Late spring hazelnut pests - Aphids, leafrollers and that weird green beetle

With the onset of warm weather, insects are out and active in hazelnut plantings. Here are a few that we've been seeing.

Aphids

Aphids have been observed in large numbers on the underside of hazelnut leaves. Aphids are small, soft-bodied, pear-shaped insects with straw-like mouthparts that they use to pierce plant tissue and suck out the fluids of a variety of crops (Figure 1). There are winged and wingless forms. Aphids can be identified by the presence of two "tail-pipes", called cornicles, near the end of the body. They are usually found in groups, or colonies. Several aphid species have been reported from other hazelnut producing areas, including filbert aphid, hazelnut aphid and green peach aphid. We are currently in the process of identifying the aphids present in hazelnut in Ontario.

Aphids are reproducing machines - a single female can produce up to 100 offspring in a week, without mating or laying eggs. Under the right conditions, these offspring, called nymphs, can develop to reproducing adults in less than two weeks. This means that aphid populations can increase very rapidly, especially when temperatures are high. Aphids are active throughout the growing season.

Aphid feeding drains fluid and nutrients from leaves, which can distort plants and cause them to wilt. They also secrete a sticky substance, called honeydew, which can promote development of a black sooty mold, which can reduce photosynthesis. Large populations of aphids can decrease yield.

Hazelnut growers are assisted in their efforts to control aphids by numerous natural enemies. Lady beetles and other predators are often found feeding on aphid colonies on hazelnut. Aphids are also susceptible to a number of fungal diseases and also tiny parasitic wasps, which lay their eggs inside the aphids. The developing wasp larva essentially eats the aphid from the inside out, killing it. When scouting for aphids, look for the presence of mummies (Figure 2), which look like papery, brown, swollen aphids - which is all that is left of the aphid after a parasitoid completes its development and the adult wasp emerges. Parasitoids can be extremely effective biological control agents. The presence of a parasitic wasp of filbert aphid in Oregon has replaced the need for chemical controls in some areas, so you may want to hold off on spraying if you observe large numbers of aphid mummies when scouting.

Figure 1 - Aphids feeding on the underside of hazelnut leaves

Figure 2 - Aphid mummies - note that they are enlarged and the skin appears papery

Leafrollers

Leafrollers have also been observed in hazelnuts, as well as other tree nuts. Leafrollers are the immature stages of a variety of species of moths. These caterpillars typically become active in early spring as soon as green tissue appears, feeding on leaves and buds. As leaves expand, the caterpillars roll up leaves using silken webbing, where they hide during the day. These rolled leaves serve as a protection from predators and also protects them from insecticide treatments. Japanese heartnuts in southern Ontario have been extensively defoliated by leafrollers in recent years.

In Oregon, the obliquebanded leafroller (OBLR) can be a serious pest in hazelnut orchards, with caterpillar feeding on nuts rendering them stained, misshapen or aborted. Although we have not observed extensive defoliation, adult OBLR have been caught in pheromone traps in Ontario hazelnut orchards in recent weeks. In Ontario, OBLR is a pest in apple orchards, where it has two generations per year. The overwintering generation hatches in late summer, feeds through September, overwinters as larvae and feeds again in the early spring. Adults from this overwintering generation are active now, mating and laying eggs for the summer generation of larvae. In Oregon, it is this summer generation which is the most damaging to hazelnut.

We don't yet know whether OBLR will cause significant damage to Ontario hazelnuts, so it is a good idea to monitor for this pest. Adult moths are light tan to dark brown with darker bands on the wings (Figure 3), while the caterpillar is up to 20-30 mm in length and light to dark to yellowish green, with a dark brown to black head (Figure 4). The segment just behind the head is often similarly dark, with a white or cream edge between it and the head capsule. OBLR adults can be monitored with commercially available pheremone traps.

Figure 3 - Adult obliquebanded leafroller.
Photo courtesy of Kathryn Carter, OMAFRA.

Figure 4 - Obliquebanded leafroller larvae.
Photo courtesy of Kathryn Carter, OMAFRA.

Green weevil

We have had a number of questions about green beetles feeding on the foliage of various tree nuts, including hazelnut. The insect in question is a green leaf weevil (Figure 5). Weevils are members of a very large group of beetles known as Curculionidea characterized by a well-developed snout, which can be quite long and narrow - they are commonly referred to as snout beetles. Green leaf weevils are members of the genus Polydrusus, feed on the leaves of a wide range of trees. They are quite common in nurseries and orchards at this time of year. Although they happily eat the foliage of apples, heartnuts and other trees, it appears that the trees are able to compensate and consequently they are usually considered only a minor pest.

Figure 5 - Pale green leaf weevil