Unidentified feeding damage

Over the last few weeks we have received numerous reports of damage to crops where no potential insect pests can be found. Agronomist, Glen Smith (3D-Ag), has experienced patchy and inconsistent feeding damage to a canola crop near Wagga Wagga, in the South West Slops of New South Wales. Leaf margins have been eaten and whole leaves have been chewed off in some instances. Glen said he has monitored for the presence of slugs using carpet squares, but has not found any pests present. Agronomist, Murray Skinner (Sullivan’s CRT), has reported crop establishment issues in a canola crop near Dunedoo, in the Central West Slops and Plains district of New South Wales. The crop is at the cotyledon - 1 true leaf stage. Entire seedlings are being nipped off just below the soil surface, and there are also signs of irregular chewing damage to cotyledons and leaves. Despite thorough searching, Murray has been unable to identify the culprits. 

Agronomist, Terry Edis (Elders), has reported pest damage to a lupin crop near Ariah Park, in the South West Slops district of New South Wales. The new growth between the cotyledons and first true leaves has been completely chewed off. Insects collected from the affected areas have been identified as soil collembola (or ‘springtails’), which are not responsible for the feeding damage. No other insects have been found that might be attacking the crop. Research Entomologist, Jo Holloway (NSW DPI), reports that she has also received several samples of soil collembola collected from canola crops with patchy emergence around Wagga Wagga. Besides the lucerne flea (Sminthurus viridis), there are very few collembola that feed on crop plants. Collembola are soil and litter dwelling insects that prefer wet, damp surroundings. They are among the most abundant of all soil-dwelling insects, and regularly found in most crop and pasture paddocks.

There are a number of strategies that may be used to determine the cause of damage to a given crop. The type of plant damage seen is the first thing that can help. Is the damage below ground, above ground or at the soil surface? Is the damage caused by sucking pests (e.g. leaf cupping, silvering, shriveling) or chewing pests (e.g. scalloped leaves, leaf holes, stems cut through)?

The next step is to thoroughly search the area, looking on the plants, at the bases, digging around the plants and checking within the soil and any trash or stubble that is lying around. If insects are not easily found during the day they could be sheltering somewhere and may be much easier to find in the evening or at night. Checking the affected area after dark can often result in surprising observations. If there is still nothing readily observable, then setting some pitfall traps can be useful. Pitfall traps can be a small plastic cup buried flush in the soil. A small amount of liquid in the bottom will help to contain the insects that fall into the trap. Traps should be left for at least 24 hours but preferably longer and are generally useful for catching insects that actively move across the ground.

To learn more about insect monitoring, including step-by-step instructions, equipment needed, and the pros and cons of the different techniques available, visit our new web-based tool pestIQ.