Effects Of Orchard-Floor Management On Stink Bug Pests
Of Pistachio
Paul G. da Silva and Kent M. Daane Kearney Ag Center, 9240
S Riverbend Ave, Parlier CA 93468
Introduction
Several species of stink bugs cause necrotic spots in pistachio nutmeats through their attacks on developing fruits. This condition, known as kernel necrosis, can affect one-third to one-half of the crop in some locations in some years.
Improved control of these pests might result from manipulation of their preferred host plants, their natural enemies or both of these elements of the food chain. The species of bugs involved, Acrosternum hilare, Chlorochroa uhleri and Thyanta pallidovirens, all native to California, have been reported from a wide variety of native and introduced cultivated and uncultivated plants and are themselves attacked by a complex of predatory and parasitic insects.
Although in the pistachio industry as a whole, especially in
the San Joaquin Valley, clean orchard floors dominate, several
growers have implemented management programs that result in vegetative
cover of varying composition and permanence. And although most
initiated these practices for other reasons, some now feel that
they are useful in pest management. Our work, which began in 1994
and is currently in progress, is measuring the effects of three
of these systems on stink bug pests and their natural enemies.
Procedures
At each of three locations within the San Joaquin Valley, an
eighty-acre block of pistachios has been divided into eight ten-acre
plots. In four of these, the grower's chosen system of establishing
and maintaining cover has been continued. In the other four, the
soil surface has been kept clean of herbaceous plants. Data collection
has included winter, spring and summer surveys of composition
of the vegetative cover in the four "cover" plots, season-long
sampling of insects and other arthropods at two heights in both
sets of plots, and postharvest crack-outs of nut samples from
all plots for damage evaluation.
Current Findings
Four features of plant and insect distribution have become apparent. First, the composition of the covers has varied greatly among orchards and throughout the season. Second, different species of pests and natural enemies have occurred in the different geographical areas. Third, at least two of the pest stink bugs have appeared early in the season on the orchard-floor plants and then have then moved into the canopy as the understory plants declined. Fourth, specialist parasites of the pests have preferred different heights within the orchard.
In 1995, stink bug numbers were extremely low in all orchards
studied. Thus it is not surprising that minimal differences were
recorded between "clean" and "cover" treatments.
Future Plans
Work will continue this year with a few changes. Increased emphasis
will be given to field monitoring of the specialist parasites.
Laboratory work will be undertaken to investigate climatic and
host-plant preferences of the pests.
Publications
Silva, P.G. da, K.M. Daane, R.H. Beede, W.J. Bentley, C. Anderson
and C. Moutou. 1995. Biological control of hemipteran pests of
pistachio: inventory and sampling. California Pistachio Industry
Annual Report, Crop Year 1994-1995, pp. 56-61.
Silva, P.G. da, K.M. Daane, N.M. Korfanta, R.H. Beede, B.A. Holtz
and W.J. Bentley. in press. Biological control of hemipteran
pests of pistachio: appearance, activity and movement of insects
in the orchard. California Pistachio Industry Annual Report, Crop
Year 1995-1996.
Silva, P.G. and K.M. Daane. 1995. Stinkbugs and Leaffooted Bugs.
In Ferguson, L. (ed.), Pistachio Production, Center for
Fruit and Nut Crop Research and Information, University of California,
Davis.
Cover Crop Research and Education Summaries