the weeds, and more than 1 million of hectares of sugar cane are infested (LORENZI, 1983). You losses are mostly due to the competition of nutsedge for environmental resources (water, light and nutrients), but also have potential allelopathic. In sugarcane plants, the substances exuded inhibit the sprouting of buds and sugarcane tillering, which results in lower stands.

In In cases of extreme infestation, culm productivity drops by 75%, in addition to 65% reduction in sucrose accumulation (KISSMANN, 1997). Because of its enormous multiplication capacity can form up to 40 tons of plant matter per hectare and also be an alternative host for fungi such as Fusarium spp. and for different species of nematodes.

Complementary management

O The main means of spreading silk grass and nutsedge is through their vegetative parts (stolons and tubers) that get stuck in machines and agricultural implements. As implements (harrows, subsoilers, furrowers) the stolons of silk grass or the tubers of nutsedge break off and are disseminated throughout the sugarcane field.

Particularly, As for nutsedge, the distribution of filter cake (a by-product rich in phosphorus), whether in ratoons or planting furrows, is also largely responsible by the dispersion of tubers. It is very common for filter cake to be contaminated with nutsedge tubers from deposit sites.

A Cleaning the internal parts of implements or agricultural machines is effective for prevent vegetative remains from being taken to other sugarcane fields, particularly for those that are not infested by the species. In that case, the preventive control is effectively added to the chemical management to be adopted on silk grass and nutsedge in sugarcane fields.  

O cultural control can also be added to the chemical management of silk grass and nutsedge, planting the crop in periods of greater humidity (December to March). It turns out that summer humidity and temperature favor the growth of sugar cane, which, by quickly shading the soil, hinders development of both weeds. It should be noted that cultural control collaborates with species management, particularly when associated with chemicals, however, alone does not result in effective control results.

Also to add to the management of nutsedge and silk grass, mechanical control must be considered. According to Azania (2006), implements, generally used in soil preparation, they segment the tubers and stolons, exposing them to dehydration by the sun on the soil surface. When preparing soil is carried out in sugarcane fields infested by silk grass and nutsedge in periods with lower humidity, generally between March and October (semi-dry and dry period), control results are better.

Recommended herbicides

According to the Ministry of Agriculture, Livestock and Supply (Map) there are different herbicides for chemical management of nutsedge and silk grass (Table 1), but they are not all selective to sugar cane. From From the proposed list, the farmer needs to identify which ones are selective to sugarcane and then the time of year in which the herbicide will be used, particularly regarding soil moisture.

For the wet period (more regular rains) use herbicides low solubility (Sw), for semi-dry, dry or semi-humid periods (rains irregular) use herbicides with intermediate or high solubility. The dose of the herbicide must be adjusted to the type of soil, avoid using the largest recommended doses for sandy soils.

Chemical planting management

The management of silk grass and nutsedge must be complemented with chemical control. Certainly, if herbicides are applied after preventive, cultural and mechanical, the effectiveness in control will still be enhanced. 

For sugarcane, at the end of soil preparation, the application of Incorporated pre-plant herbicides (PPI) will help reduce significantly the amount of stolons and rhizomes present in the soil. However, better control results are observed the longer the time that the herbicide is left in contact with the vegetative parts of the species. A minimum period of time between 20 days and 30 days is suggested before planting the sugar cane.

After planting, herbicides must also be applied preferably in pre-emergence. It turns out that with planting the soil will be rotated again when opening the furrows and it is desirable to apply herbicides specific to silk grass and nutsedge. 

Approximately 60 days after planting, there is need to level the soil surface between the row and planting line, operation called “loin breaking”. Due to soil disturbance and sugarcane fields is not yet completely closed, a new application of herbicides. In this case, it must be carried out in a semi-directed jet, avoiding the leaves of the crop. This way, during the period in which the sugarcane field is not provided enough shade to contain plant development weeds, the herbicides used inhibit their emergence flows (Figure 1).

Chemical ratoon management

In ratoons infested with silk grass and nutsedge, the producer also needs to choose one of the herbicides in Table 1, according to the rainfall regime at the time of application. For distributed infestations evenly throughout the plots, the herbicide must be applied pre-emergence of the weed plant and in total area, generally before the crop has sprouted.

For infestations distributed in reboleiras, control must be located. If there are stand failures, the crop can be eradicated in the local (reboleira), followed by application of residual herbicide. Expect the fallow (between 20 days and 30 days until the ratoon dies) and planted reboleira with pre-sprouted seedlings (MPB), complementing new application of herbicide after 40 days and using a pendant (Figure 2).

Carlos Alberto Mathias Azania, Lucas Carvalho Cirilo, João Eduardo Brandão Boneti, Ana Rosália Calixto da Silva Chaves, Vitor Simionato Bidóia, Matology Group, IAC Centro Cana

Article published in issue 228 of Cultivar Grandes Culturas, May, 2018.