Study looks into feeding habits of slaters, millipedes

Date: 16 Jun 2017

Image of Josh DouglasResearch conducted as part of a GRDC investment has identified which crops are most susceptible to damage from slaters and millipedes.

These organisms have become more prevalent across the southern region over the past decade with increasing reports of damage to crops as a result of feeding on emerging crops.

The advent of no-till and zero-till farming is thought to have produced favourable environments for millipedes and slaters to thrive with crop residues providing shelter, increased soil moisture and a food source.

University of Melbourne PhD student Josh Douglas has conducted feeding studies in shadehouse trials in an effort to understand what crops will be most affected by millipedes and slaters. This research was then compared with reports from farmers and agronomists of millipedes and slaters causing damage to crop seedlings in the field. These reports have been compiled by the PestFacts services of cesar, the South Australian Research and Development Institute (SARDI*) and the Department of Agriculture and Food Western Australia.

This work has found that millipedes only fed on and damage canola, lucerne and lupins, while slaters caused damage to all emerging crops in the trial apart from faba beans (figures 1 and 2).

Figure 1: The overall percentage of damage caused by the Portuguese millipede to seedlings of eight crops at three different growth stages. Growth stages varied from 1-21 days post-seedling emergence.  Error bars represent standard error of the mean. Source: Douglas et al, 2017.

Bar chart showing The overall percentage of damage caused by the Portuguese millipede to seedlings of eight crops at three different growth stages. Growth stages varied from 1-21 days post-seedling emergence.  Error bars represent standard error of the mean. Source: Douglas et al, 2017.

Figure 2: The overall proportion of damage caused by slaters to seedlings of eight crops introduced at three different seedling growth stages. Growth stages ranged from 1 to 21 days post-seedling emergence. Source: Douglas et al, 2017.

Bar chart showing The overall proportion of damage caused by slaters to seedlings of eight crops introduced at three different seedling growth stages. Growth stages ranged from 1 to 21 days post-seedling emergence. Source: Douglas et al, 2017.

“Field reports have also only reported millipedes damaging canola and lupin crops,” Mr Douglas says.

“Based on the results from this trial, we can confidently say that millipedes are limited in the types of seedlings they will damage.”

“Slaters, by contrast, caused damage to all crop seedlings in the trial apart from faba beans. In the field, slaters have also reportedly damaged a wide variety of crops.”

Mr Douglas says the extent of the damage slaters caused in the shadehouse trial varied greatly between crops.

“As with millipedes, canola, lucerne and lupins were the crops most susceptible to being damaged while other crops were largely only susceptible to being damaged in their first few days,” he says.

“Lentils and chickpeas, which were found to have a low susceptibility to being damaged in the shadehouse trial, have been severely damaged in the field.

“This may be due to differences in the susceptibility of varieties, or the feeding behaviour of slaters, or it may just be due to the huge numbers that can be found in fields.”

Mr Douglas says there have been no reports from the field of wheat being severely damaged by slaters.

“Therefore, we can say that wheat is a crop with low susceptibility to being damaged and we can recommend that wheat and faba bean are good crops to grow in fields where slaters may be an issue,” he says.

Mr Douglas says choosing such crops may help in the ongoing management of the pests.

Future research will look at the effect that stubble management has on the population dynamics of millipedes as well as the effect it has on the damage millipedes will cause to plants.

Currently, remedial control options for slaters and millipedes are limited as there are no registered insecticides for their control in broadacre crops.

Mr Douglas says stubble management could also play a part in the management of the pests.

“The timing of stubble management needs further research,” he says.

“Stubble is the food source of millipedes and slaters so the result of removing it could lead to the insects being starved and turning to the emerging seedlings for food.

“To that end, crop selection in paddocks most at risk of damage is another option in reducing damage caused by the pests. If practical, growers should avoid growing canola, lupins or lucerne in high-risk paddocks and instead look at other crops such as faba beans or cereals, particularly wheat.

“Increasing seed rates and promoting good early vigour will help to compensate losses from feeding damage.”

*SARDI is a division of Primary Industries and Regions SA

GRDC research codes: UM00054

More information

Josh Douglas,
0430 572 730,
douglasj2@student.unimelb.edu.au

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