|An ABSTRACT OF THE THESIS
for the degree of Masters of Science in Entomology
presented on November 10, 1994,
Oregon State University
Title: Control of Mint Root Borer, Fumibotys fumalis, With the Entomopathogenic Nematode, Steinernema carpocapsae
Field experiments were conducted to investigate the potential of using the entomopathogenic nematode, Steinernema carpocapsae (Weiser) strain All to control the mint root borer (MRB), Fumibotys fumalis (Guenee). Single and multiple applications of S. carpocapsae ranging from 1.2 to 7.4 billion infective juveniles (IJs) per hectare were evaulated in small plots and in large field plots.
Single applications were made either pre- or post-harvest. Pre-harvest applications ranging from 1.2 to 7.4 billion IJs/ha reduced MRB numbers significantly from the control, but not always below the treatment threshold of 2-3 MRBs per 929 cm2. Post-havest nematode application rates equal to or above 2.5 billion IJs/ha reduced MRB numbers below the treatment threshold and performed as well as or better than chlorpyrifos applied at 2.24 kg active ingredient (a.i.) per hectare. Multiple nematode applications using lower rates were as effective as a single application at a higher rate.
Application timing is an important consideration for successful reduction of MRB populations. Under pre-harvest conditions, nematode recovery from soil decreased significantly from 1 day to 14 days post-treatment. Limited nematode persistence, in combination with prolonged adult emergence, can lead to pre-harvest applications being applied too early. Post-harvest, fields can be treated too late. In a laboratory study, S. carpocapsae was ineffective against MRB prepupae; therefore, fields need to be treated prior to prepupal formation. Variability in MRB development between fields further narrows the treatment window. As an alternative to precisely timing a single application, multiple nematode applications appear promising.
Because applicaton timing requires the identification of MRB infestations in a timely fashion, studies were conducted to develop guidelines in diagnosing fields. Using Berlese funnels, fields monitored in 1993 were correctly identified as infested or non-infested in mid-August. Berlese funnel extraction offers advanatages over hand-sorting because it is less labor intensive and more accurate. Efforts to correlate adult density with larval infestations were inconclusive using pheromone trap catches; however, a modified sweep search correctly ranked infestation levels in fields monitored in 1994.