Limited chemical armoury and insecticide resistance will mean growers must practice ‘the science of doing nothing’ to make crops more resilient to pest attack, according to Dr Steve Ellis, research scientist at ADAS.
Speaking at the AHDB agronomists’ conference, Dr Ellis said: “A lot of new actives coming to the market are very expensive so we’re starting to question whether its cost effective to apply them.
“Thresholds are an important part of IPM and we’ve had them for years, but if we look at insecticide usage it suggests that we tend to err on the side of caution.”
Dr Ellis pointed out that just because there is insect damage, it does not necessarily mean yields will be affected.
“Physiologists have shown us that crops can tolerate pest attack and we can measure that in certain instances.”
On average oilseed rape will produce up to 200 excess buds per plant, and winter wheat will have up to 600 extra shoots per plant. AHDB work has determined that a pollen beetle will consume roughly nine buds, and a wheat bulb fly will destroy about four tillers.
Dr Ellis said: “We know pests like slugs, flea beetle and pollen beetle all reduce green leaf area. So rather than measuring numbers of slugs or flea beetle, why don’t we concentrate on trying to elucidate the relationship between green leaf area and yield? If we can measure green leaf area accurately we can get an immediate indication of whether that is going to impact the yield of the crop.”
This means there are fewer thresholds to survey and assessments can be made more precisely.
“As plant populations increase, excess bud numbers decrease. By simply measuring your plant population you immediately get an indication of the potential tolerance of that crop to pollen beetle in terms of the number of excess buds it has.”
Citing OSR and pollen beetle as an example, Dr Ellis said that on average, oilseed rape will produce up to 200 excess buds per plant, with bud numbers decreasing as plant populations increase.
Using these figures and based on an average OSR plant population 45 plant per sq.m, the control threshold for pollen beetle is 20 pollen beetles per plant, he said.
“That has only been exceeded in three per cent of crops monitored since 1981,” he added.
“So immediately we can go out and assess plant populations early in the new year and get an indication of the crop’s resilience to pollen beetle and make a decision then about whether or not we need to protect it.”