Weed control in sorghum
Whether it is grain sorghum, silage sorghum or Sudan grass, weed control is one of the most crucial elements of crop management. The success of production – especially under the unpredictable environmental conditions of recent years – depends fundamentally on the methods and active ingredients used for weed management.
In this post we present the results of the weed control trials we have carried out, and we aim to cover every element of crop management that underpins successful sorghum production.
!IMPORTANT! First of all, let's clarify what Concep III actually is
Concep III is a seed treatment belonging to the family of antidotes. As the meaning of the word ‘antidote’ suggests, it is an agent that reduces the harmful effects of certain poisons. The active ingredient of Concep III is fluxofenim, contained in the product at a concentration of 960 g/l; its purpose is to neutralise the germination-inhibiting effect of herbicides containing S-metolachlor on sorghum seed treated with this product. The use of Concep III seed treatment is therefore justified if the field is to be treated pre-emergence with Gardoprim Plus Gold. As this seed treatment is particularly expensive (HUF 3,000–5,000 per bag), it is worth considering other alternatives (which are often more effective, too)
Genetic background
As a point of interest, it is worth noting that almost all plants belonging to the sorghum group (Sorghum spp.) exude an allelopathic compound called sorgoleone. This compound inhibits the germination of propagules and the shoot-tip growth of certain weed species (e.g. common ragweed, pigweed, velvetleaf, nightshade, and certain plantain and dock species) in the soil. Among sorghums, Sudan grass and its hybrids exude this compound most strongly, so its effect is most pronounced in these crops. Of course, we cannot base weed management in our fields on this, but it can help us choose the right practices.
Field selection, previous crop, agronomic practices
One of the foundations of successful weed control is choosing the right field. It is advisable to select fields that are less infested with perennial and annual grass and broadleaf weeds. The greatest challenge is posed by fields heavily infested with grass weeds. Although one or two technologies and active ingredients are already available on the market (e.g. CONCEP III), they offer no solution to late weed infestation in sown fields.
As regards the previous crop, avoid species after which a large number of volunteers or increased weed pressure can be expected.
It is worth considering soil loosening instead of deep autumn ploughing, as in our experience this can result in reduced weed cover.
Mechanical weed control is a key element in the fight against weeds. The most suitable row spacing for production is therefore 75 cm, which also allows these crop care operations to be carried out easily.
Chemical weed control:
PRE-EMERGENCE weed control options
Successor-T: a pre-emergence herbicide that can be used successfully in sorghum crops at a rate of 2.0–4.0 l/ha. It is important to note that the product can also be applied post-emergence. Although it is currently not authorised in sorghum, the manufacturer applies for an emergency authorisation for its use every year! It is one of the mainstay herbicides in sorghum, with a broad spectrum of activity. Its effect on annual grass weeds and seedling Johnson grass is also noteworthy. It also inhibits the germination of several broadleaf weeds (pigweeds, goosefoots, thorn apple, etc.). It can also be used as a split application (pre + early post)!
Gardoprim Plus Gold: It is important to note that pre-emergence use of this product is possible solely on seed treated with an antidote (Concep III). It can also be applied early post-emergence (in this case, however, Concep III antidote treatment is no longer required!). Its spectrum of activity is narrower than that of Successor-T. It can be applied at a rate of 4 l/ha.
BOA/VIPER (active ingredient: penoxsulam): the most widely used grass herbicide in sorghum in Western Europe. In Hungary, its use is currently subject to emergency authorisation. Application rate: 0.8–1.0 l/ha. It can also be used successfully against certain broadleaf weeds. Its greatest advantage is its uniquely long duration of activity (given adequate activating rainfall)!
Pledge 50WP: It kills the weeds present in the field at the time of treatment, and the film that forms on the soil surface inhibits the germination of later-emerging broadleaf weeds. It is not effective against grass weeds; it can be combined with Successor-T (4.0 l/ha + 0.05 kg/ha) without any phytotoxicity.
