Mid West potatoes: seed production, pest and disease management

Insect pest management

To produce quality seed and consumer potato crops, follow the principles of integrated pest management:

• Gain confidence to recognise pests, beneficials and benign insects.
• Monitor weekly.
• Base decisions on insecticide use on action thresholds for pest abundance that vary for seed and consumer potato crops.
• Be aware of registered insecticides and their toxicity to beneficials.

If at the time of inspection, any aphids (green peach aphid, Myzus persicae or potato aphid, Macrosiphum euphorbiae) are found in the crop, the grower will be advised that aphid control has not been sufficiently effective and that steps must be taken.

If aphid numbers are considered excessive, the following action will be taken:

• A sample of 100 randomly selected leaves (a middle and lower leaf from 50 plants) will be examined for the presence of aphid colonies. A colony is defined as a leaf containing three or more aphids of which at least two are wingless.
• If more than five colonies are found, the crop will either be rejected immediately or the grower may choose to submit a sample to test for potato leafroll virus (PLRV) and potato virus y (PVY).

If an excessive number of aphids is found at the first inspection, leaves may be sampled at the second inspection and tested for aphid-transmitted viruses. If excess aphids are found at the second inspection, tubers will be sampled at harvest and tested. The number of samples taken must be adequate to determine compliance with the tolerances set out in the WA Certified Seed Potato Production Scheme Rules, July 2013.

Make yourself a monitoring kit which includes the identification guide references listed in Emery et al. 2005 (see Table 3 for a list of pests and page numbers) and the video Managing Virus Diseases of Potato Crops: Potato leafroll and tomato spotted wilt (2003). Potato tuber moth and leaf eating ladybird are minor pests in the Mid West. Photos of these insects do not appear in these guides.

A ‘bum bag’ is also useful containing a 10x hand lens, collecting vials, notebook (waterproof paper and 2B pencil, paper bags and self-seal plastic bags. Monitoring information should be recorded electronically to allow comparisons across seasons.

To protect seed potato crops planted in autumn (March to early April) from early aphid invasion, apply systemic insecticide to the soil at planting. This does not appear to be necessary for winter-planted crops because aphids usually appear later in the crop cycle by which time the activity of any seed applied insecticide would be too low to be effective. Soil-applied insecticide at planting is not required for ware crops because virus levels are less important compared with seed potato crops and natural enemies, especially wasps, help reduce aphid numbers to acceptable levels.

For both ware and seed potato crops, follow a regular insect monitoring program from crop emergence to die-off.

In centre pivots, check two opposite quadrants of the planted area. Follow a circular path through the crop quadrant to ensure a representative area is covered. Monitoring should include 50 destructively sampled leaves in each quadrant up to canopy row closure then 25 leaves thereafter.

Check the undersides of lower, healthy leaves for aphids (Figure 1) and aphid mummies (parasitised aphids) and thrips. Record the occurrence of other insects on leaves and the presence of pests such as potato moth, tobacco looper, Rutherglen bug, Heliothis and beneficial insects such as ladybirds, lacewings, predatory bugs and beetles, and hover fly larvae.

Figure 1 Monitor the underside of leaves for insects such as green peach aphid with nymph present here

For seed crops to the start of senescence, apply aphicides if aphids are present at up to 5% of leaves infested with winged and wingless aphids.

Be aware of the different toxicity levels to beneficial insects of registered insecticides and choose the least toxic (see Table 4). To avoid developing resistance, alternate insecticides. There have been reports of green peach aphid developing resistance to pirimicarb.

Roguing (seed crops only)

Before seed crops reach row closure, undesirable plants should be removed by roguing. Tips on how to rogue crops can be seen on a video (Managing Virus Diseases of Potato Crops: Potato leafroll and tomato spotted wilt 2003).