IPDM in focus: Helicoverpa and loopersPest and Disease Management
This article was first published in the Spring 2022 edition of AFG. It was prepared by Emily Crawford, Agriculture Victoria, using information from the revised Integrated Pest Disease and Weed Management manual for Australian Apples and Pears (IPDM manual), Hort Innovation, October 2021.
The IPDM manual provides guidance on developing an IPDM (integrated pest and disease management) plan for your orchard to identify, monitor and manage key pests, diseases and weeds through an integrated approach that aims to disrupt life cycles and prevent susceptibility while encouraging and nurturing beneficial species that can act as natural control agents in your orchard.
This article is part of a series of articles that focus on implementation of IPDM.
When fruit trees start to flower is a good time to monitor for the native budworm, the cotton bollworm and loopers.
The native budworm, the cotton bollworm and the larvae of geometrid moths, which are known as loopers, are serious pests of apple production in all Australian fruit growing regions. Management of these pests involves a combination of weed management, biological control, entomopathogens, early season monitoring and careful selection of pesticides to avoid disrupting predators and parasitoids.
The native budworm Helicoverpa punctigera and the cotton bollworm Helicoverpa armigera (also known in Australia as tobacco budworm, tomato grub or corn earworm) can attack pome fruit from pink bud through to early fruit development.
H. armigera has developed resistance to a wide range of pesticides and is generally more difficult to control. In southern Queensland it overwinters as diapausing pupae in the soil under late summer crops and emerges in spring during October but does not become the dominant species until mid- summer and autumn. H. punctigera breeds on flowering plants in inland Australia and in southern parts of Australia it overwinters as pupae from which moths emerge in spring. In Victoria it emerges before H. armigera. Both species are capable of long-distance migration on high-altitude winds that precede cold fronts. Migrating H. punctigera arrive in southern fruit growing states in August and start laying eggs. Pheromone traps can be used to monitor the activity of both species, but because they have different pheromones this requires the use of separate traps.
In pome fruit growing regions, the moths can invade orchards from pastures and other crops. Often this means that the moths have mated before arriving in the orchard around the time fruit trees are starting to flower. Pheromone traps only capture male moths, not females, and capture of males indicates females are likely to be present and laying eggs. Because the eggs are laid during the time that bees will be active it is important to make careful choices of control measures.
Budworm larvae bore into developing flower buds, flowers, developing fruitlets and unfolding leaves, and can cause considerable damage and fruit drop. Damaged fruit that remains on the tree may become deformed by a deep depression with scar tissue. These scars are larger than those caused by the apple dimpling bug and the deformities are distortions rather than dimples. Some chemical control choices will affect bees and therefore pollination; biocontrol agents that prey on the eggs of Helicoverpa and other pest species may be affected; and the costs of counteracting the side effects may outweigh the benefits of controlling the budworms.
Loopers are the larvae of geometrid moths and get their common name from their distinctive looping or ‘inching’ action. The loopers that attack pome fruit are the apple looper Phrissogonus laticostata, pome loopers Chloroclystis testulata and C. approximata, and the twig looper Ectropis excursaria. Loopers feed on the leaves and, when feeding on fruit, generally graze the fruit surface making shallow damage, which is distinguished from light brown apple moth (LBAM) damage because it occurs on exposed rather than protected surfaces of the fruit.
Occasionally loopers create crescent-shaped series of small, deeper, single holes when the caterpillar anchors itself with its hind prolegs while it bores a hole and then pivots sideways, like a mechanical excavator, to make other feeding holes while anchored to the same spot. As fruit matures, the wounds caused by the loopers become corky and sometimes develop into small lumps but generally they remain shallow and concave.
Adult looper moths are rarely seen because they are well camouflaged when resting on bark. The larvae have a habit of remaining still if they sense the presence of a predator (or human). Larvae have three pairs of true legs on the thorax and, unlike budworms, have only two pairs of abdominal prolegs that are at the end of the body. Budworm larvae, like most moth larvae, have prolegs on each abdominal segment. The looping action of the looper larvae is the result of having prolegs only towards the rear of the abdomen.
Management of Helicoverpa and loopers involves a combination of weed management, biological control, entomopathogens, early season monitoring, and careful selection of pesticides to avoid disrupting predators and parasitoids that would otherwise manage to keep other pest below economic thresholds.
The apple looper has a range of hosts, including acacia. Budworms feed on a wide range of weeds such as deadly nightshade, Noogoora burr, thistles, capeweed, dock, fat hen and marshmallow. Management of those weeds prior to flowering of pome fruit will not only reduce incidence of budworms but will also help reduce populations of LBAM and harlequin bugs. However, this does not mean leaving bare earth in the inter row! Biological control agents such as parasitoid wasps require access to flowering plants for energy sources like sugar, so it is important to maintain a balance of plants in the inter row without promoting the weeds mentioned above.
Several biological control agents actively work to control Helicoverpa and loopers. Trichogramma wasps parasitise budworm eggs and probably also looper eggs. The small black wasp Microplitis demolitor parasitises young budworm caterpillars. The predatory shield bugs Cermatulus nasalis and Oechalia schellenbergii attack Helicoverpa and other caterpillars. Green lacewing larvae, lynx spiders, and red and blue beetles are known to prey on budworms. Small caterpillars can be controlled by applying sprays containing the entomopathogenic bacteria Bacillus thuringiensis (Bt). Once the larvae have grown beyond the third instar, they are probably beyond control by Bt alone and a registered chemical insecticide may be required. Choose carefully to minimise the impact on other biocontrol agents. Refer to Chapter 6 of the IPDM Manual for information about side effects on beneficial species.
Monitoring for eggs during the fruit tree flowering period can be done at the same time you are doing blossom tapping to detect dimple bugs and thrips. Small loopers may be dislodged into the container and if that occurs then it would be prudent to look for eggs and other small larvae among the flowers. If the orchard is surrounded by pasture or field crops you may want to position some pheromone traps along the border to detect movement of moths into the orchard.
After petal fall the ‘one-minute tree inspection’ should be used to search for larval feeding activity (for more information on the ‘one-minute tree inspection’ see the IPDM Manual). Pears are particularly attractive to twig loopers and the first signs of activity are usually the presence of small cylindrical pellets of faecal matter on the upper surface of leaves. These leaves may not have been eaten but the larvae producing the pellets are likely to be detected feeding on leaves on twigs or branches above where the pellets were found. Twig loopers are sensitive to movement and will become immobile while imitating a small twig (hence the name). Once you detect the pellets, stand quietly and do not make any sudden movements but cast your eyes over the leaves. Often you will detect slight movement in your peripheral vision which then allows you to home in on the larvae.
Budworm and looper damage can continue through the season so maintain awareness while you conduct weekly tree inspections.
Insecticide applications should be a last resort because some of the suitable pesticides may also be registered against codling moth and leafrollers like LBAM, and have restrictions on the number of applications permitted per season. The most likely timing for control of loopers will usually coincide with sprays against codling moth, therefore negating the need for additional sprays to control either pest.
For more information
For detailed information on loopers see page 220 of the IPDM Manual, found on the Australian Apple and Pear IPDM webpage.
The PIPS3 Program’s Strengthening cultural and biological management of pests and diseases project (AP19002) has been funded by Hort Innovation, using the apple and pear research and development levy, contributions from the Australian Government and co-investment from Agriculture Victoria. Hort Innovation is the grower-owned, not-for-profit research and development corporation for Australian horticulture.