Integrated systems for managing nematodes on bananas

Abstract

Burrowing nematode is a major constraint to banana production worldwide. In Australia, routine use of nematicides has been the most common control strategy. However, these chemicals are expensive, toxic and declining in efficacy due to enhanced biodegradation. This project aimed at developing nematicide application strategies to prolong the usefulness of currently registered nematicides, determining the economics of nematicide application in the subtropics, the efficacy of biological control, the resistance of banana cultivars to nematodes and alternative methods of treating vegetative banana planting material.
A nematicide rotation strategy where nematicides were changed after each application was able to significantly improve the control of nematodes compared to continual application of the same product and an untreated control. The rotation of nematicides was able to reduce nematode damage below the economic threshold after four applications, which meant that treatments could be omitted. The rotation strategy was able to slow the development of enhanced biodegradation of soil applied nematicides and allowed nematicides that were being degraded to recover. Severe degradation of one organophosphate nematicide was found to increase the likelihood that other organophosphate nematicides would also develop enhanced biodegradation.
Nematicides were not cost effective in sub-tropical banana production. Improved crop management such as irrigation, regular fertiliser application, weed control and deleafing were able to increase the bunch weights of bananas, whereas, the application of nematicides was not.
The injection of the systemic nematicides Vydate 240 L ® and Nemacur 400® into the pseudostem of the following sucker was found to be as efficacious as soil application of nematicides. However, there was an increased risk of phytotoxicity damage, such as stem splitting, particularly when using Nemacur 400®.
Compost was able to suppress the number of nematodes in the roots of banana plants and maintain high levels of plant growth compared to sterile potting mix. This appeared to be due to an increase in the suppressive microorganisms around the roots of the plants. Endophytic fungi and bacteria isolated from nematode suppressive soils were able to suppress the number of nematodes on the roots of banana plants when added into the potting mix of tissue cultured banana plants.
No alternative method of disinfesting banana bits from burrowing nematode was as successful as the currently registered practice using Nemacur 400®. Cold temperatures, bleach and Vydate 240 L ® were all unsuccessful at reducing nematode numbers in banana bits. However, Nemacur 400® dipping did not eliminate all nematodes from the planting material.
A survey of current nematode management practices used by banana growers revealed a decrease in the use of nematicide. 61 % of growers in 1994 used a nematicide whereas only 39 % of growers in 2003 had used a nematicide in the past 12 months. The survey also revealed an increase in banana growers awareness of the nematode status of their crops and how to manage plant-parasitic nematodes in bananas.
A nematode management pyramid has been developed to combine all the information derived from this and previous nematode management projects for the banana industry.