Agriculture Reference
In-Depth Information
by the expanding cells inside apples that remain on the trees. In pome fruits,
plum curculios only complete their life cycles in fruits that drop prematurely.
When mature, the larvae leave the fruit and enter the soil, where they pu-
pate 1 to 2 inches below the surface. The pests overwinter as adults in litter
on the orchard floor or in other protected areas. Beside the adults that over-
winter in your orchard, adult plum curculios are strong fliers and can enter
your orchard from nearby orchards and hedgerows.
Damage from plum curculio includes early-season feeding by adults, ovi-
position injuries where eggs are laid, internal injury by larvae, and late-sea-
son feeding injury by adults. All make fruit unmarketable and, in many cases,
unusable for home consumption.
It has historically been very difficult for organic fruit growers to control
plum curculio. Pheromone traps and mating disrupters are not yet available.
Routinely disking the entire orchard floor destroys many of the fragile pupal
cases, but it severely damages the soil. Chickens and geese are effective in
scratching up and eating the pupae, particularly when grain seed is mixed
lightly into the soil on the orchard floor, but they are generally not allowed in
certified organic fruit tree orchards later than 90 days before harvest. Using
Surround to reduce plum curculio has proven quite effective and is probably
the strongest weapon in your arsenal to manage this pest. You must apply
it very thoroughly and begin applying just before bloom, and again at petal
fall. You will need to repeat applications, particularly after rain.
The Integrated Pest Management group at Michigan State University has
evaluated several organic approaches to control plum curculio. In addition
to Surround, which they do not recommend for cherries, they suggest using
Pyganic pyrethrum insecticide. Unfortunately, this material has an effective
lifespan of only about 12 hours and requires frequent applications. It is also
very toxic to predators and bees, so wait until petal fall to apply pyrethrums.
The MSU group has also suggested using trap crops, in which case the
center of an orchard is thoroughly sprayed with Surround to protect the
trees and a few border rows are left untreated but are heavily sprayed with
pyrethrum. Reportedly, 'Liberty' apple is highly attractive to plum curculio
