Camalote grass control in sugarcane

Also known as camadeira, due to the ease of dispersion of its extensive seed bank, camalote grass can lead to yield losses of up to 100% in sugarcane and 80% in ratoon sugarcane. To minimize the damage caused by this aggressive and difficult-to-control species, preventive, cultural, mechanical and chemical methods must be integrated.

Camalote grass for many years was identified by researchers as Rottboellia exaltata, but the current name for the species is Rottboellia cochinchinensis. Therefore, it is important to highlight that any of the nomenclatures found in books and magazines refer to the same species: camalote grass. 

The plant can germinate from a seed or sprout from a piece of stem and quickly grows by sending out tillers, forming a clump. When adult, the clump can have up to 50 culms measuring 1cm in diameter, in addition to growing up to 2,5 m. The leaves are thin and long and at their base they have tiny bristles that hurt people when they touch them. 

At this stage, the plant emits up to 16 seeds that fall to the ground as they mature. One part can germinate and form other plants, the other remains dormant in the soil and germinates after 4 years. The seeds are light and can be carried by wind, floods, birds and reach distant areas. From this characteristic the plant gained another name, hiker.

Dormancy in camalote grass seeds allows them to be stored alive in the soil, however, without entering the germination process. Every year, plants not controlled by herbicides produce seeds, which, when they fall to the ground; increase the “stock” of seeds. On the other hand, part of the stored seeds are stimulated by weather conditions (rain and temperature) and come out of dormancy and establish new plants. Storing seeds in the ground is known as a seed bank.

The culms have nodes (in each one there is a bud), which, when lying on the ground, sprout and also form new plants. This weed is very vigorous and prolific. A single plant is capable of sending up to 100 tillers and producing 15.000 seeds, which remain dormant in the soil for up to four years (Lorenzi, 2000)

Where is the camalote grass?

It was initially found in India and is currently present in 28 countries. It infests 18 crops, including sugar cane (HOLM et al., 1977). 

It is estimated that in Central America and the Caribbean, camalote grass infests more than 3,5 million hectares (FAO, 1992).
In Brazil, it may have arrived at the end of the 50s along with rice seeds from Colombia (DEUBER, 1992). 
Initially, its infestation occurred in the Rio-de-Janeiro region (FREITAS et al., 2004). Today it also occurs in the northeastern, central-western and southeastern states (CARVALHO, et al., 2005).

Main Brazilian locations with incidence of camalote grass

There are reports of infestations in sugarcane fields in São Paulo, particularly in Mococa, Porto Ferreira, Piracicaba, Igarapava, Dumont, Ribeirão Preto. However, the spread is not widespread among sugarcane fields, but rather isolated.

According to Bianco (2004), camalote grass should be the main weed species in sugarcane fields in the Ribeirão Preto region.

What damage was caused?

In sugarcane, R. cochichinensis caused yield losses of up to 100% in plant cane and up to 80% in ratoon cane (ARÉVALO and BERTONCINI, 1994). In other countries, such as Venezuela, there are also reports of up to 80% productivity losses (ANZALONE et al., 2006). The plant significantly reduces the production of stalks, reduces the longevity of the sugarcane field, reduces the industrial quality of the raw material and makes harvesting operations difficult (FERREIRA et al., 2010).

When to control camalote grass?

In the field, it is observed that camalote grass is sensitive to shade and when the sugarcane field is shading the soil surface the flow of new plants is reduced. However, in sugarcane, the shading that reduces the emergence of new camalote grass plants occurs when the crop is 150 days from harvest or planting. Within this period, it is common to observe emergence flows of the weed in the field.  

When considering camalote grass, the ideal is to keep the sugarcane field free of the weed for up to 180 days, but after 120 days the size of the crop becomes difficult to use equipment for applying herbicides. It must also be considered that the application of herbicides to the crop after 120 days must be done with care so that the sugarcane does not become poisoned by the product used.

How to control?

Camalote grass is an aggressive and difficult to control species. Therefore, to minimize losses, it is necessary to integrate preventive, cultural, mechanical and chemical control methods.

The use of sugarcane straw can represent an important method of controlling camalote grass, as the seeds have difficulty in overcoming the straw layer. Another important control is preventive, which, by cleaning equipment used in areas infested by plants, prevents the spread to areas without infestation. Currently, this control is of significant importance, although little adopted among producers due to the long time required for cleaning.

For the chemical control of camalote grass in sugarcane cultivation, the most used herbicides are clomazone and ametryn+trifloxysulfuron. Herbicides, for better control of the weed, must be applied sequentially to the crop. Products such as amicarbazone, trifluralin and pendimethalin or even sequential applications of trifluralin and pendimenthalin applied in full doses when planting sugar cane can result in controls of between 80% and 85% for 60 days to 90 days. However, these herbicides need to be incorporated to result in greater effectiveness. This makes the planting time more favorable.

Why is camalote grass difficult to control?

It is still not known exactly why camalote grass is a difficult to control weed. Possibly, the cause of the plant's natural tolerance to herbicides is the detriment of a set of characteristics: anato-morphological structures and differentiated metabolism. 

The plant, particularly grown from clumps, has a well fasciculated and deep root system, which can make the absorption of herbicides difficult. The products are more concentrated in the superficial layers of the soil and the deeper roots do not absorb it. This characteristic may contribute to control difficulties.

The plant experiences rapid growth that can reach up to 2m in height. The formation of culms and sheaths is very common and naturally their specialized tissues make it difficult to absorb herbicides applied post-emergence.

As with other species, nutsedge (Cyperus rotundus) and silk grass (Cynodon dactylon), which also have deep and vigorous root systems, the most effective control is chemical combined with mechanical control. The implements segment the roots and expose them to the surface under dehydration from the sun. At the same time, it facilitates the positioning of the herbicide in the soil, placing it deeper. 

Therefore, as the sprouting or germination of seeds begins, the herbicide is present in the solution and in the soil and is absorbed. As the plant is still very young, the specialized tissues are not fully formed and the herbicide may be more effective as it reaches the site of action more quickly. Given these considerations, it is concluded that the chemical management of camalote grass should be prioritized when planting the crop, when the sugarcane field is renovated.

Ana Rosália Calixto, Carlos Alberto Mathias Azania, IAC

Article published in issue 208 of Cultivar Grandes Culturas.