Tag Archives: European apple sawfly

May 25, 2016 Volume XII No. 3

 Fruit Bud Stages

In Durham and Madbury, McIntosh apple buds were at fruit set on Monday May 23rd. Blueberries were in bloom. Raspberries had many flower buds visible, but unopened.

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Apple Scab

We usually expect the primary apple scab season to start winding down now, but will not end for a while… probably early June. It is a good time now to do a check for apple scab lesions, and it would be very important to do that again about 10 days after primary season ends. The 10 days allows enough time for the latest lesions to become visible.

Weather Data, Prediction Models

Although the riskiest time for fireblight has ended for some NH orchards, I’ll give links I have been mentioning at twilight meetings and orchard visits. They can help with a number of pest events. One is Glen Koehler’s Orchard Radar. This link takes you to the radar page, and there may be sites relatively close to you that are worth checking out. Groton Massachusetts or Sanford Maine may be relatively close to some NH growers.

A second source of information is NEWA, the Network for Environmental and Weather Applications. We have one NH orchard with a NEWA station, Brookdale in Hollis. You can view the data and predictions for fireblight, (and apple scab, curculio, potato late blight and lots of other pests). Look at the map, and enlarge it to find the icon for Hollis, then clicking on it to get predictions for that site. If you’re far from Hollis, another option (maybe not quite as accurate) is to click on an icon for a nearby airport, on the NEWA map. Eventually we hope to have more NEWA sites in NH. Funding for some of that equipment is anticipated soon. We’re still waiting to hear on a second grant proposal.

Plum Curculio: Most Important Apple Insect Pest?

Plum curculios overwinter as adults, in leaf litter in the woods. They become active about when apple blocks are in bloom. They heavily depend on odor to find apple trees. Once there, attack must wait until the fruit reach 6mm in size. Then the females cut a shallow curved scar into the fruit, and lay an egg under the flap. Fruit that are attacked usually drop to the ground, and in some spots there are enough curculios to attack nearly 100% of the crop. The larva hatches from the egg and tunnels through the fruit. When mature, it drops to the ground and pupates in the soil.

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The attack period generally lasts about 3 weeks, but in sites with lots of nearby wild apples, it can extend longer. Basically, we use insecticides to control this insect. The insecticides are harmful to pollinators, plus parasites and predators of leafminers, aphids, caterpillars and mites. If we can minimize spraying, it helps preserve populations of these beneficial organisms and save money.

One way to minimize spraying is to wait to apply the first one until just before the first fruit reach 6mm size. Another option is to time your applications with the aid of a degree day model. My colleagues in New York developed one that some NH growers find useful… and others say it doesn’t work so well for them. It says to keep apples protected through 340 degree days (base 50) after petal fall. [By the way… petal fall in Durham was Friday May 20th. Did you write down your PF date?] We expect that some pesticide residue will continue to control them for a little while past that. This model doesn’t work too well in blocks with a history of heavy, long-lasting pressure. I would not rely on it completely, but it might help you determine when you can stop. In most blocks, three weeks after the first fruit reached 6mm size, there should be no significant immigration of new adults, and spraying can cease.

The insecticides we target for curculio also control the first generation of several other fruit-attacking insects: codling moth, lesser appleworm, and redbanded leafroller. They also control insects that rarely are a problem in commercial blocks, but can be serious in backyard trees: tent caterpillars, gypsy moths, winter moth, green fruitworms. The most effective for curculio: probably (alphabetically listed) Actara, Avaunt, Calypso, Imidan, Leverage and Voliam Express. The last two are combination products. For backyard growers, Sevin is probably the best alternative, in part because it is packaged in appropriate sizes. All-purpose fruit sprays are too drastically diluted to control curculio. For organic growers, Surround is the best choice, but it has to be applied very carefully to work properly. That means you need several thorough but dilute applications. Surround doesn’t kill them. It just interferes with their host recognition (and thus, attack).

