Diseases affecting our crops

LUSH CROP: Agronomist Paul McIntosh talks about diseases affecting the region's mung bean crops.
LUSH CROP: Agronomist Paul McIntosh talks about diseases affecting the region's mung bean crops. Contributed

LAST summer season I had quite a few calls about bacterial diseases affecting our mung bean crops.

Last year was perhaps the worst year I have observed the halo blight disease in some mung bean crops in different areas.

Talking to Lisa Kelly from the Department of Agriculture and Fisheries plant pathology team has given me a better understanding of this bacterial disease.

Firstly, what is a bacterial disease? Bacterial plant pathogens are single cell organisms and these organisms develop toxins that invariably break down leaf tissue.

They can arrive on healthy leaf tissue from outside events like rainfall or irrigation.

If wind is blowing the raindrops, then deposition on sensitive leaves can be much further afield.

They land on the healthy leaf surface and move into the leaf surface through small leaf wounds or the natural stomata opening, usually during high humidity situations.

After entering plant material, it can then be seven to 10 days before the symptoms become visible in the desirable temperature range of about 20degrees Celsius.

The obvious symptoms many of us know is the small lesions with the yellow green halo around them - an all too visible sign last season.

Unfortunately we have no control means to prevent these infection sites developing, and of course it can also be a seed-borne infection in our mung bean paddocks.

Then there is the added complication of a plethora of host weeds like cowvine and bellvine, plus many other bean and pea plants.

Even harvesting machines can be a spread mechanism of this bacterial disease from plant material to intended planting seed, so it is a pretty serious disease this bacterial disease called halo blight.

As I said at the start of the article, I believe last year was the worst year I had seen it in southern Queensland, so sourcing the cleanest mung bean seed - which comes from heavily inspected paddocks that the AMA seed scheme orchestrates from - is a fair start.

I also suspect that breeding resistance into new varieties will be our best defence to these bacterial disease like halo blight - and I include the other bacterial disease of tan spot in these deliberations.

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