Poljoprivreda, Vol. 15 No. 2, 2009.
Ostalo
PREDICTING THE EMERGENCE OF CORN ROOTWORM (Diabrotica virgifera virgifera LeConte) IN ESTERN SLAVONIA
Dražen Đoić
; Ministarstvo poljoprivrede, ribarstva i ruralnog razvitka, Zagreb, Hrvatska
Sažetak
Corn (Zea mays L.) is one of the most important field crops in Croatia, country as well as in the world. It is subjected to many pests, among which is corn rootworm. Corn rootworms (Diabrotica virgifera virgifera LeConte) are economically significant pests of corn, especially at successive growing of corn or single culture growing. In our corn fields, corn rootworm was a pest since its first appearance in 1995, and more significant damages were detected in 2002. The monitoring of the corn rootworm population enables the development of more efficient models for predicting adult corn rootworm emergence and the control of these pests. The objective of this thesis is to determine the influence of row spacing to corn rootworm population, larval root damages and grain yield. Then, to develop models to predict adult corn rootworm emergence in Eastern Slavonia, based on accumulated degree-days for air temperature, and to determine optimum time for monitoring and for possible control of adult cron rootworms based on ovarian development of the gravid females. The researches were conducted in 2004 and in 2005 in Gunja and Soljani, with two sowing models, row spacing of 50 cm and 70 cm. Hybrid corn OSSK 552 was sown in four repetitions at both sites. Cages and pheromone traps were placed in order to estimate the first day of corn rootworm emergence (the biofix) and to monitor the total population number. Predicting of the adult corn rootworm emergence was based on degree–days for air temperature from the biofix. In mid–July, evaluation of the larval damage was made according to the scale from 0–3. Ovarian development was determined by dissection of the gravid females, whereas the complete female gravidity and optimum time for scouting were determined based on degree–days accumulated from the biofix. The larval population was not significantly increased at the reduced row spacing. The number of the larvae per a plant was 24% higher on the average at 50 cm row spacing, and in a weak negative correlation with grain yield. The number of the adult corn rootworms in the cages was not significantly different in two row spacing models, but very significant differences occurred between localities. The number of the adult corn rootworms per a m2 was 4.05% higher at the 50 cm row spacing, compared to the 70 cm row spacing, and the root damage was 14.62% higher at the 50 cm row spacing. The evaluation of the root damage was in a weak positive correlation with the corn grain yield. The lodging was on the average 15.28% higher at the 70 cm row spacing in compare the 50 cm row spacing. Corn sowing at high plant density did not influence the increase of the corn grain yield, and it was not economically justified, because a greater quantity of sowing seeds were used. Statistically very significant difference of grain yield occurred between the localities. The average of accumulated degree–days was 5.5°C per day. More than 50% of the corn rootworm population was recorded at the sum of 221 degree–days from the biofix. Appearance of the complete adult corn rootworm population occurred at the sum of 394 degree–days from the biofix. The first gravid females were detected at 30 degree–days accumulated from the biofix, 50% of the gravid females appeared 235 degree–days from the biofix. The gravid females were present in the field until 360 degree– days post biofix. Based on the dissection of gravid females, 10% of the females have the full gravidity (III. and IV. ovary stages) at 121 degree–days post biofix. Based on the results of the adult corn rootworm emergence, degree–days from the biofix, corn rootworm population and the female ovarian development, the scouting of the WCR beetles should be between 121 and 360 degree–days, and the optimum is 221–235 degree days post biofix. Predicting the adult corn rootworm emergence and the optimum time for scouting adult corn rootworms, especially at the corn seed production, are important objectives in protecting of corn. The Doctoral dissertation is significant contribution to the science and the practice in developing new methods in controlling these pests. The described models of emergence and predicting will contribute to the control efficiency of the corn rootworms, being important in preventing economical damages.
Ključne riječi
corn rootworm; emergence prediction; degree-days
Hrčak ID:
44901
URI
Datum izdavanja:
11.12.2009.
Posjeta: 1.520 *