New acaricides to tackle return of mite problem – The Fruit Grower – Jonathan Blackman

A few years ago it seemed that IPM strategies had solved problems in orchards with predators like typhs and anthocorids controlling them naturally. ...

But now a combination of climate change and the restriction of acaricides has seen them return to become a serious problem once again.

A run of hot summers and mild winters in the South East has encouraged populations of fruit tree red spider mite to build up. Also two-spotted spider mite a new pest to many apple growers, is now being found in orchards. Predators will take care of both mite species but not at the speed of the lifecycle of the two-spotted spider mite which is much quicker to reach the adult stage than fruit tree red spider mite.

Mild winters have also brought forward the hatching of red spider mite eggs by almost a month to mid-March. Damage may not be seen during the nymph stages but leaf bronzing caused by adults becomes evident in July and can continue until September along with fruit russeting. In the first year of attack economic damage may be avoided but trees will have been weakened, so they enter the second year with depleted reserves leading to poor flower initiation. Yield losses of 20% to 30% are possible.

At the same time, IPM strategies have been disrupted by the necessity to use less IPM-friendly products to control woolly aphid in apples and pears and spotted wing drosophila (SWD) in neighbouring tunnel-covered cherry and soft-fruit crops. As a result, many orchards have seen a fall in predator numbers. Several of the most widely planted apple varieties – Gala, Jazz, Discovery and Braeburn – are also highly susceptible to red spider mite.

This spring Certis is introducing two new acaricides – Nissorun (hexythiazox) and Kanemite (acequinocyl) – which bring new hope of getting mites back under control.

Certis IPM manager Semo Kurtev says: “Both are target-specific treatments that are safe to natural predators and will facilitate IPM strategies.”

Nissorun is authorised for use as an acaricide for the control of two-spotted spider mite (Tetranychus urticae) in hops, pome fruit and fruiting vegetables, and Semo says it also has activity against tree fruit red spider mite.

Experience in French apple orchards suggests that if there is high pest pressure it should be applied between mouse ear and green cluster. Jonathan Blackman, Horticultural Technical Manager for Hutchinsons says: “It should be applied in April as it is best on eggs and recently-hatched nymphs, but with no effect on adults. It’s very selective, meaning that it’s safe to typhs.”

Semo agrees and says that if used early like this, Nissorun can provide season-long protection. But with only one treatment permitted per year, he stresses the importance of good coverage.

“It is contact-acting so good coverage is essential. Apply in sufficient water to optimise wetting of the leaves throughout the canopy and use the maximum concentration of 26ml/100 litres of water.”

Kanemite is authorised for use as an acaricide for the control of two-spotted spider mite and fruit tree red spider mite (Pananychus ulmi) in pome-fruit and stone-fruit. It also has an EAMU for use as an acaricide on hops to control two-spotted spider mite. As with Nissarun, only one treatment per year is permitted.

Active on all stages of pest mites including eggs it is considered a key acaricide in Spain and France. Semo says that it is the ideal product to follow Nissorun if the mite population bounces back later in the season. “With rapid knockdown and a new IRAC mode of action 20B, it is complementary to Nissorun and will aid resistance management.”

These two new acaricides could change the way we tackle mites. He advises: “Use Nissorun from early March onwards if crop walking detects their presence. Then, as there is a side effect on mites from the use of Batavia at petal fall/early fruitlet, check the population again via crop walking. Follow up with Kanemite if the population bounces back from May onwards. The natural beneficial population should be building up by then to take over for the rest of the season.”

With the increasing use of polytunnels and rain covers for cherry production, the two-spotted mite has become a big problem as the extra heat encourages rapid development of damaging populations. To add to the problem, SWD and aphid sprays severely reduce natural predator populations in cherry orchards.

Varieties can display individual sensitivity to sprays. Regina Kordia and Merchant showed no phytotoxicity when treated with Kanemite in 2018 with double the recommend rate.

Kanemite to be a good fit for modern systems as there are such limited options for mite control in cherries and it has a harvest interval of only 21 days. Kanemite offers cherry growers timing flexibility for controlling mites in a crop that has limited conventional options. It should be applied pre-flowering before the covers go on or after flowering as it is not detrimental to predators.

For hop growers damage from two-spotted spider mites can be very serious as, in addition to affecting the growth of the plant, it reduces the essential oils in hop cones which lessens the brewing value. Recently this damage has, in some instances, been wiping up to 20% off farmgate values.

There have been very limited acaricide options for hops for at least two years so the emergency authorisation for Kanemite last year and the year before 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 a day”. Jonathan stresses, “You must get good coverage as Kanemite works by contact action and ingestion if the mites feed on sprayed tissue”.

British hop growers now have the benefit of two authorised acaricides with hops on the Nissorso label and Kanemite with an EAMU and have been so delighted they took to Twitter to thank Certis.

Semo emphasises that the ideal timing opportunity for Nissorum is to apply to early growth at BBCH37, as this is ideal for the lifecycle of two-spotted mite and will require less product as the Target bine is only two-thirds of its way up to the top wire. If this opportunity is missed, or the spider mites are still present, he advises application of Kanemite when the bines have reached the top wire at BBCH55 and inflorescence buds are enlarged.

For both acaricides the approval is for one treatment only. There are important buffer zones, protective glove safety water, volume and spray concentration requirements to note on the product label and EAMU. The harvest intervals are 28 days for Nissorun and 21 days for Kanemite.

Future developments

Semo has good news for other growers with spider mite problems in their crops. Applications for EAMUs are to be submitted for Kanemite on cane and bush fruit post-harvest for one application per year. Nissorun EAMUs for strawberries are being applied for at one application per year with a three-day harvest interval.

Jonathan Blackman sums up the potential impact of Kanemite and Nissorun for fruit and hop growers: “Both are well respected acaricides in Europe, they are IPM-friendly, their activity is very selective they are safe to typhs and have shorter harvest intervals than alternative products like Apollo”.

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