In winter cereals the weed problem is usually noticed in spring: the weather warms up, the field turns green and poppy, wild mustard or wild oat start to shoot up among the wheat. Yet a large share of these weeds germinates in autumn together with wheat and barley, and the competition starts right then. According to the technical instructions of the Turkish Ministry of Agriculture and Forestry, the yield loss caused by weeds in cereals is around 15-20% on world average and 20-35% in Türkiye. In this article we look at the timing of autumn spraying, which field needs to be sprayed and the weather and sprayer conditions that decide success.
Competition starts in autumn
Wheat and barley are most sensitive to weeds during tillering, the stage when the plant puts out new shoots beside the main stem. A plant competing with weeds at this stage forms fewer tillers, and the ears on the existing stems stay small. The largest loss occurs when the competition falls on the step from one tiller to two. Grass weeds start competing with wheat at its two-leaf stage or even earlier; the later the control, the larger the loss.
In years with normal rainfall, tillering begins in autumn and in some years is completed in autumn. In Central Anatolia a field sown in the first week of October that receives rain after sowing goes into winter already tillered; we covered the effect of the sowing date in detail in winter barley sowing time. In a field sown late or after a dry autumn, tillering is pushed into spring, and spraying in that field usually moves to spring as well.
A common choice among growers is to wait until all the weeds have emerged and spray once in spring. The cost of that choice is that the autumn-emerged weeds keep growing until spring: by then they are past the stage where the herbicide works best, and they have used part of the base fertiliser themselves. For problem fields the sources recommend working in two periods where necessary: autumn weeds in autumn, spring weeds in spring.
The right stage: weed and crop development
The timing is set by the development of the two plants, not by the calendar. On the cereal side, the application period runs from tillering to the start of stem elongation; the Ministry’s instructions ask for spraying to be completed by the end of tillering. After stem elongation a tractor entering the field breaks the plants; when the ear is still in the boot, spraying can cause ear deformation. For this reason a field that has started stem elongation is not sprayed.
On the weed side, the measure is the number of leaves. For the common weeds of Central Anatolia the best stage is when the weed has 2-6 leaves and lies flat on the soil as a rosette; for grass weeds the preferred stage is the 2-3-leaf seedling stage. The bigger the weed, the higher the dose needed, and once it is under the crop canopy the spray no longer reaches it. Late spraying also fails to stop the weed from setting seed; the price is a denser weed flush in the field the following year.
There are also pre-emergence applications made right after sowing, before the cereal emerges. For these to work the soil surface must be level, free of clods and moist; otherwise the herbicide does not give the expected effect.
Which field needs spraying
The problem weeds differ from region to region. In a study based on interviews with growers in Konya, wild oat (Avena barbata), wild mustard, Bifora and field bindweed were named as the weeds that reduce yield most; older surveys in Ankara and Konya point to Bifora, downy brome, Neslia and Centaurea depressa.
Not every weedy field needs to be sprayed; the decision depends on the number of weeds per square metre and on the weed species. According to the Ministry’s instructions, a field with an average of 10 weeds per square metre, whatever the species, is put on the spraying programme. For some species the threshold is much lower: in Central Anatolia one plant of Neslia per square metre and two of Centaurea depressa are considered enough to decide on spraying; for wild oat the figure is 3-5 per square metre. The count needs to be done in autumn while the weeds are small, because a count left to spring often comes after the stage where the herbicide works best.
Knowing the weed species is also essential for choosing the product. Herbicides for broadleaf weeds do not act on grasses, and those for grasses do not act on broadleaf weeds; even within one group not every product controls every weed. In fields where the same product has been used for years, weeds gradually become resistant to it. According to a review on the subject, herbicide resistance has been found in seven weed species in wheat fields in Türkiye, and in some fields in the Mediterranean, Marmara and South-eastern Anatolia regions wild oat has become resistant to a herbicide group used for many years. This is why changing the product from time to time is recommended. Which product is registered against which weed is published in the Ministry’s plant protection products database and its mobile app; the type and dose are set by the label and by the agricultural engineer who writes the prescription. A dose below the label leaves the product ineffective, a dose above it damages the crop.
