Green Manure May Help Control Orchard Virus Problem
UNIVERSITY PARK (Centre
Co.) Many agricultural pests
immigrate to the United States
from other places and attack
native crops. But a plant patholo
gist in Penn State’s College of
Agricultural Science is tackling a
pest problem that developed when
imported fruit trees were exposed
to native pests.
“Fruit trees imported from Eur
ope and Asia to North America are
very susceptible to a plant virus
native to North America, tomato
ring spot virus,” said Dr. John
Halbrendt, who studies this prob
lem at the collegb’s Fruit Research
Laboratory in Biglerville. “The
pathogen is transmitted to plants
by dagger nematodes.
“Peach and nectarine growers
Mt. Joy Cooperative Holds
Banquet Meeting
(Continued from Page A 24)
lorships with Atlantic Processing
Inc., the Pa. Dairy Council, and the
Lebanon County Farmers
Association.
Dum is in partnership with his father
Samuel on a 150-acre farm where they milk
104 cows and keep about 80 young stock. He
is a graduate of Penn State University and
holds a bachelor’s degree in agricultural engi
neering. He also serves as a secretary for the
Manheim Young Farmers and is a member of
the state and national Holstein associations
and the Pennsylvania Farm Bureau.
It was also announced that Paul Hostetler,
cooperative manager is retiring and is his
duties are to be taken over by Earl Dehmey,
who is to continue to perform his oversight of
field operations, but discontinue driving truck
on a regular basis
Hostetler, who is to celebrate his 80th birth
day in July, has worked in the dairy industry
for 62 years.
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can lose entire orchards to the
tomato ring spc;l virus. It kills all
commercial rootstocks for nectar
ine and peach trees, as well as
many common plum, apricot, and
cherry rootstocks. Infested
orchards usually lose up to 10 per
cent of their trees.
“The virus and the nematodes
co-evolved with a group of
weeds,” said Halbrendt. “The
weeds aren’t harmed by the virus,
but when dagger nematodes feed
on an infected weed, they tap into
a reservoir of virus. The nema
todes then infect healthy fruit trees
when they pierce cells to feed.
“Because the rootstocks for
these trees are derived from Euro
pean and Asian plants, they have
no resistance to the virus. And
since nematodes are good at
spreading the virus, it doesn't take
many of them to cause fruit grow
ers a lot of grief.
“Orchards must be periodically
replanted, either because the trees
lose productivity or because the
grower wants to use a new varie
ty,” he said. “If the soil isn't
treated for nematodes, new trees
are likely to acquire tomato ring
spot virus. When that happens,
they’re as good as dead.”
The best way to replant infested
sites is to purge nematodes first,
Halbrendt said. “Fumigation is the
most effective method, but many
nematicides are expensive or have
been restricted recently. There’s a
critical need for alternatives to
manage this virus.”
Crop residues from cruciferous
plants such as rapeseed, mustard,
and kale may offer an environ
mentally sound alternative for
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nematode control. “Live plants
contain nontoxic chemicals called
glucosinolates,” said Halbrendt.
“When the plant decays, these glu
cosinolates combine with a plant
enzyme to create toxic by
products in the same chemical
family as some of the most effec
tive soil fumigants.
“Growing a stand of these
plants for a year or two before
replanting an orchard may control
nematodes while improving soil
structure and growth conditions,
allowing plants to maximize their
natural defenses against disease.”
A cover crop that is plowed
under to add organic matter to the
soil is called “green manure.”
While green manure has been
used to control nematodes before,
using it in rotation with fruit trees
is new.
Halbrendt’s initial studies con
firm that green manure reduces
nematode populations, but its
effectiveness depends on factors
such as plant species and age, soil
pH, temperature, and the availa
bility of sulfur. 'There’s a window
of time when glucosinolates reach
their peak and the plant is most
effective as a green manure treat
ment,” he said.
“Nematode mortality also may
be affected by how deeply green
manure is incorporated into the
soil, so I’m evaluating two diffe
rent techniques,” he said. "Nema
tode assays are taken before and
after treatment to determine the
effectiveness at various depths.
Within a few years, we should
have enough data to make recom
mendations about the best plants
to use for nematode control in
orchards.”
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