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As the 2010-1011 cotton season gets underway, mealybugs are again present in cotton crops in Emerald at low to moderate levels, DEEDI senior entomologist Dr Melina Miles reports.

The exotic Solenopsis mealybug was first detected in Australian cotton in the Burdekin in the 2008-09 cotton-growing season.  In the 2009-10 season, Emerald experienced an outbreak of the Solenopsis mealybug (Phenacoccus solenopsis).  

In 2010 the impact of the solenopsis mealybug stunted cotton plants, and in severely infested fields, this resulted in the death of plants.  While a high proportion of fields were infested, the area of severely damaged crop was relatively small. However, there are many questions now emerging about this new pest and its potential impact on cotton in Central Queensland and beyond in future seasons.

In response to the outbreak, the industry has swung into action in the region. Research has been initiated by Department of Employment, Economic Development and Innovation DEEDI entomologists, in collaboration the Cotton CRC, CSIRO and NSW I&I to gain a greater understanding of the mealybug.

Throughout winter, entomologists surveyed five fields that had a 2009 mealybug infestation from post-harvest through to planting. In all cases, mealybug persisted on broadleaf weeds, ratoons and volunteer cotton in and around the fields.  In-crop weediness over winter appears to be closely associated with the size of the infestation this season. However, there are instances where excellent weed management has resulted in a very low level of mealybug so far this season. 

Dr Melina Miles, Principal entomologist with DEEDI said that due to the cool weather and a delayed planting in Emerald, the mealybug population was not as established as it was this time last season.

“Two weeks ago, when crops were surveyed, female mealybug were established on cotton plants, but there was little reproduction. In other words, the population had not begun to grow rapidly. In some fields infested plants were showing signs of stress, reddening and stunting,” Dr Miles said.

Overseas, mealybugs are reported to move on air currents in the small crawler stage; through irrigation and tail water; and by contaminated vehicles and personnel entering fields.  This species, also identified in Texas in 1990 and in Pakistan and India in 2004 has caused significant economic loss within those cotton industries.  Native predation has declined significance of this pest in those countries in recent years. Species including lacewings and ladybirds and, in particular in India and Pakistan, parasitic wasp have been effective. 

Infestation by crawlers may be alleviated by controlling weed hosts in and around cotton fields. Managing the movement of vehicles and people in and between infested fields also needs to be a priority. 

In addition to the Burdekin and Emerald, solenopsis mealybugs have also been identified throughout the Darling Downs and St George; although only individual, or small infestations have been found at these locations. Other samples of mealybug from cotton-growing areas in NSW and Qld have been identified as the native species from the genera Ferrisia, Pseudococcus and Planococcus. This evidence further suggests that 2009 was a year conducive to mealybug being abundant.

In terms of research, the goal for 2010 is to gain some confidence in effectively minimising the impact of solenopsis mealybug infestations in cotton.

Key areas that will be addressed include:

•  efficacy of control options,
• understanding how populations develop in the field,
•  the impact of natural enemies on mealbug 
• characterising the impact of mealybug at different stages of cotton plant growth.

For further information on control of mealybug in cotton, contact Susan Maas at Emerald mailto: susan.maas@deedi.qld.gov.au or phone 07 4983 7403

The Cotton CRC has an information pack on pest control and details of who to contact.  Go to: www.cottoncrc.org.au – search for ‘mealybug’ or go to the DEEDI website: http://www.dpi.qld.gov.au/4790_16221.htm