ANTI-PEST PROTECTION OF TWO-YEAR OLD ALFALFA GROWN FOR SEEDS

Purpose. To evaluate the effectiveness of different insecticides against pests on two-year old alfalfa grown for seeds. The highest seed yield was achieved after treatment 1 with an insecticide containing active ingredients chlorpyrifos 500 g/L and cypermethrin 50 g/L applied at a dose of 1.00 L/ha and treatment 2 with insecticides containing active ingredient chlorantraniliprole 200 g/L or lambda-cyhalothrin 50 g/L applied at a dose of 0.17 and 0.15 L/ha, respectively.

reduced the populations and the numbers of insects -bean pests by 75% [16]. Moreover, it was shown that sloping plots and forest belts reduced wind speed, complicated aphid migrations and, accordingly, impacted its spread, decreasing the affection of plants by viral diseases [17]. Control of vector insects is a serious challenge, so the choice of the most effective insecticides to control them in different environments is always important [18,19].
Insects are a huge group of living organisms, but not many of them are harmful to crops. Insecticides used in crop production are selective and, as a rule, destroy all entomofauna [20]. Alfalfa is often referred to as the beginning of the food chain because it supports not only domestic animals and humans, but also many species of wild animals and birds (more than 700) and more than 1,000 species of arthropods, which is very important for the Earth's ecosystem [21].
Alfalfa grown for seeds is severely damaged by pests, both polyphagous and specialized. The cultivation duration and growing period, its high fodder value and hospitable conditions for pest overwintering favor the settlement of pests and increase in their numbers [22]. Holoborodko SP et al.'s eco-faunal conducted studies in the Left-Bank Lower Dnipro Region of the Southern Steppe of Ukraine, in which they determined and systematized the species composition of the biocenosis of seed alfalfa, with an economic assessment. Complex damage to all organs of seed alfalfa is caused by 157 pest species [23]. Alfalfa is damaged at different stages of plant development -from seed germination to ripening. Pests inflict the most significant damage to seed fields, damaging generative organs and seeds. The pest species composition and numbers on seed alfalfa are influenced by weather during the growing period and winter. Therefore, the absence of protection measures or untimely taken measures dramatically reduces the seed yield and the sowing qualities of seeds [24].
It should be noted that pests, which severely damage two-year old alfalfa grass canopy grown for seeds, are alfalfa weevil (imagoes and grubs), alfalfa plant bug, alfalfa seed weevil, alfalfa seed chalcid, alfalfa aphid, and, in some years, beet webworm. The species composition of insects -pests in alfalfa canopy, their numbers and harmfulness change markedly both zonally and during the alfalfa life in one field as well as during the growing period [25]. However, despite the extensive knowledge on the species composition of entomofauna on seed alfalfa, thorough published information on the pest harmfulness and ecology as well as on integrated protection of alfalfa fields against pest communities and individual species is extremely scarce.
Purpose. To evaluate the effectiveness of different insecticides against pests on two-year old alfalfa grown for seeds.
Materials and methods. The study was conducted in the experimental field of the Institute of Irrigated Agriculture of NAAS in 2017-2019. As to soil and climate, the study site is located in the steppe (Inhulets irrigated massif).
The filed experiments were laid out in split plots. The main plots (factor A) were for water supply conditions (no irrigation vs. irrigation); sub-plots (factors B and C) were for application of insecticides (Table 1). Seeds were sown in wide rows with interrows of 70 cm. The sowing area was 60 m 2 ; the record area was 50 m 2 ; the experiments were carried out in three replications. Alfalfa variety Elehiia was taken. The grass canopy was two years old (sown in spring). Seeds were harvested with the first mowing.
The composition of harmful insect species was determined by surveys using an entomological sweep-net (10 sweeps); their numbers and ratios of different stages were associated with the phases of plant development and weather conditions (temperature, air humidity and precipitation) [26]. The efficiency of timing and numbers of chemical treatments was evaluated by S.O. Tribel's method [27] with due account for the economic thresholds of harmfulness [28].
