Application of post-emergence herbicides in mixed crops of maize and sunflower

Mixed cropping of corn and sunflower allows for a significant increase in the harvest of high-quality feed. However, sunflower grows slowly in the first month after seedling emergence, making it extremely sensitive to weed infestation. It is during this period that floral buds are initiated, and high weed density directly reduces the future yield. Without reliable weed control, it is impossible to unlock the potential of modern hybrids.

Chemical weeding of sunflower is usually based on soil-applied products, but they have serious drawbacks. In drought conditions, the efficacy of such herbicides drops, and repeat application is not possible due to registration regulations. Furthermore, pre-emergence products are incapable of destroying perennial root-suckering weeds, such as thistle species. The solution to this problem is the application of post-emergence herbicides and their tank mixtures.

Protection during the critical phase: when and how to apply products

To evaluate the efficacy of post-emergence protection, field studies were conducted on sod-podzolic light-loamy soil. Before spraying the crops in 2021, specialists carried out route surveys to study weed infestation, covering various soil variations. The history of the fields, their characteristics, and the list of agrotechnical measures were established directly on-site. The species composition of weed plants was determined using standard methodologies and botanical keys.

Sowing of crops was carried out in the first ten days of May using conventional agrotechnical practices. In small-plot trials, plots of 20 m² were used with fourfold replication in a randomized layout. Under production conditions, tests were carried out on 1-hectare plots with twofold replication. Spraying was performed using a "Euro Pulve" manual sprayer and a tractor-mounted sprayer according to the trial scheme.

• Corn seeding rate — 90 thousand viable seeds/ha
• Sunflower seeding rate — 50 thousand viable seeds/ha
• Working solution consumption — 250 l/ha
• Sowing date — first ten days of May

Weed monitoring was conducted before spraying, one month after treatment, and 2–3 weeks before harvesting the crops. For quantitative-weight analysis in small-plot trials, two 0.25 m² (0.5 × 0.5 m) plots were sampled per plot; in production trials, 10 plots were sampled. On these plots, the species composition, number, and fresh mass of weeds by species were determined.

Application schemes for herbicides and tank mixtures

In small-plot trials, the biological efficacy of a wide range of active ingredients was evaluated during post-emergence application. Researchers tested both single-component products and ready-mixed formulations. Below is the full list of herbicides studied in the trials, indicating the concentration of active ingredients.

Under production conditions, the efficacy of three treatment variants was tested. The herbicides Extracorn, SE, Stomp Professional, MKS, as well as the tank mixture of Stomp Professional, MKS + Frontier Optima, EC, were of practical interest. To assess the impact of the products on the crop, phenological observations were conducted, and the harvest was collected plot by plot followed by analysis of variance.

Results of studies and their discussion. According to route survey data, during the cultivation of corn together with sunflower, weed infestation of crops before chemical weeding amounted to 350.3 items/m2. Annual broad-leaved weed plants dominated the crops, such as common lambsquarters (116.2 items/m2), knotweed species (53.1 items/m2), field pansy (26.0 items/m2), and shepherd's purse (17.7 items/m2). The grass component of the weed vegetation accounted for 99.0 items/m2 or 28.3% of all weeds, of which barnyard grass (66.3 items/m2) and couch grass (30.3 stems/m2) dominated. Among the frequently encountered weeds, which are distributed in 83.3–100% of the surveyed fields, 6 weed species can be listed in decreasing order of occurrence: black bindweed, field pansy, barnyard grass, couch grass, shepherd's purse, and white campion. 31 species of weed plants belonging to 13 botanical families were identified. The largest number of species belongs to the following families: Asteraceae – 8, Poaceae – 4, Caryophyllaceae and Polygonaceae – 3 each.

