Choosing the best pesticide programme can have a significant impact on input costs, crop health and environmental footprint.

Diamond Back Moth (DBM) and Cabbage Root Fly (CRF) are on the radar for Lancashire-based agronomist John Ball.

DBM has been as bad this year as it was in 2016, but there is a significant difference in the two infestations.

In 2016 it was suspected that the pest had migrated directly from Asia, whereas this year it is indigenous but a resistance to some pesticides had already built up by the time the problem arrived in the UK.

Thankfully the availability of Verimark (cyantraniliprole) which was unexpectedly given approval in 2016 has basically saved a potential disaster from happening.

In 2017 DBM was evident but only at low levels. This year, after an initial flush, levels subsided and did not return. However, I’ve seen a lot of cabbage white and silvery moth.

Left unchecked, these pests can render a crop unsaleable due to leaf damage.

The challenge with DBM is that it stays on the underside of the leaf so can’t easily be seen or treated with sprayer applied pesticides.

CRF control challenges coupled with Dursban (chlorpyrifos) Maximum Residue Level (MRL) decrease and product availability means the pressure is on for growers to protect remaining options, including Tracer (spinosad) and Verimark for next year.

Dursban is recognized for causing low-level phytotoxicity issues too, resulting in crops being knocked back. This can affect crop uniformity and evenness, ultimately making harvest more time consuming and challenging.

Verimark does not have the same negative impact on a crop’s health, which makes harvest easier, potentially in one pass.

Ultimately yields are not affected where Dursban has been used but the cost of harvest is. The key is to get plants away as quickly as possible after planting.

This year Verimark really came into its own. Getting the crop established early meant that the subsequent hot weather we experienced had less impact on the development of the crop. 

Tracer is a good alternative, but it doesn’t have the control persistency that Verimark offers. It must be applied correctly as a drench as it has very little movement through the plant. Its control comes from the active ingredient being held in the growing module, which can produce inconsistency in protection.

Verimark is the most reliable and consistent product for controlling DBM and CRF.

It moves up the plant systemically into new growth, offering six to eight weeks activity, which is the time a crop needs to establish.

By comparison, Tracer only gives four to six weeks control provided it has been applied correctly. 

Verimark takes out a broader range of pests too, including caterpillar and also gives some suppression of aphids.

In high-pressure situations it takes more than just Verimark to control aphids and monitoring is key to identify application thresholds. 

But because caterpillar can cause crop failure the key is to get a good establishment and this means using Verimark early.  

Timing is critical.

Early establishment allows a crop to build a leaf frame, which leads to a consistent head formation and potentially higher yields.

Tracer is only effective at controlling caterpillar when applied as a foliar application and only when the pest has been observed, but arguably this could be too late because the damage will have already been done.

However, growers must continue to monitor crops and local caterpillar populations throughout the growing season and if necessary follow up the Verimark drench with a foliar application of Ruma (indoxacarb) or Tracer.

It's very important to be aware of the moisture deficit when working out a pesticide strategy. The 2018 season was a good example of this because plants stopped growing due to the extreme heat and there was a reduction in control of caterpillar and aphids where Verimark had been applied because the active ingredient was not being moved around the plant as effectively. 

Cabbage root fly control was unaffected and as a result, earlier applications of foliar insecticides were required. Other insecticides were also affected unless irrigation was used. Importantly, growers must not base their control strategies on cost alone.

Although Verimark is expensive it is the most effective control option. To rely only on foliar acting pesticides would be counterproductive in the long run.

Agrovista trials have shown that Verimark can improve rooting by up to 43% compared to those treated with Dursban and this can make all the difference to a crop grown under stressful and drought-like conditions.