There’s lots of pest activity in southern Ontario hazelnut orchards at this time. New eastern filbert blight infections are getting ready to burst through bark. Gypsy moth, aphids, scale and bud mite are all active in orchards, as are their natural enemies. and Japanese beetles are starting to take flight.
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Eastern Filbert Blight
Symptoms of previous year’s infections are starting to appear as raised bumps in the surface of the bark of infected hazelnut trees. These will be the spore-producing structures, or stroma, which will eventually break through the outer bark later in the summer, and then mature into the more familiar raised black stromata. These bumps are easy to miss and more readily spotted on trees with known EFB infections. Infections on recently infected trees may not be noticeable until the dark black stromata become apparent after leaf fall, however severely infected twigs or branches may die suddenly, with the leaves clinging to the branch, which can flag the presence of cankers.
It is important to remember that because of the multi-year life cycle of this disease, raised bumps appearing now are not the result of this spring’s infections, but (for newly infected trees) entered the tree in the spring of 2020, or are part of an older, expanding canker. Infections that occurred this season will be growing inside the trees, with no visible external symptoms.
At this time, cankers with mature black stromata will only be present in orchards if they were missed during winter pruning. If found, these should be removed and destroyed to remove inoculum from the orchard. However, be aware that other issues may affect trees that can resemble eastern filbert blight. One of these look-alikes is shown in the photo below. These are egg laying scars of the snowy tree cricket. This is a minor feeder on hazelnut leaves, with little impact on the trees, however females lay there eggs in a series of holes that she makes in the bark. These can initially look to the inexperienced eye like a canker, but upon closer examination, you can see that they are series of holes, rather than a raised black fungal structure. If you split affected twigs open, you will see eggs contained in the hole.
By this time, many growers with susceptible varieties such as Jefferson have made multiple applications of protective fungicides. Many growers have been wondering when they can stop spraying. Unfortunately, this question does not have an easy answer yet in Ontario. In Oregon, where most EFB research has been done, the rule of thumb is to make roughly four applications at 2-week intervals from budswell until 8 weeks later. With budbreak occurring in many southern orchards in April, that would put the final spray in June, if we followed the Oregon guidelines. However, differing environmental conditions in Ontario may make the period of disease susceptibility longer here.
In order to cause new infections, the EFB fungus needs wet conditions and rapidly growing new tissue. Oregon has very rainy springs, but conditions get extremely dry by early June. In Ontario, rainy conditions can persist well into the summer. Furthermore, in Oregon, which has warmer winters, stromata release spores from winter through spring, although there is no tissue to infect until budbreak. In contrast, it is likely that in Ontario, the stromata become dormant during freezing winter temperatures. This means that there may be a higher load of spores present in EFB cankers during an Ontario spring than in Oregon.
So what does this mean for deciding when to stop spraying for EFB? We just don’t know for sure at the moment, but Dr. Katerina Jordan and her research team from the University of Guelph have an OMAFRA-funded project to conduct multi-year field trials in Simcoe to look at the EFB infection period and its effect on spray intervals for EFB on hazelnuts. These trials just began this spring, so hopefully we will have some better guidance once results become available in a few years. In the meantime, we are estimating that the high risk period for infection in Ontario likely ends once there are prolonged dry periods, and the growth of new tissue has slowed considerably. In the U of G-Simcoe spray interval trial, the last fungicide spray was applied this week.
Gypsy moth larvae have reached the late instar stage in most areas – once larval yellow heads have turned yellow and are longer than 2.5 cm, they are no longer susceptible to biological insecticides based on Bacillus thuringiensis, although other products will have an impact on larvae. There are no pest control products specifically registered for gypsy moth on hazelnuts in Ontario, however products registered and applied for other spring-feeding caterpillars (especially leafrollers) should also provide control of gypsy moth. See OMAFRA Publication 360E, Crop Protection Guide for Tree Nuts.
Gypsy moth have been controlled in many orchards where early applications of Bt-products for caterpillars were made. To look for stragglers, be aware that these older larvae tend to hide in protected areas during the day and can be more cryptic than earlier instars. Look for them hiding along branches or twigs or at the base of tree trunks. Larger instar larvae do the most feeding and can remove significant leaf material from hazelnut trees, especially small ones. Due to an extended egg hatching period, there are several different larval instars present in hazelnut orchards, with some very small larvae mixed in with the larger ones. Larvae will feed for another 7-14 days, and then pupate on trunks and branches, after which there will be no more feeding this year.