European Apple Sawfly

This is now a relatively minor pest, but fruit that are attacked have a long, curved scar that greatly reduces the fruit’s value. EAS adults emerge from the soil during pink stage. The females are very active in the flowers during bloom. That’s when they insert their eggs singly into the tiny fruitlets at the calyx end. In a few orchards, growers have enough trouble with this insect that they apply an insecticide at pink to control it, knowing that the first curculio spray will also help. But in blocks that have varieties with a range of petal fall dates, that curculio spray is slightly late to stop some EAS damage. My data shows that the incidence of EAS injury at harvest in NH (25 year average) has been below 3/10ths of 1 percent… so not very serious.

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Blueberries: Mummyberry and Fruitworms

Blueberry growers take note: the fungal stipes of mummyberry fungus should be releasing ascospores now during rainy periods. The spores infect tiny opening blueberry leaves, where the fungus grows and produces conidia. The conidia are splash-spread spores, and they infect the fruit, while it is still green. At first, infected fruit are symptomless, but when ripening time arrives, they turn tan and shrivel up. Some of our varieties that are especially susceptible to the disease are Bluecrop, Blueray, Earliblue, Jersey and Berkeley.

We have two species of fruitworms that attack blueberry. One is called the cherry fruitworm, and the other is cranberry fruitworm. I see a lot of highbush plantings, and in a few of them there is enough fruitworm attack to consider an insecticide treatment. In most, the attack rate is so low, the cost of treatment is probably higher than the value of the damage it would prevent. If you do decide to apply an insecticide, the timing is right after bloom ends. Usually one treatment is enough. It is designed to kill the just-hatched caterpillars.

Clipper in Brambles and Strawberries

Strawberry bud weevil is also known as “clipper”, because it attacks the unopened flower buds of brambles and strawberries, then chews off the buds in which it laid an egg. There is only 1 generation per year, and they overwinter as adults. When flower buds are present but unopened (= NOW), that is when this insect attacks. Attack rate is usually the highest in the edges of the fields, and lower in the interior of the plantings. In strawberries there are thresholds established, and you can read about them in the New England Small Fruit Management Guide. Thresholds have not yet been determined for brambles. Notice in my blackberry photo that all of the brown fruit buds are the ones that have been attacked, and are dangling.

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Alan T. Eaton
Extension Specialist
Integrated Pest Management

The University of New Hampshire Cooperative Extension is a public institution with a longstanding commitment to equal opportunity for all. It is the policy of UNHCE to abide by all United States and New Hampshire state laws and University System of New Hampshire and University of New Hampshire policies applicable to discrimination and harassment. It does not discriminate on the basis of race, color, religion, sex, national origin, age, veteran’s status, gender identity or expression, sexual orientation, marital status, or disability in admission or access to, or treatment or employment in, its programs, services, or activities.

 

May 28, 2014 – Volume X No. 4

Fruit Bud Stages In Durham

At the Woodman Horticulture farm in Durham, fruit buds on Monday May 26 were: Pioneer McIntosh Apple: fruit set. Japanese plums: fruit set. Peach: petal fall. Blueberry: bloom.

Apple Scab

In Durham, we are at the end of the rapid maturation phase of ascospore development, and now spore maturation slows down as we enter the final phase. Cheryl Smith did squash counts on May 28th in Durham and found 17% of ascospores were immature; 12% were mature, and 71% had already been released.  These figures might be off a bit, since some of the empty asci shrivel and are difficult to spot. Also, some of the “immature” spores will never finish development.

The apple scab degree day models for Durham as of the morning of May 28th show 730 DD accumulated; equivalent to about 94% spore maturation. Cold temperatures and daytime rain are forecast for today, and warm temperatures & showers are predicted Friday May 30th, and possibly Saturday 31st. Primary apple scab season will be over soon. Remember that it takes 10 days (longer in cold temperatures) for infections to become visible on the leaves.

Plum Curculio Injury

Expect plum curculio injury to begin any time after the first apple fruitlets reach 6mm (1/4 inch) size. They may enter the orchard before that, but can’t begin fruit attack until then. If we have warm temperatures (70F or higher), that really helps kick-start activity, and if we have a warm night (70F or higher) with rain, that really gets them going, too. Typically they stay active for about 3 weeks, but that varies. Some spots have lots of wild apple trees nearby, and thus have a longer PC risk period than average. A few lucky spots have slightly shorter period of activity. Some growers look at nearby unsprayed apples, to see if they have fresh PC scars. I have a close up photo of really fresh injury, to help. Notice that the cut is slightly curved, about 2 – 3mm long. If it is really fresh, then there is no discoloration or healing of the exposed surface.

