Tips and methods for controlling orobanches.

The orobanchs are parasitic plants that graft to the roots of crops, depriving them of all food. They cause considerable losses on leguminous crops, sunflower, tobacco ... With integrated control, it is possible to reduce the infestation on the short but also in the long term.

Orobanche, which is also called Halouk, L'Outed, Ben Nabbou or Farôun depending on the region, is one of the enemies that crop professionals (cereals, legumes, tobacco, etc.) dread the most. It is a holoparasite plant, that is to say, it is non-chlorophyllian, which must take the organic matter, water and mineral salts it needs on a host.

This plant-parasite belongs to the Orobanchaceae family, of which there are four main species:

O. crenata is one of the main obstacles in the cultivation of the bean but also lentils, peas and to a lesser extent chickpeas and green beans;

O. aegyptiaca and O. ramosa mainly attack tomato, tobacco, melon, potato and lentils;

O. cernua and O. cumana infest mainly sunflower but also tobacco, eggplant and tomato;

O.foetida parasitizes alfalfa and bean crops.

This enemy is spread over all regions of Morocco that grow cereals, legumes and other field crops.

From left to right: O. cernua; O. crenata; O. foetida; O. ramosa

Symptoms and damage

The growth of orobanches is at its peak during the flowering of the crops they parasitize. These holoparasites cause the wilting of the plants because they deprive them of their water, their organic matter and their mineral salts. The crops lose their vigor and the flowers fall, which leads to yield losses. In the long term, the plants die. Orobanches can cause up to 100% loss in the most infested plots.

Biology

To fight the orobanche, it is essential to know its biology and its development cycle. The majority of the dwarf species are annual and breed through tiny seeds (0.2 to 0.3 mm).


The cycle of this plant-parasite has two main phases: that of underground development, which begins with germination, and that of aerial development which begins at the moment when the first stems emerge from the soil and ends after the fructification and the maturation of the seeds. .

Fight

Several control methods have been studied. They can be used separately but it is better to combine them in an integrated fight to manage the orobanches.

Manual uprooting

Manual picking of orobanches is an effective means of control provided that it is well done and that the plot is newly or slightly infested. To be effective, we must proceed to the uprooting of the shoots of orobanche after their emergence of the soil but before the maturity of the seeds. This technique also makes it possible to limit the stock of scattered orobanche seeds since the maneuver takes place before the formation and dissemination of the seeds.

In India, where this method was tested, the pulling of O. crenata on tomato culture for 3 years showed an efficiency rate of 100%.

Cultural method

Various methods of cultivation make it possible to fight against the proliferation of orobanchs.

Crop rotation

Crop rotation is an effective means of control especially if it is practiced alternately with trap plants. The trap plants allow the germination of the orobanche seeds but they are unable to attach to the roots of the host plant which causes their death. This process is called "suicide germination". Some pea, clover, flax, coriander, mustard, etc., are effective when used as trap plants.

Planting date

The shift in sowing date is a maneuver that significantly reduces the extent of orobanche attacks. The more the crop sowing is shifted, the more the attacks are reduced. However, the shift in sowing date may affect the development of the crop.

In the case of winter crops, such as legumes, it is recommended to use an early variety and sow it late at temperatures below 8 ° C. Thus, the main root of the crop will not be parasitized by orobanches because they prefer dry soils and higher temperatures to grow. The experiments carried out demonstrate a reduction of infestation of 72.5% in the case of late sowing of 6 weeks for lentils.

Conversely, for spring crops, such as tobacco, it is recommended to sow early, that is to say when the temperatures are still low. Early planting of tobacco reduces the borer infestation by up to 70%.

Fertilization

High potassium and nitrogen fertilization reduce the presence of orobanches by 33 to 50%. On the other hand, this method involves using a large volume of fertilizer which is very expensive.

Other methods

Irrigation helps reduce infestation. In Fez and Meknes, bean crops irrigated with wastewater are less invaded.

Deep plowing also bury the orobanche seeds, which are too far from the roots to germinate and grow.

In addition, the use of resistant varieties should be considered.

Solarize

As mentioned earlier, the orobanche trees do not tolerate too high temperatures. Solarisation consists of covering the floor with plastic mulch (polyethylene) during periods of intense heat, before sowing. The best results were obtained with a solarisation of 30 to 50 days which makes it possible to obtain a temperature of 56 ° C in the first 5 to 10 centimeters of the soil.

This method is however limited to small plots. It is also effective for fungi, nematodes, bacteria and weeds.

Biological control

There are several natural ways to control orobanches, but these are often effective in the long term rather than in the short term:

*Insects: Phytomyza orobanchia attacks orobanchia without damaging the crop. It is found naturally in Morocco. 500 to 1000 insects / ha can reduce the presence of parasitic plants by up to 50%;

*Fungi: Fusarium oxysporum fsp orthoceras, Sclerotinia spp, Rhizoctonia solani, Colletotricum lagenarium and Ulocladium atrum. Fusarium oxysporum fsp o. is the most used mushroom. On tobacco growing, it improves the yield by 80.5%. However, it needs a high relative humidity and temperatures between 10 and 20 ° C;

*Bacteria: orobanches are susceptible to fluorescent Pseudomonas bacteria and Picketti ralstonia;

*Trituration waste of olives: The by-products resulting from the crushing of olives (vegetable and olive-pomace) are very effective in the fight against orobanches, they make it possible to reduce the infestation from 78 to 97% in bean cultures !

Chemical fight

Chemical treatment is the method most often used in the fight against orobanche because it is effective in the short term.

glyphosate

Although glyphosate is a very controversial product, it remains one of the best friends of farmers. The recommended rate is 60 g / ha diluted in 500 liters of water for beans and 40 g / ha for other legumes. The treatment should be broadcast at the tubercle stage of orobanche. Repeat with the same dosage two weeks later.

However, be careful with the dosage because this product can become very harmful. The effectiveness of this treatment depends on the stage at which it is applied, the setting of the sprayer, etc.

sulfosate

The sulphosate should be dosed at 100 g / ha. It is necessary to renew the treatment two with the same dosage. It is appreciated for its efficiency and ease of use.

imidazolinones

Imidazolinones are effective herbicides in the control of orobanches. Imazethapyr (100 g ai / ha) and Imazaquin (25 g ai / ha) are used pre-emergence to control O. crenata.

Integrated struggle


To manage orobanches, it is essential to establish a control program combining cultural methods, biological control and chemical treatments. In this way, the infestation can be reduced in the short but also in the long term.

Source : http://www.agrimaroc.ma