Banana caterpillar has again reappeared as a serious pest in some mature orchards this season in Bundaberg. This large brown caterpillar, see photograph 1, which rests in the leaf litter under the trees during the day and climbs into the tree during the night to feed on small nutlets, can do considerable damage in a short period of time. In some areas of badly infested orchards it is difficult to find a single nutlet. Caterpillar numbers can get very high with up to 60 caterpillars per m2 of ground area having been recorded this season in one orchard. Numbers are generally higher closer to the trunk where the largest caterpillars are often found. Again this season, up to 50 3-4cm long caterpillars have been recorded within 30cm of the trunk in some orchards. We have had several outbreaks in orchards north of Bundaberg over the last 15 years where they have done considerable damage. They were a concern in one orchard last year, but this year they appear to be more widespread and are being seen in areas where they have not previously appeared.
This pest is found throughout coastal Queensland and is an infrequent pest in other crops such as bananas. Overseas it is a pest in cocoa and this has led to its alternate common name the cocoa armyworm. Banana caterpillar can often be found in low numbers in mature Bundaberg orchards around the flowering to early nut set period. They are not often noticed due to their excellent camouflage, their habit of hiding amongst the leaf litter in the day and of ‘playing dead’ when the leaf litter is disturbed. They are also difficult to see in the tree as they move relatively quickly just after dark up into the tree where they feed on the developing nutlets. When disturbed at night the caterpillars freeze or drop from the tree to the orchard floor where their camouflage makes them difficult to see.
The caterpillar is relatively easy to identify in that it is the only caterpillar pest in macadamia that hides in the leaf litter during the day. According to the literature, the caterpillar goes though six growth stages (instars) before they pupate and become moths. In the initial stages the caterpillars have brown to light black bodies with a cream strip along the side, they also have two conspicuous white spots on either side of the body approximately a quarter of the way down the caterpillar from the head. In the later stages the caterpillars are brown with a faint cream line along their sides and small black circles along the side of their body .
Control of Banana caterpillar is difficult as there is no registered spray. The emergency permit for Lannate (Methomyl ) which was granted for controlling this pest several years ago, has recently expired. It also appears to be relatively tolerant of pesticides such as Endosulphan, Lepidex and Bulldock . Anecdotal evidence suggests that these chemicals, which were applied to control fruit spotting bug while the banana caterpillars were present, reduced caterpillar numbers, but large numbers often survived. At this time the only control measure available to growers is to blow out the leaf from under the tree to remove their hiding place and to finely chop up the leaves, and hopefully the caterpillars, using a slasher or flail.
The best way to monitor for this pest is to carefully remove the leaf litter from around the base of the trunk and look for caterpillars (photograph 3). Generally there has to be a thick layer of leaf litter present for the caterpillars to hide in and areas of dense leaf litter appear to be the best areas in which to start monitoring. During period of dry weather and at high infestation numbers, their droppings, small hard cylinders, are very conspicuous amongst the leaf litter. The other method is to go out a night and look for caterpillar in the lower limbs of the trees. Once you have your ‘eye in’ they are not too difficult to spot. Another telltale sign is that after feeding the smaller caterpillars let themselves back down to the orchard floor on a long line of silk and these silken threads can readily be se en shining in a torch beam. The caterpillars may also emit a green fluid from a gland behind the head when disturbed. At present we have no economic threshold for this pest, but at numbers of 50 3-4cm long caterpillars at the base of a tree damage can be considerable.
We will put some photographs of this pest up on the website,for growers to have a look at. If you think you have this pest present in your orchard the best thing to do is contact your local Department of Primary Industries (DEEDI in Queensland and I&I in NSW) and have the pest properly indentified. We at Suncoast Gold in conjunction with your local Department can then work out if the pest is doing economic damage and can help you devise a control strategy.