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My colleagues in New York developed a predictive model to tell when to apply last PC spray: keep apples protected through 340 degree days (base 50) after petal fall. We expect that some residue will continue to control them for a little while past that. This model doesn’t work too well in blocks with a history of heavy, long-lasting pressure. I would not rely on it completely.

For conventional growers, the most effective PC insecticides: Actara, Avaunt, Calypso, Imidan, Leverage and Voliam Express. The last two are products that combine two different insecticides. For backyard growers, Sevin is the best material that is available and packaged in backyard-garden sizes. Most backyard fruit spray mixtures are much too diluted to control plum curculio. For organic growers, Surround is the best choice, but it has to be applied very carefully to work properly. You start right at petal fall, and make a dilute, thorough application. You don’t want bright white splotches on the leaves, separated by gaps. You want a very thin, translucent coating. Then you apply another perhaps 2-3 days later. Good protection starts with the second or third application, provided rain doesn’t wash everything off. Surround doesn’t kill PC’s… it just stops them from attacking. That means the attack period is longer than with conventional insecticides… about a month.

Caterpillars Inside Apple Fruit

Codling moth and lesser appleworm are two species that bore inside the fruit. They are both common here. Look at fruit from wild trees, and you’ll find plenty of examples. In most New Hampshire commercial apple orchards, these two species plus redbanded leafroller (feeds externally on the fruit) are controlled by insecticides directed at plum curculio and apple maggot. All three caterpillar species have two generations per year here. The first generation is usually well controlled by our curculio sprays, except in some organic orchards. If a Bacillus thuringiensis-based spray is used, the timing for CM and LAW is 2-3 days after fruit set. Often, a second treatment is required perhaps 5 days later. These usually work well on redbanded leafroller and various foliage feeders: tent caterpillars (a bit late for them), white-marked tussock moth, green fruitworms and gypsy moths too.

The second generation is more likely to be troublesome, partly because it is not as synchronous as the first. For either generation, a hole in the fruit, together with some fine dry brown frass is a likely sign of attack. CM seems to prefer to attack via the calyx end (as in my photo), while the others are a bit more variable in their attack sites. Telling the larvae apart usually requires a microscope. One fairly reliable sign: if the caterpillar fed on the seeds, it is likely to be codling moth.

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In June, you might find a fruit with European apple sawfly larva inside. They look a lot like caterpillars (read below).

European Apple Sawfly

In the last issue, I showed injury from the first instar of European apple sawfly (EAS). It has the classic curved shape, beginning at the calyx end of the fruit. The adult sawfly flies during bloom, and lays her egg in the calyx. The tiny larva hatches a few days later and feeds just barely below the skin of the fruit for several days. That makes the long, curved scar. Next, it usually moves to an adjacent fruit and bores a hole inside. That’s where it completes its feeding for a couple weeks. Fruit infested with these later stage larvae have an orange stain and messy, wet reddish-brown frass coming from the hole. The fully grown larvae drop from the fruit during the last days of June, and overwinter in the soil.

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Although the larvae look like caterpillars, you can tell them from caterpillars by counting legs and body segments. Behind the head are three body segments (the thorax), each of which has a pair of legs. That’s true for both caterpillars and sawfly larvae. But here’s where it is different. In caterpillars, the next two body segments behind the thorax NEVER have legs attached. In sawflies, either one of those segments, or both of them have a pair of legs. My photo of a nearly mature EAS larva is below. Because of the way it is curled up, it is a little difficult to count the legs, but it is the best I’ve got.

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Before I move on to insecticides for EAS control, I’ll answer another common question. How do I tell EAS larvae apart from plum curculio larvae? It is easy. PC larvae have no legs.

