With Solenopsis mealybug widespread throughout QLD and confirmed in WA, NT and VIC, and mostly recently in the Macintyre valley, growers and consultants are encouraged to remain vigilant in monitoring for this pest.
Please note: all new or unusual detections of mealybug need to be reported. In NSW, call the Plant Pest Hotline on 1800 084 881. In QLD, call DAF on 13 25 23.
What to look for:
Growers and consultants are encouraged to keep an eye out for mealybug and mealybug hot spots:
- Solenopsis mealybug adults are 3-4 mm long and have two characteristic dark longitudinal bare spots across their thorax and abdomen (look like black spots).
- Mealybugs will build up in very large numbers on the tops of a small group of plants and form a “hot spot” of dead or dying plants.
- Mealybug are more likely to be prevalent in crops that are stressed, so particular attention should be paid to these areas (eg tail drains, lighter soil).
- As well as looking in crops, it is worthwhile scouting any volunteers, or hosts (eg pigweed or fleabane) that are near cropping areas.
- Mealybug have a very wide host range, so it may be useful look in surrounding vegetation including gardens, to give an indication if they are in the area.
There have been a number of factors that make this year high risk. The mild, wet winter and wet spring has encouraged higher than usual numbers of wild hosts that support overwintering populations. Surveys have shown a link between mealybug incidence and the presence of alternate hosts. Crop destruction and control of hosts including volunteer cotton will need to be a priority immediately after picking. The increased pest control required due to high pest pressure and ongoing hot temperatures will have impacted beneficial numbers, making the risk of a mealybug flare up much higher.
Mealybugs are best controlled by beneficial insects and there are currently no effective insecticides registered. Pest control should aim to preserve the natural enemies that include:
- Predators Common ladybeetles, Cryptolaemus ladybeetle, lacewings, smudge bugs, earwigs, native cockroaches.
- Parasitic wasp – Aenaisus bamabwalei, a parasitoid of Solenopsis mealybug are reasonable wide spread and are effective in suppressing populations.
What to do if you find them:
- Correct identification. While there is a high probability that you have found Solenopsis mealybug, there are other similar looking species that occasionally occur in cotton but rarely cause crop damage. The beat sheet blog link below includes good photos to help with ID, however if you are unsure email a photo to firstname.lastname@example.org
- Reporting. All new or unusual detections of mealybug need to be reported. In NSW, call the Plant Pest Hotline on 1800 084 881. In QLD, call DAF on 13 25 23.
- Mark the plants they are on, as they can be difficult to locate when in low numbers. Mealybug colonies can disappear between checks due to predation. Re-checking marked plants will enable you to judge the efficacy of any natural enemies that are present and also provide an indication of the species present when it comes to making future spray decisions and selecting options that best conserve them. Tagged colonies also provide an indication of the potential disruption that a spray decision might have had as mealybug will quickly increase in numbers when natural enemies are removed.
- Look for the presence of natural enemies. It is highly likely that there will be other colonies elsewhere in the same field, and evidence of predation and parasitism and whether or not the solenopsis colony is growing or dwindling in number will provide a picture of what is will provide you with a picture to what is occurring in your field at a broader scale.
- Come Clean Go Clean. While mealybug can be transferred by wind or water, people and machinery movement can rapidly expand the rate of spread. Wash down machinery going from heavily invested hot spots to fields without any mealybugs. Clothes may also carry bugs such as mealybugs. Aim to visit fields with mealybug last, and brush clothes down before hopping into vehicles.
For more information:
- The Cotton Pest Management Guide has the most up to date information regarding the relative impacts of the different insecticides currently registered in cotton.
- The beat sheet blog is also a good source of information and photos of key beneficials.
- Richard Sequeira, QDAF, has been leading a program of extensive pesticide and ecology research on mealybug and can be contacted on 07 4991 0810 or via email@example.com if you have concerns.
- Watch the three CottonInfo videos from Paul Grundy, QDAF, on mealybug: mealybug in cotton, mealybug hotspots, and what to do if you find a mealybug hotspot.