Crop Watch May 2021

2021 Blackspot manager forecast

The Blackspot Manager early forecasts point to a high to medium risk of blackspot in seedling field pea crops sown early to mid-May across South Australia in 2021.

View Blackspot Manager forecasts

Actual disease severity will also depend on rainfall patterns during crop establishment since moisture is necessary for the spores to germinate and infect the plants.

Numerous rainfall events will increase disease severity, but if dry conditions persist and there are few rainfall events then very little disease will eventuate irrespective of spore numbers.

What you can do to reduce crop disease risk

A number of actions can reduce your crop disease risk:

• Aim to plant this year’s crop at least 500 m from field pea stubble, and if downwind from the stubble, where possible, increase this distance up to 1 km since the spores are windblown.
• Delay the sowing date by 2-3 weeks past opening rains in medium to high rainfall districts where this is unlikely to compromise yield. The spore numbers in the air will reduce over the 2-3 week window and reduce the blackspot risk. Note, delayed sowing is not an option in low rainfall short season districts as associated yield losses will be greater than losses caused by blackspot disease.
• Consider fungicide strategies as an option in crops that have a yield potential of at least 1.5 t/ha. P Pickel-T seed dressing will reduce infection on seedling crops, and foliar fungicide sprays will reduce the spread of the disease. Sprays can be applied between 4-8 nodes; apply at 4 nodes if disease is present but delay towards 8 nodes if disease is not evident. A second spray is at early flowering to reduce spread of the disease in spring. For maximum effect, spray ahead of a rain event, since spores are spread during rainfall. Post rain spraying is generally ineffective. A number of products are registered for blackspot of field peas. Note label restrictions for chlorothalonil with respect to grazing stock.