Frit fly infestation of oats in relation to growth stage and weather conditions at oviposition

Aiming to improve forecasts of hit fly (Oscinella frit) damage, field exper iments were conducted where infestation rates of oats were assessed in rela tion to plant growth stages and daily weather conditions. Oat seedlings wer e most susceptible to infestation during growth stages DC 11 and 12 (one an d two leaves unfolded, respectively). Susceptibility decreased in DC 13, bu t significant damage could still arise at this stage if the infestation pre ssure was high. In later stages seedlings were almost completely resistant. Temperature affected daily infestation rates most, whereas sunshine and wi nd conditions were less important. No infestations occurred at daily maximu m temperatures lower than 15 degrees C, whereas high infestation rates occu rred at maximum temperatures of 17 degrees C and higher. (C) 1999 Elsevier Science Ltd. All rights reserved.