Home > Control Fallow

Control Cotton Volunteers to Prevent Cotton Bunch Top Disease
2/04/2008

Cotton bunchy top disease (CBT) has been found widely in cotton crops and on non-cultivated cotton plants this cotton season. This disease is capable of stunting the growth of cotton plants, and if plants are infected when young, of dramatically reducing yield. CBT is spread by cotton aphids when they feed.

Both cotton aphids and the disease need a host plant for survival through winter. It is likely that CBT uses a range of weeds as hosts, but this has not been studied. However, cotton is a good host and volunteer or ratoon cotton plants can be found on farms all year.

These volunteer or ratoon plants and can carry the disease and aphids through winter. Aphids can then move to cotton crops in the following spring and infect plants with the disease.

Rod Gordon, Cotton CRC extension officer said that the regular rainfall through the summer has encouraged growth of cotton volunteers, many of which were glyphosate tolerant and difficult to control with herbicides.

“Wet fields meant growers had limited opportunities to control volunteer cotton with some fallow fields and field margins containing quite high densities” he said.

“However, the importance of controlling your volunteer cotton in fallows cannot be stressed enough, it is extremely important to minimise your weed hosts, this is critical to ensure that we do not have another disaster similar to the incidence of the Cotton Bunchy top of 1998”.

CSIRO and Cotton CRC Entomologist Dr Lewis Wilson said “In recent sampling trips with Dr Grant Herron (NSW DPI) we found cotton volunteers on virtually every farm, and sometimes plants were very large, suggesting they had survived since last season.”

“Many of these volunteers showed clear symptoms of cotton bunchy top disease, such as angular leaf mottling and small leaves. We also often found CBT affected cotton plants in cotton fields in proximity to the volunteer plants.”.

“Wetter conditions through winter could favour the growth of weeds that are hosts for aphids and also increase survival of cotton volunteers that carry CBT to the next season.Growers should maintain good farm hygiene to reduce the risk of aphid or CBT problems next season” Dr Wilson said.

Mr Gordon said “Growers on farms who experienced problems with CBT in the last season could control cotton volunteers and consider planting a ‘non-host’ rotation crop, such as a winter cereal”.

Cotton aphid has a broad host range and has been recorded on members of the following families.

Fabaceae (legumes, lucerne),
Solanaceous weeds (datura, ground cherry, nightshades),
Cucurbitaceae (paddymelon),
Malvaceae (bladder ketmia, marshmallow),
Asteracae (sunflower, capeweed, daisies, thistles, bathurst burr,).

A more complete host range can be found in the IPM Guidelines, available from the Cotton Catchment Communities CRC office or website (www.cottoncrc.org.au).

Please Contact Dr Lewis Wilson on 02 6799-1550 or 0427 991 550 or Rod Gordon on 07 4671 6711 or 0428 879 900