Avoiding root rot in peas

Press, 19 February 1988, Page 12

Avoiding root rot in peas

SPURT HIIBh imon-iTOR

Common root rot of peas (caused by a soilborne fungus, Aphanomyces euteiches) is a serious disease for which no chemical controls or resistant cultivars are available.

The only practicable control measure is disease avoidance, i.e. not planting peas in paddocks with a high disease potential. This potential can be measured by a pre-plant soil test, a service provided by the M.A.F. Plant Protection Centre at Lincoln.

Farmers can use this service by submitting soil samples from paddocks intended for peas this year. All samples should be accompanied by the appropriate form which will be available from your local M.A.F. office or stock and station agent from mid-March.

A minimum sample of four litres of soil is required per paddock. The test cannot be done if less than this amount is provided.

Soil for testing can be submitted to the centre any time between the end of March and mid-July. As tests take about six weeks to carry out, growers are advised to submit samples as early as possible.

Crop hygiene Now that most arable and seed crops have been harvested, growers should be planning for the next season.

The disease status of a paddock is an important factor to be considered when selecting future crops.

Many diseases can be carried from season to season in the soil, on stubble, debris or on alternate hosts. These diseases include take-all, foot-rot, eyespot, glume blotch of wheat; scald and net blotch of barley; downy mildew of peas; Ascochyta leaf spots on peas and lentils; and dry rot of brassicae crops. If your crops suffered from any soil-borne diseases this season, the guidelines below will help to reduce risks of inflection in future.

© Crop rotation is an essential part of managed disease control. For most crops, a rotation of three years (combined with other practices suggested below) is adequate; with root crops such as potatoes, the rotation should be at least six years. © Early cultivation will help to break down stubble and crop debris thus ensuring that disease carryover is reduced. © Stubble burning will also reduce pest and disease carryover.

© Control of volunteers during the winter season will elimate the greenbridge effect whereby diseases overwinter on volunteer host plants. © Weed control will help to reduce diseases

that can survive on alternative hosts, such as take-all on twitch. Stonefruit Brown rot may be troublesome because of the recent warm, humid weather. Rovral and Ronilan can be used pre-har-vest on all stonefruit and Saprol on all except nectarines and plums. Orchards should be monitored for brown rot and sprayed where necessary. © European red mite and two-spotted mite populations have been abundant in some orchards. Unfortunately, control will be difficult in blocks that have not been harvested. If there is more than a fortnight until picking, Omite can still be applied to reduce numbers of immature mites. Apply a clean-up miticide spray post harvest. Peropal and Omite will control nymphs and Neoron will control all stages. Pipfruit The recent warm humid weather has created ideal conditions for black spot infection. Orchards should be carefully monitored for this disease, cover sprays maintained and eradicants used when necessary. However, make sure

that withholding periods are observed.

Pasture Most farmers are now aware of the significance of the ryegrass endophyte in relation to grass staggers and .insect damage. ;

A ryegrass line of known low or high endophyte level may be sought for a particular purpose on the farm. The Lincoln Plant Protection Centre is able to test seedlines or plants for endophyte content.

Total endophyte levels can be estimated in new season’s seedlines and viable endophyte levels can be estimated in seed stored for longer periods. These are useful tests whether the seed is for sale or for use on farm. O Damage from Argentine stem weevil larvae has occurred in low endophyte ryegrass pastures. Control in established pasture is not economic.

If oversowing with new pasture, consider using a high endophyte ryegrass or else drill low endophyte seed with a registered granular insecticide down the spout. Another alternative is to delay sowing until early March when adult weevils stop laying eggs, and activity declines.