May 3, 2016 Volume XII No. 2

 Fruit Bud Stages

In Durham and Madbury, McIntosh apple buds were in late tight cluster stage on Monday May 2nd.  Almost all of our peach buds appear dead.  Blueberries are at pinkbud stage.  Raspberries and thornless blackberries are still ½ to 1 inch of growth from the buds.

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Apple Scab

We are at the part of the season when we normally expect high numbers of ascospores to be ready for release, and there is a lot of susceptible apple tissue. That makes it a high risk period for apple scab. The spring has been fairly dry, and that might affect ascospore maturation, but for now, I’d assume the risk is high, whenever that next daytime rain falls.

Fireblight

As we approach the bloom period, remember that warm (60F or higher) rains when flowers are open means high risk for fireblight. We had a number of NH orchards with LOTS of FB strikes last year, so there is potential for a lot of inoculum being present. Remember that there are a couple of sources that run weather models to predict fireblight risk. It may be worthwhile to check these sites as we approach & enter the high risk time for FB. One is Glen Koehler’s Orchard Radar. 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) here. 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.

Thresholds for TPB and Leafminers in Apples

If you have a good market for #1 fruit (like pick-your-own blocks), then the threshold for tarnished plant bug in apples is a cumulative catch of 5 TPB’s caught per trap from silver tip to tight cluster stage. If  tight cluster stage comes and you still have not reached the threshold, look at the traps again at pink stage. A cumulative average of 8 or more per trap by pink would warrant control. For apple growers who aim to produce extra fancy apples, the thresholds are a cumulative catch of 3 per trap (ST to TC) and 5 per trap (ST to pink).

I’m happy that many apple growers don’t bother to spray for TPB any longer. Once bloom arrives, there’s no point to spray for TPB.

Leafminers: The red rectangle traps are very effective to predict whether or not you need an insecticide this year for these pests. Please remember they tell IF you need to treat. You’ve got a wide window for timing sprays if they are needed. The threshold varies with apple variety, because apples vary in their likelihood to drop fruit just before harvest, in response to leafminer damage. For McIntosh, it is a cumulative catch of 4 or more moths from quarter inch through tight cluster stage. For other varieties, the threshold is 9 or more moths, because other varieties are much less sensitive to leafminer damage. Now back to my point about when to treat. Some insecticides would be aimed at the eggs or very young larvae. They’d go on at pink stage. Examples: Esteem, Intrepid, Aza-direct, Assail. Others would be applied a while after petal fall, when sap-feeding stage of miners are visible. Examples: Altacor, Belt, Calypso, Lannate, Leverage, Proclaim…

There is another monitoring option. You could wait and count the sap-feeding mines shortly after petal fall. This is a trickier monitoring method than using the sticky red rectangle traps. Starting about 5 days after petal fall (try again 5 days later if find no mines) you examine the UNDERSIDES of CLUSTER leaves. You look for a slightly silvery patch on the leaf undersides. That’s where the tiny caterpillars have separated the lower epidermis layer from the internal spongy layer of the leaf. If you find 13 or more mines out of 100 leaves, it is worthwhile to treat for leafminers. I’ll show my sap-feeding mine photo now, but it should be a while before they appear.

 Green Pug Moth in Apples: Maybe a Bad Surprise?

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The caterpillars of green pug moth are tiny yellow-green loopers that start feeding on expanding tissue soon after the buds open. The older ones often have a red-brown stripe down their backs. Normally a little foliage feeding would not be too bad. But as soon as the flowers open, the caterpillars feed on their most preferred tissues: the pistils of the flower buds. Chomping down the pistil results in no fruit from that bud. Sometimes the caterpillars are in very high numbers, and in other blocks (or years) they are in very low numbers, and do no significant injury. No one has determined how many caterpillars it takes to warrant a spray, but we do know a simple way to check: at pink stage, firmly tap the branches with flower buds over a white inverted frisbee or pie plate. Check a number of spots and see if you find what you think are significant numbers. If you find enough to worry you, apply an insecticide right away… before bloom. A few New Hampshire growers have had bad surprises in recent years. My photos show the technique (above) and the tiny caterpillar (below).

