May 13, 2014 – Volume X No. 3

Fruit Bud Stages Now

At the Woodman Horticulture farm in Durham, fruit buds on Monday May 12th were: Pioneer McIntosh Apple: pink. Japanese plums: bloom. Peach: bloom. Blueberry: loose clusters to pink bud.

Rosy Apple Aphid: Look During Early Pink Stage

This isn’t a problem for everyone, but might be a slight concern for a few. One apple variety that we grow is very sensitive to rosy apple aphid: Cortland. If a colony of only a few RAA’s establishes on one or more of the cluster leaves, the fruit in that cluster can be ridged and stunted, sometimes severely. My photo was taken in late August, when that fruit should have been MUCH bigger.

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The saliva secreted by the aphids somehow causes this. Leaves also respond to feeding by this species. They strongly curl up, and that makes it extremely difficult to reach them with an insecticide. Do you see the curled up leaf at lower right of the photo below? So, if you have Cortland trees that showed this symptom last year, it might be worthwhile to look for RAA colonies at the late tight cluster or early pink stage.

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If you find some, it might be worthwhile to treat your Cortland trees with an insecticide. You recognize the colonies from the curled up apple leaves. Inside each one will be 1 or more aphids. The aphids could be dark green, yellow, powdery blue, or pink. The New England Fruit Management guide has details on insecticide options, but the critical thing (if you decide to treat) is to do so no later than pink stage. After that, the leaf curling is so strong, it encircles and protects the aphid colonies. Below is a photo of one of the aphids in May, after I uncurled a leaf.

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Green Pug: Check Apples at Pink Stage

Green pug caterpillars are tiny yellow-green loopers, which sometimes show a red-brown line down the back. They hatch in early spring, and the caterpillars feed on young opening tissues. They strongly prefer to feed on the pistil & style of the flowers, which means you get no fruit from those flowers they attack. They pupate during bloom. The time to search for them is at early pink stage. No one has figured out a threshold for them, so if you find what you think is a significant number of them, you might want to apply an insecticide. Each caterpillar can feed on more than one blossom. The time to spray is during pink stage. I like the idea of using Bacillus thuringiensis-based sprays for this insect, but you could also try Imidan, Calypso, Avaunt, Proclaim, Altacor, or I suppose a pyrethroid (I don’t like recommending them for this). The catch? If you do not have a NH private pesticide applicator’s license, your only legal choice is one of the B.t. products (Dipel, for example). That’s because the name green pug moth doesn’t appear on most labels.

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Pink Stage: Key Time for Management of Apple Rust Diseases

We have several types of rust that affect apples, and all of them have two different hosts. The spores from infections on one host infect the other, and vice versa. If you have problem with rusts on apples, 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. I think the “new” 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. If the infection sources are on your neighbor’s property, besides asking if it would OK to remove it/them, maybe you could offer a bribe. How would you like some nice fruit in exchange for cutting down an important source of rust spores?

Exirel: New Insecticide for SWD & Others

Exirel is a DuPont product, just recently registered with the EPA. It is effective on (and registered to control) spotted wing drosophila, and has a unique mode of action. That means it is a strong addition to our SWD arsenal, allowing us to rotate materials between different modes of action, and therefor reduce the risk of SWD developing resistance to any of our insecticides. It is registered for use on many vegetables and small fruits. Looking at the label, I see lots of caterpillars listed, but also aphids and a few beetles (including plum curculio).

Raspberries: Crown Borer Drench

If your bramble planting has been hit hard by crown borer, one option (in addition to destroying nearby unmanaged brambles) is to consider an insecticide drench before bloom. Not too many plantings would need this, but if yours is one of them, timing is critical.

Airblast Sprayer Calibration On Line

George Hamilton has been doing a lot of work on sprayer calibration, and in particular has partnered with Jason Deveau from Ontario Ministry of Agriculture and Food. George suggests that growers visit Airblast 101 to learn more about airblast sprayer calibration. If you follow the link on “new presentations”, you’ll note that George’s presentation is #17 on the list, and there are various others on drift and other aspects of spraying. You can pick & choose from among a wide range of topics, and look at them when it is convenient for you.

Thresholds for Leafminer Traps, Apples

For McIntosh, the threshold for Spotted tentiform leafminers on the red rectangle traps 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. Since we went over threshold at the UNH Woodman farm, we are planning a leafminer spray for the young larvae in 2-3 weeks or so.

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When Does Plum Curculio start Attacking Apples?

It is when the first fruitlets are 6mm in diameter; ¼ inch. Until the fruit get that big, they can’t do anything but lurk in the trees, waiting. Odor plays an important role in host-finding for this species, and once there are a lot of small fruitlets, they add their odor to other volatiles released by the bark, twigs and flowers. Many growers delay their “petal fall” insecticide a bit, until this point arrives. If the weather cooperates, that’s great. One negative effect of delaying that treatment is that you’ll get more European apple sawfly [EAS] damage if you delay. For many growers, that’s not a real concern, since EAS injury level is fairly low. In case you forgot what EAS injury looks like, here’s one of my photos. The injury is only skin deep, but is very obvious, and throws that fruit out of the high grades.

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Apple Scab

Pink to bloom is when we expect the big spore releases of primary apple scab season. Ascospore maturation is in its rapid phase, and there is usually plenty of tender, exposed tissue available for infection. We had some daytime rain Friday/Saturday, and we should see some daytime rain (and therefor spore release) coming this week. The temperatures may be warm, so that the number of hours of leaf wetness required for infection will be relatively short. I hope you are prepared.

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Alan T. Eaton, Extension Specialist, Integrated Pest Management

Visit the Extension IPM page.

UNH Cooperative Extension programs and policies are consistent with pertinent Federal and State laws and regulations, and prohibits discrimination in its programs, activities and employment on the basis of race, color, national origin, gender, religion, age, disability, political beliefs, sex, sexual orientation, or veteran’s, marital or family status. New Hampshire counties cooperating.

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