The crop itself also changes the priority. Among cereals, barley is the strongest competitor against weeds and durum wheat the weakest. In a field sown with a durum wheat such as Dimokritos control is not delayed, and where there are several fields that one takes priority. A tall barley such as Ramata starts the competition with an advantage, but in a heavily infested field that advantage does not replace spraying.
Weather, sprayer and calibration
The warnings that provincial agricultural directorates give to growers repeat the same mistakes: using less or more product than recommended, choosing a product that does not match the weed, spraying after the weeds have grown, and spraying in windy weather or at the wrong time of day. Most herbicides work best at air temperatures between 8 and 25 °C; above 25 °C the risk of the product evaporating increases. Some herbicide groups are also effective at around 5 °C, a difference that matters on cool autumn days. No spraying is done when frost is expected, because frost makes the plant tissue sensitive and the herbicide can then damage the crop. Spraying is also not recommended with morning dew, at sunset, in overcast weather with rain on the way or during long dry spells. After application a rain-free period of one to six hours is needed, depending on the product.
Wind is a separate risk. Strong wind carries the droplets, so one part of the field is sprayed twice and another not at all. Highly volatile products can also drift into the neighbouring field. For spraying by drone, the Ministry’s instructions require a safety strip of at least 4 metres and drift-reducing nozzles. This matters especially when a broadleaf crop such as alfalfa or forage pea is growing next door; the neighbouring field is taken into account when choosing the product.
The last point is the sprayer. The Ministry’s instructions foresee 20-40 litres of water per decare in general and make calibration of the sprayer a condition before spraying. Calibration is done in the field: the tank is filled, one run there and back is made at normal speed, the sprayed area and the water used are measured, and the volume per decare is calculated from these. How many decares one tank covers and how much product goes into the tank follow from this figure. Using flat-fan nozzles instead of hollow-cone nozzles spreads the spray more evenly over the field.
Before the sprayer: clean seed and a clean field
Weed control does not start with herbicides. Clean seed, a well-prepared seedbed, timely sowing, a seed rate within the data-sheet range and a suitable crop rotation reduce weed pressure from the outset. Some weed seeds stay alive in the soil for many years; according to published sources, wild mustard seed can remain viable for up to 35 years and poppy seed for up to 11 years. For the same reason it matters that a combine that has worked in an infested field is cleaned before entering a clean one.
Seed is the first link in this chain, and its limits are set by regulation. Under the Cereal Seed Certification and Marketing Regulation published on 17 March 2026, wheat and barley seed fields are inspected at the yellow ripening stage; for darnel and Cephalaria not a single plant is allowed in the field for the Elite and Original classes, and in the Certified classes the limit is between 0.05% and 0.1%. In the laboratory the limit for wild oat, darnel and Cephalaria seed is zero per kilogram in every class; other weed seeds are allowed up to 6 per kilogram in the Original class and between 10 and 30 in the Certified classes. Seed kept back from one’s own harvest does not go through these checks, which is why the Ministry’s instructions ask growers to use certified seed and, if they sow their own grain, to have it cleaned without fail. We explained what the certification classes mean in seed certification classes.
An experience shared on growers’ forums comes to the same point: a little rye mixed into a wheat field hardly lowers the yield, but it lowers the quality of the grain and can lead the buyer to turn the crop down; if seed is to be kept from that crop, the rye has to be pulled out of the field before harvest. Keeping the seed rate within the range given in how many kilos of seed per decare also matters; in a thin stand the gaps fill with weeds.
In short, three things decide autumn spraying: wheat and barley that have tillered but not yet started stem elongation, weeds that are small and above the threshold, and suitable weather on the day. When these three come together in autumn, control is achieved with a lower dose and smaller losses. For our wheat seed and barley seed varieties, share your field’s region and its weed history in past years with us, and our agricultural engineer will assess which variety suits your conditions: +90 506 101 01 50.