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Rosy Apple Aphid Can Harm Cortland Fruit

If you have a lot of Cortland apples, it is worthwhile to check those trees at pink stage, to see if you have many colonies of rosy apple aphid. As the aphids feed on leaves, the leaves begin to curl up. Quickly they curl so tightly that they protect the colony from pesticides. As the insects keep feeding & growing, they produce a toxin that stunts the growth of the apple(s) adjacent to that spur. Affected fruit are puckered, and often are not marketable. The vast majority of varieties are not susceptible to the damage. Why check at pink stage? That’s the last opportunity to hit them with an insecticide, before leaf curling proceeds too far. Rosy aphids can appear yellowish, but older ones are pinkish or purple with a powdery exterior. The photo that shows one just starting to turn powdery was taken in early May, while the red ones were photographed in July. When you check, search for curled leaves. THRESHOLD??

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Pink Stage is an Important Time for Apple Rust Diseases

Rusts are fungi that have two different species as hosts, and keep switching from one to the other. Galls or lesions on host 1 produce spores that infect species 2, and simultaneously, spores from species 2 infect species 1. We have several types of rust that affect apples. If you have problem with them, and have not been able to eliminate the nearby sources of spores, remember that the pink stage is usually when a significant number of infections occur. Cedar-apple rust usually hits apple foliage, while quince rust can affect the fruit. Japanese rust primarily hits apple foliage. Red cedar and some other junipers are key hosts. Even a tiny red cedar tree can produce enough spores to create problems. During rainy periods in the spring, the galls swell, and orange, fleshy telial horns appear. They are the source of the infective spores. I’ve got photos from previous years here. The round gall was on red cedar and is from cedar-apple rust. The other photo shows branches of common juniper, with slightly swollen spots from which long telial arms have appeared. They are from quince rust. The spores get released during rainy periods. My neighbor thought they looked like orange Christmas tree ornaments.

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 Mummyberry

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.

Pollination Time for Apples, Blueberries

Many commercial orchards in New Hampshire bring in honeybee hives for pollination. To get the most out of them, here are some points. Honey bees require fairly warm temperatures (60F or higher) for foraging. If there is much of a breeze, foragers huddle close to the ground, or in other sheltered spots. If the wind picks up, honey bee foraging stops. Rain stops honeybee foraging, too. Apple blossoms have a relatively high sugar concentration in their nectar, so they are readily pollinated. Pear nectar has much less sugar, so it is really difficult to attract honey bees to pollinate them, especially when there are other choices, like dandelions in the orchard floor.

Put hives in groups across the orchard, rather than set them all at one end. Place hives on pallets or boards, rather than directly on the ground. This reduces the chances of cool water soaking into the bottom, cooling & slowing down activity. Try to put them in sheltered spots, out of the wind. If you can, place them facing southeast or east, so the morning sun warms it up early in the day.

It has been pretty dry this spring. If there is no clean water within a hundred yards of the hives, consider placing shallow trays of water nearby, with rough pine boards in them (drinking bees can grip well & not fall in).

We are lucky. In many New Hampshire orchards there are lots of native bees, and they pollinate the crop well by themselves (no need to introduce honey bees). We have over 120 species of them in NH. Most live singly, not in nests with hundreds of companions. A few (bumble bees for example) live in nests with a few—perhaps as many as a couple dozen — in a colony. Many of our natives fly in relatively cool, even wet weather. If you have active bees that are not honey-colored, they may very well be natives. Please remember that significant pollination from native bees requires nesting habitat in or close to the orchard. So it pays to protect that habitat. Some bees nest in tunnels in stems, stumps and twigs. Many bumble bees nest in old chipmunk, mouse or vole nests. About 70% of our native bees nest in the ground. Most of them prefer bare, undisturbed soil to dig their nest tunnels.

 

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.

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