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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:
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.”
“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.”
Alan T. Eaton, Extension Specialist, Integrated Pest Management
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