After chemical weeding, weed infestation was 24.6 units/m², with 14.1 units/m² accounted for by grass weeds, among which common couch grass dominated – 12.2 stems/m². The number of dicotyledonous weeds was low: field pansy – 2.5 units/m², knotweed species – 1.8 units/m², common lambsquarters – 1.1 units/m², thistle species – 0.4 units/m². Also encountered were common lambsquarters, wild buckwheat, field pansy, and white campion. 22 weed species belonging to 11 botanical families were identified.

High biological efficacy and selectivity with respect to maize and sunflower were noted when using the herbicides Extracorn, SC (95.5%) and the tank mixture of Frontier Optima, EC + Estamp, EC (85.8%).

Table 1 – Efficacy of early post-emergence application of herbicides and tank mixtures in mixed maize and sunflower crops one month after treatment (field trial, RUE "Institute of Plant Protection", 2021)

Barnyard Millet Field grass Pennycress

Wild Buck- Lambs- weed Shep- White buckwheat wheat quarters (units/m²) 191.0 37.0 16.0 43.0 4.0 32.0 11.0 352.0 weed (g/m²) 1033.0 100.0 128.0 107.0 36.0 64.0 23.0 1530.0 Salsa, WP +

86.4 41.1 50.0 95.3 +62.5* 47.8 Surfactant Trend 90 – 100 100

94.2 60.0 17.2 90.6 +9.4* 70.5 25 g/ha + 0.2 l/ha Extracorn, SC – 83.9 95.5

100 100 100 100 100 100 3.0 l/ha 96.0 99.2 Basagran, SL – +71.4* +100* 90.6 67.1

100 100 100 100 2.0 l/ha +292.0* +43.8* 88.8 61.2 Dual Gold, EC – 79.0 78.6 34.4 0 75.0 71.6

100 100 1.6 l/ha 88.4 88.0 21.3 33.3 93.8 83.0 Goal 2E, EC – 99.0 67.9 67.2 50.0 81.3 81.3

100 100 1.0 l/ha 99.6 52.0 0.6 66.7 93.8 80.9 Dual Gold, EC +

98.9 87.5 67.2 77.3 Goal 2E, EC – 100 100 100 100

99.6 96.9 51.3 87.9 1.6 + 1.0 l/ha Pronit, EC – 22.4 78.6 25.0 43.8 75.0 36.4

100 100 3.0 l/ha 61.3 80.0 71.9 51.3 56.3 58.2 Trimer, WDG +

25.0 0 85.9 79.0 Pronit, EC – 100 100 100 100

+4.0* +23.4* 94.4 79.7 20 g/ha + 3.0 l/ha Ashitaka, MD +

78.6 +12.5* 50.0 83.0 Pronit, EC – 100 100 100 100

92.0 +50.0 88.9 77.8 0.4 + 2.0 l/ha Estamp, EC – 58.0 89.3 +100* 62.5 0 56.9

100 100 4.0 l/ha 62.1 60.0 +46.9 62.5 11.1 52.5 Frontier Optima, 47.6 46.4 0 0 50.0 11.4

100 100 EC – 1.0 l/ha 59.4 72.0 18.8 +267.5* 81.3 37.0 Frontier Opti-

98.4 12.5 85.9 50.0 81.3 85.8 ma, EC + Estamp, 100 100

97.9 15.7 83.1 94.4 87.5 86.8 EC – 1.0 + 4.0 l/ha Salsa, WP + Frontier Optima, 78.0 37.5 81.3 93.8 68.2

100 100 100 EC – 25 g/ha + 83.4 35.9 45.6 84.4 66.1 1.0 l/ha Notes: numerator – decrease in weed population, denominator – their biomass. * – increase, % of the unweeded control.

Efficacy reaching 100% against the weed dominant in the crop, common lambsquarters, was shown by the herbicides Extracorn, SC and Basagran, SL, and the tank mixtures of the herbicides Trimer, WDG + Pronit, EC and Frontier Optima, EC + Estamp, EC.