The insecticides that control most European apple sawflies are applied at or right after petal fall. If the material is sprayed right at petal fall, it stops the first instar larvae so quickly that there are few or no long, curved scars. If the grower decides to delay the petal fall spray, to wait until fruit have reached 6mm size (therefor aiming primarily at plum curculio), then the EAS larvae aren’t killed until after they have made their curved scars. More growers seem to be delaying the spray, and accepting a little bit of EAS injury now, hoping to control curculio with fewer sprays. In most sites, that seems to be a good decision, since I find well under 1% of the fruit at harvest with EAS scars.

White Apple Leafhoppers — Check Soon After Petal Fall

White apple leafhoppers lay their eggs in the fall, inside apple twigs. The eggs hatch at petal fall. Three to five days after petal fall is a good time to search for the just-hatched nymphs. If you had any spots in the orchard with WALH problems last year, you may want to check (especially those hot spots) before you plan to spray for plum curculio. If you find 25 or more nymphs on 100 leaves, it is worthwhile to apply an insecticide for leafhopper. Some insecticides will get both WALH and curculio.

To check, look at the undersides of CLUSTER leaves. Leafhopper nymphs are translucent when first hatched, and after a couple of days begin to look greenish yellow.

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Blueberry Pollinators and Cheaters

Blueberry flowers have long, narrow corollas, so bees that want to reach the nectar need long tongues. Some species “cheat” and cut a hole through the side of the corolla, therefor bypassing the anthers, and not helping to pollinate that blossom. I understand that some carpenter bees do this, but there may be others as well.

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Strawberry Clipper Also Attacks Bramble Fruit

Strawberry bud weevils, a.k.a. “clippers” attack strawberries, raspberries and blackberries. The tiny female weevils search these plants when the flower buds have appeared but have not yet opened. When they find a suitable one, they lay an egg inside the bud, then sever it at the pedicel. The buds sometimes dangle for several days before they drop off.

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Inside each attacked bud is a tiny egg that hatches and the tiny legless larvae feed for a couple of weeks, then pupate inside the bud, like in my photo. Later in the summer, the adult weevils emerge, leaving a hole in the dropped buds on the ground. They feed for a while before preparing for winter. There is only one generation per year, and the attack period is May to early June. Flowers that appear in July, August or September are not attacked.

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I have not seen any threshold published, to tell us how many clipped buds, or how many active adults per row foot make it worthwhile to spray for clipper on brambles. I have noticed that damage can be severe, especially on blackberries. I find that it is often worse on rows that border brush or woods. When the fruit buds appear, they are vulnerable to clipper until the flowers open. Checking just before the first flowers open is a good time… you could apply an insecticide (if you wished) before pollinators started visiting.

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On strawberries, thresholds are listed in the New England Small Fruit Management Guide. In strawberry beds, usually clipper damage is less severe on new beds, compared to older ones. As in brambles, it is usually worse in the rows next to woods or fallow fields. Some strawberry varieties have been shown to compensate for clipper damage by having the remaining fruit get larger. Unfortunately, most varieties haven’t been evaluated for this trait, so we only know about a few. Varieties that compensate well (therefor clipper damage isn’t much of a problem): Jewell and Senecca. Primetime and Lateglow are varieties that compensate somewhat, so clipper can be more of an issue. Cavendish, Earliglow, Honeyoe and Northeaster show no compensation for clipped buds.

Updated Directories from NH Department of Agriculture, Markets & Food

Gail McWilliam-Jellie just advised me of their recently updated directories, now available:

Harvest Your Own and Farm Stand

She says, “These do not include every farm that could possibly be listed, but includes a fair representation. We would like to make this as comprehensive a list as possible and can add farms at any time. We welcome you to spread the word among the farms you work with about the directories and the opportunity to be listed (for free). We will be promoting these throughout the season through various channels, so it’s another marketing avenue for the participating farms.”

Farm Stand and/or Harvest Your Own Sign-up Form

“Additionally, our 2014 Summer Season Farmers Market Directory is also on line. The directory currently has about 2/3 of the markets that were operating last year. Frequently, market contact information changes from one year to the next and the new year sign-up doesn’t get to the right person. If you don’t see markets from your area on the list. Please pass this on to the market organizers so we can make this as complete a list as possible.”

2014 Summer Season Farmers Market Directory

Market Registration Form

 

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Alan T. Eaton, Extension Specialist, Integrated Pest Management

Visit the Extension IPM page.

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