Canterbury pea crops susceptible to root rot

14-04-2010 | Not Specified

A FAR survey of pea crops in Canterbury has shown root rot is the most common disease affecting crop yields.

FAR chief executive Nick Pyke discussed the survey results with farmers at a FAR field day in Southland.

The survey of 40 paddocks during December, 2008, and January, 2009, showed the root rot disease fusarium solani was present in 83% of the crops. The initial aim of the research was to determine the impact diseases have on crop yield. They measured the effects of disease on seed and straw weight in four paddocks. There was an average of one tonne/hectare difference in yield between the diseased and healthy parts of the paddocks.

Surprisingly, no clean crops were found in the overall survey. The incidence of disease within and between crops was highly variable, ranging from 20% for some crops to as high as 85%. The median for all crops in the survey was 51%.

Crop yields were lower than expected and they were also surprised at the number of diseases identified.

Ascochyta was not the major disease present. The most common were: root rot - solani 83%, root rot - oxysporum 75%, chaetomium globosum 65%, root rot - phoma medicaginis 53%, and other fusarium were identified in 63% of the crops.

Chaetomium is a secondary fungus that invades plants after they have been infected by pathogens such as thielaviopsis basicola and aphanomyces euteiches, making these diseases difficult to culture and identify.

Pyke says it is hard to control soil-borne diseases with fungicide treatments.

While there are no specific recommendations for controlling root diseases there are some in-furrow treatments that can be used to treat the soil ahead of the seed during sowing. Some in-furrow fungicide products can have a detrimental effect on seed germination.

It is important for farmers to be vigilant and check crops regularly to look for unhealthy plants. Identifying infected plants early and seeking specialist advice will help maximise crop yield. Plants affected by black root rot have a reddish appearance in the area going down to the tiller.

FAR is also reviewing the cropping history of the paddocks in the survey to determine if there is a relationship to the incidence of diseases.

The research to date suggests the longer the period between legume crops in a paddock the less chance there is of root diseases developing.

The foundation has extended its survey area for 2009-10 to include the Wairarapa and Southland. The aim is to focus on pea crop management and disease issues that are relevant to geographic areas throughout NZ. Extending the survey will also help identify whether disease repeats from year to year.

Future research is aimed at comparing disease pathogens and finding the most effective control methods. It will also include studying different crop rotations and comparing disease susceptibility of different pea varieties.

The research will also compare the effect different tillage methods (conventional, minimal and direct drilling) have on crop yields.

FAR is also conducting trials on Faba beans in mid-Canterbury.

The trial crops are achieving crop yields of 6t/ha. Pyke says the trials are in their early stages and they are still in discussion with potential users.

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