ISSN 1644-0625 ISSN 2300-8504 (online) www.agricultura.acta.utp.edu.pl Acta Sci. Pol. Agricultura, 14(3) 2015, 15-24 THE OCCURRENCE AND HARMFULNESS OF Oscinella frit L. (DIPTERA: CHLOROPIDAE) TO MAIZE CULTIVARS CULTIVATED FOR GRAIN IN SOUTH-EASTERN POLAND Paweł K. Bereś Institute of Plant Protection – National Research Institute in Poznań1 Abstract. Long-term studies on the occurrence of frit fly (Oscinella frit) on maize were carried out in 2001-2014, in Krzeczowice, south-eastern Poland. In the analysed period, O. frit larvae damaged from 3.5 to 42.2% of plants of a medium-early maturing (FAO 240) maize cultivar (mean 25.2%), causing theoretical loss in grain yield from 0.4 to 8.1% (mean 4.5%). Studies on the susceptibility of maize to frit fly were carried out in 2009- -2011 on 18 cultivars from three earliness categories: early (FAO 190-220), medium-early (FAO 230-250) and medium-late (FAO 260-290). In the analysed 3-year period larvae of O. frit damaged, on average, from 20.4 to 32.3% of plants of cultivars, causing a mean theoretical loss in grain yield from 2.9 to 4.7%. Statistically significant differences were found between the susceptibility of cultivars to damage caused by O. frit. Medium-late maturing maize cultivars were significantly more often damaged by frit fly than the early maturing cultivars. Key words: cultivars, frit fly, maturity class, Poland, susceptibility, Zea mays INTRODUCTION Maize (Zea mays L.) has recently become one of the major crops grown in Poland. The acreage of this plant increases yearly, and in 2012-2013 it reached a level of 1.05- -1.07 m ha [GUS 2013, 2014]. The increasing acreage of maize and its dominant position in the crop rotation system on farms have resulted in a greater threat to this plant posed by harmful organisms, of which pests play a more and more significant role [Bereś and Pruszyński 2008]. Corresponding author: dr hab inż. Paweł K. Bereś, prof. nadzw. IOR-PIB, Institute of Plant Protection – National Research Institute in Poznań, Regional Experimental Station in Rzeszów, Langiewicza 28, 35-101 Rzeszów, e-mail: [email protected] © Copyright by Wydawnictwa Uczelniane Uniwersytetu Technologiczno-Przyrodniczego w Bydgoszczy, Bydgoszcz 2015 16 P.K. Bereś Currently in Poland maize fields are threatened by over 50 pest species, most of which belong to the Insecta class [Bereś 2013]. Frit fly (Oscinella frit L.) is one of the major pests emerging during spring [Lisowicz 2001, Mrówczyński 2013]. Apart from Poland, this insect has also been reported in other European countries, e.g. Hungary, France, Spain, Italy, Denmark and Germany [Meissle et al. 2010]. The first information on damage to maize plants in Poland caused by O. frit dates back to the 1950s and concerns the Wrocław region, where at that time the whole national maize acreage was located [Kania 1962]. The harmfulness of frit fly to maize increased as the cultivation of this plant became more popular. Lisowicz [1994] indicated the key factors responsible for the increase in the occurrence and harmfulness of O. frit to maize in Poland, such as decline in the acreage of oats, which as alternative host used to create conditions favourable to the development of this pest; earlier sowing of spring cereals, which made these crop species less frequently infested by the spring generation of frit fly; local increase in the acreage of grasses for seed production, which are a overwintering habitats for this pest, and the synchronised dates of the mass flight of adult O. frit individuals from overwintering places with the emergence of the first leaves of young maize plants, being attractive for oviposition. Under the soil and climatic conditions of Poland frit fly produces three generations per year, and the most harmful to maize are the first generation larvae emerging from April or May and usually feeding up to the end of June [Bereś 2014]. Lisowicz and Tekiela [2004] reported that the mean loss in maize yield caused by the feeding of O. frit accounts for about 10%. In addition, this pest increases the susceptibility of maize plants to pathogens, particularly fungi such as Ustilago maydis (D.C.) Corda. As early as the 1970s researchers pointed out that the larvae of frit fly are economically significant and may cause loss in grain yield from 360 to 960 kg·ha-1 [Dolinka and Zscheischler 1970]. Since the enforcement of integrated plant protection in the European Union from 2014 the population and harmfulness of weeds, diseases and pests should at first be controlled by non-chemical methods and, if these are ineffective, the use of chemical methods is allowed. One of the nonchemical methods is the cultural one, involving the sowing of cultivars less susceptible to damage caused by harmful species [Matyjaszczyk 2013, 2014]. The aim of this