Results of sorghum weed control trials, 2019 – Kiss Ernő, Hungarian Chamber of Plant Protection Engineers and Plant Doctors
POST-EMERGENCE weed control options
Successor-T: a herbicide that can also be used successfully early post-emergence. Application rate: 2.0–4.0 l/ha; it can also be applied as a split application together with a pre-emergence treatment. Although it is currently not authorised in sorghum, the manufacturer applies for an emergency authorisation for its use every year!
Combinations: Applied together with Casper (4.0 l/ha Successor-T + 0.4 kg/ha Casper), it provides excellent weed control with a broad spectrum of activity and, given activating rainfall, residual soil activity. It can also be used together with Cambio (2.0 l/ha Successor-T + 1.0 l/ha Cambio) without phytotoxicity.
Casper: A herbicide authorised in sorghum, applied at 0.3–0.4 kg/ha and effective against annual and perennial broadleaf weeds. It also performs outstandingly against perennial broadleaf weeds, provided the treatment is carried out at the appropriate growth stage of the weeds (e.g. creeping thistle at the rosette stage). It has no effect on grass weeds. It can be applied at the 2–6-leaf stage of sorghum. As it is a hormone-type herbicide, application at temperatures above 22–23 °C may also cause phytotoxicity, so on warmer days try to spray in the evening! It can be combined with Successor-T (3–4.0 l/ha Successor-T + 0.3 kg/ha Casper) without phytotoxicity.
Cambio: A hormone-type herbicide authorised in sorghum at a rate of 1.0–2.0 l/ha. It also performs well against perennial broadleaf weeds, provided the treatment is carried out at the appropriate growth stage of the weeds (e.g. creeping thistle at the rosette stage). Once it reaches the soil, it has – depending on the weather – a minimal effect on germinating weeds. It is not effective against grass weeds. As it is a hormone-type herbicide, application at temperatures above 22–23 °C may also cause phytotoxicity, so on warmer days try to spray in the evening! It can also be used in combination with Successor-T at a reduced rate (2.0 l/ha Successor-T + 1 l/ha Cambio).
BOA/VIPER (active ingredient: penoxsulam): the most widely used grass herbicide in sorghum in Western Europe. In Hungary, its use is currently subject to emergency authorisation. Post-emergence application rate: 0.8 l/ha. It can also be used successfully against certain broadleaf weeds. Its greatest advantage is its uniquely long duration of activity (given adequate activating rainfall)!
Gardoprim Plus Gold: In sorghum it can be used effectively and without phytotoxicity even WITHOUT Concep III antidote treatment. It has no effect on perennial grass weeds; it controls annual grass weeds most effectively at the 1–3-leaf stage and broadleaf weeds at the 2–6-leaf stage. Given adequate activating rainfall, residual soil activity can also be expected. It can be used in a tank mix with Pardner (4.0 l/ha Gardoprim Plus Gold + 1 l/ha Pardner).
Pardner: Generally speaking, the active ingredient bromoxynil does not cause phytotoxic symptoms in sorghum even at more advanced growth stages. Our trials clearly show that it can be used effectively against certain late-emerging annual broadleaf weeds up to the 10–12-leaf stage of sorghum. It is important to note that the active ingredient has contact action only, so it is strongly recommended to choose nozzles that provide adequate atomisation in order to achieve maximum coverage. It is not authorised in sorghum, so its use always requires an emergency authorisation! Application rate: 1.0–2.0 l/ha; it can be used successfully in a tank mix with Successor-T (2.0 l/ha Successor-T + 1.5 l/ha Pardner).
Results of sorghum weed control trials, 2019 – Kiss Ernő, Hungarian Chamber of Plant Protection Engineers and Plant Doctors
Before applying any of the products mentioned in this post, please be sure to check that the product in question is currently authorised for use in sorghum and, if necessary, apply for an emergency authorisation!
If you have any questions, please contact us:
Dr Fazekas Miklós: 06309211459
Fazekas Miklós: 06303378134