||Control of Mint Root Borer with
of Entomopathogenic Nematodes
Progress Report - 1993
Note: this information is considered unpublished work
and should not be used as final or finished results. It has been included in IPMP 3.0
because it may not be available from other sources, and in some cases may include
information that may not reach final publication.
Entomopathogenic nematodes can effectively control mint root borer larvae both pre-harvest
and post-harvest. The advantage of a pre-harvest application is that it minimizes damage
to the crop. In heavily infested fields, a pre-harvest application is almost necessary.
Proper timing, however, is crucial in achieving good control. Because of the limited
persistence of entomopathogenic nematodes in the soil combined with the prolonged
emergence of mint root borer adults, an application may be applied too early. Similarly, a
post-harvest application may be too late if hibernacula are already present since the
hibernacula are resistant to both the nematodes and chlorpyrifos (Lorsban).
A narrow treatment window makes timing an important factor in successful mint root borer
control. If successful, a split application of nematodes would alleviate some of the
precision required in timing an application. Also, since one of the applications goes on
pre-harvest, crop damage is minimized. A small plot experiment was conducted to test the
feasibility of split applications of entomopathogenic nematodes.
Materials and Methods
A randomized complete block design was used with the following treatments:
1. untreated check
2. 3 applications of 0.5 billion IJs/acre on 7/24, 8/5 and 8/24
3. 2 applications of 1.0 billion IJs/acre on 8/5 and 8/24
4. 1 application of 2.0 billion IJs/acre on 8/5
The experiment, replicated five times, was conducted in small plots (8'x 40') with 2'
borders surrounding each plot. The applications on 7/24 and 8/5 were pre-harvest; the
application on 8/28 was post-harvest. The nematodes were applied with a CO2 backpack
sprayer approximately l/2 hour into the irrigation set and followed by approximately one
inch of irrigation. The plots were evaluated on 9-11 and 9-13 by taking eight 1 ft2 soil
samples from each plot. The rhizomes were placed in Berlese funnels to extract mint root
borer larvae. In addition, a visual search for hibernacula was made for each soil sample.
Results and Discussion
Compared to the untreated check, both split application treatments significantly reduced
mint root borer numbers, as did the pre-harvest application of 2 billion IJs/acre. The
split application consisting of two applications of a 1 billion IJs/acre rate resulted in
a greater reduction of mint root borer than the split application consisting of three
applications of a 0.5 billion IJs/acre rate (94.9 % reduction and 84.8 % reduction,
respectively). Split applications look promising as the way to apply nematodes against
mint root borers in the future.
Table 1: Control of mint root borer using split applications of entomopathogenic nematodes
Mean no¹(+ SEM)
MRB per ft2 % reduction
2.0 ( 0.5) a
3 aps of 0.5 bil IJs/A 0.3 ( 0.1) b
2 aps of 1.0 bil IJs/A 0.1 ( 0.1) b
1 ap of 2.0 bil IJs/A 0.2 ( 0.1) b
¹ Means followed by the same letter are not significantly different. Separation of means
by FPLSD, p = 0.05.