keep your beans pest-free
How to
keep your beans pest-free
Our latest baseline
agronomy article provides
some timely advice to help
growers keep winter and spring beans free from pests,
weeds and diseases
Winter Beans
Dont change your agronomy and management of winter beans this year, just because they were drilled late, advises Anthony Biddle of PGRO. "They will catch up, but will be a bit late to harvest. However, theyll stay standing until you are ready to combine."
The second week in May is the right timing for the first chocolate spot spray, which should be done just as flower colour is showing, with a mix of chlorothalonil with Ronilan (vinclozolin) or products such as Compass (iprodione+thiophanate-methyl).
"A second spray is needed four weeks later and a triazole should be added to the chlorothalonil which will help control rust. Having tebuconazole or cyproconazole in the second spray gives this additional activity."
Rust has over-wintered on volunteers and could be a big problem this year, he believes. "If it comes in late, the beans get too tall for spraying. So control has to be done with the second chocolate spot spray or you risk damaging the crop."
The other issue with winter beans is that saturated soils mean they may not have received simazine pre-emergence for weed control. "Then the only option is Basagran, applied before flower buds are visible."
Spring beans
Like the pea crop, late-drilled spring beans will be at risk from the pea and bean weevil if the pest appears when plants are still small.
"Look for U-shaped notches around the leaf edge," advises Dr Biddle. "And spray at the first sign of damage with a pyrethroid, especially where seedbeds provide shelter for the pest."
Black bean aphid is also expected to need control because plants will be at the vulnerable stage when they arrive and numbers were high last year, so more aphids will have over-wintered. The spray threshold is when 5-10% of plants have colonies, especially if colonies start during flowering. "Theres a choice of products and no resistance problem, so control isnt difficult or expensive."
Chocolate spot is unlikely to be a problem where drilling was behind the normal schedule. "The crop wont grow too tall and plant populations arent high. So spring beans should escape the disease."
If rust is seen at flowering, spraying should be done with tebuconazole while growers can still travel. Downy mildew also comes into the spring crop regularly, and the risk this year will be no different.
"There is on-going work on predicting downy mildew," says Dr Biddle. "The variety Compass has very good field resistance to the disease, so it will be interesting to see how it performs this year."
Bruchid beetle
Bruchid beetle over-winter as adults and a warm, sunny spell for 3-4 days determines when they fly into crops.
"If they fly early in the season, they will feed on winter beans and the spring crop might escape," says Dr Biddle. "Normally they arrive at the end of May and look for flowering beans. If that is the case this season the spring beans wont be susceptible."
Spray timing is critical. Control should be done before the first pods are seen, when 5-6 flower trusses are open. "Once the eggs have been laid on the pods, its too late," says Dr Biddle. "Spray choice is between Decis (deltamethrin) or Hallmark (lambda-cyhalothrin)." *
Keeping beans clean from now to harvest will be essential to help struggling crops maximise output. PGROs Anthony Biddle (left) urges all growers to pay close attention to input thresholds in the coming weeks.
WINTER&SPRINGBEANS
• Winter Beans
• Chocolate spot control – two sprays starting second week of May.
• Incorporate rust control with second chocolate spot spray.
• spring Beans
• Spray for pea and bean weevil at first sign of damage.
• Black bean aphid threshold is 5-10% of plants with colonies.
• Chocolate spot unlikely to threaten.
• Bruchid beetle control when 5-6 flower trusses are open.