Insecticides were applied as follows: treatment 1 was at the budding onset; treatment 2 was prior to anthesis with a mounted sprayer ON-600 with operating fluid consumption of 250 L/ha. Experimental data were statistically processed in AgroSTAT, XLSTAT and Statistica (v. 13). Control (no treatment) 1-1 Dimethoate 400 g/L + lambda-cyhalothrin 50 g/L; 1.00 L/ha + 0. Results and discussion. Several pest species were found on alfalfa, differing in peculiarities of their development and damage to plants. When the two-year old alfalfa canopy (budding onset) was inspected before insecticide treatment, the average numbers of pests were as follows: alfalfa plant bug -3.0 specimens/10 sweeps, alfalfa aphid -20.0 specimens/10 sweeps, beet webworm -3.0 specimens/10 sweeps, alfalfa weevil (imagoes/grubs) -1.0/3.0 specimens/10 sweeps, and alfalfa seed weevil -1.0 specimens/10 sweeps (Table 2). It is known that the effectiveness of different insecticides against mandibulates and sucking pests is not the same, so there is a need to assess the effectiveness of universal and binary mixtures of insecticides against the pest complex.
Under rainfed conditions and with application of this insecticide, alfalfa seed weevil-inflicted damage to seeds was 0.22-0.28 seeds/pod and alfalfa seed chalcidinflicted damage was 0.08-0.10 seeds/pod, depending on the insecticide in treatment 1. When irrigated, these indicators were: 0.19-0.24 seeds/pod and 0.06-0.08 seeds/pod, respectively ( Table 3). The low pest numbers or their absences usually positively affect the development of generative organs and, accordingly, the seed productivity of plants. However, the fumigation action of this insecticide had a negative effect on the numbers of pollinating insects, interfering with the formation of pods and seeds in generative organs and further affecting the plant performance. Thus, under rainfed conditions, 6.7-7.2 pods/raceme and 2.44-2.69 seeds/pod were formed, and under irrigation, there were 7.6-8.0 pods/raceme and 3.47-4.00 seeds/pod, depending on the insecticide in treatment 1. At the same time, the under rainfed conditions, the seed yield was 330.53-390.61 kg/ha, exceeding the control by 10.54-70.62 kg/ha. When irrigated, the seed yield was 437.63-535.96 kg/ha, exceeding the control by 13.03-111.36 kg/ha. Note: RF = rainfed; I = irrigatred.
The highest seed yield was achieved after treatment 1 with insecticide containing active ingredients chlorpyrifos 500 g/L and cypermethrin 50 g/L applied at a dose of 1.00 L/ha and treatment 2 with insecticide containing active ingredients chlorantraniliprole 200 g/L and lambdacyhalothrin 50 g/L applied at a dose of 0.17 L/ha and 0.15 L/ha, respectively. With irrigation on this variant, 8.8 pods/raceme and 4.64 seeds/pod were produced, and the seed productivity was 635.16 kg/ha, which was higher than the control value by 210.56 kg/ha. Under rainfed conditions, plants formed 7.4 pods/raceme and 2.98 seeds/pod. Here, the seed yield was 452.48 kg/ha, exceeding the control by 132.49 kg/ha.
Conclusions. Insecticide containing active substances chlorpyrifos 500 g/L and cypermethrin 50 g/L applied at a dose of 1.00 L/ha was the most effective for pest control (except for alfalfa aphids). However, the fumigation action of this insecticide had a negative effect on the numbers of pollinating insects, interfering with the formation of pods and seeds and further affecting the plant performance, so this insecticide should not be used prior to anthesis (treatment 2). The highest seed yield was achieved after treatment 1 with insecticide containing active ingredients chlorpyrifos 500 g/L and cypermethrin 50 g/L applied at a dose of 1.00 L/ha and treatment 2 with insecticide containing active ingredients chlorantraniliprole 200 g/L and lambda-cyhalothrin 50 g/L applied at a dose of 0.17 L/ha and 0.15 L/ha, respectively.