[NAFEX] Curcullio question

Stephen Sadler Docshiva at Docshiva.org
Mon Apr 16 15:25:40 EDT 2007

I had this article saved:

-By Dan Kelly, Blue Heron Orchard, Canton, Missouri
My farm is 26 acres in northeastern Missouri on a bluff about a mile from
the Mississippi River. My orchard is five acres with a south-facing slope of
five to seven per cent, and is a long rectangle in shape. My soil type is a
wind-blown loess deposited at the time of the receding glaciers. My farm is
in the middle of zone 5.

I planted the orchard in 1990 on the contour using rootstocks of MM-106,
EMLA-106 and EMLA 7-cw, M-7A, M7-cw and MM 111 with some spur type apples on
seedling rootstock averaging about 100 trees per acre. I applied for and
received a Sustainable Agriculture Research and Education (SARE) Farmer /
Rancher Grant in 1995. The article is about that project and what lead me to
undertake it.

Prior to planting my orchard I had both volunteered and had later been
employed by my local soil and water conservation district. During my tenure
there I came upon an abandoned orchard of about apple 100 trees. I
negotiated with the owner to prune and mow the orchard. I would get all the
apples and she and her family could have all the apples they wanted. So I
quit the soil service and began my orchard adventure. After one year,.I
wanted my own.

I purchased land the next year and took a five-acre field out of a CRP
contract (and paid for it!), and then planted my orchard. Reading about
orchard management, I realized that the "Achilles heel" of organic
orcharding would be the dreaded plum curculio, Conotrachelus nenuphar

Through the soil and water conservation district, I became familiar with the
numerous benefits of warm season (prairie) grasses, such as their
drought hardiness, food and cover for wildlife, and erosion control. I was
fascinated with this plant community. It responds well to
and generally increases with periodic burning. One only needed some patience
to get these grasses established.

Through studying the life-cycle and habitat of the plum curculio in The
Orchard Almanac by Steve Page and Joseph Smillie, I wondered if surrounding
the orchard with prairie grasses might help me manage plum curculio (PC) by
timing the prairie burns with PC emergence. Possibly the large volume of
biomass from the warm-season prairie grasses might provide an alternative
site for over-wintering curculios. An entomologist friend, Doug LeDoux, with
whom I had been conferring, agreed to help me find out. A grant proposal
began to form. It was submitted in 1995; it was awarded; and we were off!

The first stage of the project was to clear unwanted and non-productive
honey locust (Gleditsia triacanthos) and wild plum (Prunus americana,
Marshall) thickets from the east and southeast orchard border. This brushy
habitat around my orchard was providing prime over-wintering sites for adult
plum curculio migrating out of the orchard in late summer. I replanted the
area with warm season grasses of big bluestem, indian grass, side oats
grama, and little bluestem, as well as forbs. We looked at timing PC
emergence with a degree-day model to determine when to burn the grasses. We
used a 'degree day accumulator', a device that records the high and low
temperatures for the day and calculates the degree-days.  The model we chose
had the curculio emerging at 313 degree-days with a degree-day base of
40-degrees F. The burn took place on April 19, 2006.

The new prairie would adjoin an area of prairie grasses that had been
planted two years earlier on the southwestern half and all of the west-side
of the orchard, making a unified border on three sides of the orchard. The
fourth side is a paddock and a low-mowed pasture.

The entomologist began the process of evaluating the orchard and surrounding
prairie area for evidence of plum curculio over-wintering sites. Random
numbers were generated and coordinates were plotted for collection sites in
the orchard and old prairie areas. The new prairie was not sampled. (It was
being cleared and replanted, and at this stage it was oat seedlings, dormant
prairie seed, and straw.)

Samples were taken with a Weedeater blower/vacuum (Wilson, et. al., 1993) in
November 1995. One square meter quadrates were placed over the generated
coordinates and excessive vegetation was removed with shears. The blower/vac
was fitted with a chiffon bag in its snoot to catch the fine plant material,
soil particles and insects, which were bagged and labeled for sifting and
identification. Plum curculios were not found in ground litter samples from
the orchard or prairie areas in spite of intensive sampling.  Many
non-targeted curculionids were present, however, in the old prairie samples.
One sample yielded ten, whereas the orchard litter only yielded two. While
curculionids are not the targeted plum curculios, their presence may
indicate that others, like the plum curculios, may find this to be a
suitable habitat for overwintering.

All apple trees were numbered and random numbers generated to determine
which trees to sample in the spring of 1996. Trees were sampled for
curculios after their emergence and migration (based on the degree-day model
for curculios) into the orchard. The trees were sampled by holding a cloth
tray (3 ft. x 3 ft.) below a branch and striking the branch with a stick to
dislodge curculios in the tree canopy. All curculios were captured, bottled,
and labeled. The initial sampling of trees in the spring of 1996 produced 20
adult curculios found on 48 trees. (Approximately one-third of these were
non-bearing immature trees.) By extrapolation, 41.6 per cent of the trees in
the orchard were infested with curculios.

Apple production in 1996 was low with no saleable apple crop. All apples
were collected and fed to livestock. No burning of the prairie took place
this year.

In the spring of 1997, the old prairie was burned again based on the
degree-day model for plum curculio emergence. Thirty-five trees were
sampled. (Non-bearing trees, which occupied approximately one-third of the
orchard, were not sampled, since the previous years' sampling showed that
non-bearing trees were not suitable sites for plum curculio oviposition.)
Five curculios were collected, reflecting a presence in the orchard of 14.3

The orchard produced a healthy yield in 1997 for a five-year old orchard.
One of the primary indicators of curculio infestation is the abortion of the
pome. Most of the apples completed the season, possibly resulting from lower
curculio infestation in the orchard.

Plum curculios were not found in ground litter samples from the orchard or
prairie areas in spite of intensive fall samplings in 1996 and 1997. Many
non-target curculionids were present, however, in the old prairie samples.

I noted that not just plum curculios fell into the tray. Many beneficial
insects and arthropods such as spiders, lacewings, and ladybug larvae, were
also dislodged. The presence of these beneficial insects helped me become
more aware of insect populations and to be more cautions when using
insecticides, albeit those allowed in organic production.

In conclusion, I like the idea of maintaining a buffer between the orchard
and the woods or brushy places. This fits with my permaculture approach to
agriculture. However, the time to establish a mature prairie had not been
adequate during the two-year grant period to adequately investigate the
potential of this regime. So my study is inconclusive although optimistic in
the role of prairie establishment and management to help manage plum
curculio. But the particular aspects of sustainability that the proposal
encompassed are important. These include use of an on-farm input, improving
my bottom line, reducing soil erosion, improving wildlife habitat and
creating an aesthetically pleasing place..

Now, 2005, both the 'old' and the 'new' prairie are at the same stage of
maturity. They were burned in the spring. I suggest now might be a good time
to re-investigate this control method. Unfortunately I will not have results
for 2005 as spring freezes negated chances of any significant crop. In
addition, when the study was originally conducted traps or volatile plum
essences were either not available or thought for use in trapping or
monitoring. Now ten years later might be a good time to go back and revisit
the prairie tool option, possibly with traps or volatilve plum essences, or
both, for more conclusive results.

The formal title of my project was "Sustainable Plum Curculio Control in
Apple Orchards"; Grant #FNC 95-116.
SARE maintains a database containing reports on the project it funds, which
is available at www.sare.org/reporting.

Wilson, S.W., Smith, J.L., Purcell, A.H. III. 1993. An Inexpensive Vacuum
Collector for Insect Sampling. Entomology News 104(4): 203-208.

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