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Curculio Pressure is Strong but There Are No Economic Thresholds

By Forrest Scharf, PAg, Provincial Specialist Fruit Crops, Regina

June 2021

Apple curculio
Apple curculio on saskatoon berry (prior
to feeding/ovipositing). Photo courtesy
of Simon Hegner

There are a few different types of weevil insects that infect fruit crops like apples, pears, saskatoon berries and cherries. Apple curculio (Anthonomus quadrigibbus) is one type that is prevalent in Saskatchewan, another is plum curculio (Conotachelus nenuphar). There are a few other members of the weevil family like Hawthorn weevil (Anthonomus corvulus) and black vine weevil (Otiorhynchus sulcatus) that can also infect Saskatchewan grown fruit; but they are comparatively rare and less likely to be of concern in 2021.

Apple and plum curculio are similar, with the adult beetles having jaws at the end of long snouts that can perforate the skin of young developing fruit. In apple curculio infestation; puncture holes made during feeding are often seen as round discoloured wounds located near the fruit stem (or pedicel). The females use ovipositors to place eggs relatively deep into the fruit flesh and fill holes with a bit of chewed fruit. 

Apple curculio
Apple curculio. Photo courtesy of
Simon Hegner

In plum curculio; the feeding wounds do not dig as deep into the fruit flesh and the shape is more irregular and often crescent shaped. Eggs are oviposited in a similar way, but just under the skin.

There is one generation per year and the eggs form grub-like larvae that pupate inside the fruit, feeding on fruit flesh and seeds. Frass or the chewed up fruit accumulates inside it and makes it unmarketable. After pupation the adults often exit the fruit before it is fully ripened, but where there is variability in fruit ripeness, adults may remain inside and add an unwelcome crunchiness to any human consumption.

apple curculio larvae
Apple curculio larvae feeding
inside a saskatoon berry

Scouting to identify infestations is a bit challenging, because these insects are small and are coloured similar to the bark of the plants. They will fall off branches if they are shaken. So; placing a white cloth below plants, then shaking branches vigorously will dislodge the insects and deliver them onto the cloth where they can be inspected. Often curculio “play dead” but will scurry away when they feel it is safe.

So far, in 2021 several growers have expressed concern that curculio populations are strong. Although economic thresholds that provide guidance regarding when to implement control measures have not been developed for these species, it is recommended that growers start spraying appropriate insecticides soon.

plum curculio
Plum curculio feeding and ovipositing damage
evident on developing apple fruit

First applications of pesticides should be made during and/or soon after petal fall when ovipositing is set to be in progress.

Registered neonicotinoid and pyrethroid insecticides, as well as Decis (which is registered for use on Saskatoons in the prairie provinces) are effective at controlling curculio. For more information, please contact Forrest Scharf.

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