بررسی جمعیت و میزان آلودگی آفات اول فصل در کشت نشایی و بذری چغندرقند

در راستای مصرف بهینه آب در ابتدای فصل کشت، استفاده از نشاکاری چغندرقند می‌تواند راهگشا باشد. این تغییر الگوی کشت می‌تواند بر تراکم جمعیت، میزان آلودگی و خسارت آفات در ابتدای فصل موثر باشد. در این تحقیق، مقایسه جمعیت و خسارت کک و طوقه‌بر چغندرقند، در دو روش کاشت (بذری و نشایی) در سه استان آذربایجان غربی، کرمانشاه و همدان مورد بررسی قرار گرفت. از هر یک از مزارع 10 نقطه به‌صورت تصادفی انتخاب و وجود این آفات و شاخص آلودگی به آن‌ها بر روی بوته‌ها در یک مترمربع به‌طور هفتگی در طی هشت هفته، ثبت شد. از آنجایی که دامنه تغییرات داده‌های جمع‌آوری‌شده بسیار زیاد بود نرمال کردن آن‌ها برای تجزیه‌وتحلیل آماری، حتی با تبدیل داده‌ها میسر نشد. بر این اساس مقایسه‌ها با روش غیر پارامتری (کروسکال والیس) و مقایسه توصیفی صورت گرفت. نتایج نشان داد که میزان آلودگی کک در کشت بذری با کشت نشایی در استان‌های همدان و کرمانشاه باهم اختلاف معنی‌داری داشتند(p≤ 0.01)، اما در استان آذربایجان غربی اختلافی مشاهده نشد (p≥ 0.05). در مقابل خسارت طوقه‌برها فقط در مزارع استان همدان (با اختلاف(x^2(3)=7.055 و p=0.008) و در کشت بذری سال اول استان آذربایجان غربی مشاهده شد. از طرف دیگر میانگین تراکم کک در نمونه‌برداری هشت هفته اول در مزارع بذری در هر سه استان بیشتر از مزارع نشایی بود. وجود طوقه‌برها، با تراکم کم، فقط در مزارع بذری استان همدان مشاهده شد و تیمارها در سطح پنج درصد اختلاف داشتند. بر اساس این نتایج خسارت آفات اول فصل در روش کشت نشایی بسیار ناچیز بوده و احتمالاً نوعی فرار میزبان گیاهی از خسارت آفات در کشت نشایی چغندرقند اتفاق می‌افتد.

investigation of pest population dynamics and infestation index in sugar beet during the early growing season under direct seeding and transplanting seedling cultivation

extended abstract introduction sugar beet seeds are typically sown directly in the spring across most regions of iran. however, climate change has led to water shortages and making the first and second irrigations increasingly challenging. as an alternative, sugar beet seedling cultivation has been proposed as a potential solution. various aspects of seedling cultivation have demonstrated benefits for sugar production. however, there is still a need to investigate pest population density, infestation levels, and the extent of pest damage under seedling cultivation. these factors has been shown to be less influenced by the selection of seed or seedling cultivation method for pests that are active throughout the growing season. this study focuses on evaluating these aspects in relation to two early-season sugar beet pests including the flea beetle &chaetocnema tibialis (illiger) (col. chrysomelidae)& and the cutworm &agrotis segetum denis and schiffermaller (lep. noctuidae)&.materials and methodsthis study conducted in sugar beet fields across three provinces of west azerbaijan, kermanshah and hamedan. one field was selected from each province and two plots (each one hectare) were designed per field to compare two cultivation methods (direct seeding or transplanting seedlings). in the first plot, shokofa sugar beet seeds (produced by filed crops development company) were directly sown using conventional methods in april. in the second plot, sugar beet seeds were initially sown at high density in a prepared nursery section of the field in mid-april. once the seedlings reached the 6-8 leaf stage, with a root diameter of approximately 1 cm, they were transplanted into the second plot.sampling of flea beetles and cutworms was carried out weekly under both cultivation methods (direct seeding and transplanting seedlings)  during the 2010 and 2011 growing se asons. in each plot, ten points were randomly selected, and population density and infestation levels were recorded within one-square-meter quadrats. for the sugar beet flea beetle (chaetocnema tibialis), the number of adults and infestation severity (rated on a scale from 1 to 7 based on feeding symptoms) were recorded. for the cutworm (agrotis segetum), the number of damaged plants (plants cut off from the crown) and the number of larvae present around the damaged plants were counted.due to the wide variation in the collected data, normalization was not achievable, even after attempted data transformation. therefore, non-parametric statistical analysis (kruskal–wallis test) and descriptive comparisons were used for data interpretation.results and discussion the results showed a significant difference in the flea beetle infestation index between direct seeding and transplanting seedling cultivation methods in hamedan and kermanshah provinces (x2(3)=8.695; p=0.003 and x2(3)=27.068; p=0.000 respectively), however, no significant difference was observed in west azarbaijan province (x2(3)=2.669; p=0.1). cutworm damage was recorded only in hamedan province (x2(3) =7.055; p=0.008), while in west azerbaijan province, it was observed exclusively in seed cultivation plots. furthermore, the average density of flea beetle during the first eight weeks of sampling was consistently higher in direct seeding cultivation compared with transplanting seedling cultivation across all three provinces (hamedan, (x2(3)=24.816; p=0.000), west azerbaijan (x2(3)=8.266; p=0.041) and kermanshah (x2(3)=14.497; p=0.002)). the weekly trends of total flea beetle counts and contamination index under direct seeding and transplanting seedling cultivation methods across three provinces were illustrated.the results indicate that although the sugar beet flea beetle is present in both direct seeding and transplanting seedling cultivation methods, the infestation index is consistently higher in direct seeding fields. this trend was  particularly evident in hamedan province, where simultaneous sampling was conducted. it appears that during the sampling period, the sugar beet plants had reached a growth stage sufficient to tolerate flea beetle feeding. it is important to note that flea beetle damage is considered economically significant only up to the eight-leaf stage.in contrast, cutworm infestation was observed only in certain fields. this variation is primarily associated with the biological characteristics and life cycle of the cutworm. since the cutworms overwinter as larvae, their population density and resulting damage are affected by several factors, including the type of crop grown in the previous season, overwintering conditions, and tillage practices. as a result, the presence and damage of this pest tend to occur sporadically and unpredictably. in this study, cutworm larvae were observed at low density only in direct seeding cultivation plots in hamedan province, with a recorded difference of 5% (x2(3)=10.510 and p=0.015).based on these findings, pest-related damage during the early season under transplanting seedling cultivation was low which suggests that transplanting seedling cultivation in sugar beet may contribute to a form of host plant escape.conclusionthe seedling cultivation technique is effective in reducing the need for early irrigation and minimizing the use of chemical pesticides. with regard to early-season pest control-particularly of the flea beetle and cutworm, which are among the most significant pests in sugar beet cultivation-this method offers a more controlled approach as the initial stages of plant growth occur under greenhouse conditions, pest exposure is limited, and the need for pesticide application is considerably reduced. furthermore, in the context of rising global temperatures due to climate change, which is leading to earlier and more intense pest outbreaks in the field, seedling cultivation presents a valuable non-chemical management strategy. by accelerating the early growth stages of the crop, this method allows for a form of host plant escape, thereby reducing pest impact during the most vulnerable periods of plant development. consequently, transplanting seedling cultivation can be considered a sustainable and environmentally friendly approach to managing early-season pests in sugar beet farming.