Get on top of spider mites early – The Fruit Grower – Jonathan Blackman
Starting early to reduce spider mite populations can save money and allow natural enemies to take over and keep a balance in orchards and hops ...
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 Certis was to use Nissorun (hexythiazox) as soon as crop walking detected a presence which could be from early March in apple orchards, and follow up with Kanemite (acequinocyl) if the population bounced back from May onwards. But it is hard to change the habits of a lifetime.
Targeting eggs and larvae when there are few adults to be seen can be counter-intuitive for growers who are used to waiting for numbers to build into a target big enough to be worth treating. And with just one spray of each in the armoury growers understandably fear running out of options in the summer when previously numbers exploded.
However, the first year of commercial use has 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’ lifecycles and starting earlier.
Jonathan Blackman, Horticultural Technical Manager
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 that they missed the opportunity to use Nissorun and then had to apply Kanemite at the maximum dose of 0.9 litres/ha in 1,000 litres of water to achieve coverage of the crop. Henry says: “if left late like this, often the crop is so dense that the best efforts to achieve 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 in the season by dealing with overwintered 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 that 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 applying, for example, 0.13 litre/ha of product in 500 litres/ha of water rather than being forced up to 0.39 litres/ha in 1,500 litres/ha of water. 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 to 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 that 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 Kanemite to get things back under control,” adds Henry.
“If you start low it’s easier to stay low,” is how Jonathan Blackman, Horticultural Technical Manager at Hutchinsons, 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 because they worry about having nothing left 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 that encourages spider mite populations to explode. However, Jonathan says that 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 the control options are so limited, and it has a harvest interval of only 21 days. The need for its use is greater because so often beneficials fall victim to broad spectrum robust spotted wing drosophila (SWD) programmes. The messages here are very similar. Henry Welham 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
For hop growers spider mite damage particularly two spotted spider mites, can be very serious, with the quality of hop cones being reduced by an uncontrolled outbreak.
The loss of Agrimec (abamectin) in hops, left growers short of effective acaricides, so the emergency EAMU for Kanemite in 2018 and 2019 was very welcome, according to Jonathan Blackman: “It can be very effective, with quick knockdown 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 much like those for tree fruit, and sometimes application needs 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, in April. May applications would have been too late in 2020 due to a very warm dry spring. He recommends that, 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.
Jonathan also stresses that spraying in spring when only 200 litres/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 1,500 litres/ha water would be required and a higher dose rate of Kanemite.
Email Us