Effect of Weather During Spring on the Time of Arrival of Bird Cherry-oat Aphid (Rhopalosiphum padi L.) in Spring Barley (Hordeum vulgare L.) Fields
Bird cherry-oat aphid is the principal pest of spring barley in Denmark. The time of arrival in the fields is an important element in deciding whether chemical control is needed. This paper describes a regression model managed by climate variables, which incorporate the biology of the bird cherry-oat aphid on its primary host, the bird cherry (Prunus padus L.). In the period 1987-1998, three to nine spring barley fields were monitored annually for the first occurrence of bird cherry-oat aphid. Different climatic variables were analysed in relation to the time of arrival, with a view to constructing a model. The analysis showed good correlation between the date of arrival into the fields after 1 May (D), day-degrees (DD) in February (TF), DD in March (TM), DD in April (TA), precipitation in April (PA) and precipitation in May until 15th (PM) according to the following model: D = 0.61TF - 0.17TM + 0.30TA - 0.46PA + 1.85PM (r2=0.98, P<0.001, df=51). DD were calculated with a threshold temperature of 3°C. It is concluded that the model gives a prognosis of the time of arrival of bird cherry-oat aphid in spring barley fields sufficiently reliable to serve as a decision-making tool in managing problems with bird cherry-oat aphids.