study was to identify the degree of infestation and estimate the harmfulness of frit fly on maize grown in Krzeczowice in 2001-2014. This study is the next stage of research initiated in 1997 by Lisowicz [2001] and carried out up to the year 2000. In addition, we analysed the susceptibility of 18 selected maize cultivars from different earliness categories (FAO from 190 to 280) to damage caused by frit fly. MATERIAL AND METHODS The study was carried out in Krzeczowice, south-eastern Poland (49°59' N; 22°27' E). The occurrence and harmfulness of frit fly larvae was monitored in 2001-2004 on the Limko medium-early maize cultivar (FAO 240), and in 2005-2014 on the San medium- early cultivar (FAO 240). In 2009-2011 an experiment was established to assess the susceptibility of selected maize cultivars of different earliness to the larvae of O. frit. In the experiment we used 18 maize cultivars, representing 3 categories of earliness identified in Poland: Acta Sci. Pol. The occurrence and harmfulness... 17 − early (FAO 190-220): KB1903, ES Ballade, Cedro and NK Ravello, − medium-early (FAO 230-250): Dumka, Lober, DKC 2960, Eurostar, Nekta, Zidane and KWS 5133 ECO, − medium-late (FAO 260-290): DKC 3420, Ronaldinio, Vitras, Koherens, KB2704, Chambord and Krabas. Long-term monitoring of the occurrence and harmfulness of frit fly larvae and studies on the susceptibility of selected maize cultivars to damage caused by this pest were carried out on 50 m2 plots (4 rows of 16.5 meter length) using the random block method in four replications. In all years maize was grown in a crop rotation system. No insecticides were used for the control of frit fly and other pests on experimental plots. Maize was sown at an optimum date for this part of the country, i.e. in the last ten days of April. The harmfulness of O. frit larvae was assessed in the second half of June, when maize plants were developing 8-9 leaves (BBCH 18-19) [Adamczewski and Matysiak 2011]. For that purpose on each plot plants in two central rows (50 consecutive plants in each row, 100 plants per plot in total) were inspected by searching for symptoms of larval feeding on above-ground plant parts. Based on this, the mean percentage of plants damaged by the pest was calculated. To determine the degree of damage in individual maize cultivars caused by frit fly we used a 4-degree scale proposed by Lisowicz [1996], where individual degrees indicate: − 1o – minor damage to leaves (minor discolourations along leaf veins resulting from larva feeding), − 2o – moderate damage to leaves (numerous discolourations along leaf veins, sometimes with small perforations; newly formed leaves unfold with difficulty), − 3o – severe damage to leaves (newly formed leaves unfold with difficulty; leaves are curly and lacerated, with numerous cracks along leaf veins), − 4o – severe plant damage (growth cone destroyed, main stem decayed, side shoots produced or plant death). Theoretical loss in grain yield was calculated using the formula below: (n1×8) + (n2× 25) + (n3× 60) + (n4×90) Sp(%) = n where: Sp – loss in grain yield expressed in %, n1, n2, n3, n4 – number of plants with a damage degree 1, 2, 3, 4, n – total number of analysed plants. Results for the susceptibility of maize cultivars to frit fly were analysed using statistical methods. The analysis of results from 3 years was based on a mixed variance analysis design which assumed a constant effect for a cultivar and a random effect for a study year. The significance of differences between mean values was analysed using the Tukey test, at a significance level of p < 0.05. Regression analysis was used to estimate cause-and-effect relationships between the earliness of the studied cultivars expressed Agricultura 14(3) 2015 18 P.K. Bereś by the FAO number and the percentage of damaged plants and the theoretical loss in grain yield. Mean values from 3 study years (N = 54) were used for the formulation of regression equations. All calculations were carried out in Statistica 10.0 PL software. RESULTS AND DISCUSSION In 2001-2014 weather conditions in Krzeczowice varied significantly. In 2001-2004 the weather between April and May was unfavourable for the intense flight of adults and eggs laying. In these years a prolonged drought was observed (2002, 2004), but also low temperatures and heavy rainfall (2001, 2003) at an early period of maize vegetation, which did not favour infestation by adult individuals, oviposition and larvae development. The weather improved in these years usually in late May or in June, so maize plants grew rapidly. In 2005-2014 the weather was more favourable for the development of frit fly. In April and May low temperatures were recorded frequently, delaying the growth of maize plants but also facilitating the infestation of plants by O.