Introduction
A component of the approach to developing control measures for nematodes in carrots is, at least in the short term, to identify alternative chemical control measures. In Western Australia this has been prompted by the failure of metham sodium and fenamiphos (Nemacur) to provide reliable nematode control. There are few nematicides available in Australia that were considered potentially suitable for use on carrots.
Both root knot nematodes (Meloidogyne spp.) and root lesion nematode (Pratylenchus spp.) have been responsible for damage to carrot crops in Western Australia.
In late 2001, both Telone (active ingredient 1,3 dicloropropene, Dow Chemicals) and the Telone/chloropicrin mixture called Telone C35 were registered in Australia for nematode control on vegetable cropping land.
In Western Australia, Telone C35 became available before Telone and commercial scale trials with Telone C35 commenced in 2001. Both products require injection into the soil using a tyned injection rig. Telone is of greater interest as a nematicide for carrots as it is less than half the cost per hectare of Telone C35. Telone C35 however has a broader fumigation activity than Telone and should help control a range of soil-borne diseases.
Myalup site
On a commercial vegetable farm near Myalup, south of Perth, Telone C35 was applied to an area with a root knot nematode history. A control section was left untreated within the block and both treated and untreated areas were monitored for nematode infection.
Contractor Glen Jones of Duratech applied Telone C35 at 270kg/ha on 31 December 2001 and carrots (cv Stefano, South Pacific Seeds) were sown into the area on 23 January 2002. Plant samples were taken on 26 February 2002 and again on 19 March 2002. At the first sampling very few root knot nematode egg masses were detected however by the second sampling high levels of nematode infection were observed (Table 1).
It was noted that crop in the Telone C35-treated area had markedly greater vigour than the untreated area.
| Treatment | Taproot | Taproot and/or lateral roots |
|---|---|---|
| Untreated | 26.4 | 48.7 |
| Telone C35 | 1.2 | 2.2 |
Nematode infection in seedlings was reduced from 48.7 per cent in the untreated area to 2.2 per cent in the Telone C35 area (Table 1).
At the final harvest carrot samples from each area were washed, graded and weighed. Results are presented in Table 2.
The strong trend was for carrots from the Telone C35-treated area to be higher yielding and of better quality than from the untreated areas. Total yield was 14 per cent higher in the treated area and similarly export packout was 33 per cent higher. The proportions of misshapen and forked roots was reduced in the Telone C35 treated block (Table 2).
Veining was more severe in carrots from the Telone C35 treated block (Table 2). Observations are that veining is a physiological disorder that is more severe in vigorous crops. Reduction in early fertiliser application in fumigated crop could help reduce the incidence of veining. The grower observed that weevil damage to roots was reduced with fumigation.
|
| Untreated | Telone C35 |
|---|---|---|
| Plant density (/m2) | 51.1 | 54.2 |
| Total yield (t/ha) | 86.0 | 98.2 |
| Export yield (t/ha) | 37.4 | 70.2 |
| Short market (t/ha) | 0.4 | 0.0 |
| Export (%) | 40.3 | 71.5 |
| Forked (%) | 19.9 | 3.4 |
| Misshapen (%) | 37.6 | 15.9 |
| Veined (%) | 1.7 | 8.8 |
In soil samples taken at harvest, Meloidogyne spp. counts after four week extractions averaged 0.3 for each 200g of soil from the Telone C35-treated block and 251 from the untreated block.
Fumigation with Telone C35 before planting improved carrot yield and quality on this site. Based on the yields recorded in this trial, the increase in export yield of 32.8 tonnes per hectare at $280 per tonne would improve gross income by over $9000 per hectare.
Gingin site
Telone by itself has been trialled by growers for nematode control. On one property near Gingin, north of Perth, high levels of root lesion nematodes (Pratylenchus ssp.) had been damaging carrot crops. Telone was applied at 100kg/ha however the application was not uniform and some rows within the crop were growing on treated areas while others appeared to have received little chemical.
The crop developed a striped appearance with stunted yellow rows (no Telone) among vigorous green rows (+Telone). Soil and plant samples were taken from these areas. Pratylenchus counts were as follows:
| Soil (100g) | Roots (g dry root) | |
|---|---|---|
| No Telone | 106 | 14 962 |
| +Telone | 0 | 295 |
Pratylenchus numbers extracted from roots were more thab 50 times higher in the untreated area, while numbers averaged zero from the treated soil and more than 100 per 100mL from the untreated soil.
Conclusion
Telone and Telone C35 were highly effective in reducing nematode infection and associated symptoms in carrots. Telone is an effective alternative to metham sodium and fenimaphos for nematode control in carrots.
The registration and availability of chemicals for pest, disease and weed control changes regularly. Consult a trained and experienced horticultural agronomist or the Australian Pesticides and Veterinary Medicines Authority (APVMA) website for chemicals which are currently registered or have a permit for use on this crop.
The information on the label or permit for a chemical must be followed, including the directions for use, critical use comments, withholding period and maximum residue limit. Quality assurance (QA) schemes for horticultural crop production require producers to have current information on chemical registrations readily available.
Registered chemicals should be used in conjunction with cultural management practices as part of an integrated pest management program. Chemicals used are to comply with resistance management strategies.
Acknowledgement
This work was conducted by Elaine Davison and Allan McKay as part of a Horticulture Innovation Australia Ltd and National Vegetable Levy funded project coordinated by Frank Hay, University of Tasmania.