We are also getting reports from forested areas of gypsy moth larvae succumbing to infections of Nuclear Polyhedrosis Virus (NPV), which is an indication that the natural diseases of this insect are starting to catch up with populations. Hopefully these natural enemies will be able to start to bring down the epic populations we have been experiencing over the past few years.
This has been a banner year for aphids in many crops, including hazelnuts, possibly due to the early onset of warm temperatures, which favors their development, in combination with other factors. We have seen unusually high numbers of aphids in several hazelnut orchards, especially in those orchards where broad spectrum insecticides were used for caterpillar control, which reduced populations of natural enemies that normally keep them in check. Aphids drain fluids from hazelnut leaves and buds. They often do not need to be controlled in hazelnut orchards, but if populations get high enough, they can cause distortion and wilting of leaf tissue and may event reduce nut fill and size. There are no thresholds for aphids in Ontario, but in Oregon, a threshold of 30-40 aphids/leaf after checking 3 leaves/terminal on 3 terminals/tree on 20 trees, warrants control. If scouting shows many infested leaves, with numbers increasing over time and limited activity of natural predators or parasites, then pest control product application may be warranted.
Fortunately, recently there have been signs that natural enemies are starting to increase in hazelnut orchards. All stages of lady beetles are being observed in hazelnut orchards in southern Ontario. Adults are familiar beetles – oval, convex and brightly coloured with spots. Larvae are also distinct – they are black with prominent yellow-orange patches and covered in spines. Pupae are dark or yellow-orange, hunched in appearance and are attached to leaves.
For more information on beneficial insects that might be present in your orchard, refer to the beneficials section of Ontario Crop IPM (http://www.omafra.gov.on.ca/IPM/english/apples/beneficials/index.html).
Lecanium scale is also present in higher than normal numbers in many hazelnut orchards. The protective covering is still present as bumps on twigs and stems, however eggs have now hatched into tiny crawlers. Baby crawlers are still under the shell and consequently protected from any insecticide sprays or natural enemies. These crawlers will move onto the leaves in the next week or so, after which they will be more susceptible to insecticide sprays, if required.
Ladybeetles and other predators will also feed on scale crawlers, so control may not be required in orchards with high numbers of natural enemies. Some growers have noticed 2 different colours of scale in orchards and wondered if they are dealing with 2 different species. Black-coloured scales are typically dead – if you lift up the covering you will generally see liquid instead of live crawlers.
Now that trees are fully leafed out, buds infested with bud mite are easily spotted. Affected buds are swollen, enlarged, often fail to leaf out, or produced distorted leaves and will stand out among trees. If you split open these swollen buds, you will see fairly large numbers of tiny, cigar-shaped white worm-like mites in the decayed interior tissue. This suggests that mites have not completed their annual migration from old buds to developing new ones. Predatory mites can sometimes be seen within the buds, feeding on the bud mites. There is nothing registered for bud mite control on hazelnuts. In smaller orchards, affected buds can be removed from trees.
They’re back….Japanese beetles have started to emerge
A Japanese beetle was spotted in the Simcoe Research station orchard yesterday, which means adults are emerging and starting to take flight. These are large, shiny green and copper beetles with a very wide host range that includes hazelnuts. Adult beetles feed on the upper surface of leaves, chewing tissue between veins and leaving skeletonized foliage with a lace-like appearance. Mature trees can generally tolerate this feeding damage but very young trees, or those which have already sustained feeding damage from other insects, such as gypsy moth, can be more severely affected. Beetles often begin by feeding in the upper canopy, so it is important to check the tops of trees for early feeding.
Monitoring traps for Japanese beetles are not necessary, because adult beetles are very conspicuous and easily spotted. If in small orchards with small trees, beetles can be knocked off trees into a bucket of soapy water. This should be done as beetles appear, before there is significant feeding damage, since damaged leaves release chemicals that can attract more beetles. There is nothing specifically registered for Japanese beetles on hazelnuts, however some products that growers may be applying for caterpillars or aphids may have some effect on Japanese beetle. Refer to OMAFRA Publication 360 E, Crop Protection Guide for Tree Nuts and consult Table 3-3 – Activity of Insecticides and Miticides on Hazelnut Pests.