Vegetative mass of barnyard millet decreased by 96.0–100% in the variants using the herbicide Extracorn, SC, and the tank mixtures of the herbicides Frontier Optima, EC + Estamp, EC and Salsa, WP + Frontier Optima, EC. The post-emergence application of the herbicides Goal 2E, EC; Estamp, EC and Frontier Optima, EC weakly suppressed barnyard millet.

An increase in the population of wild buckwheat was noted in the variants with the application of herbicides Basagran, SL; Estamp, EC; and the tank mixtures Trimer, WDG + Pronit, EC and Ashitaka, MD + Pronit, EC. Its complete death was noted as a result of weeding with the herbicides Extracorn, SC and Dual Gold, EC.

The highest green mass yield of the mixture was obtained in the variants using the herbicide Extracorn, SC – 521.1 c/ha and the tank mixture of the herbicides Frontier Optima, EC + Estamp, EC – 404.6 c/ha.

Good productivity indicators for sunflower (216.0 c/ha) and maize (181.0 c/ha) were noted against the background of early post-emergence application of the herbicide Estamp, EC.

As a result of assessing economic efficiency, it was determined that the herbicide Goal 2E, EC and its tank mixture with Dual Gold, EC had a suppressive effect on maize. In the variant with the application of the herbicide Goal 2E, EC (1.0 l/ha), the green mass yield of maize was the lowest in the trial (100 c/ha).

Before the application of herbicides to crop seedlings under production conditions, total weed infestation was 162–263 units/m². Among the weed species in the crop, common lambsquarters (79–116 units/m²) and barnyard millet (47–102 units/m²) dominated. Wild buckwheat, rough cocklebur, and others grew in smaller quantities (from 1 to 11 units/m²).

One month after herbicide application, biological efficacy against annual weed plants was 66.1–82.2% by population, and 74.9–87.0% by biomass. The population of common lambsquarters decreased by 58.3–87.5%, biomass – by 79.3–90.0%, wild buckwheat – by 55.0–70.0%, vegetative mass by 47.4–78.9%, field pansy – by 78.6–100% and 83.3–100%, respectively. Annual bluegrass, rough cocklebur, and field pennycress died completely.

The maximum green mass yield of the mixed maize and sunflower crop when applied at the 2–3 leaf stage of maize (325.6 c/ha) was obtained in the variant with the application of the herbicide Extracorn, SC. In the variant with the use of the herbicide Stomp Professional, CS, the mixture yield was 316.9 c/ha, and when using the tank mixture of the herbicides Stomp Professional, CS + Frontier Optima, EC – 321.4 c/ha. Table 2 – Economic efficiency of early post-emergence application of herbicides and tank mixtures in mixed maize and sunflower crops (field trial, RUE "Institute of Plant Protection", 2021)

Green mass yield, cwt/ha Saved yield, cwt/ha

Treatment incl. total maizesunflowerm aizesunflowe r

Control without weeding 135.1 65.5 69.6 – –

Salsa, WP + Surfactant Trend 90 –

233.6 108.6 125.0 43.1 55.4 25 g/ha + 0.2 l/ha

Extracorn, SE – 3.0 l/ha 521.1 316.4 204.7 250.9 135.1

Basagran, SL – 2.0 l/ha 354.4 157.8 196.6 92.3 127.0

Dual Gold, EC – 1.6 l/ha 302.4 144.6 157.8 79.1 88.2

Goal 2E, EC – 1.0 l/ha 300.9 100.0 200.9 34.5 131.3

Dual Gold, EC + Goal 2E, EC –

316.9 112.8 204.1 47.3 134.5 1.6 + 1.0 l/ha

Pronit, EC – 3.0 l/ha 312.5 127.3 185.2 61.8 115.6

Trimmer, WG + Pronit, EC –

373.2 155.9 217.3 90.4 147.7 20 g/ha + 3.0 l/ha Ashitaka, OD + Pronit, EC –

266.8 266.8 – 201.3 – 0.4 + 2.0 l/ha

Estamp, EC – 4.0 l/ha 397.0 181.0 216.0 115.5 146.4

Frontier Optima, EC – 1.0 l/ha 296.3 131.5 164.8 66.0 95.2

Frontier Optima, EC +

404.6 200.8 203.8 135.3 134.2 Estamp, EC – 1.0 + 4.0 l/ha Salsa, WP + Frontier Optima, EC –

