Get on top of mites early

Starting early to reduce spider mite populations can save money and allow natural enemies to take over to keep balance in orchards and hops.

Jonathan Blackman, Horticultural Technical Manager, H L Hutchinson
Henry Welham, Certis technical specialist

A year ago, the launch of two new acaricides was heralded as bringing new hope of getting mites back under control, if growers changed the way they tackled the pests. The new approach advocated by manufacturer Certis was to use Nissorun (hexythiazox) as soon as crop walking detected presence, which could be from early March in apple orchards, and follow up with Kanemite (acequinocyl) if population bounced back from May onwards.

But it’s hard to change habits of a lifetime and targeting eggs and larvae when there are few adults to be seen and it can be counter intuitive for growers used to waiting for numbers to build into a sizeable target worth treating. And with just one spray of each in the armoury growers understandably fear running out of options in summer when previously numbers exploded.

The first year of commercial use has however shown that the opposite is true and that growers can make significant savings and achieve much better control than previously by understanding how the product is affecting the pests’ life cycles and starting earlier.

Think about both mite pests

Henry Welham, technical specialist at Certis emphasises: “We want growers to be proactive in their approach to both mite pests: fruit tree red spider mite and two-spotted spider mite. These two mite pests should be thought about and a strategy planned early rather than having to react to pest pressure.”

Last year in many situations growers didn’t deal with mites until there was significant pest pressure. This meant they missed the opportunity to use Nissorun and then had to apply Kanemite at the maximum dose of 0.9L/ha in 1,000L water to achieve coverage of the crop. Henry says: “If left late like this, often the crop is so dense that best efforts to achieving adequate coverage and therefore efficacy fall short.”

His advice to tree fruit growers this year is to start with Nissorun. It’s a product that has an extremely good IPM profile and will help alleviate the pressure later on in the season by dealing with over wintered spider mite eggs as well as early stages of the pest. When applied early it can be used in sensible water volumes as the canopy is less dense making coverage much easier to achieve. By ensuring the maximum concentration is used in line with water volumes the dose required will often be much lower than the label maximum. This can make the difference between using, for example, 0.13L/ha of product in 500L water per hectare early rather than being forced up to 0.39L/ha in 1,500L water later in the season. In other words, as soon as you start to see spider mites, get on top of them quickly. If you wait until there is a very large dense canopy you will struggle to get coverage and therefore efficacy. This is especially important when the pest tends to hide on the undersides of leaves.” The IPM profile of Nissorun and Kanemite is excellent too so Henry says: “You’re helping your beneficials stay in control. Go early, get covered, get control and allow your beneficials to do the rest!”

Growers have the peace of mind that the background populations of spider mite have been taken care of while protecting beneficials. This adds some flexibility and in a low risk year means beneficials may be able to handle the rest of the season without any additional help from products. “If the season becomes conducive to spider mite population explosion, then growers know that they still have the use of Kanemite to get things back in control,” adds Henry.

“If you start low it’s easier to stay low,” is how Jonathan Blackman horticultural technical manager from H L Hutchinson sums up the approach tree fruit and hop growers should use to control spider mites. “It boils down to a numbers game when controlling spider mites,” says Jonathan. “They are a problem only if numbers get out of hand so start early with control to keep the numbers low. It’s welcome that Certis have brought Nissorun and Kanemite to the market as we have lost or are losing so many acaricide products.”

Growers wary of mid-summer explosion

The problem has been that growers are wary of using acaricides early in spring because they worry about having nothing left later in the year in July. They are concerned that, as both Nissorun and Kanemite can only be used once, they should keep them in the armoury to use later in case we have a hot dry summer which encourages spider mite populations to explode. However, Jonathan says if you start early there will be a much-reduced population of mites come summer so even if it does turn very hot the natural predator population will have a greater chance of keeping the pests in check.

Richard Killian, fruit agronomist and technical coordinator, at Agrii stresses: “It’s all about balance. A proactive approach with Nissorun and Kanemite maintains the balance between predatory mites and pest mites. This allows for natural suppression through the remainder of the season.” In a trial last summer on mature Gala trees at the Agrii i-farm at East Malling comparing Nissorun and Kanemite with industry standards, mite control was just as good but with the added benefit of being IPM friendly.

In cherries only Kanemite is approved for spider mite control and is a good fit for modern systems as control options are so limited plus it has a harvest interval of only 21 days. The need for its use is greater because so often the beneficials fall victim to broad spectrum robust SWD programmes. The messages here are very similar. Henry at Certis emphasises: “We are still wanting cherry growers to be proactive in their approach to using Kanemite – don’t leave it too late. Monitor pest pressure, and understand that intervention is often needed. When the pest pressure outweighs the capabilities of beneficial insects to maintain control, Kanemite helps bring things back into balance.

Start early in hops too

For hop growers’ spider mite damage, particularly two spotted spider mites, can be very serious with the quality of hop cones reduced by an uncontrolled outbreak.

The loss of Agrimec (abamectin) in hops, left hop growers short of effective acaricides so the emergency EAMU for Kanemite in 2018 and 2019 was very welcome according to Jonathan Blackman at H L Hutchinson “It can be very effective with quick knock down of mites. It immobilises the mites and they are dead within two days”. Jonathan stresses that “you must get good coverage as Kanemite works by contact action and ingestion if the mites feed on sprayed tissue”. Certis has worked hard to get approvals for their two acaricides for hops in the UK. From 2020 Nissorun has on label approval and Kanemite has off label approval.

The messages for hop growers are similar to those for tree fruit and sometimes application has to be even earlier than with apples. Jonathan’s experience last year with using Nissorun on hops was that the best control came where it was used early during April. May applications would have been too late in 2020 thanks to a very warm, dry spring. He recommends if two-spotted spider mites are found in spring, using Nissorun to get on top of them at the start of the season controls the eggs and recently hatched nymphs. Kanemite which targets adults can be kept for later if required.

He also stresses that spraying in spring when only 200L/ha of water is required to get good coverage whilst sticking to the maximum concentration will significantly reduce the cost of an application compared with later in the season when 1,500L/ha water would be required and a higher dose rate of Kanemite.

More on Kanemite and Nissorun can be found here

Article originally published in Fruit Grower.

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