Expert advice

Controlling weed in the spring

One of the basic components of proper crop farming is the execution of effective weed control. In practice, one can choose between an autumn and a spring herbicidal treatment – the choice of time depends on the preferences of the farmer and/ or the weather conditions.

The autumn of 2015. saw particularly unfavourable conditions for the planted cereals – no rain and a prolonged drought. As a result of the lack of humidity, the emergence and development of winter cereals was significantly delayed. Farmers themselves delayed the time of sowing waiting for rainfall. The delay in the sowing of winter wheat stemmed also from the position within crop rotation, shifting to grain following sugar beet or maize. At most plantations, the drought was felt not only by the crop, but also by weed – their emergence was significantly limited or did not occur at all. Unfavourable humidity conditions of the soil did not encourage any control of weed in the cereals before emergence. On the other hand, this type of treatment does not presently enjoy much popularity.

Following a dry period without rainfall, the occurring rain also prevented the farmers from performing weed control treatments under optimum thermal conditions. With regard to the overlay of negative factors, the decision to perform the herbicidal treatment was significantly delayed in time. The treatment was often carried out in late autumn, at temperatures that were borderline for the usage of the products – accordingly, their effectiveness was not always satisfactory.

A second group is made up of winter cereal plantations that were planted comparably early, with herbicidal treatment carried out at the end of September or beginning of October. In such a situation, the time from the moment of execution of the treatment until the end of the growing season is extended. The action of active agents used in the soil and contained in the herbicides is diminished with time, hence, in favourable thermal conditions, new weed may sprout and a secondary weed infestation may emerge.

The execution of a herbicidal treatment of winter wheat in Poland was very extended in time – from the end of September/ beginning of October until the first decade of December. The development of weed is facilitated by relatively high temperatures for this time of year. In February, temperatures reached a few degrees over freezing, and nights saw no temperatures below zero. Growth was already initiated by e. g. common windgrass, a very troubling weed, which in favourable conditions is able to sprout across all of winter, even under the snow.

Should present weather conditions persist and should the pressure of weed be intense, due to the short crop rotation period, one would have to consider executing a corrective spring treatment or to assume a regimen of two treatments already in the autumn. Completely forgoing the autumn treatment would be very risky, because in case of extended autumn growth, the development of cereals may be heavily limited due to the pressure from weed. Weed competes with the grown crop to get nutrients and water, and it reduces the health of the field overall.

Irrespective of whether the spring herbicidal treatment would be aimed at amending the autumn treatment, or whether it would be the first step in controlling weed – it should be amended by a field visit. First, one should determine the types of weed present at the plantation and their relevant development phases; then, one selects the product and the dose. In order to expand the range of controlled weed (monocots and dicots) and to use active substances exhibiting diverse modes of action and ways of entry of the plant, one should consider using a spray mix or a product with more than one active substance. When determining the dose, one should use information included in the product label, remembering at the same time that the higher of the recommended doses should be used if the weed is in further development stages. When making the decision about the choice of weed control products, one should be also guided by the speed of action. This is very important, especially at the time of fast growth in spring – weed competes with the crop to get nutrients and space and, through excessive densification, worsens the phytosanitary conditions of the field. In such a situation, an important component of the treatment will doubtless be an active substance based on a growth control agent.

Depending on the pressure of the individual weed types, the plant protection products can be used separately or as spray mixes. Effective products used to make spray mixes are Saroksypyr 250 EC/Aloksypyr 250 EC, which accompanied by other products from the sulphurea derivatives group will control most of the more burdensome dicots. Saroksypyr 250 EC/Aloksypyr 250 EC may also be used alone in order to primarily control cleavers – in every stage of development, and, for instance, the common chickweed and wild buckwheat. A further product that is perfect as a component for many spray mixes is the Harpun 500 SC (active agent: isoproturon). Used in the spring, this product works against the common windgrass and assists in the reduction of pressure of selected dicots in spray mixes with products from various chemical groups. One needs to remember, however, that the common windgrass is most effectively controlled in its earlier development stages.

MCPA-based products (Chwastox 750 SL, Chwastox Extra 300 SL) attack a broader range of dicots. In this regard, they can be components used to create spray mixes together with other products from various chemical groups, or for individual use.
In order to increase the volume of species of controlled dicots, we suggest fusing in a spray mix the products Chwastox Turbo 340 SL (MCPA, dicamba) with Chwastox MP 600 SL (mecoprop – P) or Chwastox Turbo 340 SL with Ambasador 75 WG (amidosulfuron) – these mixes control most of the burdensome dicots present in cereals. In case of lesser pressre of weed they can be used separately. The fusion of three active agents – dicamba, MCPA and mecoprop-P in Chwastox Trio 540 SL ensures a broad dicot control spectrum. After the product is used, all burdensome weed of winter cereals will be eliminated – cleavers, the common poppy, the cornflower, the field chamomile and the false mayweed. The achievement of high effectiveness is possible through the use of two roads of entry of the product to the plant. MCPA and mecoprop–P are taken up through the leaves, and dicamba is taken up both through leaves as well as roots. This assists in control of weed that is just emerging in the spring and have a very small leaf surface or if the leaves are covered by the growing field body.

The use of growth control agents guarantees very quick reduction of weed growth and development. The effect, under optimum thermal conditions, is visible already on the next day. Weed dies out quickly – and stops competing with the crop.