272.8 116.4 156.4 50.9 86.8 25 g/ha + 1.0 l/ha

Table 3 – Biological efficiency of herbicides and tank mixtures in mixed plantings of maize with sunflower one month after application (production trial, UKSP "Sovkhoz Dobrovolets", Klichev district, 2023)

Common Barnyard Cheno- grass field vio- let

Treatment (pcs/m2) 144.0 33.0 13.0 9.0 4.0 11.0 236.0 Without (g/m2) 657.0 79.0 57.0 12.0 11.0 23.0 908.0 weeding Extracorn, SE – 87.5 52.0 55.0 78.6 82.2

100 100 3.0 l/ha 86.9 77.1 78.9 83.3 87.0 Stomp Professional, 58.3 88.0 70.0 66.1

100 100 100 CS – 3.0 l/ha 79.3 49.2 57.9 74.9 Stomp Professional, CS + Frontier 84.7 55.0 82.2

100 100 100 100 Optima, EC – 2.0 + 90.0 47.4 83.4 1.0 l/ha Note: in the numerator – reduction in the number of weeds, in the denominator – reduction in their mass.

Table 4 – Economic efficiency of post-emergence application of herbicides and a tank mixture in mixed plantings of maize with sunflower (production trial, UKSP "Sovkhoz Dobrovolets", Klichev district, 2023)

Green mass yield, cwt/ha Saved yield,

Treatment incl. cwt/ha total maize sun- maize sun- flow- flow- er er

Control without weeding 86.0 39.1 46.9 – –

Extracorn, SE – 3.0 l/ha 325.6 184.5 141.1 145.4 94.2

Stomp Professional, CS – 3.0 l/ha 316.9 185.3 131.6 146.2 84.7

Stomp Professional, CS + Frontier

321.4 173.9 147.5 134.8 100.6 Optima, EC – 2.0 + 1.0 l/ha LSD05 22.4 21.7

Conclusions. In mixed plantings of maize with sunflower, according to route surveys conducted before weeding, dicotyledonous weeds predominate: common lambsquarters, knotweed species, field violet, shepherd's purse. The grass component of the weed vegetation is mainly represented by barnyard grass (66.3 pcs/m2) and couch grass (30.3 stems/m2).

High biological efficiency and selectivity towards maize and sunflower were shown by the application of the herbicide Extracorn, SE (both in small-plot and production conditions) and the tank mixture of herbicides Frontier Optima, EC + Estamp, EC (in small-plot conditions) and Stomp Professional, CS + Frontier Optima, EC (in production conditions).

The maximum green mass yield of the mixture in small-plot and production trials was obtained in the treatment using the herbicide Extracorn, SE.

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A. V. Stashkevich, N. S. Stashkevich, L. I. Soroka RUE «Institute of Plant Protection», Priluki, Minsk region

MIXED PLANTINGS OF MAIZE AND SUNFLOWER

AND THEIR PROTECTION FROM WEEDS

Annotation. The paper demonstrates the route surveys data on the infestation of maize and sunflower mixed plantings. The biological and economic efficiency of the herbicides and their tank mixtures is presented when applied to maize at the 2-3 leaves stage and to sunflower at the 2-4 leaves stage. A high biological efficiency and selectivity towards maize and sunflower are noted in small-plot experiments (Extracorn, SE and tank mixture Frontier Optima, EC + Estamp, EC), in production experiments - herbicide Extracorn, SE and tank mixture Frontier Optima, EC + Stomp Professional, MCS.

Key words: maize, sunflower, efficiency, weeds, herbicide, tank mixtures of herbicides, efficiency.