M. Demirci, Y. Nemli* , Y. Kaya**

Basf Turk, Şehit Fethibey Cad., No:49/603,Cankaya, Izmir, Turkey

*Ege University, Agricultural Faculty, Izmir, Turkey

** Trakya Agricultural Research Institute, Edirne, Turkey

Introduction

Sunflower is one of the important oil crops of Turkey. Trakya region is the main area and has 75 % of all sunflower production area of Turkey. The rotation system is sunflower and wheat in the region. However, 80 % of sunflower production area is infected by new races of O. cernua in the region. Broomrape caused epidemic each 20 years (1960, 1980 and 2000) and broke resistance of sunflower cultivars. During the last five years, probably three more races of O. cernua than known (A,B,C,D,E) appeared in the region. Although some resistant and tolerant sunflower hybrids are planted, these cultivars could have susceptibility after a couple of years, due to high virulence attack of these new races. Besides, using Imidazolinone resistant sunflower hybrid, the public research institute and private companies in Turkey continue their research to control O. cernua with Imazamox+Imazapyr (33+15 g/l) post emergence herbicide. The objectives of this study were to determine the relationship between temperature and penetration of O. cernua to sunflower roots and growing period after this stage, and to find the accurate time of post emergence herbicide application based on this research results.

Material and methods

The research were conducted in 2002 at four different locations which had distinct climate three locations with natural infestation since at least 40 years (Malkara, Edirne and Kirklareli) and one location with artificially inoculated field (Akhisar). The temperature data was collected from detectors each 30 min. at 15 cm under soil from planting to the time of broomrape reaching 1 cm height over soil surface. The average day and night temperature were calculated based on these data. Additionally, phenological development of sunflower was observed from planting time to flowering time. Broomrape phenology and penetration was controlled at sunflower roots each three days. Broomrapes were counted weekly in certain plots to check maximum emerging time.

Results and discussion

The average day temperature was the lowest at Malkara and Kirklareli followed by Edirne and Akhisar respectively (Figure 1). On the contrary, time of Orobanche emergence at soil surface was reduced based on increasing temperature (Table 1). Therefore, the temperature affected broomrape attachment and emergence rate positively.

Broomrape attachment on primer sunflower roots varied between 23 to 37 days from planting and the duration to reach 1 cm over soil surface varied between 44 to 50 days. However, these data did not fit to the average temperature data properly. Soil type and seedbed preparation practices were other observed reasons for delaying broomrape emergence. Therefore, sunflower primer root growth decreased in relation to soil temperature and this action retarded broomrape inoculation to roots. Broomrape infection which is leaded by temperature started on sunflower between V4 and V6 phenological stage (Schneiter , 1981). Based on the relationship between the average day temperature and broomrape and sunflower phenology, the temperature stimulates broomrape growth which affects sunflower development directly. We could conclude that the reason of this all variation of sunflower and broomrape phenology was related to temperature in all locations. Increasing average temperature stimulates sunflower growing and minimize maximum attachment time of broomrape. These results quite similar to those obtained by Weaver et al.,1988 and Torres et al., 1996.

Table 1. Planting date, average temperature, broomrape and sunflower phenology at different locations.

A main result is that sunflower growth period from V6 to V14 is very important to control O. cernua by post emergence herbicides application in natural conditions. These herbicide applications should be made at this period to get success effectively. But V6 to V8 stages was the most suitable herbicide application timing for providing maximum yield in farmer conditions.

References

Garcia-Torres, L. , M.C. Munoz, M.J. Exposito and F.L. Granados. 1996. Modelling the the economics of controlling nodding broomrape (Orobanche cernua) in sunflower (Helianthus annuus). Weed Science 44:591-595.

Schneiter , A.A, and J.F. Miller. 1981. Description of Sunflower Growth Stages. Crop Science 21:901-903

Weaver, S.E., Tan, C.S. and P.Brian 1988. Effect of temperature and soil moisture on time of emergence of tomatoes and four weed species. Canadian Journal of Plant Science 68:877-886.